# Another Rotary Phase Converter



## JimDawson

I'm getting ready to build a RCP to power up my new (to me) CNC lathe.  All this is going to power up is the axis drives and spindle, the three small 3 phase motors for the coolant pumps and the hydraulics will be powered by VFDs from a separate feed, as will the computer and controls.

I have a 15HP compressor motor to use as the idler.  2 pole, 3450 RPM, 240 volt.  I tried to remove the motor from the compressor head, but it turns out that the armature shaft and the screw are one piece.  So I pulled out the mating screw, greased the bearings and put the housing back together.



Here is the schematic of the RPC.  Comments are solicited and welcome.  Starting is with the 3/4 HP, 3450 RPM, single phase pony motor to minimize the start load on my electrical system.


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## countryguy

Wow. New format here look smooth.  Me like!    
JD,  how does the pony motor help?    Never heard the term or seen a schemo with one.  Does it just stay running?


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## JimDawson

All it does is spin the idler motor up to speed before it's energized.  That way there is very little start load.  Once up to speed, the switch will thrown to the RUN position momentary which will then pull in the main power contactor.  That will take the pony motor out of the circuit, but it will still be mechanically driven by the idler motor.


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## countryguy

Cool.   Just took a spin on this thread. http://www.paragoncode.com/shop/rotary_converter/

My next one will be the same too.   My only note is to select the best caps you can on the budget. At my aerospace place long long ago.... Caps would go esr bad until we started spec'ing the 105c or higher rating and the new needed  to use quality mfr lines.    Just a thought.  

Peace and may the wild leg be happy and joyous--- ha.... Long day if I am typing junk like that. :-(


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## Blackjackjacques

JimDawson said:


> I'm getting ready to build a RCP to power up my new (to me) CNC lathe.  All this is going to power up is the axis drives and spindle, the three small 3 phase motors for the coolant pumps and the hydraulics will be powered by VFDs from a separate feed, as will the computer and controls.
> 
> I have a 15HP compressor motor to use as the idler.  2 pole, 3450 RPM, 240 volt.  I tried to remove the motor from the compressor head, but it turns out that the armature shaft and the screw are one piece.  So I pulled out the mating screw, greased the bearings and put the housing back together.
> View attachment 244517
> 
> 
> Here is the schematic of the RPC.  Comments are solicited and welcome.  Starting is with the 3/4 HP, 3450 RPM, single phase pony motor to minimize the start load on my electrical system.
> 
> View attachment 244512



15 Hp seems like a big motor to operate with only two legs - especially considering the light loading.    Your schematic shows three L-L receptacle banks, but no single three-phase takeoff to supply a  3-phase load.


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## JimDawson

Blackjackjacques said:


> 15 Hp seems like a big motor to operate with only two legs - especially considering the light loading.    Your schematic shows three L-L receptacle banks, but no single three-phase takeoff to supply a  3-phase load.



3 phase output is on the right side; U, V, W.  Not so lightly loaded, about 12.5 KW at max load.  The spindle motor is 7.5 KW + the 1.5 KW live tooling drive.


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## Blackjackjacques

ok - so you are driving a ~10 hp motor --so you do have that 15hp motor well loaded - maybe too much given that it is operating on only two legs.  May want to watch heat and what your waveform looks like, etc.


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## talvare

Blackjackjacques said:


> 15 Hp seems like a big motor to operate with only two legs - especially considering the light loading.    Your schematic shows three L-L receptacle banks, but no single three-phase takeoff to supply a  3-phase load.



I believe those are capacitor banks for voltage correction, not receptacles and he does show 3 phase output at the right side of the schematic.

Ted

Well Jim, I guess we were typing at the same time !


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## Blackjackjacques

JimDawson said:


> 3 phase output is on the right side; U, V, W.  Not so lightly loaded, about 12.5 KW at max load.  The spindle motor is 7.5 KW + the 1.5 KW live tooling drive.




I gotcha now -- what i thought were receptacles are caps  -- i see now.. thanks


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## Ulma Doctor

nice work Jim!


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## JimDawson

talvare said:


> I believe those are capacitor banks for voltage correction, not receptacles and he does show 3 phase output at the right side of the schematic.
> 
> Ted
> 
> Well Jim, I guess we were typing at the same time !





Blackjackjacques said:


> I gotcha now -- what i thought were receptacles are caps  -- i see now.. thanks



My fault for the confusion, I should have use the correct symbol for a cap.  I started drawing a pictorial rather than a schematic and didn't correct the drawing.


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## Blackjackjacques

np ..every trade uses their own.  I think the thing that also threw me were the switches on each cap - do you plan to switch the caps in and out?


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## JimDawson

Blackjackjacques said:


> np ..every trade uses their own.  I think the thing that also threw me were the switches on each cap - do you plan to switch the caps in and out?



I'm thinking about switching them in and out.  That might be overkill, since it's just for setup.  Sometimes I over design things.  

I do have a question about setup.  For initial testing I'm thinking about building a load bank out of stove top elements.  I'm wondering if a resistive load will work to get kinda close to a balanced output.  I would rather fry an $8.00 heating element than a rather expensive servo drive.


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## markba633csi

The load bank sounds like a great idea Jim.
Also having a switch per cap (use cheap house wall switches) will help tune it in fast.
Mark S.
ps no timer in the circuit?


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## JimDawson

markba633csi said:


> The load bank sounds like a great idea Jim.
> Also having a switch per cap (use cheap house wall switches) will help tune it in fast.
> Mark S.
> ps no timer in the circuit?



In this one I don't need a timer or start caps.  The pony motor is manually switched in, then when up to speed, I will manually switch to the idler motor.  I thought about putting in a potential relay, but I can flip a switch


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## Blackjackjacques

You can use whatever rotgut loads you have available as long as the voltage is compatible.  For a jiffy test, I have gathered up whatever available, including old space heaters, and have even mixed 3-phase devices/appliances with single phase devices - wired accordingly , and roughly eyeballed for balance.  If balancing is your concern, borrow a 3-phase motor close to the actual load. All those switches are probably overkill in that you are asking for impractical precision.   I would just estimate cap values you need based on your actual loading, and if you want to play with it and fine tune, you can manually connect a candidate cap while monitoring current on that line.  If anything, you probably want to fuse the caps, and throw in a bleeder resistor across the caps to drain them.  I found this attached design online from the practical machinist forum -- it appears robust to me and well thought out and includes the calculations used - however, it is for a 10 hp motor.


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## JimDawson

Thank you for posting the PDF, very informative.


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## Robert LaLonde

One thing to bear in mind is that you over engineer, but often everything else is over engineered as well.  My 4HP Hurco mill actually has a 5HP motor on it.  It came that way.  I figured I needed a minimum 5HP (after derating VFD) but it had a 3.7Kw 3ph derated to about 2.4Kw (3HP~ish) since I am feeding it single phase.  I didn't have the cash for the VFD I wanted at the time so I just ran what I had.  Its been that way for many years now, and I use that mill all the time for aluminum, 4140, 4140HT, 1018, mystery metal, brass or whatever else needs cutting.  I don't have to put a 5HP load on it just because it has a 5HP motor.  In all my calculations I put 1.5 down as my max spec, and it removes metal at incredible rates. Sure I could cut at 3HP loads still, but its hard on that old 1981 Hurco mill. 

Anyway.  Yes a 15HP RPC might be a little light if he was running all his motors at peak load, but in reality that just isn't going to happen. The worst current will be inrush, but we aren't talking about a universal motor.  We are talking about an induction motor.  Its sure not going to be 10hp 7.5kw to start.  Then how would I know.  Maybe he plans to do high feed high DOC hard steel all day long and throw chips big enough to take out small animals in their path.  LOL. 

If you want another example.  Go look at your home service entrance.  Its very likely if you add up all the breakers they exceed the current of the main breaker.  How often do you trip your main breaker? 

Now we are talking about shop equipment.  If you are running all your equipment at the same time, and it all starts a hard cut, hard start up, or crash at the same time...  Then you will be lucky if your main trips right away.  LOL. 

Anyway, I would agree in general to go bigger, but as long as he isn't running actual 10HP loads I wouldn't worry to much about it for occasional use.


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## markba633csi

Small animals beware when Dawson fires things up
M


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## Keith Foor

I can't say that I have ever seen Power Factor correction capacitors used in a phase converter.  That's a new one.  Your values for your run caps are not shown.  All I can say is watch overdoing it with the run capacitors on the RPC.  Too much capacitance and you will get a wild leg in the 300 to 500 volt range with no load.  
I have tuned most every one I have touched down to within 5% A to C and B to C voltage wise and they are typically very stable under load.  

Now as far as the motor.  Is it compressor rated or not?  
If compressor rated, what type of compressor?
It's important to understand that rating.  If it's rated for a screw compressor then your fine.  It's 100% duty cycle.  
COmpressor motors are typically NOT rated to be run for hours on end.  Think about how your compressor works.  You use air, it comes on and pressure builds up and it shuts off.  It's off for a while then cycles again.  
RPC's run and run as long are you are using them.  You also give up some efficency for starting torque with a compressor motor.  Meaning it will draw a bit more power, and generate a bit more heat than a pump or fan motor.


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## JimDawson

Keith Foor said:


> I can't say that I have ever seen Power Factor correction capacitors used in a phase converter.  That's a new one.  Your values for your run caps are not shown.  All I can say is watch overdoing it with the run capacitors on the RPC.  Too much capacitance and you will get a wild leg in the 300 to 500 volt range with no load.
> I have tuned most every one I have touched down to within 5% A to C and B to C voltage wise and they are typically very stable under load.
> 
> Now as far as the motor.  Is it compressor rated or not?
> If compressor rated, what type of compressor?
> It's important to understand that rating.  If it's rated for a screw compressor then your fine.  It's 100% duty cycle.
> COmpressor motors are typically NOT rated to be run for hours on end.  Think about how your compressor works.  You use air, it comes on and pressure builds up and it shuts off.  It's off for a while then cycles again.
> RPC's run and run as long are you are using them.  You also give up some efficency for starting torque with a compressor motor.  Meaning it will draw a bit more power, and generate a bit more heat than a pump or fan motor.



I'll be very carefully monitoring the voltage and Power Factor with built in instrumentation.  Measuring leg to leg output parameters as will as input voltage, current, and power factor.  The input and output will will be measured with separate devices attached across their respective legs.  Like I said above, I tend to over engineer stuff.  

The capacitors are roughly calculated by this formula:
CL1-L3 = 4 to 5 times the motor horsepower = 75  (20+20+10+10+10+5+5+5+5)
CL2-L3 = 10 to 15 times the motor horsepower = 180 (60+60+20+20+10+10+5+5+5+5)
PF COR = (10+5+5+5+5)
Where the capacitors will be switched in and out manually by toggle switches for now.  Once I get the system running, they may be adjusted on the fly by a PLC if needed.

The compressor motor is a rotary screw driver, rated for continuous inverter duty, 12.5KW, 3600 RPM nominal.  Also interestingly enough rated for 6700 RPM at 114 Hz.  Would make a heck of a spindle motor If you had something big enough to run it on.


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## JimDawson

CL1-L3 = 4 to 5 times the motor horsepower = ~75 uF
CL2-L3 = 10 to 15 times the motor horsepower = ~180 uF
Where L3 is the manufactured leg. 

Question:  Given the large difference in capacitance L1-L3 vs. L2-L3, how do you know which is which when first testing?  Is this dependant on idler motor rotation direction?   Connections at the motor?


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## JimDawson

Got some work done on the RPC today.  Bet you have never seen a RCP with an oil filter on it.   The compressor has been gutted, but the main screw is part of the motor armature shaft so I kept the housing intact to use the bearings.  The pony motor is the fan motor from the compressor.  It's a 1/2 HP, 3 phase, so I'll run it with a small VFD to start the system.  I used the base from the compressor to mount everything on.



The pony motor mounting is adjustable in all axes to get proper alignment on the coupling.  I think a fan is going to go on the shaft to provide some cooling. 



Tomorrow I'll do the panel cutouts for the switches and instrumentation.  Once completed, the whole assembly will go on a pallet rack to get it out of the way.


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## markba633csi

Jim: just put a fan to blow in from the side- much easier amigo
Mark S.


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## Ulma Doctor

JimDawson said:


> Bet you have never seen a RCP with an oil filter on it.



No sir, that's the first RPC i have seen that has twin filtration!
(most other hyperdrive generators are single filter units )

what weight of RPC fluid are you gonna use???
What brand???
can i get some RPC fluid too???


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## Ulma Doctor

JimDawson said:


> CL1-L3 = 4 to 5 times the motor horsepower = ~75 uF
> CL2-L3 = 10 to 15 times the motor horsepower = ~180 uF
> Where L3 is the manufactured leg.
> Question:  Given the large difference in capacitance L1-L3 vs. L2-L3, how do you know which is which when first testing?  Is this dependant on idler motor rotation direction?   Connections at the motor?



Hi Jim,
i'm not an expert, but here is how i get to doing it.
you'll test voltage from a-b{L1,L2} , b-c{L2-L3} , a-c{L1-L3}.
you'll see one leg that is very low in comparison to the others.
in a 240v system, you'll identify the generated leg pairing, it may come in around (a-c)205v or so (in the unbalanced state)
that's the pairing that should get the larger capacitance for balancing
the other pairings may appear as 240v (a-b) and (b-c)226v respectively during operation, all dependent on rotation. (also in the unbalanced state)
this b-c pairing will require less capacitance to balance.

yes, Jim rotation of the idler motor will be a factor as to which legs get which capacitance.


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## JimDawson

Thank you Mike.  You confirmed what I guessed at.   I only want to wire this thing up one time, so all I have to do is reverse the rotation if my cap connections are backwards.  The caps will be available to switch into circuit per the above formula.  Since I'm starting the system with a 1/2 hp, 3 phase pony motor connected to a small VFD, all I have to do is flip the switch and start the system in the other direction.

I test ran the mechanical systems last night, the pony motor spins up the idler motor just fine.  But I ran into a bit of a problem.  I left the main screw in place, and it started seizing on me at 3450 RPM, ran fine at 2000 RPM.  Not sure where that was coming from, but maybe it didn't like the grease I used in the bearings, couldn't find any scrape marks anywhere.  So I spent today extracting the main screw.  The system was designed to be non-serviceable so that was a bit of a challenge.  But I was able to extract the screw without damaging anything that I need to use in the system.


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## JimDawson

I got a bit more work done on the RPC over the last couple of days.

Here is what the cabinet door is going to look like



Here is a picture of the power meters.  I found these on EBay, $14.00, supposed to be good for 100A and 250V.  We'll see how accurate they are   These will be checked against my Fluke meters.  If I can get comparative values between the panel meters I'll be happy.
https://www.ebay.com/itm/100A-AC-LC...814329&hash=item1c90f0f879:g:FPUAAOSwo-NZsPKK



And what the door looks like right now.  I know the top meter might be redundant, but it will be wired ahead of the idler motor contactors.  The others will be wired at the output.



And the back view




And the cabinet back panel




And a better view of the cap rack.  Two pieces of 0.125 aluminum spaced 1 inch apart and 1 inch off of the back panel




I still need to order the VFD for the pony motor and the wireway to keep things neat.  So in a couple of days I'll start wiring it up.  The VFD will be mounted just to the right of the 2 terminal power block.

So why would you put a VFD in a RPC?  Well, the pony motor is a 3 phase, 1/2 hp motor so I need 3 phase power to run it.  But the best part is that the VFD has a programmable relay output.  I'll program it so that when the system ramps up to speed, about 10 seconds, the relay closes, switches in the main power to the idler motor and simultaneously turns off the run command to the VFD.  From there the pony motor just coasts and the system is running on the idler.  Starts with minimal load that way.


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## mksj

Hey Jim,

I would have one main question/concern in using a VFD in this application, when the VFD gets a stop command, the pony motor will continue turning. The VFD may go into a fault mode from voltage regeneration. It is possible to program the VFD to free run or possible shut down with a timer circuit, but I still do not know if it will go into a fault mode when it receives the stop command because it expects the motor to be stopping. Also how this would affect the output section, or feedback into the line. I would run the vFD in the V/Hz mode. Might call the VFD company and speak to someone in tech. Another option might be to use a static converter and a timer relay. I use a timer relay in my mill to control the motor blower. They are SS and have a wide  range of timing functions. This 822 has two channels each with a trigger.


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## JimDawson

The VFD (AD GS1) can be programmed to Coast to Stop.  In that stop mode, the output section just turns off when the run command is interrupted and allows the motor to coast.  I don't know about other VFDs, but I have used AD VFDs with large flywheel loads and never had a problem doing this.  This particular VFD is only V/Hz.


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## Firestopper

Nice Jim, 
Defiantly the coolest RPC I'v ever seen. I'v wanted to add meters to my system from the start but lost motivation. You just reignited my interest.
Your work is always inspiring.


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## JimDawson

Thank you Paco.  This is my first RPC so I thought I would jazz it up a bit.  Originally I was just looking for some volt meters, but I found those power monitors and they were cheap.  We'll see how well they work.


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## markba633csi

Jim just so you know they DO make little clips you can buy for mounting caps, you don't have to make swiss cheese panels for em.  I know, you
needed an excuse to fire up the CNC. 
I didn't know you were planning to keep all those switches in the design- some of them you'll probably throw once and never again.  Hey as long as it works, right?  Looks impressive that's for sure. 
Mark S.


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## JimDawson

markba633csi said:


> Jim just so you know they DO make little clips you can buy for mounting caps, you don't have to make swiss cheese panels for em.  I know, you
> needed an excuse to fire up the CNC.
> I didn't know you were planning to keep all those switches in the design- some of them you'll probably throw once and never again.  Hey as long as it works, right?  Looks impressive that's for sure.
> Mark S.




I looked at those clips.  They wanted about $4.00 each and you have to drill & tap two screw holes per each.  And as you said I have a CNC.    I decided to just put the switches in, makes the setup easier.  Thank you.

I should just have bought a 15HP motor, using this compressor motor has turned into more trouble than it's worth. After removing the screw I had to modify the front bell bearing bore, build motor mounts, and fight with it.  Just about done now.  Hopefully I'll get back to the wiring tomorrow.


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## markba633csi

Well if it's any consolation I've spent ridiculous darn fool amounts of time rebuilding my bandsaw.  Just finishing the hydraulic feed now, there's light at the end of the tunnel- pics soon.  
Mark S.


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## JimDawson

There have been some questions about what I'm going to run with this RPC.

Here is a picture of the electrical cabinet on the CNC lathe


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## JimDawson

Making progress, may have it done tomorrow.


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## Firestopper

These came up in Tucson craigslist. Not a bad price. 
https://tucson.craigslist.org/tls/d/electric-motors-baldors/6366232392.html
Looking forward to seeing you make some chips Jim.


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## JimDawson

firestopper said:


> These came up in Tucson craigslist. Not a bad price.
> https://tucson.craigslist.org/tls/d/electric-motors-baldors/6366232392.html
> Looking forward to seeing you make some chips Jim.




First time I've seen a newer motor that wasn't dual voltage.  A little unusual.


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## JimDawson

The first test run did not go well.    The pony motor spun up the idler and everything switched in as planned.  The idler took over and ran just long enough for me to look at the voltages (which seemed about right), about 15 seconds or so.......then the 50 amp breaker tripped.   *^^%^&.  So disconnect the idler and do a quick phase to phase check with an ohmmeter:  0.4, 0.4, 0.2.  That's not good, I think it has a shorted winding.   Maybe that's why the air compressor failed.  Headed to the motor shop on Monday, I'll have them put it on the bench.  I have no way to properly test a 15 Hp, 3 phase motor in my shop.  I really kinda hope it is the motor, at least that would mean I didn't foul something up.  It was running unloaded, no caps in circuit.  Rated at 15 Hp, 48 amps at full load, there is no way that motor could be drawing >50 amps unloaded if it's healthy, even single phasing. 

Here is a couple of pictures of the nearly finish panel.  Still have to wire in (gray cable) the current transformers (little black things) for load monitoring.

That's a big ball of wires, wrapped with spiral wrap at the bend.



The back of the door



And the main panel



My son designed and machined a mounting bracket for the current transformers, mounts under the 3 terminal power block.
Here is the design, I'll post more pictures later.  Made of UHMW.


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## Ulma Doctor

this may sound a little crazy or irrelevant, but is not meant to be disrespectful-

i think you could reduce the start capacitance and try to run a smaller motor first on the system (without balancing caps either) 
to test your system before hooking up a 15hp motor.


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## JimDawson

Ulma Doctor said:


> this may sound a little crazy or irrelevant, but is not meant to be disrespectful-
> 
> i think you could reduce the start capacitance and try to run a smaller motor first on the system (without balancing caps either)
> to test your system before hooking up a 15hp motor.



Mike, your comments are always welcome.  

But...There is no start capacitance.  The system is spun up to operating speed by a pony motor to reduce the start load.  Upon reaching operating speed, the pony motor switches out and simultaneously the idler contactors pull in.  The lights didn't even flicker when I fired it off.  It ran on the idler for about 15 seconds before the breaker tripped.  It sounded a little growly but I assumed that was because there were no balancing caps switched in.  I do have a small 3 phase motor I could lash up and see how it reacts with that.

If you have any other ideas I could use some suggestions.  Maybe I'm missing something.


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## Ulma Doctor

Hi Jim,
that's right, you are using a pony motor to start the idler, my mistake.
if the pony motor is up to speed and then single phase power is applied to the idler- it should run if everything is copacetic with the motor.

3450 rpm RPC's take a second longer to spin up


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## JimDawson

Ulma Doctor said:


> Hi Jim,
> that's right, you are using a pony motor to start the idler, my mistake.
> if the pony motor is up to speed and then single phase power is applied to the idler- it should run if everything is copacetic with the motor.
> 
> 3450 rpm RPC's take a second longer to spin up



That's what I was thinking. 

My RPC works is a little different than most I have seen.  The pony motor is powered by a small VFD.  The accel is set to 10 seconds.  Once it reaches operating speed, 3450 RPM, the output relay in the VFD is programmed to energize and that energizes a control relay which kills the run command to the VFD and simultaneously pulls in the idler contactors.  The VFD is programmed to coast to stop, so the output section just shuts off and allows the pony motor to freewheel.


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## Ulma Doctor

got it!
yes sir, the design is a bit different- but i like the thought put into the creation. very nice engineering.

i'm sure it will work, we just gotta pin down the problem.
the low resistance on the 15hp motor winding sounds like the real problem

you should only get a grumble from the system when it runs right before balancing is switched in
the idler motor is already spinning so the inrush should be low and momentary.

something else to consider
make sure that the idler and pony motors are running the same relative rotation.
i'd hate to think of what would happen if the pony spun the motor in one direction when the idler would want to run in the other direction.


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## JimDawson

Ulma Doctor said:


> something else to consider
> make sure that the idler and pony motors are running the same relative rotation.
> i'd hate to think of what would happen if the pony spun the motor in one direction when the idler would want to run in the other direction.



That would be a major problem.  

But let's see if I understand something correctly.  Since the idler is already spinning at speed and direction, shouldn't want to continue spinning in the same direction when the single phase power is applied?  Does the phase relationship apply to the single phase input?  Now I'm realy confused.


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## Ulma Doctor

anytime you switch the single phase supply legs, you reverse rotation
the same is true in 3 phase supply

something to consider anyway


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## JimDawson

Ulma Doctor said:


> anytime you switch the single phase supply legs, you reverse rotation
> the same is true in 3 phase supply
> 
> something to consider anyway



Well that's interesting.  I'll try reversing the pony motor after I check the resistance of the individual windings.  I didn't go into it that deep yesterday.


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## markba633csi

"anytime you switch the single phase supply legs, you reverse rotation"
is that really true? It isn't for a single phase motor IIRC
Mark


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## JimDawson

Ulma Doctor said:


> i'd hate to think of what would happen if the pony spun the motor in one direction when the idler would want to run in the other direction.



In this case it seems to make no difference.  Same result, about 15 seconds and the 50 amp breaker trips.  I tried all possible combinations of rotation and connections with no difference.  The load seems to be about 15KW, or about 62 amps.  In checking the individual windings, I got 0.1 ohm across the board.  I'm thinking a bad motor.

I managed to get a screen capture of the operation, the red line is the shop power, the blue line is total property power.  Power in KW is vertical.  The first spike was me hitting the E-stop before it was fully energized.  The next two spikes are the time before breaker trip.  When I had it wired as the original test, and only reversed the rotation of the pony motor it ran a couple of seconds longer than the second test.  But in the second test the breaker was already warm so that may have been the time difference.


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## Ulma Doctor

markba633csi said:


> "anytime you switch the single phase supply legs, you reverse rotation"
> is that really true? It isn't for a single phase motor IIRC
> Mark


i have tested the rotation thing on RPC's that i have built
when controlling 3 phase motors, if you swap any 2 motor legs the rotation is reversed.
we are still powering with a 3 phase motor whether it is running on single phase supply or 3 phase supply, and the same rules apply
i'm sorry if my posts seem to be untrue


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## markba633csi

What I meant was with a single phase motor it's the start leg (cap, centrifugal switch) that sets the direction- swapping the ac won't reverse-as in
the case of throwing a drum switch quickly from forward to reverse; motor continues to run in forward direction until stopped and restarted. With a 3 phase motor powered by single phase I wasn't sure what happens when L1 and L2 are flipped- I assumed like Jim that the idler would be happy running in either direction
M


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## Ulma Doctor

if L1 and L2 are flipped, no big deal as far as the single phase power is concerned the direction will remain the same.

i should have specified that if T1 or T2 are interchanged with T3, the motor direction is reversed
my apologies for mixing terms


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## markba633csi

Darn I was hoping for an easy fix


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## markba633csi

Jim, Mike: Do you think it's possible that the physical phase angle between the two motor shafts could be "wrong" enough to cause a huge
power surge when the idler motor kicks in?  I'm just thinking out loud here 
Mark


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## Ulma Doctor

you may be onto something Mark.

what i'm envisioning at this point,
is that he has some bad windings in his 15hp motor or something else is wrong with the wiring

i'm of the mind to recommend starting a/or/the 15hp motor from single phase power outside his system
to verify we have a working motor, and verify rotation, take readings on voltage/amperage
if we can start it outside the system ,
we certainly can start it inside the system once we know which direction it turns for the desired pony output
i'd also recommend leaving the balancing caps out of the motor circuit until we can verify the starting system works.

another concern i have, (it may be unjustified),
is that the pony motor being coupled to the idler has to be generating some kinda electromagnetism.
even though it doesn't have power going to it, i have to think there is gonna be some kind of feedback.
whether it is detrimental to the VFD over long periods of time, is what i question


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## markba633csi

I was thinking that with the huge mass of the idler rotor if it comes on line at the wrong phase angle it may draw excessive current until
it catches up with the incoming line phase- but something tells me that's not too likely because there is no load on the idler yet.
I guess the best test would be to try to start the idler up on caps instead of the pony and see what happens then.
Mark
ps I follow what you said about the back emf from the pony damaging the vfd- certainly a concern


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## JimDawson

Here is a really good tech manual from WEG electric motors, everything you ever wanted to know about 3 phase motors.  This should keep you entertained for a few hours http://ecatalog.weg.net/files/wegne...f-electric-motors-50039409-manual-english.pdf

OK, onto the problem.  Let's break down what I did:

First the latest drawing



I am highly confident that the system is wired as above.
None of the caps have been switched in yet.
The VFD is set to coast to stop
The output relay in the VFD energizes CR2 on reaching operating speed.
The VFD run command is dropped out by CR2 and
C2A and C2B contractors supply the power to the idler motor are energized by CR2

EDIT:  I should note that the system was tested with light bulbs prior to connecting the idler motor.

Assuming there is something weird going on between the 0.5 HP pony motor and the 15 HP idler motor.  The idler motor should have enough torque to twist the tiny flex coupling into a pretzel even running on single phase.  That doesn't seem to be happening.  Even if the 0.5 HP pony motor were operating at full torque, in the opposite direction, the idler still should have more than enough power to overcome that and the VFD would trip out due to overcurrent, it's set at 2.2 amps.

Changing wiring combinations and pony motor rotation has no effect on the outcome.

Trying to start the idler outside of the system would be a bit hard, and electrically would really be the same because I would still be connect to the same breaker panel.

Feedback from the pony motor to the VFD?  Maybe that's possible.  Haven't been able to run it long enough to find out.  If that's the case, I can fix that.

The only thing that really makes sense to me it that the idler motor is bad, it came out of a known broken air compressor said to have a fried brain, but that is somewhat indeterminate.  It could be that the motor failed and that's what took down the system.  Unless there is some revelation in the next few hours, I'm headed to the motor shop in the morning.

I suspect there will be a new idler motor in my future 

I'm still open to suggestions


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## markba633csi

Yeah I just looked at your ohm readings again 0.4, 0.4, 0.2.  too far off to be normal I think
Keep us posted...
Mark


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## JimDawson

markba633csi said:


> Yeah I just looked at your ohm readings again 0.4, 0.4, 0.2.  too far off to be normal I think
> Keep us posted...
> Mark



Worse than that, what you may not have noticed was my winding to winding resistance test on the motor later.  0.1 across the board.  But that is way low according to the research I've done in the last couple of hours.  I seems the the winding resistance should be > than 1 ohm and more like 1.5 or so.  That would indicate that the windings are shorted.


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## Keith Foor

OK, So I am looking at the wiring and design on this.  And while I hate to pick apart things, I really hate things getting smoked and giving people issues.  So, I see how you are wiring up your run capacitors with independent switches.  Might be a good idea, but Im not seeing individual wires running back to a high current buss connection.  What wire are you shipping the high current back from?  Each cap seems to have 12 gauge wire on it, but do they go to a number 6 or something that runs to the motor lugs or is it run on 12 gauge?  The running current in each cap with 12 gauge wire will be fine.  But the caps as a whole will have alot of current flow.  Something to think about.  Might also look at the switches.  for the smaller caps, a 5 amp switch would be ok, but bigger caps bigger currents.  Switches may be rated in HP and not amps.  Once your switches are set, make sure that you are not going to exceed the current rating of the switches.  Only reason I bring this up is I have seen home built and factory built RPC's that had all the caps jumpered together with 12 gauge wire, and then a single 12 gauge wire running over to the motor.  On a 1 or 2 HP converter, it's fine.  On a 10  or bigger HP RPC, 12 gauge ain't gonna cut it and what typically happens is all the current, remember that EVERY amp of current in the created leg WILL flow across the run capacitors, overheats the 1/4 blade connector, and it gets weak, starts arcing, gets hotter and finally burns off the wire.  If you have already thought of this, then disregard all this.... if not, it might be something to consider.


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## JimDawson

Keith Foor said:


> OK, So I am looking at the wiring and design on this.  And while I hate to pick apart things, I really hate things getting smoked and giving people issues.  So, I see how you are wiring up your run capacitors with independent switches.  Might be a good idea, but Im not seeing individual wires running back to a high current buss connection.  What wire are you shipping the high current back from?  Each cap seems to have 12 gauge wire on it, but do they go to a number 6 or something that runs to the motor lugs or is it run on 12 gauge?  The running current in each cap with 12 gauge wire will be fine.  But the caps as a whole will have alot of current flow.  Something to think about.  Might also look at the switches.  for the smaller caps, a 5 amp switch would be ok, but bigger caps bigger currents.  Switches may be rated in HP and not amps.  Once your switches are set, make sure that you are not going to exceed the current rating of the switches.  Only reason I bring this up is I have seen home built and factory built RPC's that had all the caps jumpered together with 12 gauge wire, and then a single 12 gauge wire running over to the motor.  On a 1 or 2 HP converter, it's fine.  On a 10  or bigger HP RPC, 12 gauge ain't gonna cut it and what typically happens is all the current, remember that EVERY amp of current in the created leg WILL flow across the run capacitors, overheats the 1/4 blade connector, and it gets weak, starts arcing, gets hotter and finally burns off the wire.  If you have already thought of this, then disregard all this.... if not, it might be something to consider.



Keith, I appreciate your comments.  Please read the description below and see if there is a flaw in my thinking.

It's a little hard to see in the pictures in the posts above.  The switches are fed from 60 amp terminal blocks (red and black) on the door which in turn are fed with dual #10 wires from the power distribution block.  My biggest concern is really the jumper strips on the terminal blocks, I've had problems with those in the past and will be re-tightening them down the road a bit.  The switches are rated at 20 amps.  The manufactured leg bus (yellow) is a row of 60 amp terminal blocks fed with four #12 wires (I couldn't find any #10 yellow THHN).  You are correct, the caps are connected together with #12 wire, with the exception of the the 60uF caps which are connected to the buss with dual #12's.  From the switches to the caps it is all #12 with the exception of the 60uF caps which are fed with #10.  The total value of each row of caps adds up to 30uF or less, with the largest cap in the row nearest the buss on the right.  The connectors I used are high quality and have a high spring rate for a good grip, hopefully they will be OK.  Like you I have seen many push on connectors fail, and if these give me any problems, I'll do something different.  I couldn't figure out how to calculate or even guestimate the expected current in each row of caps so I gave it my best shot and also kind of went by a professionally built 20HP RPC that I installed for a customer a while back.

The main power wiring between the power distribution blocks and the main contactors is all dual #10.  The motor will be connected with short run # 8 wire from the 3 terminal power block.  The lathe will be connected to the 3 terminal power block with a run of #6 THHN.


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## JimDawson

I'm learning a lot about 3 phase motors.  I just got back from the motor shop with some interesting results.   The motor shop had never seen one like it.  After some head scratching, they hooked up the motor to a 150V, 60 Hz, 3 phase supply and it ran, but was drawing 22 amps which is way high for that motor unloaded operating at reduced voltage, and is consistent with the results I experienced when I tried to fire it up on 240 volts.  The conclusion is that either the windings are internally shorted, or........ possibly the motor is so special and designed to run at a minimum of 84 Hz that there are fewer turns on the windings and using bigger wire to run at the nameplate rating of 84 to 114 Hz and that it just won't run at 60 Hz.

Unfortunately the shop didn't have a 15 Hp motor in stock, so I'm on the hunt for one.  There was a Baldor on the local Craigslist a few days ago for $200, but the ad is no longer up.  I have a couple local guys I'm going to check with before I widen my search area. 

Stay tuned for the continuing saga


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## Karl_T

Man, i must be lucky. there's a place called Borchart Industrial ,  http://www.borchartsteel.com/index.html  about 40 miles from me. They must have a 1000 three phase motors in an old warehouse. Their initial asking price is $100 plus $5 a horse. But they will deal if your money is green, if you want several, you'll take an ungly one, yada yada.

I'm sure a new motor will solve your converter issues.


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## mksj

Interesting, I am always learning new things by following these posts. Hard to know if it the design of the motor or a fault, as it runs.
May want to go for a new motor, but shipping is going to be killer if you need to go that route and can't find anything local. Dealer's Electric often has reasonable NOS and lists one recommended for use as a phase converter.
http://dealerselectric.com/S2532.asp

eCrap special maybe if you can reasonable shipping and are looking for something new. Like the industrial duty Leeson, Marathon and Baldor motors.
https://www.ebay.com/itm/New-Leeson-AC-electric-motor-15HP-1765-RPM/332231194245

Super build quality, nicely done on the cabinet.


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## JimDawson

@mksj Thank you for the kind words.   That GE motor looks like a nice heavy duty motor.


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## Ulma Doctor

well that's a first for me!
i have not seen a motor with a 84 to 114 Hz ratings 

was the motor from a screw compressor??? that would explain some things if it were


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## JimDawson

Ulma Doctor said:


> well that's a first for me!
> i have not seen a motor with a 84 to 114 Hz ratings
> 
> was the motor from a screw compressor??? that would explain some things if it were



Yup..  http://www.hobby-machinist.com/threads/what-did-you-buy-today.55645/page-26#post-511268


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## Ulma Doctor

JimDawson said:


> Yup..  http://www.hobby-machinist.com/threads/what-did-you-buy-today.55645/page-26#post-511268


a whole lot of stuff just made sense
the motor speeds are adjustable for pneumatic demand


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## JimDawson

A little update, nothing is happening on the RPC    I'll have a new motor here in a week or so.

But..... A small problem.  We brought in a 25 KW, 3 phase generator to test the lathe.  That didn't go well...Tripped the main breaker in the control panel instantly.  Based on some very quick troubleshooting, it looks like there is a short somewhere in the main servo drive power circuit.  I need to isolate the individual devices to track down the problem.  I guess the 1700 mile trip home didn't agree with it.


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## Karl_T

There's something about moving old CNCs... Seems to just kill them.

I bought a really nice Vectrax mill (Brand sold by MSC) with a Fanuc 0M and it ran fine till I moved it into my shop. Now a gremlin lives in there   I am about to give up and refit the machine to a control I can maintain.  The trouble is probably easy to solve by an experienced Fanuc technician. But that guy just don't live in this rural area.

Hope your issues are easier than what I've experienced.

Karl


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## JimDawson

Karl_T said:


> There's something about moving old CNCs... Seems to just kill them.
> 
> I bought a really nice Vectrax mill (Brand sold by MSC) with a Fanuc 0M and it ran fine till I moved it into my shop. Now a gremlin lives in there   I am about to give up and refit the machine to a control I can maintain.  The trouble is probably easy to solve by an experienced Fanuc technician. But that guy just don't live in this rural area.
> 
> Hope your issues are easier than what I've experienced.
> 
> Karl



I hope so too.  It wouldn't bother me at all to rip out the entire control system and install my own, including my software.  I'll bet I can get enough money out of the Fanuc hardware to more than pay for a complete retrofit.

I've had a chance to do a bit more troubleshooting and it looks like the main power transformer may have a shorted winding.  Phase to phase resistance is 0.8, 0.4, 0.8 ohms.  That is not a good sign.  Next I'll check the inductance on the windings to see what that looks like.  Then maybe head to the local transformer shop to see what they have to say.


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## markba633csi

That's lousy news Jim- seems you've had more than your share of winding problems lately
Mark


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## Blackjackjacques

Running an AC motor at frequencies less than designed for should cause a pretty quick and substantive increase in magnetizing current and ultimately saturation.  With respect to cooling, speed as well as magnetizing current,* typical *AC motors are designed for a narrow window of both voltage and frequency (V/Hz).  You can run a 50 Hz motor at 60 Hz power line frequency and not have a problem with cooling, mag current, but speed will increase 6/5 and pf will also denigrate. If you go the other way, cooling is denigrated as well as mag current, and rpm will, of course, decrease to 5/6 -- generally meaning you have to derate the motor at the very least. VFD rated motors are specifically designed to consider the wider frequency window, and provide adequate cooling means, increased current, etc for worst-case (e.g., lowest speed, etc) circumstances.   It sounds like the subject 84 - 114 Hz motor to be an application specific type motor permitting a 1.4 speed range window -- or maybe perhaps subject to some frequency control, etc.  Good luck


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## JimDawson

UPDATE:  IT'S ALIVE !!!!!!!!!

Finally have a working RPC.  We found a Baldor 15HP motor on ebay for $300, with FREE shipping.  Not a bad deal.  Had to put bearings in it but that was cheap.




Fired right up, was drawing about 24.5 amps on L1-L2 unloaded with no capacitors switched in.  So I started switching caps in and got the legs kinda close before I ran out of caps to switch in.  Need to do some swapping around on the caps.  As I switched in caps, the current draw went down to about 16 amps unloaded.  Once I complete the balance I suspect that will drop more, then I'll start switching in power factor correction and get it down more.  Ideally, I can get the idle apparent power down to zero, we'll see how that affects the new smart meters, kinda curious about that.

Then we load tested it.  This is the 6500 watt, 3 phase, Flux Resistor.   ~8 HP worth.  Interestingly enough, when loaded, the current was only about 25 amps, which means the incoming power didn't even see the RPC motor, because the load was about 25 amps.  Note the ground clamp on the left 





With the caps switched in the T1 T3 leg is a bit high (255V) unloaded and is low when loaded (223V),  but the T2 T3 balanced out to within 1 volt of T1 T2 (239V vs. 238V)  I have a bit of voltage drop on the line to my shop, the picture is in the unloaded condition.











Anyway, it has been a long arduous journey to get to this point.  In hindsight we should have just bought a motor to start with, would have saved a week's worth of work.  But we didn't expect the motor problems we had.

But the good news is that it works now, and we'll get it wired into the lathe this weekend.


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## JimDawson

Final update  We finally got the RPC wired into the lathe.

It doesn't seem to matter which way you spin the idler motor up to start.  I tried it in both directions, and the only thing I noticed was the minor vibration changed a bit between CW and CCW, but nothing bad happened in either direction.  Took some experimenting to get the low leg on the correct set of caps, but swapping leads at the motor end fixed that.

I made a slight tactical error when I chose the enclosure, I grabbed a 6 inch deep box off of the shelf and I should have used an 8 inch deep box, I have 2 of them on the shelf.  The door won't shut all the way  The caps hit the wireways on the door, poor planning on my part.  I'm going to build a 1 1/4 inch extension for the box, not a huge deal, but irritating.

I'm pleased with the voltage balance. 239 (incoming), 237, 239, 236. Incoming power is running 1.4KW with the lathe powered up and the spindle running unloaded. Max system load seems to be about 9.5KW with the spindle at 150% power on accel. What I find a bit odd is the incoming power is 11.8 amps, but the 3 legs of the 3 phase are right around 20 amps. I guess the PF correction is doing its job, glad I added that. Hopefully the power company will only see the 11.8 amps.   But I suspect the new smart meters read KVA rather than KW like the old ones did, I'm going to see if I can figure that out.  The incoming power reads about 25 amps with the PF correction out of the circuit. These numbers verified by my Fluke clamp on. Everything seems to run OK.


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## Karl_T

You have my vote for the neatest 3 phase converter ever built


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## JimDawson

Thank you Karl.


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## Firestopper

Very nice Jim, getting close to making chips!


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## Blackjackjacques

Nice - when redoing your door, remember to leave about at least an inch of clearance between the panel door and any current carrying part.   I cannot for certain figure out what is going on with your pf and the meter readings.  The pf corrected circuit should normally read substantially less current than uncorrected. From your photos, the L1 L2 meter shows 11.8 A before pf correction and about 21A when corrected -- if I am reading your meters correctly and assuming that L1L2 is your single phase input and T1 T2 T3 is your derived 3 phase output.  It would be helpful if you can provide a simple one-line schematic showing the connection of the motors, including the load motors and how everything is wired.


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## JimDawson

Blackjackjacques said:


> Nice - when redoing your door, remember to leave about at least an inch of clearance between the panel door and any current carrying part.   I cannot for certain figure out what is going on with your pf and the meter readings.  The pf corrected circuit should normally read substantially less current than uncorrected. From your photos, the L1 L2 meter shows 11.8 A before pf correction and about 21A when corrected -- if I am reading your meters correctly and assuming that L1L2 is your single phase input and T1 T2 T3 is your derived 3 phase output.  It would be helpful if you can provide a simple one-line schematic showing the connection of the motors, including the load motors and how everything is wired.



It is a bit confusing.  The L1-L2 meter at the top is showing PF corrected incoming power and the CT is on the input leg.  From the panel T1, T2, T3, go to the motor, the lathe is paralleled off of the motor leads at a J-box on the wall.  There is a CT on each leg in the panel.  Once the two power contactors pull in, the PF correction caps are across T1(L1)-T2(L2), and the balance correction caps are across T1-T3, and T2-T3.




Actually I have just figured out how to build an over unity machine, puts out more power than it is supplied with


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## Blackjackjacques

JimDawson said:


> It is a bit confusing.  The L1-L2 meter at the top is showing PF corrected incoming power and the CT is on the input leg.  From the panel T1, T2, T3, go to the motor, the lathe is paralleled off of the motor leads at a J-box on the wall.  There is a CT on each leg in the panel.  Once the two power contactors pull in, the PF correction caps are across T1(L1)-T2(L2), and the balance correction caps are across T1-T3, and T2-T3.
> 
> View attachment 251419
> 
> 
> Actually I have just figured out how to build an over unity machine, puts out more power than it is supplied with



For over unity it is called a synchronous condenser, or just a synchronous motor to provide leading power factor. If you are making more power than put in, then Elon Musk and the Nobel committee would like to talk with you.  

In the old days, engineers used to mix, where they could, synchronous motors with induction motors to balance pf where the motors are on at the same time, etc.  However, having too much leading VARs can be as bad as having too much lagging VARs.   I'm confused as to what the meters are showing. I assume that the Idler and Lathe motors are both wired Delta. If you can provide the particulars for these two motors, I can run a quick analysis for you to model and predict the actual parameter values, VA, VAR, I, etc.  Motor nameplate data will do, but if you have actual resistance/inductance for the windings, I give you a precise picture.


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## JimDawson

Blackjackjacques said:


> I assume that the Idler and Lathe motors are both wired Delta.



The idler is a standard 9 lead, Y connected.  http://www.baldor.com/catalog/CEM2333T#tab="specs"

The lathe 1 hp hydraulic pump is also a 9 lead, Y connected, but the other motors are all AC servos.


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## Blackjackjacques

JimDawson said:


> The idler is a standard 9 lead, Y connected.  http://www.baldor.com/catalog/CEM2333T#tab="specs"
> 
> The lathe 1 hp hydraulic pump is also a 9 lead, Y connected, but the other motors are all AC servos.




The following analysis may help your efforts to validate the design and if you are getting the targeted performance of your system.  Double check my math, but it seems viable.

On the 15 hp Baldor - since you are running 2 Y (low voltage)or two identical Y windings in parallel, the impedance of the windings would be half than if you ran it in the 1 Y configuration. The 0.83 power factor rating for the motor does not indicate if that is for the motor running 1Y or 2Y, but my expectation is that the winding configuration would impact power factor.  This is where having the actual measured impedance of the motor windings would have been more valuable – and especially when we are configuring this 15hp motor to be placed in parallel with yet another (load) motor winding system.  But let's  go with the manufacturer’s .83 rating for now:

*Looking at the 15 hp motor alone and to take the pf from 0.83 to 0.95*

*AT.83 PF*
Watt(P) (input) to motor = HP x 746 / eff. = 12.11 kW (bottom of the pftriangle)
VA(S) =P/pf = 14.6 kVA
VAR(Q) = VA Sin Θ= 14.6 kVA Sin 33.9 degrees = 8.14 kVAR
I= VA/V = (14.6 kVA/(230 x 1.73)) = ~36.7 A

*AT.95 PF*
Watt(P) (input) to motor = HP x 746 / eff. = 12.11 kW (bottom of the pftriangle)
VA(S) =P/pf = 12.7 kVA
VAR(Q) = VA Sin Θ= 12.7kVA Sin 18.2degrees = 3.97 kVAR
I= VA/V = (12.7 kVA/(230 x 1.73)) = ~32A

So 8.14 - 3.97 kVAR = 4.17 kVAR leading are needed or C=kVAR/ώ_V_2=4.17 kVAR/2*Π*f*V2=209mfd. Connecting the capacitors in DELTA across the 2Y connections =209 mfd/3 = 70 mfd across each line.

So this approach improves the power factor for the 15 horse motor from0.83 to 0.95 and reduces the current from 36.7 A to 32 A.

*Looking at the 1 hp motor alone and using typical NEMA values for eff. = 82.5% and pf = 0.8:*

*AT.80 PF*
Watt(P) (input) to motor = HP x 746 / eff. = 0.9 kW (bottom of the pftriangle)
VA(S) =P/pf = 1.13 kVA
VAR(Q) = VA Sin Θ= 1.13kVA Sin 36.9degrees = 0.678 kVAR
I= VA/V = (1.13 kVA/(230 x 1.73)) = ~2.8 A

*AT.95 PF*
Watt(P) (input) to motor = HP x 746 / eff. = 0.9 kW (bottom of the pftriangle)
VA(S) =P/pf = 0.95 kVA
VAR(Q) = VA Sin Θ= 0.95kVA Sin 18.2degrees = 0.297 kVAR
I= VA/V = (0.95 kVA/(230 x 1.73)) = ~2.4 A

So 0.678 – 0.297 kVAR = 0.381kVAR leading are needed or C=kVAR/ώ_V_2=0.381 kVAR/2*Π*f*V2=19mfd. Connecting the capacitors in DELTA across the Y connection = 19mfd/3 = 6.3mfd across each line.

So this approach improves the power factor for the 1 horse motor from0.82to 0.95 and reduces the current from 2.8A to 2.4A

Therefore, with the 15 hp generator motor in parallel with the 1 hp load motor, the total capacitance across-the-lines would, in theory, be 70 + 6.3mfd = ~75 mfd to bring the system pf to 0.95 and the total corrected rms current you should see on your Fluke should be about 34.5 A. 

What is missing in the analysis is the fact that the 15 hp drive motor is being driven with one broken leg, so its shaft hp would be reduced at least one third and the inrush power requirements will increase correspondingly, and its anybody's guess how the power factor will present until the motor comes to steady-state speed. 

 However, the analysis is valid if the drive motor was operated in a true motor-generator configuration.


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## Ulma Doctor

Great Job Jim!!!!!


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## JimDawson

Thank you Mike


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