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Another Rotary Phase Converter

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JimDawson

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#1
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.
1508285305044.png

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.

1508284601028.png
 

countryguy

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#2
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?
 

JimDawson

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#3
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.
 

countryguy

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#4
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. :-(
 

Blackjackjacques

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#5
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.
 

JimDawson

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#6
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.
 

Blackjackjacques

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#7
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.
 

talvare

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#8
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 !
 

Blackjackjacques

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#9
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
 

JimDawson

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#11
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 !
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. :confused 3:
 

Blackjackjacques

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#12
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?
 

JimDawson

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#13
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. :rolleyes:

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.
 

JimDawson

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#15
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 :)
 

Blackjackjacques

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#16
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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Bob La Londe

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#18
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.
 

Keith Foor

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#20
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.
 

JimDawson

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#21
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. :grin:

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. :)
1508369388503.png
 

JimDawson

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#22
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?
 

JimDawson

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#23
Got some work done on the RPC today. Bet you have never seen a RCP with an oil filter on it. :grin: 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.

1508891322645.png
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.
1508891358922.png

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.
1508891391736.png
 

Ulma Doctor

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#25
Bet you have never seen a RCP with an oil filter on it. :grin:
No sir, that's the first RPC i have seen that has twin filtration!
(most other hyperdrive generators are single filter units :grin big:)

what weight of RPC fluid are you gonna use???
What brand???
can i get some RPC fluid too??? :grin::grin big:
 
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Ulma Doctor

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#26
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

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#27
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.
 

JimDawson

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#28
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
1509325931788.png

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 :cautious: 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
1509326215167.png

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.
1509326503441.png

And the back view
1509326541759.png


And the cabinet back panel

1509326667638.png

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

1509326762418.png

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

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#29
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

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#30
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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