# Input On My Pieced Together Rpc



## fleckner's garage (Sep 9, 2016)

I am new to running 3 phase machines and i have a pieced together RPC that i'd like some input on what people think about it, if its ok, etc?  

To start i have a TEMco 4-8hp static phase converter that is supplied by a manual disconnect 30amp 220v single phase circuit from a 100amp sub panel in my garage.



Appears to utilize only one start capacitor and one run capacitor? this is where my electrical knowledge is severely lacking.



from this static converter I have 4 wires running to a junction box T1.T2.T3 and a ground. from this junction two sets of 4 wires leave with one set going to a idle 5hp 3 phase motor wired for 220v. while the other set of 4 wires run to my mill (Kearney trekker 2CH 5Hp vertical mill) This mill has a transformer on the back that i believe steps up to 440v as the motor came that way originally, and also uses a 110v input to supply a contactor/switch(I'm a car guy and would call this a relay, using lower power to switch on and off a higher power system)  with a built in circuit protection.

So when I throw the main 30amp disconnect to fire up the idle motor it starts up immediately and runs smooth(although the little static converter is louder than the 5hp motor itself!)

then when the mill is turned on it spins up immediately too and runs fine. (both idle and mill motor spin in the same and correct direction)

Voltage on the 3 phase side runs at 230v's 230v's 212v-ish unloaded. engage spindle and some power feeds to add a load and my third leg hoovers in the 208v range. too much gap in voltages to my ghost leg? would more  or larger run caps even this out? am i doing damage to my 3 phase motor with that kind of voltage difference?

also, are the more expensive static converters or RPC's quieter? or should i just move the converter further away from my work station and add some sound insulation? its pretty loud and obnoxious.

thanks for reading


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## Ulma Doctor (Sep 9, 2016)

you could increase the run capacitance by adding a run cap, that will better balance the low leg.
the converter should have a potential relay that switches the capacitors in and out of circuit
the only thing you may wish to avoid: don't use the generated leg to power the step up transformer- you may destroy the static converter.
RPC's can get quite obnoxious when idling if there is a large difference in phase voltage


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## fleckner's garage (Sep 9, 2016)

Ulma Doctor said:


> you could increase the run capacitance by adding a larger run cap, that will better balance the low leg.
> the converter should have a potential relay that switches the capacitors in and out of circuit
> the only thing you may wish to avoid: don't use the generated leg to power the step up transformer- you may destroy the static converter.
> RPC's can get quite obnoxious when idling if there is a large difference in phase voltage



Thanks for the reply. 
So recommendation of removing the step up and switching the wires at the mill motor to run 220v? 

Am I correct in thinking that I may damage the converter but not necessarily my load motor? 


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## Ulma Doctor (Sep 9, 2016)

if you have the ability to change wire taps at the motor to change it from 440v to 220v, i would recommend it.
the control circuit may have been compromised, i'm wondering what/why the separate 110v supply is necessary?
did someone not put a control transformer for the correct voltage, and are "fixing' the problem by adding another source of control voltage???

the static converter itself should make very little noise or no audible noise, the idler motor may grumble a bit until it is lightly loaded - run capacitance would alleviate that condition
for me, i'd consider starting the idler with the static converter with a momentary normally open switch, then once the idler started i'd make provision for the run capacitor(s) to return to the circuit and completely bypassing the static converter's third leg output.
it will do 2 things
1: your run capacitance could be tailored to the actual loads incurred
2: your static converter will last a lot longer by not having hundreds of unnecessary start cap dumps as the potential relays are actuated during low voltage conditions

the motor itself is only slightly affected by a low leg , in comparison, a static converter that is overworked will soon fail.


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## Keith Foor (Sep 10, 2016)

OK, hope you are getting this before the caps let loose.
First, if that is a picture of the actual caps in the unit, they are both start caps.
Run caps will be in a metal can not a plastic one.  

Second, if the static converter is making ANY sort of noise the potential relay they are using to control the start caps is not opening and the start caps are staying in the circuit.   This WILL cause them to blow up.  While I realize that there are a lot of manufactures out there that utilize potential relays for controlling start caps in a RPC it's not a good idea.  It's cheaper and a better option to run a pushbutton start that controls the caps and then drops them out once you release the button.

Post a full set of pics of the interior of the static so I can see what's in it and give you better direction.   Also include a pic of the idler motor information plate.


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## fleckner's garage (Sep 12, 2016)

Keith Foor said:


> OK, hope you are getting this before the caps let loose.
> First, if that is a picture of the actual caps in the unit, they are both start caps.
> Run caps will be in a metal can not a plastic one.
> 
> ...



I've been away from the shop and might not be back untill Friday but I will most certainly post pics of the whole system and a quick video of in use. I've logged about 20 or so hours on the system with nothing bad happening but will refrain from use untill I get some more info


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## Keith Foor (Sep 13, 2016)

If you have run it that long and the caps are still intact, they are probably going to be fine, but if the box is making any sort of noise, that needs to be addressed.  Personally I don't care much for using potential relays for start caps.  The way they work is they are normally closed (connecting the start caps to the motor) and look for a certain voltage to develop between the created leg and one of the other two powered legs.  Once the voltage hits the relays preset voltage it switches the caps out of the circuit.  Now for a guy that is building one at his house, and knows what voltage is going to develop across the legs, they are viable.  But depending on your electrical provider, your 220 power may be 225 or 230 and mine may be 222 or 220.  So what you need and what I need are two different things but that's not typically addressed with a store bought unit.  The other issue is that alot of builders will look at the start current of the motor from the name plate and install a relay that is rated for that value.  We are not starting these idler motors on 3 phase which is what the name plate indicates.   The start currents are higher with an idler motor and that puts more load in the potential relays contacts occasionally causeing them to weld together.  This brings a quick and loud end to your start caps.  It's why I use a high current contactor (60 amp typically) and a time delay relay that controls it.  The other plus to this is if you have a unit with this design, and it doesn't quite fully start, you open the cabinet and adjust the relay adding time to the closed part of the cycle.  That hold the start caps in longer and gets the motor fully started before taking them out of circuit.


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## Keith Foor (Sep 13, 2016)

OK, I went back and read your posts again.  I see the issue.  Your created leg voltage is LOW.  Potential relays are designed for a voltage window to trip.  My guess is that the window on yours is right at 208 on the bottom side and since you are at 212 / 208 loaded, it's chattering.  That could very well be the noise you are hearing.   I am going to assume that the cabinet has no run capacitors in it, or only has one run cap in it.  This is done in cheap static converters because although they technically will work it's an additional 15 or 20 bucks for the builder to put one in.  A good RPC will have 7-10 uF from L1 to L3 and 3-5 uF L2 to L3 per horsepower of the motor as labeled.    For CNC type loads that are picky about their input power this may need to be tuned for the best voltage, but it's a good starting point.  If you are only going to run a manual mill and/or lathe with no electronics other than BASIC control circuits (meaning no 3PH VFD's ) then you will be fine.  

You still need to address the noise in the Static converter though.  that's a problem that will get bigger and cause a serious headache.


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## gi_984 (Sep 13, 2016)

This is what I use:  American made, with a warranty, easy installation, UL listed, won't burn my house down, quiet (stand right next to it and talk ), talk to a real live person tech support if ever needed, one push button on, sips electricity, very reasonable price,  etc. etc. 

https://www.americanrotary.com/products/view/ar-pro-series


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## fleckner's garage (Sep 13, 2016)

Keith Foor said:


> OK, I went back and read your posts again.  I see the issue.  Your created leg voltage is LOW.  Potential relays are designed for a voltage window to trip.  My guess is that the window on yours is right at 208 on the bottom side and since you are at 212 / 208 loaded, it's chattering.  That could very well be the noise you are hearing.   I am going to assume that the cabinet has no run capacitors in it, or only has one run cap in it.  This is done in cheap static converters because although they technically will work it's an additional 15 or 20 bucks for the builder to put one in.  A good RPC will have 7-10 uF from L1 to L3 and 3-5 uF L2 to L3 per horsepower of the motor as labeled.    For CNC type loads that are picky about their input power this may need to be tuned for the best voltage, but it's a good starting point.  If you are only going to run a manual mill and/or lathe with no electronics other than BASIC control circuits (meaning no 3PH VFD's ) then you will be fine.
> 
> You still need to address the noise in the Static converter though.  that's a problem that will get bigger and cause a serious headache.



Ok here's the setup.








Idler motor





Static and idle motor firing up 





Mill(load) firing up





Static converter making its noise, it's decibel level isn't too high it's just kind of annoying.

I think everything is running as good as that static can be, assuming it's obviously of the cheaper models you speak of. 

I'm comfortable enough with electricity and Internet research to build my own static portion, can't justify buying a new rpc for 6-700$ when I know most of that costs is for the idler motor which I already have that works fine.

Would love to hear your continued thoughts on what I have after seeing the photos and the videos.

Thanks 


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## Ulma Doctor (Sep 13, 2016)

something sounds very wrong to me.
i'd isolate the 3rd leg output with a momentary switch
just to be clear
L1 and L2 should get 240v input
T1,T2,T3 are output to the idler.
one of those legs gets the dual start cap arrays' charge to jolt the motor to start or add more power into the leg that is really low, during load conditions that actuate the potential relay

if you want a alternative that will work for years to come:
http://www.hobby-machinist.com/threads/rpc-simple-design-unbalanced.12712/

i can make one for you if you'd like and even balance it for you


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## fleckner's garage (Sep 13, 2016)

Ulma Doctor said:


> something sounds very wrong to me.
> i'd isolate the 3rd leg output with a momentary switch
> just to be clear
> L1 and L2 should get 240v input
> ...



Thank you for the offer! I feel like i could probably figure it out my self with hours of research and some trial and error.

whats your cost on a custom balanced system for my 5hp system?


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## Keith Foor (Sep 14, 2016)

Yep all sorts of wrong here.  
First issue and the biggest by far.  The potential relay is buzzing because it's not getting quite enough voltage for it to fully open.  
You need to start to RPC up (and make sure it's ALWAYS run with the cover in place.  ALWAYS) let the RPC run for a couple minutes, shut it down and see what is getting hot.  Either the potential relay is getting hot, the caps are getting hot or they are both getting hot.   The caps should NEVER get hot.  They are only suppose to be in circuit for a few seconds to start the motor.  If they are staying in (I don't believe they are or your 3rd leg voltage under no load would be around 400 volts with that much capacitance) they will get hot and then come apart, which is why you need to run the cover at all times.  Of course when checking for heat, make damn sure that the power is OFF to all of it.  And don't touch any of the wiring regardless as the caps can hold a charge and bite you even with no power connected.  If you are not comfortable with using your hand, get a non-contact infrared thermometer.   

Second issue and as stated by others, no run caps are why your 3rd leg voltages are low.  Now, here's the thing with an RPC.  Real honest to God 3 phase power is 3 legs of 230 volts that are 120 degree's opposed leg to leg.  Single phase (in truth split phase) house power is two phases at 120 volts that are 180 degrees opposed leg to leg.  You will NEVER generate true 3 phase with a phase converter.  The split phase transformer feeding your house will not allow it and will force the two powered legs to be 180 degrees apart no matter what.  So what you are doing with this design of static phase converter is using brute force (read that high current and big power bill) split phase to run a 3 phase motor that you are starting with start caps.  It's not designed for that. In fact most factories and businesses that are running 3 phase 208 or 460 have special devices connected to the 3 phase feeds from the utility that monitor for whats called a phase out condition.  This is where one of the 3 phases stops providing current to the building.  When it senses this, it sets off an alarm and may even drop the switch gear out putting the building dark.    Reason is that if you have running motors that are 3 phase and try to run them off 2 of the 3 phases they will overheat and burn up.  Which is EXACTLY what your static phase converter is doing.  How do I know this?  Well I got to replace 13 exhaust fan motors in a warehouse that had a phase out condition for about 6 hours one day and that morning the fans were all started up.  The phase loss happened about 9 AM and no one thought to shut them off until a couple of them started smoking.    Building was built in 71 and the 3 phase monitoring stuff was not available at that time or was not deemed as needed.  Now that's when you are running a 3 phase motor on 2 legs that are 120 degrees apart.  This is running them 180 degrees apart.  Which is a bit easier on them but still not good.  It still draws tons of current (hi electric bill) and causes heating of the motor.   

Enter the run capacitor phase converter.  
So what does the run capacitor do in a RPC that cleans stuff up, lowers current draw and makes things smoother?
A motor is an inductor.  Like any coil of wire.  Gonna get into some basic AC electronics type stuff here so bear with me.  What an inductor does is as current is applied to it, it builds a magnetic field around it.  As the power is removed the magnetic field collapses in on the coils of wire inducing voltage across them.  This causes current flow out of the inductor when it has something it's connected to.  Now all of this can be calculated with the voltage and time.  And remember that we are talking about AC power here.  It starts at 0 volts, increases to 240 volts, then begins to go back to 0 volts.  It then passes 0 volts and heads to a negative 240 volts.  Then back to 0 and on to 240 positive volts.  This cycle happens 60 times a second, or at 60 Hertz.  You yanks got shorted 10 cycles per second and run at 50 Hertz, but you concept is the same.  Now, the capacitor.  It does the same thing.  It will charge up and hold a charge as well. But it's different.  Where an inductor has it's charge via a magnetic field. the Capacitor holds it electrostaticly via two plates that are seperated and partly insulated from one another.  Now.... here's the cool part.  And anyone that has a RPC without an output contactor and lights connected to their RPC will tell you that when they turn it off the light stays on for a time.  But how is this possible?  Because the combination of a capacitor and an inductor in parallel is called a tuned circuit.  And that circuit will RING.  By this I mean that the inductor will collapse it's magnetic field, and charge the capacitor for a certain amount of time.  Then the capacitor will discharge into the inductor for a specific amount of time. and back and forth it will go.  Now why is this important?  Simple... the value of the inductance (measurement of the inductor) and the value of the capacitance can be mathematically figured to oscillate (RING) at 60 or whatever Hertz that you need it to.  And then you have a third leg, that can generate current, that's oscillating it's happy self along creating the third leg.  And the split phase power kicks the wheel a bit to keep it going.  And it's why that you really need to have run capacitors in an RPC.  It gives the RPC the ability to generate more usable power.    To this point.  I have started and run 20 HP motors that were just sitting on the floor with nothing connected to their output shafts with a 10 HP RPC. I do it all the time when I am testing idlers out before building them into full RPC units.  So the capacitors do work, do help and will benefit you in the long run.

Now that you know WAY more about RPC's than any RPC manufacture will EVER tell you.  I have some advice.  If you can hook up an RPC to a motor and get it running you have enough smarts to build a full RPC with a bit of guidance.  If you don't believe this, and want a box that will hang on the wall, and make your idler motor into a proper RPC there are a number of manufactures out there that will sell you just the box.  The motor is your responsibility to provide and connect, which is sort of what you have tried to do here.  

Ask questions.  Message me, if you want.  I actually prefer you ask  right here.  I promise that any question that you have someone else will also have and if the answer is here they can find it too.


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## fleckner's garage (Sep 14, 2016)

Keith Foor said:


> Yep all sorts of wrong here.
> First issue and the biggest by far.  The potential relay is buzzing because it's not getting quite enough voltage for it to fully open.
> You need to start to RPC up (and make sure it's ALWAYS run with the cover in place.  ALWAYS) let the RPC run for a couple minutes, shut it down and see what is getting hot.  Either the potential relay is getting hot, the caps are getting hot or they are both getting hot.   The caps should NEVER get hot.  They are only suppose to be in circuit for a few seconds to start the motor.  If they are staying in (I don't believe they are or your 3rd leg voltage under no load would be around 400 volts with that much capacitance) they will get hot and then come apart, which is why you need to run the cover at all times.  Of course when checking for heat, make damn sure that the power is OFF to all of it.  And don't touch any of the wiring regardless as the caps can hold a charge and bite you even with no power connected.  If you are not comfortable with using your hand, get a non-contact infrared thermometer.
> 
> ...




Thank you so much for the detailed reply.  I certainly knew nothing about 3 phase power and very little about split phase AC power a short time ago when i ordered the cheap static converter to try and piece together a cheap rpc because i was anxious to try out a new machine and make some chips.

I now understand much more .

correct me if I'm wrong.

seems like i could wire in run capacitors to what i already have, add a magnetic contactor for safety(instead of just using a 30amp fuse disconnect), and use a time delay for the start capacitors to get rid of the potential relay and have a much more useable system? some googling leads me to believe around 80 uf for run capacitors will do my 5hp idler just fine? Im seeing capacitors for less than 6 dollars, the magnetic contactor the most expensive piece I'm missing.

The tiny box the static converter components came in obviously has no room and the joke of plastic buss connectors hardly fit appropriately gauged wire so I'm thinking of starting from scratch.

thanks again for the advice so far and to come...


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## Ulma Doctor (Sep 14, 2016)

you are correct, you could use one of the start caps from the other unit and construct you own starter.
if you add a 20 to 40 uf oil filled run cap and you'll have a nice system


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## Keith Foor (Sep 14, 2016)

Yes, I am in agreement with Mike.  You can salvage the start caps and other parts from your static converter and add a few more and have a good RPC.  
As far as run cap values, I will need to look it up and you will still need to adjust slightly off my numbers.  But again Mike should be close.  Might be a bit more.  But you want to run them L1 to L3 and L2 to L3 not just L1 to L3 as I see many do.   It makes the RPC more stable.  
The contactor for the run caps can be a 2 contact unit saving you some money as well.  Just have it switch the L1 and L2 connections for the run caps.  The L3 can be hard wired. 

Now I would get another single pole contactor and control it with a push button for the start caps (cheapest route) but if you what to ry using the potential relay going forward, it might work since your L3 voltage will be higher with the run caps and it may not buzz like it is now.


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## fleckner's garage (Sep 14, 2016)

Keith Foor said:


> Yes, I am in agreement with Mike.  You can salvage the start caps and other parts from your static converter and add a few more and have a good RPC.
> As far as run cap values, I will need to look it up and you will still need to adjust slightly off my numbers.  But again Mike should be close.  Might be a bit more.  But you want to run them L1 to L3 and L2 to L3 not just L1 to L3 as I see many do.   It makes the RPC more stable.
> The contactor for the run caps can be a 2 contact unit saving you some money as well.  Just have it switch the L1 and L2 connections for the run caps.  The L3 can be hard wired.
> 
> Now I would get another single pole contactor and control it with a push button for the start caps (cheapest route) but if you what to ry using the potential relay going forward, it might work since your L3 voltage will be higher with the run caps and it may not buzz like it is now.




ok so i would say I'm mostly understanding all of this, one more question for now....

topic of the contactor- my brain works well with analogies of a topic i understand to explain something i don't.  Is a contactor in the RPC similar to a relay used in an automobile headlight schematic. were a small gauge and amp switch(switch on the dash of your car) are used to open or close a larger amp load(headlight)? contactor being the relay to connect or disconnect the legs from the single phase input/balanced phantom leg to the load/idle motor?

i think I'm to the point to where i can look at a picture of other RPC's or schematics and make it happen but id just like to understand a  little more.

thanks


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## John Hasler (Sep 14, 2016)

fleckner's garage said:


> ok so i would say I'm mostly understanding all of this, one more question for now....
> 
> topic of the contactor- my brain works well with analogies of a topic i understand to explain something i don't.  Is a contactor in the RPC similar to a relay used in an automobile headlight schematic. were a small gauge and amp switch(switch on the dash of your car) are used to open or close a larger amp load(headlight)? contactor being the relay to connect or disconnect the legs from the single phase input/balanced phantom leg to the load/idle motor?
> 
> ...


A contactor is just a big relay.


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## Keith Foor (Sep 14, 2016)

The term contactor vs the term relay are interchangeable. The only thing I ever heard that separates the two is the amount of current that one can handle and the number of poles (each pole is a separate switched line connection).  Now the nice thing about some contactors is that they have both high current and low current poles.  The low current ones can be used in conjunction with a pare of momentary switch's to control incoming power and provide a stay off when the power fails feature.  The way this works is you put a normally open button across the poles of a contactor that power flows through to energize the coil on the contactor.  So when you push the button, the contactor closes and the poles close and continue to power the coil.  For the off part, you run one leg of that coil through a normally closed button.  When it's pushed, it actually breaks the circuit and stops power from flowing letting the coil relax and the contactor opens.  Due to the fact that the contactor is closed by power flow and not a mechanical toggle on / off switch, when the power stops for any reason the coil will relax and stay relaxed until the on button is pressed again.


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## fleckner's garage (Sep 15, 2016)

ok heres one for you guys, I know you know the answer.

topic: connecting l1-l3 and l2-l3 in the run caps. circuit as mentioned above by keith to help with balancing.  

is that as simple as running from the single phase l1 through my series of proposed run caps and out the other side to ghost leg l3. and in parallel doing the same with l2 through the caps and out the other side to host leg l3? or do i have to have two separate banks of run caps, just curious if the anatomy of the run caps include diodes so that two individual currents can run parallel with out shorting?

I feel i probably explained that as poorly as i could but hoping you guys are smart enough on the subject you can see through my ignorance and provide some light. I will reply with a simple drawn diagram of what I'm questioning.


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## fleckner's garage (Sep 15, 2016)

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## Keith Foor (Sep 18, 2016)

Nope you do have to have 2 banks of run caps.  No diodes in a run cap.  Just the cap.  Wiring them together would indeed put a dead short across L1 to L2 and of course that would be bad.  

Cap sizes are going to run 10 to 15uF per horsepower of the idler motor.  

Now too much capacitance can be as bad as too little or no capacitance.  When the capacitance is too high the L1 to L3 and L2 to L3 voltage increases, and it can be significant.  I have seen it up near 300 volts when experimenting with RPC's.  Obviously you don't want that so you will have to adjust your values to get your voltages right.


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## fleckner's garage (Sep 18, 2016)

Keith Foor said:


> Nope you do have to have 2 banks of run caps.  No diodes in a run cap.  Just the cap.  Wiring them together would indeed put a dead short across L1 to L2 and of course that would be bad.
> 
> Cap sizes are going to run 10 to 15uF per horsepower of the idler motor.
> 
> Now too much capacitance can be as bad as too little or no capacitance.  When the capacitance is too high the L1 to L3 and L2 to L3 voltage increases, and it can be significant.  I have seen it up near 300 volts when experimenting with RPC's.  Obviously you don't want that so you will have to adjust your values to get your voltages right.



Thanks! I kind of figured so after looking at the tabs closer, I've got a bunch of 10uf on order so I'll be experimenting soon. Was thinking about running two banks equaling 30uf then adding smaller increments from there for my 5hp idler, 

I assume I may see some changes when a load is added to the rpc?

Thanks again. 


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## fleckner's garage (Sep 20, 2016)

Keith Foor said:


> Nope you do have to have 2 banks of run caps.  No diodes in a run cap.  Just the cap.  Wiring them together would indeed put a dead short across L1 to L2 and of course that would be bad.
> 
> Cap sizes are going to run 10 to 15uF per horsepower of the idler motor.
> 
> Now too much capacitance can be as bad as too little or no capacitance.  When the capacitance is too high the L1 to L3 and L2 to L3 voltage increases, and it can be significant.  I have seen it up near 300 volts when experimenting with RPC's.  Obviously you don't want that so you will have to adjust your values to get your voltages right.



Ok here's my schematic with all the components I believe you guys were recommending.  Anxious to hear if you guys think this looks ok. Assume the start and run caps are sized appropriate that I will be doing with your recommended starting point with balance tuning from there . 





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## Ulma Doctor (Sep 21, 2016)

there are many ways to skin the same cat.
i'd consider making a line connection to the start caps, otherwise you'll have a hard time charging the start caps
in your configuration, the contactor must close in order to charge the caps.
it's ok for the run caps, but, you'll need an initial charge to start the idler


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## fleckner's garage (Sep 21, 2016)

Ulma Doctor said:


> there are many ways to skin the same cat.
> i'd consider making a line connection to the start caps, otherwise you'll have a hard time charging the start caps
> in your configuration, the contactor must close in order to charge the caps.
> it's ok for the run caps, but, you'll need an initial charge to start the idler



Ok you stumped me again. Can you explain what you mean by a line connection to the start caps?

Thanks


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## Ulma Doctor (Sep 21, 2016)

You'll supply an unbroken connection to 1 power leg
The cap output can be broken with a relay


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## fleckner's garage (Sep 21, 2016)

Ulma Doctor said:


> You'll supply an unbroken connection to 1 power leg
> The cap output can be broken with a relay



Like this? Add a jump from the start contactor that goes straight to the l3 output in parallel with the start capacitors. The way I illustrated it would only see power while holding the normally open start switch then that and the start cap circuit would be completely out of play when the button is released and the l3 would only see power through the l1-l3 and l2-l3 run caps.





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## Ulma Doctor (Sep 21, 2016)

maybe on the other side of the contactor and use the contactor to make/break the cap output


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## fleckner's garage (Sep 21, 2016)

Ulma Doctor said:


> maybe on the other side of the contactor and use the contactor to make/break the cap output



Alright so the third leg likes full time supply from one of my real legs in addition to the run capacitor circuits. 

Sounds simple enough, wife just sent me a picture of all the usps boxes on the porch so I should have everything to start wiring tomorrow when I get home. 

Thanks again for the recommendations 


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## Ulma Doctor (Sep 21, 2016)

in effect you will be switching start caps and run caps in and out of the circuit if things are working correctly.
you shouldn't use run caps and starts caps at the same time.
when the start caps charge is introduced there should be no run caps in the motor circuit until the start caps are out of the circuit


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## fleckner's garage (Sep 21, 2016)

Ulma Doctor said:


> in effect you will be switching start caps and run caps in and out of the circuit if things are working correctly.
> you shouldn't use run caps and starts caps at the same time.
> when the start caps charge is introduced there should be no run caps in the motor circuit until the start caps are out of the circuit



Ahhh. I get it. I need to re work my run circuit as I have those powering up right away at the same time as the start caps.


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## John Hasler (Sep 21, 2016)

fleckner's garage said:


> I have those powering up right away at the same time as the start caps.


That's what I do.  Works fine.  The effective starting capacitance is the sum of start and run capacitance.


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## Ulma Doctor (Sep 21, 2016)

you just don't want the start caps dumping into the run caps


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## John Hasler (Sep 22, 2016)

At startup all the caps are connected in parallel.  When the motor reaches running speed the relay disconnects the start caps which then discarge through the shunt resistor.  There is no opportunity for anything I'd call dumping.  It's just like a capacitor-start capacitor-run single-phase motor.


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## Ulma Doctor (Sep 22, 2016)

i agree, as long as the caps are in parallel the will be no issues-
making series connections will not work as intended


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## fleckner's garage (Sep 25, 2016)

Alrighty guys, got this thing preliminary up and running.  everything seems to be working as it should.  Its essentially wired exactly how my drawings looked.  I think i need to add some more Run caps still.  unloaded Im getting l1-l2=235v   l1-l3=224v   l2-l3=216v.   Light load  230v,208v,208v.  I either am too low on run capacitors or i need to add a jumper line from a real leg to L3 as Im only connected through run caps. and of course the start caps when those are in play.

She gets to full speed quicker than I can let go of the start button so I'm confident in my start system.

as far as run cap values, is  the "10-15uf per idler HP" per bank or total?  Im running 45uf between l1-l3 and 50uf between l2-l3.  Maybe I need to get closer to the 15uf per HP and have around 75 per bank.

Curious to hear your guys feedback.


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## John Hasler (Sep 25, 2016)

fleckner's garage said:


> I either am too low on run capacitors or i need to add a jumper line from a real leg to L3


No, no.  Don't do that.  Your motor is *generating* L3: that's the whole point.  You're within 10% and the voltages are balanced.  Leave it alone.


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## fleckner's garage (Sep 25, 2016)

John Hasler said:


> No, no.  Don't do that.  Your motor is *generating* L3.  You're within 10% and the voltages are balanced.  Leave it alone.



 I immediately tried adding that jumper after posting and she wouldn't even start. Learned that doesn't work. 

So am I crazy to think I could get it more balanced? My math says I'm 9.5%. Adding a few more uf's in small doses won't get me closer to possibly 5%?


Sent from my iPhone using Tapatalk


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