Need Help with my RPC

Hi guys. I recently acquired a Kondia Clausing CNC knee mill, model FV1. I have built a rotary phase converter and have good voltage but the spindle will not start, it tries but then pops a 30 amp breaker before the RPC or pops a reset in the machine control. Let me explain my RPC and see if maybe I have something wrong or if it is maybe just too small.
First I have a Louis Allis Pacemaker 3 hp motor type COG4B. I'm using a Cutler Hammer A10BN0 contactor switch for the start capacitor circuit. I'm using a knife switch and a push button for control. I have 240 volts from my breaker panel going to the knife switch, from there I pulled 120 from one side and the neutral to power the contactor with a push button. Im using both the 120's from the knife switch to go to L1 and L2 on the motor. Im using 120 from L1 to go into one side of the contactor, when it comes out of the contactor it goes to my start caps. I have 2 108 t0 130 330 volt caps wired in parallel. I then come from the other side of the start caps and go into another leg on the contactor, from there I come out the other side of the contactor and go to L3. The start system is working quite well. I have run caps wired between L1 and L3, I have a 30, 10 and 7,5 mfd wired in parallel. I have run caps wired between L2 and L3, I have 35,30,30,5 and 5 mfd wired in parallel. When I check voltage between L1 and L3 it is 245. between L2 and L3 is 242 and L1 to L2 is 240.
A friend that has built a few RPC's said that if I check from L1 and L2 to neural each should be 120, and L3 to neutral should be 260. I have 120 on L1 and L2 but only 210 on L3. Im afraid to go much higher with L3 because I think this will take me way over 240 volts, when checking from leg to leg. any comments or help would be greatly appreciated!

I forgot to mention that the mill is 3 hp

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Your line voltages appear correct, doesen't necessary have to be 240-260 volt on L3. Did you check to see what voltage the motor is wired for? 220 or 440V? Is the drum switch wired correct?

Ken

Thanks Ken . Yes I did check both of those and they are correct. I was wondering if the mill might need more than the 3 hp at initial spindle start up? I can fire it up and move the table around and pretty much everything else except the spindle start.

May need a bigger RPC. but my brother runs a 3 hp RPC to run his 3 HP motor on his lathe with no problems. His RPC doesn't have any run capacitors that I know of other than the ones for the static converter. Hummm

Ken S.

With the RPC running and table feed motor running at the same time, there should be plenty of starting power to start the mill motor. I used to have a Gorton mill years ago that I jumped started from a big Avey drill press, once the Gorton mill motor was started, turn on the feed motor, turned off the drill press. The Gorton was a two speed motor, with the feed motor running I could start the mill motor in low speed, once up to speed, kick in the high speed and it would change speed, a little sluggest but worked.

Ken

thanks Ken I will try that but Im not sure it will work. The mill is CNC and Im pretty sure that everything else stops when you turn on the spindle or it might throw a fault. but I will give it a try.

I didn't read between the lines that your mill is CNC. Have to get some of the other experts out there to advise what to do. I know there has been a couple of post in the past about getting all three legs balanced within a few volts in order for CNC equipment to operate properly.

Ken S.

Thanks Ken I tried to run the table and start spindle today. It faults out. I agree about the 3 legs needing to be ballanced close together. I have them within 5 volts highest to lowest. This machine came from the shop I work for and I have personally ran it a few times so I know it works well, and our actuall 3 phase there is no where near as close as my phase converter, I think we have around 25 volts high to low?

A neat drawn circuit diagram of your rpc might get you your answers quickly.
You can use photobucket.com to host your drawing.

thanks rons. I will try to get a drawing up here soon.

Sorry I havent gotton a diagram up yet, been too busy messing with it. lol Tonight I moved some run caps around and added a few and was able to start the spindle of the mill. It starts kinda slow so Im thinking of maybe moving a few more run caps around. I checked the voltage from the manufactured leg to neutral and it is 263.

Your circuit diagram will help, without it I am guessing that your RPC is a liittle small for your CNC mill. When it tries to start it pulls your generated legs voltages down too low and the amp draw goes too high and you blow a breaker.

Balancing the two generated legs to a little higher voltage will help. I would not target a L3 to neutral voltage, but target L1 to L3 = L2 to L3 = 1.1 L1 to L2 as a minimum for your setup. Or in your case L1 - L3 should equal L2 - L3 should equal about 252V.

A larger idler would also help. With a larger idler (5HP or more) I would target the L1 to L3 = L2 to L3 = 1.05 L1 to L2.

-Joe

thanks Joe. I was thinking the same about a larger idler.

well I just picked up a 7.5 hp motor today from the scrap yard. I hope it is good. lol it cost me .47 a pound. ended up being 112 lbs and cost $53.00

I am just beginning my machine experience but why would you use a rfc when you could use a vfd?
I just brought home a lathe that will need a vfd or rfc so that is the reason for the question.

In a word, cost. I can build a very cheap RPC, so far I have around 125.00 in mine.

A RPC is a good backup power source. If your tool already has a variable speed
pulley arrangement then a VFD is not necessary unless you don't like using a
secondary motor. A RPC is going to be a lot more dependable as well.

here is a sketch of my wiring diagram, hopefully you can make it out, its kinda light.