RPC starts in wrong direction - new issue

Okay Brainiacs

Here lately I have been having an issue that occurrs more often. Press the start button and it drops the juice on the RPC idler or doesn't sound right. Come to find out that the 40HP Idler is starting in the wrong direction.

So I give the shaft a twirl and go inside to start and it starts normal, sounds good and voltages are sweet. Anyone else have an issue like this?

Frank S. in Tennessee

An RPC doesn't have a wrong direction.

If CW is A-C-B and you need A-B-C, then you interchange A and C.

IF CCW is A-C-B and you need A-B-C, then you also interchange A and C.

If you are using a balanced RPC, also called a Fitch-type RPC, the large start cap should be temporarily placed across the larger of Cab or Ccb, during starting.

I think that you don't have quite enough start capacitor. In one of your previous posts you mentioned that it took about 3 sec to get the idler turning and that is just a smidge long.

The "sounds funny" is probably the motor groaning / growling while trying to start. Mine did that for a while until I added more starting capacitor. The interesting thing was if I hit the start button and heard it growl, I could immediately hit the stop button and then hit start again and it would usually start fine.

It is tricky to size the amount of start capacitor without having the motor there. There are some rules of thumb that will get you close, but without the actual motor it is really hard to do, so unless the start caps are well under the 70 - 100uF per HP, you can't really blame your pannel builder.

-Joe

Frank
I do remember that you did remove some run capacitors to adjust the phase voltage's. The question that I have is before you removed the run caps, was the RPC starting up faster then after you removed the run caps? If the answer is yes, then just add the removed run cap's to the start capacitor circuit.

macplus - It has always taken about 5 - 6 seconds for the motor to come up to speed. It is a lot of mass to start which is a good thing. On those occasion when we have a power spike it seems we have a bit of cushion to press feed hold. I couldn't be more satisfied with the panel and I don't know why Joe would think that I am blaming the Panel builder.

Maybe I need to add a run capacitor on both legs to see if that will adjust the phase voltage better. Right now I have two caps on one side and four on the other. I never considered the startup to be excessive. The inrush quickly drops and the amp draw drops nicely to a steady 15 amps.

At more than 100% on the machines load meter I have not seen more than 30 amps on the incoming line. I chart my power consumption and someone said that RPC cost more to run than does a Phase Perfect setup. My daily power use runs from 1.60 to 3.00 per day for running the RPC and machine and A/C window shaker (220V).

So power wise it runs well, just this oddity in start direction.

Joe - "The interesting thing was if I hit the start button and heard it growl, I could immediately hit the stop button and then hit start again and it would usually start fine."

On mine I have to let the motor stop all the way before restart otherwise it is trying to overcome a lot of rotating mass.

Maybe I do need some more start caps. It has never taken less than 5 sec to come up to speed. Jacques my E-mail is [email protected] - just let me know how much for a couple more start caps.

Frank S. in Tennessee

This weekend is Memorial Weekend - please take a moment to thank all those that gave so much. My Father-in-Law passed this morning, he was a Veteran (Korean War). We were so blessed to have him here for 26 years past his first quad bypass, he enriched so many lives and was an advocate for the aging and Nursing Home reform. A Citizen of the Year recipient, he will be missed by many.

Mitty,

There were some initial comments from myself and others about your the internals of your pannel and I just wanted to make sure that you understood that this particular issue (if it was a little low on start cap) would be very hard for any pannel builder to never encounter since the large variety of motors out there take a large variety of cap to start them.

I think the start contactor looked marginally sized originally and adding start caps will reduce that margin so consider that too. Hopefully you have rewired to remove the "current sharing" on the start cap contactor.

-Joe

Well life is sucking right now because it won't crank up right. I went out and put the removed cap back into the run set and no difference. I measured the output and it seems that the manufactured leg is low on voltage. This has me baffled. I switched the incoming leads (Power company leads) and didn't make a hill of beans difference.

I get the groaning sound and like a rattle in the panel when it tries to start

The start contactor was replaced with an appropriate sized one from Jacques, and up until just the other day gave me no problems.

I don't understand how it can be running just fine and now runs like crap and is not making juice like it should. This is so weird. Maybe the local (which is 25 miles away) Grainger store has some caps. But that is a Monday deal and I have parts to run.

I couldn't find a direction spec. on the motor, but I am pretty sure that it ran CCW and now starts CW. Well I did detail the voltages that I got before when running it (on a different thread) and so I will compare what I get now to what I had then.

Frank S. in Tennessee

Doin nothin instead of doin parts

New Voltage measurements

So now I printed out the previous voltage readings from the old thread and took new readings.

Current situation:

Contactor 1-2 224V

1 to gnd - 101.2
2 to gnd - 124

A - B 144 V
A - C 224 V
B - C 216 V

A - gnd 123 V
B - gnd 145 V
c - gnd 100 V

So it seems like A-B is low by abt 70 - 80 volts

So did a cap open up ? No obvious damage that I can see!

Frank S. in Tennessee

Frank
Sorry for not getting back sooner, out of town for the holiday. In your panel I would check the the back 4 run capacitors bank to make sure a jumper or lead wire did not come off, as this would cause your rpc to turn over slowly and a low output voltage between A-B. If you still need some start capacitors, just send me your mailing address.
P.S. sorry to hear about your father-in-law passing away.

Hi Jacques

I checked the back 4 run caps and didn't see anything out of the ordinary.

Mailing address:
Mitty Industries
72 Eldad Road
Trenton, TN 38382

Thanks - it was unfortunate that we lost Bernie (he lived in the North Country in Dekalb Junction, NY). I think he knew that he wouldn't be coming home and at least he didn't suffer. We actually lived in Philadelphia, NY for a while to be near to them and spend some quality time.

Update

So last night I swapped the bank of big silver run caps on the legs of the incoming single phase. Didn't help other than switch which side had the low voltage from the wild leg A-B - B-C. I did notice that the start Contactor is hanging up. Maybe it has user serviceable areas that can be cleaned up and polished. I don't know. Just a smidge frustrated.

Maybe some miracle will happen and the demons will be exorcised from it to day on Sunday. If it gets up and runs, it may not shutdown for a few years.

So Joe your saying I need between 2800 - 4000 uf of start caps? I have 2700 now.
Is there a ratio for run caps?

Frank S. in Tennessee

My take on it...

Frank-

Since you had a fine-running system before, and the way it degraded... leaves me with the feeling that either you had a cap go bad, a wire (to a cap) go bad, or your start-contactor has developed some pretty bad contact characteristics.

Reason being- you apply single-phase across two legs, and the third, under startup, gets enough 'phase shift' to kick the rotor in the proper direction. With the growling being high, and the nebulous direction attitude, the answer is that there's not enough phase shift, or current flow to the third (manufactured) leg to kick it in the proper direction.

Caps can go open... they can also short... they can also burn internally and lose capacity. With your machine requiring a very LONG start cycle, those capacitors take a heckuva beating. MY 10hp homemade RPC will go from dead-stopped startup, to full run speed in under a half-second, and the start caps are hooked in for only about 0.7 second.

I have, under testing conditions, forced my start circuit to stay engaged for over 10 seconds, and the caps and wiring get mighty hot... I can't imagine your extended-start cycle not burning up caps with frequency.

If I had that large an RPC, I'd use a two-stage idler system- start a small (2hp) idler, and then use an across-the-line engagement of secondary idler to bring up the bigger capacity. The small motor will help the big'n get goin' the right way.

Dave

After messing with it the last few days, I'm thinking that it's a two prong solution. Up the number of Start Caps and maybe approach that 4000uf range broken into three groups so I don't have current sharing as Joe mentioned (maybe three groups of 5*270uf=1350*3=4050uf). I probably should add some run caps as well to see if that is part of the problem as Jacques thinks (he designed the Panel). With the motor being a big sucker I can't see it coming up to speed in a half second.

The Start Contactor was not the one replaced before it was the Contactor for the incoming 1ph lines. The Start Contactor is hanging a bit and I'm not sure if it needs to be replaced with something bigger. I noticed that its only rated at 10hp @ 240 volts. One thing is for sure, I need to resolve this asap. I have parts to run and machine payments to make and can't have the VMC sitting idle too long.

I though about a pony motor to spin it up but that complicates it a bit. The RPC Idler is outside and the panel is inside. I also need to check with Jacques about some digital meters to monitor power out. It may have started earlier and I wasn't aware of the issue until too late. Jacques has a two year warranty on the Panel and I'm sure that he will help us get a resolution. He has been great about customer service. I wish he made a 40hp Gold Series Panel.

Frank S. in Tennessee

P.S. I know what you mean about quick starts. My 5HP RPC is almost instant and is running 540uf for 5 hp. Hit the switch and bang she runs. I just can't see the 40 hp doing that although it is bolted to concrete with 3/4" bolts and on big rubber washers.

mitty38382 said:

So now I printed out the previous voltage readings from the old thread and took new readings.

Current situation:

Contactor 1-2 224V

1 to gnd - 101.2
2 to gnd - 124

A - B 144 V
A - C 224 V
B - C 216 V

A - gnd 123 V
B - gnd 145 V
c - gnd 100 V

So it seems like A-B is low by abt 70 - 80 volts

So did a cap open up ? No obvious damage that I can see!

Frank S. in Tennessee

Click to expand...

Frank
I will be sending out some more start capacitors tomorrow ( right now you have 10 start caps rated at 270-324mfd each, which gives you a avg of 3000mfd's ), this will help your idler motor come up to speed faster ( your starting current will increase ). But this will not solve your voltage issue problem, I would double check all connections on everything ( including single phase side ). As your past thread for this panel had the voltages pretty well balanced.

Also...

Check the contacts on your starting-contactor- you're right to worry about it's capacity, as the start-cap circuit will show some incredible currents during certain portions of the startup-ramp... a prime example of how Kirschoff's Law is not-necessarily-true. FWIW- I burned up a few start-contactors doing my own first-RPC build... for exactly the same reason.

What are the numbers on the 3 pole contactor that controls the start caps?

I saw the numbers 3040 on it in a previous picture which makes me think it is a 3 pole 40 amp DP contactor. 440uF of cap could deliver 40 amps, so that contactor may be underrated if it is switching 1000 uF per pole, or about 100 amps per pole.

If the contactor is a NEMA sized unit rated for 10HP you are in much better shape than if it is a 40 amp DP contactor since the NEMA ratings take motor inrush into account.

My guess is that you do have a two pronged issue. You might need closer to 4000 uF to start your particular idler, and you may have a contactor that is not working properly. It could also be that the long start cycles have degraded the start caps. They are usually rated for only 3 second starts 20 starts per hour...

It could be the contactor controlling the start caps that is undersized. It could also be the main contactor since it also switches all of the start caps on it's center leg (yellow wires), but it is less likely since it only switches them on not off.

-Joe

Frank
I sent out 4 more start capacitors to you, if you still have the 75amp 3 pole contactor ( I would recommend to use this contactor inplace of the start contactor that is mounted in the panel now, as your starting current will increase because of the extra start caps ).
As I stated before in this thread, the start capacitors will not solve your voltage issue that you are having when your RPC is up to speed.

Thanks Jacques, I'll be looking for them. I still need to work on the Run Caps issue. Why all of a sudden I'm having an issue is puzzling. I might redo the wiring on the run caps and solder the push on terminals to the wire.
I will also rewire to take out the current sharing on the Starting Contactor. I need to fit that in the box since its quite a bit bigger.

Frank S. in Tennessee

How did the start caps go? USPS, UPS, FedEx?