Troubleshooting My Phase Converter

Troubleshooting My Phase Converter

Two weeks ago my home made 15 year old, 7 ½ HP, phase converter died. As I tried to start it, he motor just hummed. After looking I found the starter overload tripped and a 3 amp fuse for the control circuit blow. Resetting the overload and replacing the fuse did not solve the problem.

I took the starter (AB 505 Size 1) out and put in all new contacts, as they were heavily burned. No joy. I then removed both the start caps and the balance caps from the circuit. Now I wired direct out of the starter to the motor. Tried to start with a rope, but still just humming.

While the motor was spinning from the rope, and just humming, I had an amprobe on the inputs to make sure that both legs were getting current. First one then the other looked to pull 60 amps for a second or so.

I also took the motor to a local rewind shop. It was checked for grounds with a megger, ohms on each leg checked, and finally started up on 3 phase. The motor started and ran smooth and quiet. I feel that things point to the motor, but I saw the thing run. Guys I am stumped.

John

Sounds like the start circuit stopped working.
You may not be able to spin a 7.5HP motor fast enough with a rope to get it going and apply power at the same time.

When it is single phasing on startup, it should trip the overloads, that's what their there for, to prevent winding burnout.

The control fuse blowing suggests, that something is amiss with the control circuit wiring or components. That could be why the start circuit is non functional.

You need to show us what you have for better suggestions.

SAF Ω

Agree

If both legs are showing up from the mains, then the start circuit INCLUDING THE CAPS is the prime suspect.

You could short around te starting relay (Steveco or similar?) and see if the start caps will get the motor turning. Just disconnect right away. Start caps leak smoke when asked to preform as run caps.

Piling on ........ Start circuit not working is essentially a guarantee..... since the motor runs well on 3 phase.

SAF
What you are saying makes a lot of sense. If you are right about not spinning the motor up fast enough, that will explain why the motor checked good, but would not start.

The guy at the motor shop offered to check out the caps and had replacements if needed. Given that the start caps are at least 15 years old, I think replacements are in order.

CalG
No signs of smoke loss at the start caps.

Looks like a trip to the big city Monday for 2 start caps. I will report back, and thanks for your help guys.

john

Do you have a tester for the caps? If not I would suggest picking one up.. Not expensive and it is very easy to check out caps. Mine saves me many trips for unneeded parts...

Check on that voltage relay before you run out to get caps. You might need both......

Voltage relay should default to being connected, and when the voltage comes up, it should open. if it does that reliably, it's OK.

swatkins said:

Do you have a tester for the caps? If not I would suggest picking one up.. Not expensive and it is very easy to check out caps. Mine saves me many trips for unneeded parts...

Click to expand...

Got 2 new caps today, but it will be Wednesday before I can install them.

I saw testers on ebay from $5 to $50. Any specific recommendations?

SAF said:

You need to show us what you have for better suggestions.
SAF Ω

Click to expand...

Here is a view of the phase converter, and the wiring schematic.

John Allan said:

Got 2 new caps today, but it will be Wednesday before I can install them.

I saw testers on ebay from $5 to $50. Any specific recommendations?

Click to expand...

I always believe in buying the best tools you can afford that are suitable for the application and the use it will receive. A 5 dollar tester is not in that category.

My tester also has a clamp meter and voltage tester, a true multi use tester. I think I paid around 100.00 for it but I'm sure you can find something similar for less..

John Allan said:

Here is a view of the phase converter, and the wiring schematic.View attachment 179366View attachment 179367

Click to expand...

From the looks of things, my guess would be your CR1 capacitor start relay. The contact for the start capacitors is burned up. That relay is designed for control loads 10A or less. In this application your using it for heavy surge currents for the starting capacitors.

The relay has capacity of 4 poles as standard, 8 with an adder deck. picture is a little fuzzy to tell, but yours looks to be an 8 pole unit.

Your schematic shows using only 2 poles. One for the motor starter coil at 120V, the other for the start caps @ 250V. The contact blocks in that type of relay are usually replaceable and convertible from NO to NC, and also interchangeable between slots in the relay housing. They are of open construction and can be visually examined when removed. Flipping them over, changes function from NO to NC, the little tab on the end will show which side is what function.

Running 2) 259Mfd start caps through a 10 relay contact would surely cause the light duty contacts to burn away with repeated use. You could parallel the contacts to get a little heavier rating with multiples, instead of just using one for capacitor currents.

Just transposing the possibly bad contact with an unused one could possibly get you back in working condition, if indeed the existing contact is the source of the problem. If it were me, I would probably replace that control relay with a definite purpose contactor with some 30A rated contacts for longevity.

Check the NO contact for continuity when the coil is energized, or the relay armature is pressed in manually. If no continuity exists or it is poor, your start caps will not be connected, even if they are good or replaced.

Curiosity... the print shows voltage balancing caps, but the photo doesn't, do you have them installed ?
The run caps help the starting caps get things moving, without them the start caps will be working harder.

SAF Ω

John Allan said:

Got 2 new caps today, but it will be Wednesday before I can install them.

I saw testers on ebay from $5 to $50. Any specific recommendations?

Click to expand...

here is a link for the one I use... SC24 - Fieldpiece SC24 - SC24, Compact Clamp Meter w/ Temperature. It lives in my truck and has been a decent tool. A fluke meter is the everyday tool with the Fieldpiece used for clamp on and cap checking...

Sent from my SM-N900V using Tapatalk

SUCCESS
And a confession.

The problem was the way the 2 start caps were wired. For the 10 plus years of operation, the caps were wired in parallel. During my troubleshooting these wires became disconnected. And as I went to hook them up again I referred to the schematic I produced when I made the converter. The schematic shows the caps wired in series. So I guess that as I initially got the converter working, I failed to update the schematic.

So the only hardware problem was the failure of the contacts in the Allen Bradley starter. The rest was am operator / troubleshooter problem.

Thanks guys for all the help and suggestions.

john

SAF said:

Curiosity... the print shows voltage balancing caps, but the photo doesn't, do you have them installed ?
The run caps help the starting caps get things moving, without them the start caps will be working harder.
SAF Ω

Click to expand...

Just got lazy and used an old picture taken during the original build. I figured the one I used was showing all the relevant components. Balance caps are indeed mounted and wired.
john