dc motors ?

[cra]

Hi: Can anyone tell me why a 24volt dc motor I had rebuilt will work on 12 volts but not 24 volts as it trips the fuse. It starts slowing down and overheating immediatly on 24 volts without a fuse.
Thanks,
Royal

 

[forumlicker007]

Is it a rewinding? THen probably you've chosen wire with higher diameter than the older one.

 

[cra]

Yes ,it was rewound. He told me that if it works on 12 volts that it would work on 24, but as I explained,it started smoking and quit within a couple of seconds.

 

[forumlicker007]

You've rebuilt it as a 12V motor!
Try increasing turns. Use same diameter wire as the older one.

 

[Leftyretro]

If you had it rewound for 12v operation why did you try and run it at 24v ?

Lefty

 

[colin55]

There is a mistake in the direction of winding of one of the poles. A 12v motor will operate on 24v and just have a higher RPM to counteract the higher voltage.

Run the motor on 6v and see if it has a dead spot.
Alternatively, hold the shaft on 6v and turn it slightly while applying the power to see if it has uniform torque.

 

[Hero999]

You've rebuilt it as a 12V motor!
Try increasing turns. Use same diameter wire as the older one.

I doubt that would work because the wire probably wouldn't fit on the core.

 

[forumlicker007]

Hero, I mean unwind his turns and rewind again using the wire size exactly same as what the original one had. A tight wiring is good. I assume two reasons for the smoke:
1. He has chosen a higher diameter wire so the overall resistance is low which needs extra turns but the core will overflow.
2. His winding might be a loosened one , so he ended up with less number of turns than required.
Start winding the wire from one pole, once finished go to the second one wind on same direction, then to the next one etc. Finally attach the two wire ends together.Suppose you have three poles. You end up with three wire sections in between the poles. Just remove the enamel on the center of the each section and attach to the split ring. Split ring will have three sections.

 

[tcmtech]

How many poles does it have and how big is it?
Is it a permanent magnet type or a shunt or series type?
If smoke came out its already damages and will most likely need rebuilding again.

 

[cra]

cra

The shop new it is a 24volt motor,it says so on the casing. It says max amp 15 with no load. It runs a small hydraulic pump that operates a cylinder for about a 5 second cycle.

 

[tcmtech]

Did the moter smoke when ran by it self or when it was connected to the pump system?
If it was on the pump system you may have a bad hydraulic pressure relief or blocked flow some place.
Depending on the pump design if it was rotory vane type (which many small ones are) running at 12 volts may very well have been below its vane engaging speed. Going up to 24 volts it would have then engaged and built up back pressure until the motor overloaded and smoked, making it apear that it slowed down on the 24 volt input when in fact it was loaded down!

Some more system setup info would be helpful.

 

[cra]

Thanks for the reply.
It was not hooked up to anything when tested. When 24 volts were used,it ran for about 3 seconds.It started fast and slowed to a stop and started smoking.The bearings are fine as it turns freely by hand. It tripped the fuse when it was hooked up to the pump.My suspicion is it was rewired wrong and would like to know what possably was done wrong so I can tell the shop that did it. I paid $300. to have it done and he says it worked on 12 volts and it will work on 24 volts as he had no 24 volt supply to test it with when I picked it up.

 

[wizard]

Hi all,
I came back to this forum!

I guess you have lost (fried) your winding when you have operated the motor for the first time.
Why that problem did happened, you ask? Well maybe you have overloaded the motor after it has been rewound (a short time stall can burn the winding easily)?
Maybe you have lost the commutators due to a fault before rewinding the motor?
Maybe the repairman has rewound the motor in an incorrect way or direction or maybe he has used the wrong wires for the windings?

colin55,
Why do you think that each motor is able to work at 2 times of its normal operating voltage?

 

[colin55]

I didn't say "each motor" but most 12v motors that require a small current such as 1.5 amp will operate on 24v and run at a higher RPM.

The motor was definitely re-wound with a fault. It may have a short between turns or a short to one of the poles or a winding may be wound around the wrong way or connected incorrectly.
It is very unlikely it was wound with the wrong number of turns as the wire gauge would have been the same and you can only fill the poles to a certain amount.
The original poster did not say the motor produced a very high RPM when connected to 24v.
You have to do the test I explained previously to see if a pole is not functioning correctly.

 

[Thunderchild]

what sort of a rewinder is he unless he can test his own work ? sounds like a dodgy repair place to me

 

[Hero999]

I paid $300. to have it done and he says it worked on 12 volts and it will work on 24 volts as he had no 24 volt supply to test it with when I picked it up.

How much would a new motor cost?

 

[cra]

He says it's the bushings that are making it lock up. The brush end is a 1/4 inck shaft with .003 clearance to the bushing and the drive end is 5/8 of an inch with .003 inches clearance to the bushing. I don't buy it but any opinions ?

 

[Sceadwian]

Sounds like normal bushing clearance to me.
https://www.electro-tech-online.com/custompdfs/2009/04/CL77-1-205R.pdf
Google is great.

It definitely sounds like he did not rewind it properly. Print the PDF and show it to him, ask him why your bearing clearances match the recommended clearances from a company that makes parts of Nascar. Considering the cost it's probably worth your time to go to small claims court over it.

Unfortunatly I don't know much about motor windings =) What you need to find is someone that does. Maybe call around to a couple other rewinding shops and tell them what's going on they might cut you a break and take a look at the motor real fast or tell you what you can do to determine if it was rewound properly. If you tell them the situation a decent person would be willing to spare a few minutes of conversation on the phone to help someone out. And if you find someone that will once you get things straightend out get your motors rewound by them =)