# DC motor wiring



## RobW (May 5, 2013)

Hello all, I am having an issue with my DC motor housing showing continuity through to the chassis. I have checked out my controller with Paul Holmes help and the problem is not in the controller. My motor is a Caterpillar fork truck motor and has 4 lugs. I have my battery pack positive side (from controller) on the lug stamped S1. I have a jumper wire from S2 to an unlabeled lug that I am assuming is the armature. Then my M1 wire to the second lug on what I am assuming is the armature side. I am including a picture of my configuration and I wanted to ask if I possibly have this thing wired wrong. If the wiring looks ok, (the motor has been running this way) then can someone that understands these motors tell me why my case is getting continuity through both S1 and S2 lugs? Obviously with the wiring the way it is, I'm getting continuity all the way through.

Thanks!


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## Sunking (Aug 10, 2009)

First thing to do is take all the wiring off the motor, then measure the motor again and see if the problem remains or goes away. If it remains the motor is the source of the fault. If it goes away, the issue is in your wring somewhere for you to find.


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## dougingraham (Jul 26, 2011)

Brush dust can cause this problem. I also suggest you remove the cables from the motor and measure the resistance to the case from each terminal. There really isn't any way you can wire it wrong and still have it work so that is not the cause.

The most common cause of frame leaks is lack of isolation in instrumentation. This is where you accidentally connect the traction pack negative to the vehicle frame through an instrument.

Hope you find it quickly.


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## RobW (May 5, 2013)

I have measured the continuity with the cables disconnected. The S1 and S2 lugs have continuity, the front two don't. If I understand correctly the S1 and S2 lugs are for the stator side, right? So would that mean that there is ground between the stator and case of the motor?


It would seem to me that the case of the motor is grounded through the transmission and drive train to the chassis. Would my assumption be right?

Thanks!


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## Sunking (Aug 10, 2009)

RobW said:


> It would seem to me that the case of the motor is grounded through the transmission and drive train to the chassis. Would my assumption be right?
> 
> Thanks!


Yes that is correct, but none of the motor electrical system is grounded (ground is the wrong term, BONDED is correct) and becomes very dangerous if it does.

People think systems are grounded for safety which is some what false. Electrical systems are grounded for economics because it is easy and cheap to use fuses and breakers. But a grounded system becomes unreliable, prone to unnecessary interruptions, and dangerous to work with. 

Thus EV's high voltage systems are not grounded. A smart design will include a Ground Fault Detector to alert the operator a fault has occurred and in need of repairs by a trained professional. It still works as is intended by not grounding the system, but it becomes very dangerous for electrical shock and electrical fires, and needs immediate action. 

That is why industry does not use grounded systems. They cannot afford unnecessary outages, injured personnel, and liability risk.


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## RobW (May 5, 2013)

Thanks! Glad you are here to straighten me out on this! I'm glad I noticed the "bonding" through the chassis. I will keep all disconnected until I figure out what to do next. 

Thanks again!



Sunking said:


> Yes that is correct, but none of the motor electrical system is grounded (ground is the wrong term, BONDED is correct) and becomes very dangerous if it does.
> 
> People think systems are grounded for safety which is some what false. Electrical systems are grounded for economics because it is easy and cheap to use fuses and breakers. But a grounded system becomes unreliable, prone to unnecessary interruptions, and dangerous to work with.
> 
> ...


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## Sunking (Aug 10, 2009)

RobW said:


> Thanks! Glad you are here to straighten me out on this! I'm glad I noticed the "bonding" through the chassis. I will keep all disconnected until I figure out what to do next.


You are welcome and from the sounds of it you are on your way as you have isolated it to the motor. Time to pull the motor off, take it apart and fix it. 

Get busy and lets us know what you find. As suggested look for Brush Dust, and a good idea to replace the brushes if equipped while you got it apart. 

Good Luck


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## RobW (May 5, 2013)

Now my next question is: what do I do to fix this "bonding"?

In my picture the lugs top to bottom, are:

Top right S1
Bottom right is S2

The left side lugs are not labeled so I am assuming that they are for the armature, and would be A1 and A2.

Oh, and there is a small lug near the back side of the housing too. I have no idea what that is for. I had assumed a ground.

So if S1 and S2 are the stator side, then the bonding would be somewhere between the stators and the wall of the housing or case. Do I have that assumption right?


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## Sunking (Aug 10, 2009)

One last thought for you to consider. Now that you got the motor off and have torn it apart. Consider sending it to a motor shop for a new Beasty Core like from Dang Quick Motors or somebody at a local shop.

If you find the problem is costly to repair, I would send to a motor shop for a new core if I were you. Get a brand new motor likely to have more power at half the cost of a new motor.


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## Sunking (Aug 10, 2009)

RobW said:


> Now my next question is: what do I do to fix this "bonding"?


I gotta pass the buck Rob. I am an EE and not much experience as a motor mechanic. I tell electricians what they need and where to stick it. Its up to them to figure out how to stick up there.....

I do small scale stuff with golf carts. Only thing I have done is replace brushes or replace the motor. Hopefully when you open it up, the problem will be visible. I understand brush dust is the most likely cause. If it is insulation breakdown means a new core or rewinding the motor. 

That is about all I know to tell you. Hang on a while and I am certain more experienced members will chip in. In the mean time take the motor off and take it apart.


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## kennybobby (Aug 10, 2012)

Are you saying that you measure continuity between the S1 or S2 terminals and the case? If so then you have a 'shorted' winding--it is not supposed to be grounded or bonded to the case. A wire in the stator has rubbed against the back iron or some sharp corner, etc. and worn thru the insulation such that it now has a short-circuit path to the chassis/case.


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## RobW (May 5, 2013)

Ok Thanks!

I found out that the little lug on the motor is "NOT" a ground. It is somehow connected to the stator. (Continuity between the little lug and S1 & S2.)

I had that wired to the controller platform. That would "at least" be part of the problem. After removing the wire: "NO" continuity between stator and housing.

Soooo.... It sounds like I may not have to pull my motor after all. WoooHooo, but I will wire things back up and check all again just to be absolutely sure!

Any other comments would be greatly appreciated. Thanks!


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## Sunking (Aug 10, 2009)

RobW said:


> Any other comments would be greatly appreciated. Thanks!


Get the wiring right before you burn up something.


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## Sunking (Aug 10, 2009)

Rob don't get offended, was not my intent. There is only so much we can do for you. We have no idea what your capabilities are. All we can do is judge by the questions you ask about your skill level. 

Last thing I want to do is to tell you something to do that is beyond your capabilities and you get hurt. With electrical, especially once you start working with batteries and higher voltages mistakes are not tolerated and can end in injury, property damage, and even death.

So don't get offended, I care about you and your safety. If I feel you are in above your head, I will tell you to seek qualified help. So I am telling you to get some help and take it slow.


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