Frame Ground Is 10V

[InvalidUsername]

Originally Posted by Volt_Ampere

Did you try the light bulb test? It only takes a little bit of stuff to make a high resistance path.

No I haven't tried light bulb test because I'm still trying to figure out the logic of how a current path can exist with lithium batteries sitting on wood inside of a plastic battery case that has been thoroughly cleaned more than once.

Nothing electrical in the cart is attached to any metal except at the motor. Carbon is a conductor. There's 18 years of carbon dust build-up inside my motor. It's logical to assume that some of that dust could be bridging between a bare electrical connection inside the motor and the metal motor case, which is attached to the frame. So it's real easy for me to see voltage leakage there.

So I'm not saying you're wrong, I just don't see it.

[Volt_Ampere]

The fact that it's 10V suggests a high resistance path. Do the lamp test and the voltage will probably drop to zero. It can be tricky to find out where that path is. You could be right that it's not at the battery if it's Lithium and in a clean case. If the lamp test shows that it's a high impedance leakage then you need to try disconnecting things until it goes away. I would NOT disconnect the motor wires with the battery hooked up though. That can damage the controller if wires touch.

[InvalidUsername]

Originally Posted by Volt_Ampere

The fact that it's 10V suggests a high resistance path. Do the lamp test and the voltage will probably drop to zero. It can be tricky to find out where that path is. You could be right that it's not at the battery if it's Lithium and in a clean case. If the lamp test shows that it's a high impedance leakage then you need to try disconnecting things until it goes away. I would NOT disconnect the motor wires with the battery hooked up though. That can damage the controller if wires touch.

So why would I look for other paths when there's an explainable path in the motor? I bet if I disconnect the motor leads the leak will go away

[Volt_Ampere]

Try it. I have not seen that happen but it's certainly possible.

[InvalidUsername]

Originally Posted by Volt_Ampere

Try it. I have not seen that happen but it's certainly possible.

Too much work lol. I'll let the OP try it if he wants

[ufjaz]

Originally Posted by Volt_Ampere

Through battery case to frame. Your meter is high impedance so it will measure voltage on the frame due to "leakage". To test that, try connecting a 12V lamp between frame and battery negative. (I assume you are measuring the 10V from battery negative to frame.) I bet it won't light and if you put your meter across the lamp, you won't measure 10V anymore. This is not uncommon by the way. Only way to really eliminate leakage is to clean the battery cases and the battery tray to eliminate any trace of leaked battery acid.

Today, as a baseline, I tested the potential between the frame and the first battery negative pole. The frame was 8.0 V higher than the battery. Just for fun I measured the potential between the positive and frame. The positive was 0.5 V higher.

I connected the bulb between the battery's positive and negative poles. It illuminated. I then connected the 12V lamp from the negative pole to the frame. It did not illuminate. I connected the lamp between the battery positive post and the frame and it did not illuminate. To me that implies the frame is not even used as part of the ground in the cart's electrical circuit. Does that make sense? I always thought it was a ground point.

Any comments?

[ufjaz]

Originally Posted by InvalidUsername

I've noticed the same. Since the only metal to metal contact between the electrical system and the frame is the motor I'm suspecting that there is carbon dust buildup in the motor that's causing a low current short to the frame

I guess you already told me that the electrical system does not use the frame. It didn't sink in.

Is the carbon dust build something that should concern me? How do I clean it? Thanks.

[InvalidUsername]

Originally Posted by ufjaz

I guess you already told me that the electrical system does not use the frame. It didn't sink in.

Is the carbon dust build something that should concern me? How do I clean it? Thanks.

I don't worry about it. The way to check and clean would be to take apart the motor an blow it out with compressed air outside. It can make a real mess if you do it inside. I'll only do that if I have to replace the brushes

[ufjaz]

Thanks Invalid. So to summarize my takeaway from all this is: The frame potential has nothing to do with the electrical system potential (2 isolated systems) - other than the possibility the frame's potential may be affected by a carbon dust build up in the motor leaking a small current. And Volt_Ampere's 12V lamp test does prove this. Is that accurate? (I'd like to learn a lesson here.)

[ufjaz]

BTW, how do you know if the brushes need to be replaced?