# Tracking down a traction pack ground leak



## Ziggythewiz (May 16, 2010)

What kind of gauges do you have? I know my analog ones have some leakage.

Do you get progessive readings if you read from the chassis to the pack in a few places down the string?


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## powerhouse (Apr 1, 2011)

Ziggythewiz said:


> What kind of gauges do you have? I know my analog ones have some leakage.
> 
> Do you get progessive readings if you read from the chassis to the pack in a few places down the string?


No guages installed on the car. The only things that the battery ends are connect to are the contactor, charger terminals (disconnect from charger at the moment) and a pack tap for the BMS. I disconnected the pack tap, as well as the battery taps from the BMS when I was trying to find the leak. 

I can't really tell if I am getting progressive readings, the voltage begins dropping (1v / s) the second I connect the multimeter.

weird stuff


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## Ziggythewiz (May 16, 2010)

My ground leaks are usually capacitive, maybe because the controller isn't isolated, so that will cause a surprising initial shock but nothing significant with continued contact. That would also explain the slow voltage drop. 

If it's only dropping by 1v/s you should be able to move the meter down the line and watch it steadily decrease or increase with each cell. If you can get it down to 0 that's where the ground fault is.


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## powerhouse (Apr 1, 2011)

Ziggythewiz said:


> My ground leaks are usually capacitive, maybe because the controller isn't isolated, so that will cause a surprising initial shock but nothing significant with continued contact. That would also explain the slow voltage drop.
> 
> If it's only dropping by 1v/s you should be able to move the meter down the line and watch it steadily decrease or increase with each cell. If you can get it down to 0 that's where the ground fault is.


Hey Ziggy,

Thanks for the suggestion! I went outside and figured that your method wouldn't work because the voltage dropped too quickly, but lo and behold I was able to find it! 

I tracked from 280 to 160 to 40 and eventually to a 3.2v potential between the car and the battery pack.

Unfortunately, the short is in a difficult position to reach, so I will update later to see if this fixes it! 

Thanks for all the help


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## powerhouse (Apr 1, 2011)

Well I guess I spoke too soon.
I tore apart my front battery box today to get to the module that was leaking voltage to the chassis. 

Heres a picture of the box in question, notice the blue foam sheet on the bottom









Once the cells on the bottom have been inserted









More pictures to illustrate how it looks



















I have no clue how, but I thought the cell in the middle, nearest to the top of the box (closer to the engine bay) was the problem. 
When I measured using a multimeter, I found 56v between the last cell in series and the box, and when I poked my multimeter around the voltage would drop to 3v and -3v when i moved between cell groups in the top, middle module.

So I took it out, and for some reason there is still voltage between some of the cells and the box. It doesn't make much sense to me, because it seems like that cell couldn't even be touching any metal in the first place.

Im confused, help!


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## TEV (Nov 25, 2011)

How about the " clasic " leak of the motor(s) ?

Disconnect the motor(s) and see if your leak it's gone.


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## powerhouse (Apr 1, 2011)

Disconneted motors, sadly no cigar


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## dragonsgate (May 19, 2012)

Have you checked the DC converter?


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## powerhouse (Apr 1, 2011)

dragonsgate said:


> Have you checked the DC converter?


Unplugged on the traction pack side


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## powerhouse (Apr 1, 2011)

Any ideas guys?


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## Ziggythewiz (May 16, 2010)

With one or both battery connections disconnected do you still see the leak?

I'd put a non-conductive coating over the whole box as well.


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## powerhouse (Apr 1, 2011)

Ziggythewiz said:


> With one or both battery connections disconnected do you still see the leak?
> 
> I'd put a non-conductive coating over the whole box as well.


I believe so...
I can't really tell at this point, it seems like the voltage is very unpredictable, and doesn't increase as I move down the pack.


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## dragonsgate (May 19, 2012)

powerhouse said:


> Hey everyone
> 
> I have recently noticed that whenever I touch a motor lug when holding onto the chassis, or whenever I touch a battery terminal and an holding onto the chassis, I receive a shock. I can't describe how substantial the shock is, as I have never actually shocked myself with the full battery pack, but it is enough to make me pull my hand back instantly. Not a pleasurable feeling.
> 
> ...


Have you tried a 12 volt light tester to see if it will light up? I had a similar problem when I first did my conversion. I got a nip when I touched a battery and my forearm touched the edge of the fender. It felt like a hair being plucked out. I did a bunch of crawling around testing for shorts. I found that there is continuity from motor housing and the frame through the transmission, drive axels and shocks. There is no way to isolate that that I can figure. If you get a build up of brush dust that could cause a voltage reading. At the time my car was to new to have any build up of carbon dust. I was getting fluctuating readings of 20 to 40 volts and higher with the multi-meter. I tried a 12 volt light tester in various places and couldn’t get it to light so I tested for amps and got nothing. I was getting frustrated and ready to try anything. While I was checking voltage from battery to chassis for the umpteenth time I noticed that when I put one probe on a battery I got a reading before I put the other probe on the chassis. I checked various batteries and could get a voltage reading with one probe on the battery and the other in the air. I thought either I had discovered Tesla’s single wire motor or maybe the humidity had something to do with it. I checked and the humidity was around 70%. I never have found anything that will fix my conundrum. I have noticed that when it is humid I get readings and when the weather is dry voltage reading is nonexistent. MY DISCLAIMER. I am not proficient in electricity but this is my story and I am sticking to it.


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## powerhouse (Apr 1, 2011)

Getting about 2v or so when I measure the voltages, up to 5v sometimes

When I run a 10k ohm resistor in line with the multimeter I never read more than 2v


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## powerhouse (Apr 1, 2011)

dragonsgate said:


> Have you tried a 12 volt light tester to see if it will light up? I had a similar problem when I first did my conversion. I got a nip when I touched a battery and my forearm touched the edge of the fender. It felt like a hair being plucked out. I did a bunch of crawling around testing for shorts. I found that there is continuity from motor housing and the frame through the transmission, drive axels and shocks. There is no way to isolate that that I can figure. If you get a build up of brush dust that could cause a voltage reading. At the time my car was to new to have any build up of carbon dust. I was getting fluctuating readings of 20 to 40 volts and higher with the multi-meter. I tried a 12 volt light tester in various places and couldn’t get it to light so I tested for amps and got nothing. I was getting frustrated and ready to try anything. While I was checking voltage from battery to chassis for the umpteenth time I noticed that when I put one probe on a battery I got a reading before I put the other probe on the chassis. I checked various batteries and could get a voltage reading with one probe on the battery and the other in the air. I thought either I had discovered Tesla’s single wire motor or maybe the humidity had something to do with it. I checked and the humidity was around 70%. I never have found anything that will fix my conundrum. I have noticed that when it is humid I get readings and when the weather is dry voltage reading is nonexistent. MY DISCLAIMER. I am not proficient in electricity but this is my story and I am sticking to it.


I am beginning to feel as though I may be experiencing something similar to you. I can't really see where any of these cells can be grounded to the chassis. 

With that said, I do live on a river and the humidity is currently 81% in Daytona Beach FL, so.....


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## PStechPaul (May 1, 2012)

When you use a high impedance DMM it will pick up small amounts of voltage and current just from capacitance and humidity and surface leakage which can be significant if there is a light coating of salt or other ionic substances, which can pick up moisture and become conductive. The DMM leads act as antennae and can pick up RF ranging from power line frequencies to broadcast bands. An isolated battery pack will develop some DC potential to ground and there can be enough capacitance to provide a "jolt" of enough current to exceed the sensation and pain thresholds. Thus I would suggest adding a "drain" resistor of a size to conduct a harmless and barely perceptible current of 2-5 mA at the maximum potential of the battery pack, so 72 to 31 kOhms. Best place might be the middle of the pack so it will be near zero volts and the two ends would be +72 and -72V. If there is no drain resistor, it is possible for the isolated pack to float to several thousand volts or whatever the insulation breakdown level of the insulation and solid state devices might be.


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## powerhouse (Apr 1, 2011)

PStechPaul said:


> When you use a high impedance DMM it will pick up small amounts of voltage and current just from capacitance and humidity and surface leakage which can be significant if there is a light coating of salt or other ionic substances, which can pick up moisture and become conductive. The DMM leads act as antennae and can pick up RF ranging from power line frequencies to broadcast bands. An isolated battery pack will develop some DC potential to ground and there can be enough capacitance to provide a "jolt" of enough current to exceed the sensation and pain thresholds. Thus I would suggest adding a "drain" resistor of a size to conduct a harmless and barely perceptible current of 2-5 mA at the maximum potential of the battery pack, so 72 to 31 kOhms. Best place might be the middle of the pack so it will be near zero volts and the two ends would be +72 and -72V. If there is no drain resistor, it is possible for the isolated pack to float to several thousand volts or whatever the insulation breakdown level of the insulation and solid state devices might be.


Ahh you know too much about this stuff

Excuse my ignorance, but where exactly would this drain resistor be placed? Between the positive and negative terminal of the middle cells? How would that work....


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## PStechPaul (May 1, 2012)

That would be a good place for it. You can probably crimp or solder one lead to a lug and bolt the ring to the battery connector bus bars. I would use a 5 watt or 10 watt resistor only because they are more durable. It should also be mechanically secured so vibration doesn't cause the leads to break.


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## TEV (Nov 25, 2011)

powerhouse said:


> Ahh you know too much about this stuff
> 
> Excuse my ignorance, but where exactly would this drain resistor be placed? Between the positive and negative terminal of the middle cells? How would that work....


I think he means between the middle of the battery pack and the body of the car. Any way, you should wait and see what others will advice you before doing that, or do it but just for testing and don't permanently install that resistor yet.


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## palmer_md (Jul 22, 2011)

TEV said:


> I think he means between the middle of the battery pack and the body of the car. Any way, you should wait and see what others will advice you before doing that, or do it but just for testing and don't permanently install that resistor yet.


it would not be permanent anyway...just for testing to insure that you are not seeing stray voltage with the meter. Either that or use a meter that has a deflected needle instead of the DMM. They will always read better in this situation since they draw more current to provide the reading.


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## kennybobby (Aug 10, 2012)

*checked the modules?*

It appears that you are clamping the terminal tabs of pouch cells to build up into modules, then strapping those modules together to make the strings of your pack. Are the module frames aluminum? Is the outer cover surface of the pouch cells an aluminized plastic or some sort of conductive film? Are there any separators between pouch cells or are they pressed tightly against each other? 
Have you bench tested each module to determine that the frame and frame screws are isolated from the module terminals? Maybe a tab has folded under in such a way to contact a frame, or some metal scarf has wedged between pouches and shorted, or metal dentrites formed in a pouch and punctured the cell case and shorted, etc. --For whatever the case may be, you may need to take the pack out and measure each module to find the leak or verify it's integrity.


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## dragonsgate (May 19, 2012)

*Re: checked the modules?*



kennybobby said:


> It appears that you are clamping the terminal tabs of pouch cells to build up into modules, then strapping those modules together to make the strings of your pack. Are the module frames aluminum? Is the outer cover surface of the pouch cells an aluminized plastic or some sort of conductive film? Are there any separators between pouch cells or are they pressed tightly against each other?
> Have you bench tested each module to determine that the frame and frame screws are isolated from the module terminals? Maybe a tab has folded under in such a way to contact a frame, or some metal scarf has wedged between pouches and shorted, or metal dentrites formed in a pouch and punctured the cell case and shorted, etc. --For whatever the case may be, you may need to take the pack out and measure each module to find the leak or verify it's integrity.


Kennybobby could be on to something. I was concerned with all the exposed cooper on the batteries giving a lot of area to touch something. The modules look well built and I suppose the parts you used to make them were designed for that purpose. It would be a good idea to test any plastics that might be touching the batteries to see if they conduct electricity. In the 1980’s when I lived in the high desert I was living off the grid and building my own wind and solar power I converted a wringer washer to 48 volt dc. When I first tried it out it would give a shock. After some head scratching and testing I realized that automotive heater hose rubber was not a good insulator.


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## powerhouse (Apr 1, 2011)

*Re: checked the modules?*



kennybobby said:


> It appears that you are clamping the terminal tabs of pouch cells to build up into modules, then strapping those modules together to make the strings of your pack. Are the module frames aluminum? Is the outer cover surface of the pouch cells an aluminized plastic or some sort of conductive film? Are there any separators between pouch cells or are they pressed tightly against each other?
> Have you bench tested each module to determine that the frame and frame screws are isolated from the module terminals? Maybe a tab has folded under in such a way to contact a frame, or some metal scarf has wedged between pouches and shorted, or metal dentrites formed in a pouch and punctured the cell case and shorted, etc. --For whatever the case may be, you may need to take the pack out and measure each module to find the leak or verify it's integrity.


Hmm
The modules are compressed together by two PVC end plates on each side. Threaded rod is employed to compress the plates, but have about 1/2" of clearance on each side of the batteries, so that isn't touching. 
On top of that, all the edges are taped with kapton tape to avoid any voltage leaks, but the cell pouches *shouldn't* be conductive. 

I really think it may be humidity, as I can measure a free standing cell and still get 1-2v between the chassis and the cell, even when it is just sitting in the box not connected to anything.


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## powerhouse (Apr 1, 2011)

I take what I said above back.
Put everything (front battery pack + wires that connect front and rear packs) back together and I still get shocked.
My rear battery pack is innocent, if you disconnect the large 4/0 gauge wires that put it in series with the front battery pack there is 0v. 
However, the front battery pack is still acting strange. 
At this point, I am nearly certain that it is the BMS tap wires that are causing this strange behavior. Earlier today for no particular reason I decided to measure the voltage between the chassis and the cell tap wire shielding (which is supposed to be grounded to chassis but I have yet to do that), and found that the SHIELDING is about 6v. 

Not really sure wtf to think about that. Perhaps it has something to do with the wire that I am using? 
The cell tap wire is 6 conductor cable designed to be used for home alarm wiring. Each conductor is 22awg. Maybe it wasn't rated for this stuff?

Guess I will have to continue investigating


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## PStechPaul (May 1, 2012)

I found some alarm cable rated 50V RMS:
http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/254799.xml

Others are 300V:
http://www.southwire.com/products/SecurityFireAlarmCableCMRShielded.htm
http://www.awcwire.com/ProductSpec.aspx?id=Shielded-Multi-Conductor-Plenum

and some even 600V, yet are termed "low voltage cables". That generally means "power limited":
http://www.tappanwire.com/uploads/pdfs/MiniCatalog2012_88.pdf (7 MB)

If you are reading several volts from shield to chassis, and it is grounded somewhere, there is probably current running through it, or the shield is discontinuous (possibly damaged). It should be grounded at one place only, and if there is voltage between any two supposedly grounded parts of the car frame, it's wise to add bonding jumpers of sufficient capacity to carry any normal current. Most modern cars use ground return wires for accessories, but older cars often used the metal body to carry return current to the battery.


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## powerhouse (Apr 1, 2011)

PStechPaul said:


> I found some alarm cable rated 50V RMS:
> http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/254799.xml
> 
> Others are 300V:
> ...


Thanks for the response paul 

The wire I am using is Tappan wire 2280AB6M/CMP/WHITE. Surprisingly it seems difficult to find any specific technical data, but it seems to be rated to 300v. 

With that in mind, I wonder how much the voltage ratings matter considering that each cell tap wire should be carrying only that cells voltage (3.3v). 

The part that concerns me is the length of the cabling. Because the BMS is in the rear of the car, and the front battery pack (pack causing all the trouble) is located all the way in the front, each wire needs to be 14 feet long. There are 9 modules up front, and each module require 1 6 conductor wire, so 9 wires going up. 

I did my best of keeping the cabling safe by putting it in loom and taping / heatshrinking everything together.
I made two of these long wires (each has 6 wires)

















The wire exposed at the ends is the shielding and was later tidied up using heat shrink and crimp connectors.


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## PStechPaul (May 1, 2012)

That much cable may have a fair amount of capacitance as well as leakage. Since all the batteries are in series, there will be a fairly high voltage potential between the positive and negative terminals, and with the shield disconnected (as I now noticed), it may become charged to a significant potential to chassis ground. Connecting the shields to ground may help. You can use an insulation tester to find out if there is an actual breakdown or deterioration of insulation, but you must be careful that the voltage applied does not damage any sensitive components. You can choose test voltage from 250, 500, 1000, 2500, and even 5000 VDC, and there are also AC dielectric testers. You can get one for about $50:
http://www.ebay.com/itm/VC60B-Digit...-Megger-MegOhm-Meter-USA-Seller-/320898816590

Good luck!


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## powerhouse (Apr 1, 2011)

This morning I disassembled the entire front battery box, removing all A123 cells and making checking each individually. 
Nothing out of the ordinary with the A123 modules, I will begin reassembling soon, checking for a ground leak with every BMS wire that I connect.

I will keep you guys posted!


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## kennybobby (Aug 10, 2012)

*Isolated BMS?*

Is the BMS tied to chassis ground or isolated--maybe that provides a leakage path since you are measuring pack voltages and likely interfacing with low voltage relays or instrumentation or gauges also. Obviously a schematic would help understand what is connected...


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## powerhouse (Apr 1, 2011)

*Re: Isolated BMS?*



kennybobby said:


> Is the BMS tied to chassis ground or isolated--maybe that provides a leakage path since you are measuring pack voltages and likely interfacing with low voltage relays or instrumentation or gauges also. Obviously a schematic would help understand what is connected...


Good thought.

I ran out of light, but reassembled the entire front battery pack today and currently have no ground leak! The BMS tap wires are installed on the cells and the wiring runs to the trunk, but I removed the BMS unit entirely so nothing is plugged in. Currently only the (+) terminal is connected to zilla, all else is disconnected (motor (+), motor (-), battery (-) ). At the moment there are no ground leaks, and the wire shielding has no charge (phew). 

Not sure what I did but so far it seems like I fixed it ?


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## PStechPaul (May 1, 2012)

Some electronics, as well as most people and dogs, need to be fondled occasionally to achieve proper behavior... 

When I worked as an engineer in the 1980s, someone wrote up a set of "laws" pertaining to each employee's work style. "Paul's Law" was "Anything will work if you fiddle with it long enough", and my fellow engineer's "Rick's Corollary" was "If you continue to fiddle with a functional unit, it will cease to function".


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## dragonsgate (May 19, 2012)

*Re: Isolated BMS?*



powerhouse said:


> Good thought.
> 
> I ran out of light, but reassembled the entire front battery pack today and currently have no ground leak! The BMS tap wires are installed on the cells and the wiring runs to the trunk, but I removed the BMS unit entirely so nothing is plugged in. Currently only the (+) terminal is connected to zilla, all else is disconnected (motor (+), motor (-), battery (-) ). At the moment there are no ground leaks, and the wire shielding has no charge (phew).
> 
> Not sure what I did but so far it seems like I fixed it ?


I’ve had this happen with mechanical as well as electrical stuff. Something will not work so you take it apart can’t find anything so you put it back together exactly the way you will swear it was before and it works. Electricity is lazy and likes to take the path of least resistance so maybe you moved something or tightened something that changed everything. I hope you found the cure. If you are like a lot of us probably are you will constantly be checking things for months to come. Since watching this thread I have gone over my car with the testers.


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## Joey (Oct 12, 2007)

*Re: Isolated BMS?*

One possibility is a stray strand of wire sticking out of one of the crimps in the BMS connector. I always try to find a cause for a problem, because I always worry it will come back unless I know what solved the issue.


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