# HV pack voltage to chassis!



## Hollie Maea (Dec 9, 2009)

Have you done a Hipot test from your battery to ground? when using metal boxes it's important to keep appropriate creepage distance for your voltage (I presume it's ~400V). If you are so close to ground that you're getting a significant capacitive connection, you might be too close. You'd hate to get an arc-over the first time it gets too humid...

Edit: You can determine how much capacitance you have by plotting the voltage decay over a known resistance and seeing how long it takes to decay via these equations:
https://en.wikipedia.org/wiki/RC_time_constant


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## Sunking (Aug 10, 2009)

You gotta leak some where. One suspect would be the motor controller like a RFI, MOV component from line-to-chassis. You just have to isolate it to find it. 

Lift the HV and sensors terminals from the motor and work your way back to the battery to find the leak. When you remove the guilty party from the circuit, problem goes away and you found it. Start at the very end of the Traction Battery circuit which should be the motor terminals, and work your way back to the source aka Battery Term Post.


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## CKidder (Dec 12, 2009)

Thanks for the advice so far. I guess when I say the cells are close to metal what I mean is within around a quarter of an inch. It isn't as if they're nearly touching. But, I'll double check the distances.

Here is the strange part - I lifted everything from the HV+ point of the pack and tested from HV+ to ground and still got the same result. So, it isn't due to anything I had connected. It has to be in the pack somewhere. I have a maintenance switch and if I pull it the problem seems to go away. That seems odd since there was no "circuit" in the first place. (well, there must be but there wasn't supposed to be). With the pack disconnected from everything it still does it but not if the maintenance switch is pulled. That switch is installed with roughly 3/4 of the pack on one side and 1/4 on the other. What is stranger, with the maintenance switch pulled (well, it's a fuse with a handle and a latch and you can pull it out) I get about 15V to ground on one side and 25V on the other. That makes no sense since I should get a result of around 300v but divided between the two sides, shouldn't I? So, I don't know why it is doing this. I also tried to check various points on the pack to see what happens when I measure to ground. I get random voltages under 12v basically anywhere I test. I'm wondering if I'm going to have to insulate all of these 4 packs from each other and the metal cages... For the record these are old Thundersky 40AH cells. They're yellow plastic cells so I don't know how they're leaking like this. I guess I'll keep looking for the source of the fault.


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## kennybobby (Aug 10, 2012)

What is the resistance from pack (-) to 12V battery (-) and/or chassis?


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## CKidder (Dec 12, 2009)

kennybobby said:


> What is the resistance from pack (-) to 12V battery (-) and/or chassis?


Well, that's an interesting story. The resistance is hard to measure since the pack - side is about -5v compared to ground. So, there is some kind of coupling there too. I was able to get the meter to give me a resistance reading of about -5 megaohms sometimes and infinite other times. I've now disconnected both sides of the pack and it still does it. The voltage is perhaps a little bit different, I think 250V now as opposed to resting at 270V while measuring it. I've found that the voltage to ground does change based on where in the pack I measure but nowhere seems to actually ever read zero. 

So, my best guess is still some sort of capacitive coupling since I can watch the voltage rise and fall based on what I do. A resistive leak should snap immediately from one extreme to the other. If it is resistance based then the voltage divider would immediately happen. Instead I see it sink when I connect a voltage meter. If I test a given spot in the pack, let it sink, then remove the probe and quickly place it back I'll see the voltage start at a lower point than if I wait longer. This all leads to the theory that it is capacitive despite being such a large voltage. The solution seems to be to wrap the batteries in rubber or something and better isolate them from the metal battery racks. Does that sound right? At the moment the plastic of the batteries is directly touching the metal battery frames. Perhaps that can't be the way things are mounted.


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## kennybobby (Aug 10, 2012)

And i should have mentioned to measure the voltage difference between pack (-) and 12v battery (-). But it looks like you did that and got a reading of -5, so that indicates to me that the pack short to chassis is occuring at the second or third cell up from the bottom of the pack (-).

Is the yellow plastic conductive, or maybe it has dielectric properties that is causing the capacitance effect?


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## skooler (Mar 26, 2011)

Have seen this before with old thundersky cells, series dc brush dust and also on a dcdc converter. 

What is the setup you are using?


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## Coulomb (Apr 22, 2009)

Do you have an Elcon, TC, or Chennic charger?

These have a 1nF capacitor from pack positive to chassis. It's a proper Y capacitor, one of those sky blue ones crammed with ratings agency logos on it.

No extra charge! (Well, so to speak.) It's on the normally closed contact of the output relay, so when the charger is charging, that capacitor isn't there. I don't know why they put it there.

This is a part of the unofficial schematic that hasn't been updated yet.


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## CKidder (Dec 12, 2009)

skooler said:


> Have seen this before with old thundersky cells, series dc brush dust and also on a dcdc converter.
> 
> What is the setup you are using?


It's a UQM Powerphase 100 motor and controller and I'm using a DC/DC converter nobody's ever heard of. But, I get the same thing with *nothing* connected to the pack positive and negative points. With the pack supposedly connected to almost nothing (it still does have little voltage taps for a BMS) it still has voltage from HV+ to ground. So, it seems impossible that the entire problem could be anything connected unless I did something dumb with the voltage taps for the BMS. I suppose it might be time to try disconnecting those too to see what happens. I haven't really touched the car in a couple of days since I've been busy with other things but I'll try wiping off the tops of the cells to see if there was some sort of conductive dust on the cells and I'll try taking off the voltage taps too.


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## CKidder (Dec 12, 2009)

Coulomb said:


> Do you have an Elcon, TC, or Chennic charger?
> 
> These have a 1nF capacitor from pack positive to chassis. It's a proper Y capacitor, one of those sky blue ones crammed with ratings agency logos on it.
> 
> ...


Well isn't that fabulous. I've found that I do seem to get a little less capacitive coupling with the charger out of the car. That Y cap might explain it. It doesn't explain the whole issue because it happens with nothing connected to the pack at all but it could explain the increased severity when the charger is installed.


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## Coulomb (Apr 22, 2009)

CKidder said:


> I'll try wiping off the tops of the cells to see if there was some sort of conductive dust on the cells ...


I've read that the brush dust from DC motors gets everywhere. So it could be contributing a film of slightly conductive dust.

[ Edit: I've just read that you have a brushless motor. So one would expect brush dust to not be an issue  ]

I'm amazed that this doesn't cause flashovers, but I guess there is way too little conductance for that. It would certainly be good for peace of mind to locate the leakage, even if it isn't hugely serious right now.


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## kennybobby (Aug 10, 2012)

In the interest of learning something here that might help the next guy down the line, what charger and BMS are you using?


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## Agust Sigurdsson (Oct 25, 2009)

I suppose that you have eliminated everything but the BMS and potential manufacturing damage in some of the battery cells. 
Check the BMS first by disconnecting it totally from the cells. 
If problem still exists it must be the battery insulation, i.e. casing. Split the battery pack in two and check each half etc.

Agust


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## CKidder (Dec 12, 2009)

kennybobby said:


> In the interest of learning something here that might help the next guy down the line, what charger and BMS are you using?


The charger is an ElCon PFC4000 and the BMS is an EVTV BMS which only three people on the planet have so that won't be that helpful. The BMS is a custom designed board that monitors the pack in quadrants through 50k resistors. I suppose if I had done something dumb then one of those resistors might have connected to chassis ground. 50k is a high enough resistance that only about 6ma could flow under even the best circumstances so having something like that happen would certainly give a shock but not a super serious one. Still, the way this is presenting itself is more like a 1M ohm resistance that is somewhat capacitive as it seems to charge up over time. I still haven't gotten back to the car to figure this out but I will at some point this week.


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## tomofreno (Mar 3, 2009)

What kennybobby said makes some sense. A resistive connection to ground near the negative end of the pack would give you a small negative offset of pack negative to chassis ground, and when you pull your switch that divides the pack into 2/3 and 1/3 that would disconnect the pack positive from that leakage path to ground in the bottom 1/3 and your +270V would disappear. I'd investigate those bottom few cells. Maybe disconnect and jumper past them.


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## racunniff (Jan 14, 2009)

tomofreno said:


> What kennybobby said makes some sense. A resistive connection to ground near the negative end of the pack would give you a small negative offset of pack negative to chassis ground, and when you pull your switch that divides the pack into 2/3 and 1/3 that would disconnect the pack positive from that leakage path to ground in the bottom 1/3 and your +270V would disappear. I'd investigate those bottom few cells. Maybe disconnect and jumper past them.


I agree - I had something similar, and it was in fact the BMS that was the root cause (it was a faulty module) - see http://www.diyelectriccar.com/forums/showthread.php/isolation-fault-ideasi-96104p2.html

Your BMS sounds a little different, but it should be high on your list of things to check.


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## Coulomb (Apr 22, 2009)

CKidder said:


> But, I get the same thing with *nothing* connected to the pack positive and negative points. With the pack supposedly connected to almost nothing (it still does have little voltage taps for a BMS) it still has voltage from HV+ to ground.... I'll try wiping off the tops of the cells to see if there was some sort of conductive dust on the cells and I'll try taking off the voltage taps too.


Just to be clear: you still have the voltage taps for connection to the BMS at this stage (so some wires, the resistors, and a connector), but the BMS itself is disconnected from these taps?

So it's really just the battery, some wires, and the resistors that cause this problem. Is there a battery heater in there?


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## eldis (Sep 3, 2013)

I would blame the batteries in your metal boxes. I've heard about this issue before with these Chinese cells, and that capacity you are reporting is not little.. The usual way to get around it is to connect your battery pack negative through a high value resistor with a small cap in parallel to it to chassis. What troubles me a bit is that you had some nonzero voltage on that resistor you've connected to chassis - that means that there is a significant leakage current from your HV pack, and not just capacitive coupling.

Also measuring any voltages between different points in the car with a regular multimeter has no practical information. If you connect your multimeter between neutral and ground in your house, you will see quite high voltage as well. That's why electricians are using special meters with much lower impedance (typical general purpose meters have well over megaohm).


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## GerhardRP (Nov 17, 2009)

With no connections to plus or minus, what voltages do you get throughout the pack? I would measure chassis to each separate battery terminal in the pack. At some point you should find zero volts. That is where the short is.



CKidder said:


> It's a UQM Powerphase 100 motor and controller and I'm using a DC/DC converter nobody's ever heard of. But, I get the same thing with *nothing* connected to the pack positive and negative points. With the pack supposedly connected to almost nothing (it still does have little voltage taps for a BMS) it still has voltage from HV+ to ground. So, it seems impossible that the entire problem could be anything connected unless I did something dumb with the voltage taps for the BMS. I suppose it might be time to try disconnecting those too to see what happens. I haven't really touched the car in a couple of days since I've been busy with other things but I'll try wiping off the tops of the cells to see if there was some sort of conductive dust on the cells and I'll try taking off the voltage taps too.


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## jddcircuit (Mar 18, 2010)

in this paper
http://www.tdipower.com/PDF/white_paper/Ground-Fault-White-Paper.pdf

page 3 they show a resistor divider (mega ohms) being used by the controller to detect a HV leakage. If the voltage is out of range then there is a leak somewhere

i think my Prius inverter uses something like this

then on page 4 they model the stray capacitance between the HV bus and chassis to be 1.5uF x 2

i measure 40nF between the positive input of my Prius inverter and chassis

it sounds like what you are seeing may be normal. Measure the inverter resistance and capacitance to chassis.

here is another reference discussing inherent parasitic y capacitance in the HV system
http://www.google.com/patents/US20140058687


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## ACEVS4US (Jul 21, 2011)

eldis said:


> Also measuring any voltages between different points in the car with a regular multimeter has no practical information. If you connect your multimeter between neutral and ground in your house, you will see quite high voltage as well. That's why electricians are using special meters with much lower impedance (typical general purpose meters have well over megaohm).


You don't want a low input impedance on your meter. An ideal volt meter would have infinite input impedance. This is because in order to measure a voltage you need to supply a current to the load through the load resistance. Voltage can then be computed via ohms law. Ideally all the supplied current should go through the load resistance and no current should go through the meter as this will affect the accuracy of the reading. 

The fluke 115 Collin is using has a rated input impedance of >10Mohm in DC Volts mode. This would make the meter reasonably accurate (10%) measuring voltages across a 1Mohm resistance from HV to frame. 

I suspect capacitive coupling between the pack and the chassis of the car. If you only get a shock initially and then subsequently nothing, then that points strongly to purely capacitive coupling. If it were resistive then the electric shock would be continuous.


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## CKidder (Dec 12, 2009)

I figure I should update on the progress. I have gotten the voltage down to around 50V. That's a big improvement but I'm hoping to get it a bit better. It seems the the issue was conductive dust on the cells. 

Blowing the cells off with air didn't cut it. I've had to wipe around on the top of the cells and into crevices with alcohol soaked paper towels and q-tips. It's a terribly fun way to spend your time. What's interesting is that, if I check the leak voltage after wiping off cells it'll be sky-high - something like 200-300v. But, once the alcohol completely dries it settles back to a much lower voltage. When the voltage is sky high it "looks" like the alcohol had all evaporated but I guess not. This tells me that these old chinese cells really are extremely prone to some form of leakage if there is even the slightest hint of impurity anywhere near them. Apparently they must be totally pristine or they leak.

So, I might try the idea of grounding the HV- side of the pack through a high ohm resistor and suitably rated capacitor but it appears as if thorough cleaning of the tops of the cells has done quite a bit of good.


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## Jgx64 (Oct 18, 2015)

Hi, it seems that i have the same problem as yours.
i currently have installed CALB last generation 100Ah cells reparted in 2 x 16s banks on each side of a Mini Moke replica. Nominal voltage is 102VDC.
Motor is Motenergy brushless ME0913
Controller is Sevcon Gen4 size6
Charger is TC Ch PFC3000 and Bms is Emus with Canbus communication modules.
Cables are paralleled twin 35mm2 shielded Radox. Connectors are Anderson SB175
The top of the cells+modules are 100mm distance of any chassis point.
All the measured values are changing random but some values appears many time ir stabilize sometimes.
I have voltage between HV+ and chassis (60V) and HV- and chassis (9V) 
Those are the max values I get. Disconnecting the charger drops the voltage a bit.(45V/5V)
Disconnecting everything but the bms drops the voltage down to 2V
Measuring the Load side when disconnected gives me 0V and 3.5MOhms
i will start disassembling the whole thing to find what is what and I will keep you informed.
Please tell me if you solved your problem on your side.


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## beshan (Dec 17, 2013)

I have the same problem as yours. We see a voltage discharge between the chassis and the pack terminal. Any update from you all on the progress or solutions ?


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## Moltenmetal (Mar 20, 2014)

Thanks for bumping this thread- I will have to go back to check this on my own vehicle, both with the charger connected and disconnected. I have a much lower voltage pack so am less worried, but that crud build-up on top of the cells is definitely there. My cells are Sinopoly 180 Ah and I had one of them lose capacity by losing electrolyte through its vent for no apparent reason. I've replaced the cell but have noticed dust building up on my polycarbonate finger protection over the top of my front pack. I would be very surprised if the same dust and crud wasn't accumulating on the tops of the cells, and there are places where the cell terminals aren't very far from the (chassis earthed) battery box frame.


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## Hollie Maea (Dec 9, 2009)

Moltenmetal said:


> and there are places where the cell terminals aren't very far from the (chassis earthed) battery box frame.


It's not a bad idea to put some formal isolation in places like that...not only to protect from conduction if a connection is made, but also to protect from arc over (although at low voltages the arc gap is miniscule). Formex is thin and bendy but gives you thousands of volts of isolation.


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## Moltenmetal (Mar 20, 2014)

There's nowhere the terminals are less than about 1/2" from grounded structure- anywhere the clearance is less, they're separated by a sheet of polycarbonate. But a thin layer of crud 1/2" long and 2" wide might drop to a megohm of resistance over time.


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## poprock (Apr 29, 2010)

Hi guys: The electrician came to inspect my Suzuki Carry van today as in AU an EV comes under AS3000/2000, which is the same as for a house. The paste below is taken from the AU National standard for EV's. He measured only .3ma, far short of the 20ma allowed. I didn't see your measurement, or missed it, but it must be higher than that to be felt.

" 2.9 Hazardous Voltage Isolation
Any HAZV traction battery system must be isolated from the chassis of the vehicle, and also from any auxiliary ELV components and wiring. Isolation must be designed such that there is a leakage current of less than 20 mA between any part of the HAZV system and either the chassis or ELV components in the vehicle, measured when the vehicle is at rest.
This requirement means that both the HAZV battery pack positive, and the HAZV battery pack negative, are to be floating relative to the chassis during normal operation, and both are to be treated as HAZV components.
A ground fault detection circuit or device MAY be used to identify that either the battery pack positive or battery pack negative have come into contact with the chassis or ELV part of the vehicle, and flag this as a fault to the driver or service technician. "
The key word in all of that is MAY, in the notes MAY means optional, so I won't be putting a warning light on. A warning light similar to "check engine" would be a good idea though, as brush dust or corrosion tracking over time could repeat your issue.Awaiting your results


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## Jgx64 (Oct 18, 2015)

Sorry for my late reply, I was far from my EV (France + August = holidays).
Since I wrote my last message, I have been in an EMC/EMI laboratory for EU EMC/EMI new rules validation.
They confirmed that the floating voltages was due to EMC/EMI noise and there is nothing more to be done on the isolation. I could improve the shielding but it is not necessary as the current is less than 30mA.
In addition, the EU legislation has changed in 2016 and now we must install an isolation check system that controls any leakage from the pack (+ and -).
I have recently installed a device extrapolated from Industrial cranes, and I will pass the EU tests...as soon as an official testing company will be qualified by the european administration!
I will keep you informed as soon as the tests will be passed


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## Lowcoe (Jul 3, 2020)

7 years later I found this thread interesting as I’m experiencing similar issues for the second time. First was using rubber radiator hose between busbars and metal box as a spacer. This time I believe it was sandwiching a hv cable between the busbar and metal box endplate…. Not confirmed yet but after reading this thread I believe I know where to look…


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## remy_martian (Feb 4, 2019)

Radiator hose is conductive, lol









Radiator hose - MyScienceWork


Radiator hose: A radiator hose which comprises, in an outermost la




www.mysciencework.com


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## Lowcoe (Jul 3, 2020)

I removed all that from my setup and things seemed all good. Then I hooked up the remaining 4 of 16 modules and kinda smashed the hv cable between the lid and bus bars and proceeded to take my amazing maiden voyage. All was good and then I started digging into the Orion BMS when, low and behold, I got a high voltage isolation fault code. When I tested from HV most positive to battery box (chassis). I got a pretty high reading which would slowly drain down. I tore the sealed box lid off and freed up the wires and tested again. This time the voltage would start at 50 and drain down quickly to 3.5 ish volts. I feel like maybe I’ve violated some ground rules about how close HV components can be to metal battery boxes. They talk of formex, a thin poly propylene material as a good insulator. Or maybe the mica sheets that were inside the original pack??


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## remy_martian (Feb 4, 2019)

If you're charging by capacitance, insulation is part of being a capacitor and is not going to change induced charge buildup. Yes, you can slow down the rate at which the charge builds up, but it'll still charge up to HV.

You have to bleed the charge off...hence the high value resistor* this thread talked about.

*Edit: it can't be any resistor. It needs to have the appropriate voltage rating and needs to be installed so it does not short the HV to chassis in a collision or upset. There may be other safety considerations as well, that I didn't think of off the top of my head, so do your own homework on this.


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