# Voltage between chassis and HVDC



## evmetro (Apr 9, 2012)

When my charger is running, I can stick the ground lead of my multimeter to the chassis and the positive lead to my traction pack and it reads -170 volts. When the charger shuts off, it goes away. Apparently it has been this way since I built it, but I never noticed until I touched a bus bar and the chassis at the same time. I have the AC main ground wire connected to the chassis, and run a Manzanita PFC 20 in this rig, and the AC main ground is connected here as well. Pack voltage is 144 volts. I tested my other conversion that has a 108 volt pack and a Manzanita PFC 40, and got the same reading while charging as well. Both conversions have the same AC main ground wire configuration. What did I do wrong?


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## dragonsgate (May 19, 2012)

Check to see if there is any amperage. There have been accounts of others getting readings between the battery pack and car body but no measurable amps.


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## Tesseract (Sep 27, 2008)

dragonsgate said:


> Check to see if there is any amperage. There have been accounts of others getting readings between the battery pack and car body but no measurable amps.


Yes, this, BUT... the safe way to see if there is actual leakage current is to put a 10k resistor across the meter probes when measuring voltage. If the voltage reading doesn't drop to zero (or close to it) THEN put the resistor in series with one of the probes and switch the meter over to measure both AC and DC current (mA scale). Anything more than 5mA is considered a potential hazard and indicates a ground fault somewhere in the traction circuit (ie - battery, controller, motor).


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## GerhardRP (Nov 17, 2009)

evmetro said:


> When my charger is running, I can stick the ground lead of my multimeter to the chassis and the positive lead to my traction pack and it reads -170 volts. When the charger shuts off, it goes away. Apparently it has been this way since I built it, but I never noticed until I touched a bus bar and the chassis at the same time. I have the AC main ground wire connected to the chassis, and run a Manzanita PFC 20 in this rig, and the AC main ground is connected here as well. Pack voltage is 144 volts. I tested my other conversion that has a 108 volt pack and a Manzanita PFC 40, and got the same reading while charging as well. Both conversions have the same AC main ground wire configuration. What did I do wrong?


Could you be a little more specific. 
1. Is that 170 VDC to the plus side of the battery?
2. What is the voltage on the low side of the battery? [170-144 VDC maybe?]
3. is there an AC component of the voltage.
Gerhard


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## Tesseract (Sep 27, 2008)

GerhardRP said:


> ...
> 3. is there an AC component of the voltage.
> Gerhard


Good point; whether the voltage is AC or DC will provide a strong clue as to its origin...


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## Russco (Dec 23, 2008)

evmetro said:


> When my charger is running, I can stick the ground lead of my multimeter to the chassis and the positive lead to my traction pack and it reads -170 volts. What did I do wrong?


You didn't do a thing wrong. Except use a DIY type non-isolated charger. The AC line voltage, thru rectification to DC voltage, will be present on the battery pack to the vehicle chassis. The 170 volts your noted is the peak voltage of 120 VAC.

Dangerous situation: Don't touch a battery connection while charging and use a GFI.

Better yet, use a real isolated battery charger.


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## evmetro (Apr 9, 2012)

I have not done the other tests yet, but when I first discovered this 170 volts its path was between my hands. It got me motivated a lot quicker than drinking a red bull. I have pre built EMW chargers for the two builds I am doing right now, hopefully they do not behave the same way. I would like to have the 10k resistor to perform the above test, so I will head off to radio shack and pick one up. I do not know much about buying resistors.. is there anything I need to look for when buying it other than the 10k?


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## GerhardRP (Nov 17, 2009)

evmetro said:


> I have not done the other tests yet, but when I first discovered this 170 volts its path was between my hands. It got me motivated a lot quicker than drinking a red bull. I have pre built EMW chargers for the two builds I am doing right now, hopefully they do not behave the same way. I would like to have the 10k resistor to perform the above test, so I will head off to radio shack and pick one up. I do not know much about buying resistors.. is there anything I need to look for when buying it other than the 10k?


If the 170 volt source is low impedance, then the power in your 10k resistor would be 170^2/10000 = 2.85 watts, so get a 5 watt resistor.
G.


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## Tesseract (Sep 27, 2008)

GerhardRP said:


> If the 170 volt source is low impedance, then the power in your 10k resistor would be 170^2/10000 = 2.85 watts, so get a 5 watt resistor.
> G.


Technically true - and if Radio Shack has a 10k/5W resistor in stock then by all means the OP should get it - otherwise a 1/2W resistor will survive plenty long enough to make a couple of quick voltage and current measurements.


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## GerhardRP (Nov 17, 2009)

Tesseract said:


> Technically true - and if Radio Shack has a 10k/5W resistor in stock then by all means the OP should get it - otherwise a 1/2W resistor will survive plenty long enough to make a couple of quick voltage and current measurements.


Also, notice that the first measurement of the voltage across a 10KOhm resistor is also a current measurent where I=V/10000.
Or interpreted another way, the Fault resistance is determined by Rfault = ((170-V)/V) *10K

Gerhard


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## kennybobby (Aug 10, 2012)

So is it +170 or -170 that you are reading?


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## evmetro (Apr 9, 2012)

kennybobby said:


> So is it +170 or -170 that you are reading?


It's 170 volts, but my meter shows that the chassis is the positive. When I reverse the probes, the minus symbol goes away


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## Nabla_Operator (Aug 5, 2011)

*CURRENT between chassis and HVDC Re: Voltage between chassis and HVDC*

What counts (for safety) is the resistance / current through the connection between chassis and HVDC. 
Now I want to bring my (unanswered) question about a safety device under your attention, guys: Has anyone of you made / bought an insulation monitoring device for this problem? 
See link.


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## Tesseract (Sep 27, 2008)

*Re: CURRENT between chassis and HVDC Re: Voltage between chassis and HVDC*



Nabla_Operator said:


> ...Now I want to bring my (unanswered) question about a safety device under your attention, guys: Has anyone of you made / bought an insulation monitoring device for this problem?
> See link.


Your approach won't work very well for the following reasons:

1. It intentionally introduces the very thing you are trying to avoid - leakage from the HV side to the LV side;

2. It won't detect a hard fault from the pack midpoint (e.g. - 130V) to chassis ground at all;

3. Measured fault current will be proportional to the difference between the midpoint voltage and where the fault actually occurs. If it is only 1 or 2 cells away from the midpoint and the resistors connected to either end of the pack are high enough in value then measured fault current will be miniscule, vastly understating the danger.

Detecting ground faults is almost trivial in low amperage AC systems (ie - 15-20A residential outlets) but deceptively difficult to do in an EV whic runs on DC and where operating currents are 10-100x higher.

I suggest looking at Bender's line of isolation/ground fault monitors, specifically the IR155-3204.


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## kennybobby (Aug 10, 2012)

*you got to keep 'em separated...*

Either your pack (+) terminal is shorted to chassis, or the charger has a design 'feature'. 

So from your measurement it seems that the positive battery charger clamp is somehow shorted to the earth protection ground on your chassis and you are reading the rectified line voltage [170 VDC] between the chassis and the (-) side of the battery pack. 

The fact that you have two of them on different sized packs that exhibit the same voltage makes me think it is in the design or wiring of the charger. 

If the (+) side of the diode rectifier bridge was internally connected to the earth ground then you could see a voltage reading such as you have. 

Maybe you can take some measurements on the bench of an unpowered charger, check if there is continuity between the charger case and the earth ground pin in the ac cord, and also check between the (+) charger output wire and the ground pin. Then you could power up the charger on the bench and check to see if you measure the 170 vdc between the earth ground (the charger case) and the (-) charger output wire.


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## major (Apr 4, 2008)

The Manzanita charger is not isolated so of course you'll have potential between the output and ground


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## major (Apr 4, 2008)

KenBob 

Mine was a reply to the OP and thread in general, nothing directed to you specifically. Sorry for the confusion. But we have a whole thread stating the obvious when using a non isolated charger, don't we?


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## Tesseract (Sep 27, 2008)

major said:


> The Manzanita charger is not isolated so of course you'll have potential between the output and ground


Oops. I somehow missed that. I thought for sure the OP had an Elcon charger...


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## Russco (Dec 23, 2008)

Tesseract said:


> Oops. I somehow missed that. I thought for sure the OP had an Elcon charger...


Seems that was brought up long ago on post 6. 

Problem solved. Nothing wrong but charger choice. End of story.


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