# Ground Battery to Frame.



## Sunking (Aug 10, 2009)

OK I know it should not be done, and I think I know why but need a sanity check. 

1. Lessen the chance of being electrocuted and accidental faults to frame.

2. Prevent self discharge through contaminants.

Am I all wet? Is there a automobile standard?


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## mhud (Oct 19, 2009)

I'm no expert, but I thought the big reason was so there's less chance of blowing out your 12V accessories. If you were sure to keep the systems separate, it might be ok, but I'll just say I don't want 120V waiting to flow through me from nearly every surface in the car. 12V I'm not so concerned about.


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## Tesseract (Sep 27, 2008)

Sunking said:


> ...
> Am I all wet? Is there a automobile standard?


There are both European and N.A. regulatory requirements that the traction pack must be isolated from the frame.... that said, the acceptable isolation level is - uh - shockingly low... only 500 Ω/V in the case of DOT Part 571.305. I believe the European (ISO/e-mark) standards are significantly more restrictive (as they usually are) but I can't remember what they are off the top of my head... mainly because I only go with total isolation at the old VDE standard (3750V with 3mm minimum clearance) when designing stuff for this environment.


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## Sunking (Aug 10, 2009)

Thanks Jeff. Then according to the DOT regulation it is to aid in preventing electrical shock. Is that the only reason? I would think it would also aid in preventing self discharge? No?


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## Tesseract (Sep 27, 2008)

Yeah, the DOT is only concerned about safety. The e-mark compliance I alluded to is also concerned with EMI/RFI and that's another good reason to isolate the pack from the frame (common mode filtering caps from pack +/- to the frame aren't a bad idea, though; same for motor +/-).

Isolation has other benefits, too, but no one cares if your circuit discharges the battery pack... as long as it doesn't cause any safety or EMC issues, that is


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## TX_Dj (Jul 25, 2008)

Sounds like this question has a lot of potential. Har har har.


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## Jimdear2 (Oct 12, 2008)

TX_Dj said:


> Sounds like this question has a lot of potential. Har har har.


 
OOOF that was bad

12 slaps with a 10 day old carp for that one

But I admit it was electrifying news


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## PTCruisin (Nov 19, 2009)

Jimdear2 said:


> OOOF that was bad
> 
> 12 slaps with a 10 day old carp for that one
> 
> But I admit it was electrifying news



Now I'm all charged up!

On the topic of isolation: Does an isolated EV charger like the elcon have a ground lug on the ac plug and should the chassis of the charger be grounded to the car frame?


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## Tesseract (Sep 27, 2008)

PTCruisin said:


> ...On the topic of isolation: Does an isolated EV charger like the elcon have a ground lug on the ac plug and should the chassis of the charger be grounded to the car frame?


1. It should
2. If the charger is installed in the vehicle, and there is permanently installed AC wiring to supply it then the NEC requires that the "device" (in this case, the vehicle) be grounded or else it must be "double insulated". The latter isn't practical, really, so grounding it is.


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## Sunking (Aug 10, 2009)

Isolation techniques are no stranger to me. I work in the Telecom sector and have written industry standards on how and why it is used in the Telecom sector. For example we use a lot of what we call Isolated Ground Planes, and Ground Windows with With Single Point Grounding of power supplies and equipment frames. The techniques is used to prevent any signal, load currents, or outside fault current to flow inside the Isolated Ground Plane. I just was not sure of exactly why it is not done in EV's.

My suspicion was if referenced to the vehicle frame, leads to the possibility of load currents flowing in the frame which can cause corrosion problems depending on which polarity is referenced, but more importantly greatly increases the risk of electrocution from accidental contact with the traction battery circuits.

Does that sound about right? In addition do the commercial manufactures install ground fault detectors?


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## ewdysar (Jun 15, 2010)

Sunking said:


> My suspicion was if referenced to the vehicle frame, leads to the possibility of load currents flowing in the frame which can cause corrosion problems depending on which polarity is referenced, but more importantly greatly increases the risk of electrocution from accidental contact with the traction battery circuits.
> 
> Does that sound about right? In addition do the commercial manufactures install ground fault detectors?


In another EV world, EV boats specifically, ABYC (American Boat and Yacht Council) has published specs/standards for electrical propulsion systems. TE-30 states that any system greater than 50V, needs to be broken into packs less than 50V, each pack needs a contactor on both the positive and negative leads, all high voltage connections should be protected in a fire resistant box and the entire system needs a ground fault detector. All in all, fairly reasonable stuff.

Eric


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## mhud (Oct 19, 2009)

You guys have sparked an interesting conversation. 

I'm just confirming that my ElCon (PFC2000+) is wired with a ground pin. It's mounted on aluminum diamond plate onto the chassis but I'm not sure how conductive the diamond plate is.


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## Sunking (Aug 10, 2009)

OK we have established there are standards. That is great, but I want to know WHY exactly those standards exist and what they prevent.

In my minds eye I can see:


Increased risk of electrocution
Conductive paths formed by acid contamination causing batteries to discharge.
EMF/RFI radiation
Load currents flowing in frame work or other unintended paths.
I know some of you are out there in the EV industry, please chime in. I mean heck even golf carts do not bond to the frame.


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## azdeltawye (Dec 30, 2008)

Tesseract said:


> .... The e-mark compliance I alluded to is also concerned with EMI/RFI and that's another good reason to isolate the pack from the frame (common mode filtering caps from pack +/- to the frame aren't a bad idea, though; same for motor +/-)......


What size and type of capacitor would you recommend for common mode filtering?


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## Tesseract (Sep 27, 2008)

azdeltawye said:


> What size and type of capacitor would you recommend for common mode filtering?


Erf.. that's a tough one to answer. These need to be very high quality capacitors with low dissipation factor across a wide frequency range so ceramic (NP0/C0G), or polypropylene (MKP) or mica or even oil filled KVAR correction caps would be appropriate. The value of each isn't critical, it just has to be well-balanced. Anything from 1000pF to 1uF but keep in mind that the rms current rating required will go up with capacitance, so... maybe 0.01 to 0.1uF. Obviously they need to be rated for an appropriate voltage relative to the pack as well! (I know you know this Darren, I'm just trying to be complete for the non-engineers!)

But if you aren't having a problem with electrical noise (whining from the radio, etc.), why bother? If you are having noise problems, first try running the battery cables next to each other. Next try adding common mode caps from each motor terminal to vehicle ground. Next from each battery terminal on the controller to vehicle ground. Finally, pitch the radio and listen to your ipod instead. That solution ALWAYS works, I've found


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## mhud (Oct 19, 2009)

Tesseract said:


> I know you know this Darren, I'm just trying to be complete for the non-engineers!


Much appreciated -- Thank you for helping to educate us lurkers.


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