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  #1  
Old 07-19-2010, 08:39 PM
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Default Ground Battery to Frame.

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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Old 07-19-2010, 11:29 PM
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Default Re: Ground Battery to Frame.

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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Old 07-20-2010, 04:47 AM
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Default Re: Ground Battery to Frame.

Quote:
Originally Posted by Sunking View Post
...
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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Old 07-20-2010, 07:47 AM
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Default Re: Ground Battery to Frame.

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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Old 07-20-2010, 08:37 AM
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Default Re: Ground Battery to Frame.

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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Old 07-20-2010, 10:27 AM
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Default Re: Ground Battery to Frame.

Sounds like this question has a lot of potential. Har har har.
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Old 07-20-2010, 11:30 AM
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Default Re: Ground Battery to Frame.

Quote:
Originally Posted by TX_Dj View Post
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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Old 07-20-2010, 11:49 AM
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Default Re: Ground Battery to Frame.

Quote:
Originally Posted by Jimdear2 View Post
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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Old 07-20-2010, 01:05 PM
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Default Re: Ground Battery to Frame.

Quote:
Originally Posted by PTCruisin View Post
...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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Old 07-20-2010, 01:08 PM
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Default Re: Ground Battery to Frame.

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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