# [EVDL] Small shock on car frame



## EVDL List (Jul 27, 2007)

Can someone help me understand what is going on here? Is this due to
residual acid on the top of my batteries? If I lick my fingers and touch
the most positive terminal of my pack and ground, I get a shock but it only
lasts for a fraction of a second. I can hold my finger on but the shock
doesn't continue. It is a significant shock (way more than a good static
shock) but not so bad that it stops me from repeating several times. It is
sort of like discharging a capacitor. If I lift my finger for a few seconds
and touch the post, I get the same small short shock but if I leave my
finger on, there is no shock after the initial jolt. My Fluke reads almost
the full pack voltage from the post to ground even though my pack is not
grounded. However, I only measure a continuous 0.070mA when I short the
most positive to ground with the Fluke. That is pretty much nothing, but
still something. The most negative battery to ground gives me nothing. So I
disconnected the power cable at the most negative battery thinking the leak
was happening at the controller or charger. However, I still read nearly the
same 0.070mA from 120V terminal to ground even with my most negative battery
completely disconnected. I tried cleaning the terminals on the first 6
batteries and it dropped to 0.065mA but that might just be measurement
error. Do I have a problem that warrants further testing or is this pretty
normal?
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## EVDL List (Jul 27, 2007)

"Hey Doc, it hurts when I do this."

"Well, don't do that!"

I would suggest NOT touching your pack and ground to look for
problems. Independent of the source of the problem, you don't want to
find a bad problem by electrocuting yourself.

Dave Cover



> Steve Skarda<[email protected]> wrote:
> > Can someone help me understand what is going on here? Is this due to
> > residual acid on the top of my batteries? If I lick my fingers and tou=
> ch
> ...


----------



## EVDL List (Jul 27, 2007)

> dave cover <[email protected]> wrote:
> 
> > "Hey Doc, it hurts when I do this."
> >
> ...


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## EVDL List (Jul 27, 2007)

perhaps it is as you describe. A capacitive shock. you have a very low
capacitance setup by your car and battery, charged to 120V. When you
touch it, it discharges through you quickly.
Just an idea

-Jon Glauser
http://jonglauser.blogspot.com
http://www.evalbum.com/555

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General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
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## EVDL List (Jul 27, 2007)

Be sure that the ground fault detector/monitor does not _create_ the 
dangerous ground fault you are trying to guard against.

The circuit must be _very_ well designed and thought out so that 
there is no possibility to create the current path from the battery 
pack to the frame of the car. If your circuit connects the battery 
pack to the frame via a resistor, you have created the ground fault 
you are trying to detect, but your detector will never see it!

Bill Dube'

At 12:09 PM 7/15/2009, you wrote:
>


> dave cover <[email protected]> wrote:
> >
> > > "Hey Doc, it hurts when I do this."
> > >
> ...


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## EVDL List (Jul 27, 2007)

> Bill Dube <[email protected]> wrote:
> 
> > Be sure that the ground fault detector/monitor does not _create_ the
> > dangerous ground fault you are trying to guard against.
> ...


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## EVDL List (Jul 27, 2007)

With your circuit connected, what will happen when _you_ touch the 
frame and the terminal at the end of the pack with your hand?

Current will flow through _you_ to the pack, then to the center of 
the pack, then through the resistor, then through the frame, 
completing the circuit. Up to 60 mA will flow.

When you connect your unisolated charger, what happens when someone 
touches the frame of the car and touches something grounded with the 
other hand?

Bill Dube'

At 02:44 PM 7/15/2009, you wrote:
>


> Bill Dube <[email protected]> wrote:
> >
> > > Be sure that the ground fault detector/monitor does not _create_ the
> > > dangerous ground fault you are trying to guard against.
> ...


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## EVDL List (Jul 27, 2007)

Thanks Bill. I really appreciate the advice from veterans. I'll draw up
some details and share it here for peer review before I try anything. You
have brought up some good points that I hadn't fully considered. With a
little larger resistor, I can keep the ground fault to a safe level but I
better understand your original comment that the circuit requires careful
consideration.



> Bill Dube <[email protected]> wrote:
> 
> > With your circuit connected, what will happen when _you_ touch the
> > frame and the terminal at the end of the pack with your hand?
> ...


----------



## EVDL List (Jul 27, 2007)

> Bill Dube<[email protected]> wrote:
> 
> > Be sure that the ground fault detector/monitor does not _create_ the
> > dangerous ground fault you are trying to guard against.
> ...


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## EVDL List (Jul 27, 2007)

This is just a guess on my part, but I suspect that the commercial 
ground fault detectors use some sort of AC coupling instead of a DC 
coupling to detect the presence of a ground fault. I suspect that 
they use a high-quality capacitor instead of a resistor to connect to 
the traction wiring and determine if they can find another path to 
the frame. They may even use multiple probe frequencies to prevent 
false trips due to stray capacitive coupling of the traction system 
to the frame. Again, this is just a wild guess on my part.

The problem is that to determine if a ground fault exists, your 
detector must in some way "complete" the circuit and see if current 
flows, but you have to do this in a way that does not create a 
dangerous ground fault. This is not so easy to do.

Another difficulty is that the device must detect a ground fault that 
occurs _anywhere_ in the traction circuit. A simple detection device 
might not be able to detect a ground fault at or near the point where 
_it_ connects to the traction system.

Bill Dube'

At 04:36 PM 7/15/2009, you wrote:
>Thanks Bill. I really appreciate the advice from veterans. I'll draw up
>some details and share it here for peer review before I try anything. You
>have brought up some good points that I hadn't fully considered. With a
>little larger resistor, I can keep the ground fault to a safe level but I
>better understand your original comment that the circuit requires careful
>consideration.
>
>


> Bill Dube <[email protected]> wrote:
> >
> > > With your circuit connected, what will happen when _you_ touch the
> > > frame and the terminal at the end of the pack with your hand?
> ...


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## EVDL List (Jul 27, 2007)

EV ground fault detectors exist as a commercial product. Not cheap, 
but they exist.
http://www.bender.org/Product_PDF/UG140P.pdf


At 05:04 PM 7/15/2009, you wrote:
>


> Bill Dube<[email protected]> wrote:
> >
> > > Be sure that the ground fault detector/monitor does not _create_ the
> > > dangerous ground fault you are trying to guard against.
> ...


----------



## EVDL List (Jul 27, 2007)

> Bill Dube wrote:
> >> Be sure that the ground fault detector/monitor does not _create_ the
> >> dangerous ground fault you are trying to guard against.
> 
> ...


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## EVDL List (Jul 27, 2007)

I was just wondering how you discovered it. =


Stub

Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: dave cover <[email protected]>

Date: Wed, 15 Jul 2009 13:41:13 =

To: Electric Vehicle Discussion List<[email protected]>
Subject: Re: [EVDL] Small shock on car frame


"Hey Doc, it hurts when I do this."

"Well, don't do that!"

I would suggest NOT touching your pack and ground to look for
problems. Independent of the source of the problem, you don't want to
find a bad problem by electrocuting yourself.

Dave Cover



> Steve Skarda<[email protected]> wrote:
> > Can someone help me understand what is going on here? Is this due to
> > residual acid on the top of my batteries? If I lick my fingers and tou=
> ch
> ...


----------



## EVDL List (Jul 27, 2007)

> Bill Dube wrote:
> > Be sure that the ground fault detector/monitor does not _create_ the
> > dangerous ground fault you are trying to guard against.
> >
> ...


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