Hello Roger,
In explosive proof areas, operating rooms, fuel stations we install a Ground
Detection system which detects a conductance path to ground. For this to
work, the installation has to completely isolated, meaning no direct
electrical grounds connected to any metal housings, conduit and electrical
panels. All this installation and electrical is isolated by using a large
isolation transformer and sometimes a capacitor bank.
The only thing you can detect on a EV is the DC leakage from the battery
pack to the frame of the EV. You first unplug the AC input plug which may
have a self grounding pin in the plug.
Next take a volt meter set in the lowest scale and place one lead on the
most positive and to the frame of the EV. If you should indicate a voltage,
then some where in the pack, a battery is conducting a current to the frame.
Lets say it reads 10 volts from the most positive to frame, then move the
test lead from the most positive to the next battery, you will see that this
voltage will drop until you get to the battery or batteries that are leaking
current the most.
Keep the meter connected and start cleaning the batteries until the voltage
indication drops as low as it can go.
Now, increase the voltmeter scale higher then the charging voltage of the
charger and turn on the battery charger. If the voltage indication on the
meter is the same voltage as the output voltage of the charger, this is
normal for a non-isolated charger. The meter it self is shunting this
current at this time.
You can do a permanent installation, by installing a panel volt meter
connected to switch to a 1 amp fuse which is then connected to the most
positive post of the pack. The other lead of the volt meter than is
connected to the vehicle frame.
If you use a low voltage meter, then you first must turn off this test meter
switch, as so not peg the volt meter if you forgot to turn off this switch.
You could also use a 2 pole double throw switch where in one position to
test out the ground fault while the other position of the switch it keeps
off the AC input power by use of a AC magnetic contactor. Turning the switch
in the other position, turns off the test meter and turns on the AC
contactor.
These ground detection units can be purchase from GE, Westinghouse, Square
D, etc. In any case when they detect a current leakage above a set
perimeter, it then is use to turn off a AC magnetic contactor.
Roland
----- Original Message -----
From: "Roger Daisley" <
[email protected]>
To: <
[email protected]>
Sent: Friday, October 15, 2010 9:38 AM
Subject: [EVDL] Measuring Ground Fault Current
> As many EV'er know, popping a GFCI when charging their EV is fairly
> common.
> It is especially embarrassing when it happens at a location other than
> home.
>
> I am hoping that someone can describe a simple way to measure and monitor
> this leakage current so preventive action can be taken before it gets to
> the
> "popping" stage. I'm thinking that perhaps a GFCI could be tapped in some
> way to measure the current it is seeing.
>
> Roger Daisley
>
> ElectricVW.blogspot.com
>
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