Divide and conquer. This is the key to troubleshooting.
1) Disconnect whatever portions of the HV traction system that you can
disconnect easily.
2) Using a voltmeter, with the range set on a DC voltage slightly higher
than the pack voltage, starting with the battery, check the voltage
between the chassis and various HV points.
3) Check both ends of the battery pack, and points in the middle of the
battery pack if it is easy. When you find a voltage greater than a few
volts that is steady for a few minutes, write it down.
4) If you have detected voltage between the battery pack to chassis
("ground" but not really) the voltages measured will tend to indicate
exactly where the leak to chassis is.
5) Check other points outside the battery in the _disconnected_ _from_
_the_ _battery_, traction system for voltage to ground. If all are zero
volts to chassis, set the multimeter to ohms (like the 10,000 ohm scale)
and check the resistance to chassis of those zero volt points. Any
reading not full scale (greater than full scale ohms) is a leakage suspect.
Typical chassis leakage causes:
Battery electrolyte leakage causing the terminals to form a
weak bridge to the pack case. -> Clean off the the tops of the cells and
do a voltage leakage test again.
Brush dust in DC motors causing leakage to the motor case. ->
Blow out dust and check again.
Road salt/moisture/dirt on electrical components. -> You know
the drill.
Component overheating or failure. -> Again, replace and check
voltages again.
If you don't find any voltage to chassis anywhere with the car off,
and you didn't find any suspect resistances to chassis in the zero
voltage points of the car, then you probably need to do a voltage check
with the system live. (No fun at all.) Be careful doing this, and
_never_ ever stand in front or behind the car while it is live. Never. Ever.
You _really_ need to find this chassis to traction system fault
("ground" fault.) There are several serious consequences that may occur.
1) _You_ may become the conductor that completes the circuit to chassis.
Basically, there is one chassis fault, and you may get juiced by
touching a live part of the car and completing the circuit.
2) At the moment, you have one (1) "ground" fault. _One_ place in the HV
system has made a connection to the chassis. The consequences are dire
if the car finds a second point in the HV system to connect to ground.
Folks typically get an unnoticed ground fault in the pack, and then get
another one somewhere else, like the motor. They switch on the vehicle,
this completes the circuit, and the vehicle bursts into flame. Flames
are what results from a two chassis ("ground") faults.
Few folks regularly check for chassis faults in their home built
EV's. They only become aware of them when they trip a GFI type breaker,
get juiced, or the vehicle goes up in flames.
Bill D.
On 5/2/2020 4:26 PM, John Lussmyer via EV wrote:
I know my truck has a weak Ground Fault - just enough to trigger SOME GFCI
breakers.
What is a good way to measure it, and track down just where it's occuring?
--
Tigers prowl and Dragons soar in my dreams...
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