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Off-the-shelf module to do Electric Vehicle charger isoaltion test?

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treez

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Hello,
Every time, before our 3.8kw offline EV charger charges a vehicle battery, the charger must always first carry out an isolation test, to check that there is sufficent isolation between the car’s electrical chassis and the rails of the high voltage battery bus. (as per page 32 onwards of this)

Page 32
https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2013/R100r2e.pdf

Do you know if there are special modules for sale which can do this for us, and spit out a voltage to say pass or failed?
 

Not sure if this might resemble the same concept as a GFI. It detects current level going through one wire, and coming back through the other wire. If there is the slightest imbalance, a breaker trips, on the principle that somewhere current is escaping through a path it's not supposed to.
 
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thanks, it does indeed resemble that. We are allowed 100ohm/volt, so we can have minimum of 41000 ohms between chassis and either of the power train bus bars (battery bus).
 

If you put a potential divider across your battery of 1:1, and measure the voltage between the centre of it and chassis. If there is no leakage the voltmeter will read zero. If one terminal of the battery has a lot of leakage then you will measure up to +- 200 V. A better way could be to use two photo darlington opto isolators, connect the LEDs back to back and the transistors in parallel.
Frank
 

Thanks, I can see how to do the above tests myself with a voltmeter etc, but is it normal to get a charger to do this isolation test automatically, every time before it charges a battery?
 

Do you know if there are special modules for sale which can do this for us, and spit out a voltage to say pass or failed?
Click to expand...
State-of-the-art isolation monitors (a major vendor is Bender Germany ) use a low-frequency switched voltage for reliable measurements in presence of leakage currents and noise.

The linked standard in post#1 seems to prescribe a high measurement voltage, which isn't supported by Bender as far as I'm aware of.


I'm under the impression that the unece standard is partly unaware of isolation monitoring state-of-the-art and I doubt that the specification details describe the way to go. I would check the safety measures in recent DC HV chargers from major automotive companies.

but is it normal to get a charger to do this isolation test automatically, every time before it charges a battery?
Click to expand...

It's not unusual to have some kind of isolation monitoring for isolated (IT) HV power sources. It's particularly required for mobile electrical installations.
 

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