On my opinion John,
If you were able to properly isolate that fault to ground right to
your DC-DC converters, you should fix that (independently how critical
those DCDC are for your Zilla or anything else). On a HV system, safety is
the most important thing to be taken into consideration over anything else.
With that said, I would recommend you to:
- First: identify if the fault is just in one DC-DC or both, if its one,
probably you could have a defective component inside or just some 'dirt'
terminals, connector, trapped moisture, etc. creating that small current
leak. If both DC-DCs got the fail, don't even attempt to replace them by
same PN. throw them away and get a completely new brand/version with
similar capabilities.
- Usually all OEM EVs have two main contactors, one for +, one for -. So
does BMS; also have the ability to check either the + and the - sides for
isolation faults. This is in order to minimize the risk of an electrocution
to human bodies over all. Check for your BMS for the ability to do both + &
-, if not, You should perform the missing side manually to ensure no more
faults.
- Once you have fixed/replaced your DC-DCs/isolation problem, 'test' your
BMS to confirm it is properly detecting new ground isolation faults and
that has the ability to 'disable' your main contactor(s). Or at least,
notify you there is an isolation problem so you don't attempt to ever touch
any + or - terminal at any time.
- Your BMS must be also able to track isolation issues from your AC onboard
charger while charging, so if should also 'disable' your charger in case
there is a ground fault on it as well.
Marco Gaxiola
On Sun, Nov 10, 2019 at 11:45 AM John Lussmyer via EV <[email protected]>
wrote:
> I seem to have a ground fault in my truck.
> I was working on the BMS, and when my finger touched one of the busbars, I
> got a shock. (forearm was leaning on the truck frame.)
> To find where it was coming from, I put a 1K resistor in series with my
> meter lead, tied the other end to ground, and set the meter to read ma.
> Touched the other lead to the pack, about 1/3 from one end - about 1.3 ma.
> Turned off the main breaker, which splits the pack into 4 (odd sized)
> sections.
> No leakage from the middle 2 sections, but about 0.4ma leakage amounts
> from either of the 2 "end" sections (about 32v ea). (both still have one
> end connected to the truck systems.)
> So I start disconnecting truck systems.
> Found that the leakage seems to be coming from the 2 small DC-DC
> converters (actually, power supplies) that I use to keep the Zilla powered
> up, and maintain the 12v battery. Both of these are UL approved isolated
> power supplies.
>
> Now what? I need the DC-DC's, but I really do NOT want a ground fault.
>
> --
> Worlds only All Electric F-250 truck!
> http://john.casadelgato.com/Electric-Vehicles/1995-Ford-F-250
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