Sevcon Gen4 fault

Joined
Apr 5, 2020
Messages
4
Hi Forum goers,

Here is video if you'd prefer not to read another cry for help and you'd rather listen and watch me plea.
https://nc.init.nz/s/TGDkPPpLXxbJfRM

Otherwise read on...
I recently acquired a broken Polaris Ranger EV - Exciting times, I never thought my first EV would be a mud swinger.
Its got a size 6 Gen4 Sevcon controller in it, and I'm pretty sure that's the broken part.
The controller when powered on emits three green blinks, and the Sevcon datasheet tells me that either a software fault or bad MOSFETs. Once I got time to check over the vehicle, I found some pretty bad corrosion on the battery terminals inhibiting current. I suspect the sevcon unit was working hot and thus damaged the MOSFETs

I've read on this forum when testing resistance between the motor phase terminals and the positive terminal I should get the same/some resistance on all three phases, but not zero. I measured 12k Ohms on Phases A and C but zero on B. I suspect the entire row of 10 MOSFETs for that phase (B) have failed. The previous owner said the vehicle died when they were going up hill with a load on the back.

Is anyone able to confirm that zero resistance is not the expected reading on phase B between it and the positive terminal?

I also suspect this unit is hard to service both digitally (thanks sevcon) and physically. From the physical aspect trying to replace the MOSFETs looks like it will be rather difficult as the are held by very, very firm spring pressure. I assume they were placed in base/heatsink first and the board on top soldiered last.

Also if anyone has an ex Polaris ranger Sevcon unit (48v) they'd like to trade or sell let me know as I think that might be a better option at this stage.

Thanks for reading, loving this forum, great resource.
 
Zero resistance is a blown Fet. It is probably 1 blown in parallel aray but it is difficult to identify without desoldering, unless it is physically damaged. It is also a good habit to change the whole parallel group as the rest could take some damage to and Fets should be matched as well. Said that, I changed 1 Fet in some cases and got lucky.
 
I have some n Chanel mosfets left over from a failed Kelly controller attempted repair.
I’ve opened a sevcon g4 s2 and was able to pull apart the board reassemble it using a long flat bar cut to a specific Width so that when you turn it horizontally it would open up the spring soon as you get mosfets through first hump pull the flat bar out and waddle the rest of the way in that green thermal insulating tape should be replaced also if damaged. Mosfet Rework possibly As long as it didn’t shoot plasma balls and circuit traces is intact it’s repairable check your drivers for shorts to grn.
 
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