Thursday, March 24, 2016

Seriously, This is Getting Old

Yes, another fried contactor, this time the rear mid-pack unit. It's clear that there is something fundamentally wrong with the precharge setup, and I've changed the circuit scheme three times and still welding contactors shut. One thing that hasn't changed is the precharge resistor. Even though it's been replaced once, the 500 ohm 100 watt unit I've been using may be mis-sized for my 400 volt pack. I still have the precharge resistor and relay that came with the battery pack, and surely it must be a match. Only problem is that I welded those contactors on my first precharge mishap. 

Fortunately, the Panasonic contactors used in the Better Place pack can be found from time to time on eBay, and I picked up a couple from a Canadian seller at a very reasonable price. I like the packaging on the Better Place contactor/precharge module and since I designed the mount for it in the first place, it went back on pretty easily.

 I took the opportunity to ground the shielding on the inverter cables and revise the wiring to the time-delay control relay. This setup certainly looks cleaner than the former one, and all of the terminals and connections are safely contained inside the plastic housing.

We'll test this in the neighborhood for a bit before we go too far afield, but I'm hopeful that this will solve the precharge challenges. There is lots more I want to do, but this needs to be stable and reliable before moving on.


  1. I just read this in the newest version of Jack's GEVCU manual. What hardware version do you have?


    All GEVCU 5 and earlier series GEVCUs are NOT suitable for use for precharge procedures. The SAM3X microcontroller, when first powered up, sets ALL digital outputs to ON for about 80 milliseconds. This has the effect of closing all contactors if the GEVCU precharge procedure is used as designed and tends to destroy the contactors with capacitor inrush current.

    It is recommended that you NOT use the GEVCU for precharging and implement a manual precharge strategy instead.

    This hardware design flaw will be addressed in future GEVCU hardware releases.

    1. Right you are! Jack added that paragraph after I told him and Collin that my test lights showed my GEVCU 4 was turning on both contactors at boot before the initial firmware load. Even noticed the cooling fan spin for an instant at boot. That was at EVCCON last year. Now on top of that, I've had precharge resistors fail, so I'm back to the kit that came with the pack. So far so good. Other than that, the GEVCU has been pretty much bullet proof.

    2. Fred, did you also happen to hear that Collin/Ed/Jack now have a retrofit that resolves this issue by adding a couple of judiciously-placed pulldown resistors? Details here:!topic/gevcu-development/7z1wJLHIL8w

    3. Jason, thanks for the pointer. Yeah, I was one of the canaries in the mine shaft on this, and it's good to see the team has a solution. I added a time delay relay to my precharge circuit and stopped using the GEVCU for that function. Since I published this blog page, I've gone over two months without incident, so I'm pretty sure I have this particular wrinkle ironed out. Thanks for following!