Managing automatic pre-charge of the DCDC when AC charging

[Boxster EV]

For the last two years, I’ve being running my DCDC with the HV negative side behind the contactor. Upon plugging in to charge, I’d set-up a manual relay logic that would close the negative contactor and enable the DCDC during charging (+ side in front of contactor). It’s worked fine until last week when it let out the magic black smoke. I don’t know whether it was the lack of pre-charge that killed it but I suspect it was a contributor.

I wish to be a little kinder to the new DCDC and intend to pre-charge. My question is, how are folk managing contactor control to enable the DCDC when charging?

P.S I do not want the DCDC permanently connected to the DC bus.

[arber333]

I wish to be a little kinder to the new DCDC and intend to pre-charge. My question is, how are folk managing contactor control to enable the DCDC when charging?

P.S I do not want the DCDC permanently connected to the DC bus.

You could install NTC inrush limiter on HV lines. You would need to calculate them for nominal current consumption, but i would bet that would spare DCDC much pain.
https://product.tdk.com/en/techlibrary/ ... miter.html

[Boxster EV]

Thanks for responding. I’ll look into those.

I was also thinking about using one of these (just to manage the charging contactor control).

https://zero-ev.co.uk/product/low-volta ... cba1185463

Not sure whether it would work or not, but I have one on the shelf to test.

[johu]

I use the pack voltage reported by the BMS and the bus voltage reported by the inverter. When the two match within a tolerance of 10V I close the positive contactor.

Not sure how much control you have and whether you have access to all necessary data

[Boxster EV]

I use the pack voltage reported by the BMS and the bus voltage reported by the inverter. When the two match within a tolerance of 10V I close the positive contactor.

Not sure how much control you have and whether you have access to all necessary data

Thanks! I have the necessary inverter data mapped to my VCU, but the BMS is running at a different speed so I’ll need to overcome that…

As I’ve got the contactor controller board to hand I’ll give that a go first.