Okay to use non-inductive radiator heaters to discharge battery pack through MOSFET based BMS?

[ironhalo]

Question for those of you who have used an oil filled radiator or some other type of non-inductive AC heater to test/discharge your battery packs (using DC current only)... Is this fine to do with the current flowing through a solid-state mosfet-based BMS like a JK or a Daly? I've done it a lot with setups that use a mechanical contactor, however the one time I tried with the current flowing through a mosfet-based BMS it totally fried the BMS, despite only pulling ~15A on a BMS rated for 100A. So I've never tried it again. I'm inclined to think that it was just a crappy off-brand BMS that self-destructed for other reasons, but thought I’d ask just in case there is some inherent danger in doing this that I’m not aware of.

I just finished building a new pack (72V 50Ah LiFePO4), using a Daly SMART BMS 250A, and I am beginning to load test it. Right now I'm pulling 30A from it using 4 oil-filled radiators, but running the current through an external contactor driven by the BMS output... but naturally I’d prefer to be running the current through the BMS itself to take advantage of the built-in ammeter and coulomb counter. I can’t think of any reason why using these heaters as a load would be dangerous for the mosfet-based BMS, however I am gun shy after having fried one solid state BMS this way in the past. Thoughts? Thanks in advance.

 

[dominik h]

Yes ot works fine.
I've done this full to empty test with resistors and with an 7kw electronic load with the ANT BMS in between. As I built my 21S100Ah battery for my scooter.

 

[ironhalo]

Yes ot works fine.
I've done this full to empty test with resistors and with an 7kw electronic load with the ANT BMS in between.

Cool, thanks. It makes sense that it shouldn't cause a problem, as these heaters are just large resistors with a mechanical thermostat attached. Was just feeling a little uneasy since I toasted one BMS before doing it.

What was your 7kw electronic load?

As I built my 21S100Ah battery for my scooter.

Sweet! Must be a pretty large scooter frame, 100Ah is a decent size pack! What kind is it? My scooter barely fits 50Ah worth of cells into the chassis.

 

[dominik h]

The scooter is a Masini Extremo which was rebuilt in 2020/2021. At first it was equipped with a Sabvoton SVMC72260. But I killed it while playing with weakening field. Then I drove 10000km with an SVMC72150 and now changed to a Fardriver ND72680 which is set to 250A at the moment. This gives better starting tourque and better acceleration. Soon I want to upgrade from a QS60V5000W motor (40mm magnets and 13.3mm phase wires) to a QS72V10000W with 60mm magnets and 25mm phase wires. Hoping that this motor can take more power as I want to get over 300A battery current. My old motor heats up very quick and sometimes I run into motor the temperature limit which reduces the power.
The load test was done with 83A setting from full to empty. 7kw electronic load was EA EL 750V 250A max 7kw continious. The test gave a usable 97Ah. My battery is made from power pouch cells 105pcs 20Ah with 8c continous rating. Resistance at the controller terminal screws was 13mOhms.

 

[dominik h]

I would put a fan or Ventilator in front of the radiator to be shure the internal temperature switch does not turn of the radiator. A voltage spike from switching off could probably kill the bms.

 

[ironhalo]

I would put a fan or Ventilator in front of the radiator to be shure the internal temperature switch does not turn of the radiator. A voltage spike from switching off could probably kill the bms.

Yeah, good call. I have 2 fans pointed directly at them already.

 

[ironhalo]

The scooter is a Masini Extremo which was rebuilt in 2020/2021. At first it was equipped with a Sabvoton SVMC72260. But I killed it while playing with weakening field. Then I drove 10000km with an SVMC72150 and now changed to a Fardriver ND72680 which is set to 250A at the moment. This gives better starting tourque and better acceleration. Soon I want to upgrade from a QS60V5000W motor (40mm magnets and 13.3mm phase wires) to a QS72V10000W with 60mm magnets and 25mm phase wires. Hoping that this motor can take more power as I want to get over 300A battery current. My old motor heats up very quick and sometimes I run into motor the temperature limit which reduces the power.

Wow, impressive! That's the largest amount of lithium I've ever seen packed into a scooter frame. I bet that thing is fun to ride!

7kw electronic load was EA EL 750V 250A max 7kw continious. The test gave a usable 79Ah.

Do you own the EA EL unit, or you just have access to one? How much does something like that cost?

 

[dominik h]

I have only acces to it. Costs 5000Euro. It is an indaustrial electronic load.
The test gave 97Ah usable , sorry had a typo in the numbers.
The battery weights 73kg and I had to lenghten the wheelbase to fit it in there. With the storage type pouch cells from the same manufacturer with only 2C continous discharge I could have fitted 160Ah in the same space and weight.
One day the cells stood at my working place with a sticker on it :" please dispose".

 

[ironhalo]

Yeah, I figured it was at least a few thousand dollars. Would be nice to have access to that. Wow, really nice cells for free!!

I'm currently drawing 42A through the BMS using six radiator heaters. All good so far.