how to limit dcqc rate

pbui19 · Feb 22, 2019

so I am finding myself doing dcqc almost exclusively this winter for a number of reasons: paranoided about on-board-charger failing, cooler weather, a free station 1-mile from home, and another practically free ($0.06/kwh) on the way home. Because my house is at 2200-ft elevation, with a 50-mile round trip commute, the iMiev gets frequent charging akin to a cell phone.

I am concerned about damaging my pack. I feel that it would be ok if the dcqc can be limited to 1C rate, or even 20kw rate max. Does any one have any idea how ?

I've thought about temporary tricking the BMS to think it's cold or fooling the SOC. Fooling the temperature reading would be bad during the warmer months. That initial 40kw rate just seems so high. It's around 17kw around 45-50F pack temp.

Canion's capacity history is showing diminishing Ah, but seems to correlate with lower pack temperature. I am hoping Ah will go up with higher pack T come spring time.

PV1 · Feb 23, 2019

Chilling the pack would've been my method. Are there any 25 kW CHAdeMO units around you?

pbui19 · Feb 26, 2019

I may be a bit panaroid about this, as the duration above 40kw only lasts a few minutes. There is a 25kw station and I've used it.

if I can trick the BMS to think the SOC is around 50%, then the charge rate is limited to ~20kw. I am afraid it involves hacking the CAN bus messages.

But I think I need to re-calibrate the software integrator, as Chargepoint is reporting 7.5 kwh input while the iMiev gauge goes from 3 bars to 14 bars; implying 7.5kwh/11 bars = 0.75kwh/bar.

Do I need to drive down to two remaining bars then charge up until auto-shutdown ? and is L2 charging ok ?

Thanks

PV1 · Feb 27, 2019

.75 kWh/bar implies around 80% remaining capacity (82.5% by my math), but that's assuming 16 kWh actual new capacity. When my i-MiEV got a new pack in 2015, it topped out just over 45 Ah, for a usable capacity of 14.7 kWh. Accounting for the 12% reserve below the 1st bar, this works out to .81 kWh/bar.

At .75 kWh/bar, your usable capacity is near 13.5 kWh, which would be 41.3 Ah (around 91% usable capacity compared to a new pack). Being that these cars are getting old, I think this is a good number to be at. It's better than my silver i-MiEV with its original 2012 pack.

As for charging current, regen can peak out around 40 kW, although only for a couple seconds as the car decelerates quickly at this rate. I'm concerned about the chargers in my cars as well. I would think level 2 charging would be better on the charger as it spends less time active. Although pricey, this is becoming an attractive alternative:

https://www.evseadapters.com/collections/ev-chargers-and-evses/products/portable-chademo-ccs-combo-dc-quick-charger

6 kW off-board charger that charges through the CHAdeMO port.