Titanium48
Posts: 148
Joined: Thu Jan 31, 2019 7:33 am
Delivery Date: 25 Jan 2019
Location: Edmonton, AB

Regen does not account for HVAC

Tue Nov 12, 2019 2:06 pm

I thought I noticed this last year, so I used the -18°C morning yesterday to confirm it - the allowed regenerative braking power (at least in my 2016 SL) does not seem to account for power used by climate control. I charged the car to 100%, set the heat at 20°C and the fan to 4, resulting in just over 3 kW being used for heating according to the energy display, with another 600 W or so for the fan, seat heaters and other accessories. When slowing down (either D mode or B mode) or braking under these conditions, only the tiniest blue sliver appeared on the motor power dial on the display, no more than 1.5 kW. I would have expected at least 4 kW of regen to be available under these conditions, plus whatever small amount can be safely put back into the battery when it is cold and near fully charged.

This behavior is also consistent with the state of charge ending up at 90% after a full preheat cycle following a full charge, which happens when it is very cold even though the car is still plugged in. I expected some battery drain as I only have a 16 A EVSE, but losing 10% in 30 minutes suggests that less than the full 3.6 kW available from the EVSE is actually being used, as if the charger is ignoring the power being drawn by the heater and is applying to the same low charge rate it would use for a cold battery that is almost fully charged in the absence of any power draw.
2016 SL

Lothsahn
Posts: 654
Joined: Thu Apr 05, 2018 4:35 pm
Delivery Date: 04 Jan 2018
Leaf Number: 007797

Re: Regen does not account for HVAC

Tue Nov 12, 2019 8:40 pm

Unfortunately, that behavior is normal. My 2011 behaves the same way, even when at 5KW+
2011 Silver SV, purchased 2018, lives in Missouri (previously in CA)
LeafSpy Pro + BAFX Products OBDII dongle
Battery swap 2019/04/24 (87% SOH, 12 bar)

Titanium48
Posts: 148
Joined: Thu Jan 31, 2019 7:33 am
Delivery Date: 25 Jan 2019
Location: Edmonton, AB

Re: Regen does not account for HVAC

Tue Nov 12, 2019 11:44 pm

Interesting that the BMS obviously uses a more complex algorithm than just a constant voltage (which would automatically adjust for any power draw), but there is no alternative accounting for accessory power draw. Anyone know if this apparent programming oversight was fixed in the 40 and 62 kWh cars?
2016 SL

goldbrick
Posts: 915
Joined: Tue Aug 01, 2017 3:33 pm
Delivery Date: 01 Aug 2017
Leaf Number: 311806
Location: Boulder, CO

Re: Regen does not account for HVAC

Wed Nov 13, 2019 10:16 am

I don't know if it's a programming oversight or intentional. The battery at high SOC is at high voltage, regardless of whether it is supplying power or not. My guess is that the BMS limits the charge rate based on battery voltage regardless of how much power is being simultaneously drawn from the battery.

Titanium48
Posts: 148
Joined: Thu Jan 31, 2019 7:33 am
Delivery Date: 25 Jan 2019
Location: Edmonton, AB

Re: Regen does not account for HVAC

Wed Nov 13, 2019 11:05 am

The battery has some amount of internal resistance, so the voltage will be lower if it is supplying power than it will be at the same SOC when it is not supplying power. Likewise, to charge the battery the charger must increase the voltage above the open circuit voltage to force current to flow in the opposite direction. The magnitude and direction of current flow through the battery depends on the difference between the actual voltage and the open circuit voltage, and on the internal resistance. If there is a power draw while the charger is operating, the voltage (and thus the charge rate) will be reduced unless the charger power is increased by the same amount. If the charger can hold voltage constant when something else starts to draw power, the charge rate will stay constant.

I understand that varying temperatures and cell balance in a multi-cell battery necessitate something more complicated than a simple constant voltage charge strategy, but I would have thought that once the algorithm has determined what maximum charging voltage is appropriate for the observed set of conditions, it would try to maintain that voltage if possible.
2016 SL

jjeff
Posts: 2138
Joined: Wed Jan 13, 2016 9:10 am
Delivery Date: 13 Jul 2014
Leaf Number: 422121
Location: MSP MN

Re: Regen does not account for HVAC

Wed Nov 13, 2019 3:50 pm

I've also noticed significantly less regen in cold conditions, particularly on my 8 bar '12 but also on my 11 bar '13. Unfortunately when it's cold is just when you need more regen(due to less overall range). Note the 8-bar also has significantly overall less regnen than the 11 bar Leaf which again is unfortunate as being only 8 bars it could sure use more not less regen :(
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a

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