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I discovered the other day during a full charge to 100% with my Level 2 Juicebox Pro 40 set at 32 amps, and once the charge is complete and the EVSE shuts down, if you turn on cabin preconditioning the car will start the EVSE back up drawing 32 amps again.

The problem I see is that the full battery can?t handle 32 amps being forced back in by the preconditioning trigger. I know that the preconditioning uses a good amount of power, like 8amps maybe, but some 20-24 amps goes to charging. I can imagine this is bad for the battery, glad I only did it once.

From now on, at least during the cold months charging will be done in Hilltop Reserve. This allows room for that extra juice to be placed, giving slightly more range then Hilltop Reserve anyone, during a 20min preconditioning session.

Please correct me if I?m wrong, and if I?m right I hope to save some people from overcharging their batteries.

-Cheers
 

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the car draws amps. you can't push them in. i = V/R where voltage is fixed. current will change based on the load/resistance. pretty sure the heater is a very large load and that's why you see 32 amps. It might even take more initially until it warms up. Then it might drop to maintain the temperature. Some have stated that the heater is 9kW. Where your 32 amp charger can only provide 7.8kW.
 

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The car knows how much power to draw, don't worry about this. Your Juicebox is rated for 32 amps, it doesn't need to push 32 amps into your Bolt all the time. I have a 40 amp charger, but the Bolt won't charge at 40 amps. Preconditioning won't overcharge your battery, the Bolt charger won't allow this.
 

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Preconditioning while plugged in will not trigger charging. Preconditioning while plugged in just means the car will draw all the power it can/needs from the EVSE and the grid instead of the battery in the car. If the car is plugged into a source that doesn't give it enough power to run the heater it will then draw from the battery in the car for the remaining power it needs.

The heater running at full power will draw up to 9kW. 9kW at 240 volts is 37.5 amps. So yeah, the heater at full power should easily be able to use all 32 amps available from your EVSE. Your EVSE of course can only put out 7.8kW at 240 volts which is 32 amps.
 

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;)Thanks for the three explanations and facts!
 

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Discussion Starter #6
Thanks for the responses. That makes total sense. I stand corrected, and feel much better turning off hilltop Reserve if I feel so inclined. Thanks.
 

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Note that the supplied 120v EVSE can only push ~1.2kW to the car, so preconditioning while using it will still draw power from the battery and reduce range.
It's not a bad argument for a 240v EVSE.
 

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I have the 120v charger (that came with my 2019 Bolt) at home and L2 charging at my parking garage at work.

I understand that turning on the heater while plugged into my Level 1 home charger will still draw power from the battery - but I’m still trying to wrap my head around how “pre-conditioning” works... so..

My main goal: what’s the best way to have the heater running hot when I get in on a cold morning (with only a 120v charger)?

A. Just leave it plugged in up until I pre-warm car for 20 min
B. Don’t even bother pre-warming the car because it’s a huge range drain
C. Schedule the charge to stop 30 min before leaving - so the battery conditioning can happen- making options A and/or B more efficient

Maybe I got it wrong- but it’s my understanding from other posts here that the battery won’t pre-condition and warm itself (& the coolant?) while it’s still charging itself - and with a 120v charger at home- please assume that I’ll never get to a full charge before having to leave for work (hence my question about scheduling it to stop charging to allow for pre-conditioning)
 

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that the battery won’t pre-condition and warm itself (& the coolant?) while it’s still charging itself
I manually remote start the vehicle using my key fob (wireless remote key entry transmitter) while it's still plugged in. It will use as much as it can from your EVSE. Do you absolutely need 100% charge to get to work?
 

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I manually remote start the vehicle using my key fob (wireless remote key entry transmitter) while it's still plugged in. It will use as much as it can from your EVSE. Do you absolutely need 100% charge to get to work?
XJ12: No - let me clarify: I don’t need 100% charge to get to work. When I said “assume I’ll never get to a full charge ...” I meant that I know the 120v trickle charge will never fully recharge my battery overnight - so my concern isn’t trying to get the most charged up battery at home- it’s trying to understand how to optimize pre-conditioning so when I start driving - the battery is already warm.

Ultimately - I want to know how to get my car’s heater to be quickly hot when I leave for work in the morning
 

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Ultimately - I want to know how to get my car’s heater to be quickly hot when I leave for work in the morning
The car's heater is a 7.5 kW tankless water heater connected to a normal heater core under the dash. The entire heater loop contains 2.1 quarts of antifreeze, so if you turn the temperature knob to HI/90 F, and med-high fan, the air coming out will be over 100 F very quickly. If you want to heat up the interior surfaces of the car, and the window glass, before you leave, that will require running the heat for 15-20 minutes, which is the length of one cabin preconditioning cycle. Running the system on high, as I described will pull 7.5 kW from the battery to start, and as the cabin reaches 90 F the current draw will drop to more like 2-3 kW. All of the energy for the heater comes from the battery, whether or not you plug in the car. With the car plugged into you 120 volt trickle charger, if you set it to 12 amps, you will be replenishing the battery at a bit over 1 kW.

You probably won't get the car's 2 + kW battery heater to come on with any procedure, on the trickle charger. But the battery will get somewhat warmer just by having juice being pulled out, and put back in.
 
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