Why not simply keep the charger plugged in (say at 80% max)? Seems like a simpler approach to accomplish the same end?
As far as I know, once the car is charged, and there are no timers, being plugged in will not keep the battery warm. I believe the recommended approach, and what I'm doing, is keep the charger plugged in, and then either with a timer, or by manually clicking the precondition button on your phone when you wake up, start the 60-minute preheating before driving. Note that it is the webasto resistance heater that is doing this preheating of the battery (if it is below 50F) and interior (if it is below the prescribed temp), so being plugged in is good.
It is super expensive to heat a garage with an electric heater. (I tried this one year when I was doing some woodworking in my garage and it doubled my bill.)
if you fall below your pre-set max (let's assume 80%), the battery will charge...so any drain on the battery will be made up by shore power
It does though. We have timers set to finish charging at 5:00 AM and pre-heat at 8:15. Below is the graph of power usage for our whole house last Friday in 15 minute increments. You can see the 15 KWh charge finishing at 5 and then there's another spike at 8:00 which is the power draw on the house from the battery being pre-heated. Note that it only draws "shore power" when preheating on the timer. If I initiate a pre-heat from the app it heats from the battery, not the EVSE.
Love the data! However, I think you're wrong about the App. Asking to "Pre-Heat" only applies to the cabin temperature, seat heater, etc.It does though. We have timers set to finish charging at 5:00 AM and pre-heat at 8:15. Below is the graph of power usage for our whole house last Friday in 15 minute increments. You can see the 15 KWh charge finishing at 5 and then there's another spike at 8:00 which is the power draw on the house from the battery being pre-heated. Note that it only draws "shore power" when preheating on the timer. If I initiate a pre-heat from the app it heats from the battery, not the EVSE.
If the garage is not insulated (most are not in the PNW), heating it will be expensive whether you tie it to your central heating or not. If your central heating runs on natural gas, it might be cheaper than electric heating, but in the end it's the same amount of energy required to heat that garage. If you really want one heated, start by insulating it, then heat with your method of choice.
Are you sure it's actually heating from shore power, rather than deplete the battery and then start charging to replenish it before departure? What is your max EVSE current and do you have a graph showing KW rather than KWh? That could show us if it was drawing just enough to heat, or was it drawing the max in order to charge the battery.It does though. We have timers set to finish charging at 5:00 AM and pre-heat at 8:15. Below is the graph of power usage for our whole house last Friday in 15 minute increments. You can see the 15 KWh charge finishing at 5 and then there's another spike at 8:00 which is the power draw on the house from the battery being pre-heated. Note that it only draws "shore power" when preheating on the timer. If I initiate a pre-heat from the app it heats from the battery, not the EVSE.
That's KWh in 15 minute increments. The EVSE max draw has been 10.8 to 11 KW. So what you're seeing just prior to 5 AM is the EVSE drawing 2.7 KWh in each 15 minute span on top of the background consumption. Then again in the 8 to 8:15 segment that's power going through the EVSE It's going into the high voltage system bus. It could be drawing at full power, but the battery is absolutely being heated during that time and the charging timer is set to finish by 4:55 AM and the garage is kept at 45 degrees, so it's the preheat timer that's causing the power to be drawn.
