Charging current

[Boza]

I have the luxury of using different charging current because I am not usually in a hurry. Does anyone have insights about the optimum current? If is it too high then the BMS kicks in to cool off the battery; if it is too low then the car may be awake for too long. I am talking about L2, not Superchargers.

 

[garrett5688]

I remember an old thread where there were recommendations of around 30A, sweet spot of charging speed and minimal waste heat in the charge cord/handle. Who knows how this has changed over the years though…

 

[nwdiver]

IMHO ~50% of the circuit rating is probably good. I charge at 20A... plenty fast for what I need and it doesn't take forever.

The heat generated is current squared. So even lowering it to 30A from 40A is going to help reduce thermal stress on connections by ~50% with ~25% slower charging.

 

[Boza]

IMHO ~50% of the circuit rating is probably good. I charge at 20A... plenty fast for what I need and it doesn't take forever.

The heat generated is current squared. So even lowering it to 30A from 40A is going to help reduce thermal stress on connections by ~50% with ~25% slower charging.

To clarify. I meant battery heat, not cables/junctions.

 

[nwdiver]

To clarify. I meant battery heat, not cables/junctions.

Oh... I have zero worries about the battery. It's designed to take >100kW from a Supercharger. Even 80A (20kW) from L2 is literally nothing.

 

[Boza]

But it will start the cooling, which has mechanical parts. So, I can lower the current in order for the battery to use passive cooling but that could keep the car awake for hours and hours. So, what is the optimum point?

 

[ucmndd]

It really doesn’t matter at all. Any difference is negligible with the exception of very low ~L1 power being particularly inefficient given the relatively high overhead of running the computers and charging circuitry (like 300 watts).

No L2 charging in any normal ambient temperature range is going to cause active battery cooling (as in running the AC compressor). To my knowledge pretty much any charging, regardless of amperage, will cause the coolant pump to run. But that’s more about keeping a uniform temp throughout the pack/modules during charging (a good thing), not trying to dissipate heat.

 

[nwdiver]

But it will start the cooling, which has mechanical parts. So, I can lower the current in order for the battery to use passive cooling but that could keep the car awake for hours and hours. So, what is the optimum point?

.... maybe a little but it's just a pump and a fan. If those were components that wore out easily we'd likely hear about it. My 9 year old S hasn't had any problems. Burned out wires connecting HPWCs and UMCs on the other hand.... hear about those A LOT.