Best charger setting for 2019 VW e-Golf?

[jasakel]

Hi folks,

I recently purchased and had installed by an electrician...

* 2019 VW e-Golf SE
* ChargePoint 16-50 amp Level 2 charger hardwired (future-proofed for higher capacity car)
* The charger has settings for 16A, 24A, 32A, 40A, 48A, 50A.

What is the best MAX amperage I should set the charger to to both protect the battery for longevity and still charge as fast as possible?

Thanks!

 

[f1geek]

Congrats on your e-Golf and home charging station!

First, that thing on the wall is not technically a charger - it is an EVSE and merely supplies AC current safely to your car. The charger in the car is what charges the battery by converting AC power to DC power to charge the battery.

Second, what is the circuit you had installed? You must not pull more than 80% of the circuit rating or you may cause a fire. If your charging station is connected to a 50 amp circuit, the maximum the station should pull is 40 amps. Your electrician should have already told you this or made sure the station is configured correctly. Once you know the circuit capability (determined the circuit breaker size), set the charging station to NO MORE than 80% of that value.

Third, the maximum AC power the e-Golf on board charger can accept is 30 amps at 240 Volts. It is common to decide based on C rate the charging speed experienced by the battery. C rate is charging power divided by battery gross capacity. In other words, if you charge at 30 amps (7.2 kW), that is a C rate of 7.2/35.8=0.2C. Yes, the e-golf has no active battery pack cooling, so the lower the C rate, the less the pack will heat up. The e-golf DCFC speed is limited to about 40 kW, or 1.1C, and this does heat up the battery pack. Remember from physics, P=I^2R, so the power lost to joule heating is a square of the current, so at 40 kW (about 110 amps) the power lost to internal resistance is 13 times greater than at 30 amps. So, 0.2C is already pretty low and I don't see this as a problem. I do not believe you will be able to measure much of a temperature increase in the battery pack (using an OBD reader) at 7.2 kW. Of course, you could charge at a slower rate (say at 13 amps, or 3.1 kW, one of the e-Manager settings), but if you do, choose that setting in the car e-Manager, not using the charging station. If your car's battery pack were already really hot, from DCFC, hot ambient temps (Arizona hot), then yes, it makes sense to charge at a lower amperage. Under normal conditions for most people, I suspect dropping below 7.2 kW will not measurably alter battery pack life.

I hope this makes sense.

 

[jasakel]

Congrats on your e-Golf and home charging station!

<span>First, that thing on the wall is not technically a <a href="http://www.amazon.com/s/?field-keywords=electric%20vehicle%20charger&tag=myelecarfor-20" class="interlinkr" target="_blank">charger</a> - it is an EVSE and merely supplies AC current safely to your car. The charger in the car is what charges the battery by converting AC power to DC power to charge the battery.</span>

Second, what is the circuit you had installed? You must not pull more than 80% of the circuit rating or you may cause a fire. If your charging station is connected to a 50 amp circuit, the maximum the station should pull is 40 amps. Your electrician should have already told you this or made sure the station is configured correctly. Once you know the circuit capability (determined the circuit breaker size), set the charging station to NO MORE than 80% of that value.

<span>Third, the maximum AC power the e-Golf on board <a href="http://www.amazon.com/s/?field-keywords=electric%20vehicle%20charger&tag=myelecarfor-20" class="interlinkr" target="_blank">charger</a> can accept is 30 amps at 240 Volts. It is common to decide based on C rate the charging speed experienced by the battery. C rate is charging power divided by battery gross capacity. In other words, if you charge at 30 amps (7.2 kW), that is a C rate of 7.2/35.8=0.2C. Yes, the e-golf has no active battery pack cooling, so the lower the C rate, the less the pack will heat up. The e-golf DCFC speed is limited to about 40 kW, or 1.1C, and this does heat up the battery pack. Remember from physics, P=I^2R, so the power lost to joule heating is a square of the current, so at 40 kW (about 110 amps) the power lost to internal resistance is 13 times greater than at 30 amps. So, 0.2C is already pretty low and I don't see this as a problem. I do not believe you will be able to measure much of a temperature increase in the battery pack (using an OBD reader) at 7.2 kW. Of course, you could charge at a slower rate (say at 13 amps, or 3.1 kW, one of the e-Manager settings), but if you do, choose that setting in the car e-Manager, not using the charging station. If your car's battery pack were already really hot, from DCFC, hot ambient temps (Arizona hot), then yes, it makes sense to charge at a lower amperage. Under normal conditions for most people, I suspect dropping below 7.2 kW will not measurably alter battery pack life. </span>

I hope this makes sense.

Wow, thanks for the tremendous detail, and yes, makes sense. I learned a great deal. Follow up questions if I may: So if I were to set the EVSE to 32 amps then the car will step that down to its max 30 amps? That seems to make the most sense rather then choosing the lower 24 amp setting on the EVSE, no? Also, the car has a DC fast charger built in, so does that mean then too it's accepting max 30 amps?

 

[f1geek]

If you only have a 30 amp circuit, you can not set it to 32 amps - must be 24 amps. If you have a 40 amp or higher circuit, 32 amps is fine, but why not just set it to the max for your circuit? My thought is if you get a car that can pull 40 amps, you don't need to fool with the setting.

The car on-board charger queries the EVSE and finds out what the maximum amperage it can supply and then based on the e-Manager settings (or if you use the immediate charge button on near the charge inlet on the car), it will pull the correct amps. The car will only pull a maximum of 30 amps AC because that is the specification of the on board charger. It will not attempt to pull more than 30 amps (at either 240 V at home or 208 V at a public charging station).

The DC Fast Charger is indeed an off-board charger and is not in your car. DCFC bypasses the on board charger and sends DC power directly to your car's battery pack. Again, the car and the DCFC "talk to each other" and the car directs the DCFC how much DC amps and volts to send into the battery pack. Based on pack state of charge, pack temperature, and probably other variables, the car can pull as much at ~110 amps DC at about a maximum of 350 Volts (not sure of exact values).

In short, the car's BMS is always in control of charging power, given external constraints imposed by the available volts and amps supplied.

 

[jasakel]

So appreciated! I was just concerned based on what I've read that using DC fast charging too often isn't ideal for the battery longevity (good to alternate between that and home AC) and, therefore, I was concerned to "push" the charging on the everyday AC charge beyond the 30 A by going with 40 A.

 

[f1geek]

There has been a lot of discussion on this forum about consecutive DCFC sessions. High temperature is what damages lithium ion cells, and high temps plus high SoC (state of charge) is worse. That is why VW warns about alternating DC with AC because AC (at low C rate) does not generate much temperature rise in the pack. If the e-Golf had an active pack cooling system, this would be a non-issue.

Also, if you want to extend life of pack, keep SoC routinely between 20% and 80% (or 90% if you need the range daily).