DC fast charging comparison

[ironmanco]

Can someone help me with the math or concept of comparing DC fast charging to AC charging.

If I'm DC charging 320v at 20A (tail end) how does that compare to 120 or 240v AC charging at the same 20A?

-Andrew

 

[Valdemar]

Simply put

Power = Voltage * Current,

So given identical current but lower voltages you're pumping in less energy (kWh) over the same time.

 

[ironmanco]

I would assume there's a loss as well going through the charging unit (rectifier) of the leaf as well that is not an issue with DC charging.

 

[arnis]

Charging stations usually show the tail end like you mentioned.
DC chargers can't choose the voltage. It is the battery that sets the voltage.
320V is possible but at very very low state of charge.
There are no conversation losses if we exclude losses in the station itself.
But there is a small loss in the battery too (it gets converted to heat).
Not much, few percents.

Leaf either has 16Amp onboard charger or 32A.
If it has 16Amp then maximum speed is 240V * 16A ~3600W.
There are conversation losses, cooling losses in addition to battery internal losses.
So we can expect 3000W of real charge.
To get 20A charging on AC you must have 7,2kW onboard charger and limited
AC input.

On 120V line losses for conversation are bigger, cooling and battery losses the same.
Trickle charges in US is 120V 12A = 1440W. Battery gets around 1000W.

120V 20Amp charging is not possible and not recommended. 120V charging is not recommended in general.

How did you get 20Amp on DC station?!

 

[ironmanco]

Ok - now I think I get it.

The EVgo fastcharge station connects and does it's fast charge at 320v. I actually think it starts at this voltage and for the most part keeps that constant. I'll look the next time I do it.

It starts off with 100+A and then when it reaches 85%+ its starts throttling down. I do recall seeing it at 95% charge running at 20A or even below.

 

[Valdemar]

How did you get 20Amp on DC station?!

With a degraded pack and around 10C ambient I regularly see 20A, and it tapers down to this level fairly early around 70% SOC.

 

[ironmanco]

fully operational battery (2016 SL) and temps around 50F. Getting leafspy hooked up would give me a good profile but I haven't done that yet.

 

[arnis]

It may start at 320V but as soon as it starts charging voltage goes really high.
When it tapers down voltage is somewhere between 380-396V.

20A is normal for 70%SOC if pack is really cold.
But QC should happen after a longer trip. Battery usually heats up 5C during the trip.
So at 10C ambient pack should be 15-20C when arriving to QC.

 

[GRA]

It may start at 320V but as soon as it starts charging voltage goes really high.
When it tapers down voltage is somewhere between 380-396V.

20A is normal for 70%SOC if pack is really cold.
But QC should happen after a longer trip. Battery usually heats up 5C during the trip.
So at 10C ambient pack should be 15-20C when arriving to QC.

Nominal max. voltage for the original 24kWh pack is 394V IIRR. It's fairly typical for a Li-ion pack to charge at constant (high) current until the pack reaches max. voltage, and then it switches to constant voltage with the current continuously decreasing.

 

[ironmanco]

Charging stations usually show the tail end like you mentioned.
DC chargers can't choose the voltage. It is the battery that sets the voltage.
320V is possible but at very very low state of charge.
There are no conversation losses if we exclude losses in the station itself.
But there is a small loss in the battery too (it gets converted to heat).
Not much, few percents.

Leaf either has 16Amp onboard charger or 32A.
If it has 16Amp then maximum speed is 240V * 16A ~3600W.
There are conversation losses, cooling losses in addition to battery internal losses.
So we can expect 3000W of real charge.
To get 20A charging on AC you must have 7,2kW onboard charger and limited
AC input.

On 120V line losses for conversation are bigger, cooling and battery losses the same.
Trickle charges in US is 120V 12A = 1440W. Battery gets around 1000W.

120V 20Amp charging is not possible and not recommended. 120V charging is not recommended in general.

How did you get 20Amp on DC station?!

Thank you for playing....though you didn't win, we have some great gifts for you
As far as the DC charging is concerned I didn't find any of the above to be the case. The charges I use certainly choose the voltage - or at least something in the system is.

From my images below, with a starting SOC of 26% the charger started out at 361VDC and 98A. Towards the end >93% SOC, it got just above 390VDC but was only pulling about 10/11A. Near the very end with a SOC of about 96% it was as low as 9A but still maintaining a voltage of about 388VDC.