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What is the efficiency factor for the 220 V charger?

Posted: Tue May 25, 2010 7:26 pm
by rokibler
The battery capacity is 24 kWh. How many kWh will I have to use from the power company to fully charge an empty battery? In other words, what are the losses associated with the conversion from 220 VAC to the high voltage DC needed to charge the battery?

Thank you.
Rob Kibler

Re: What is the efficiency factor for the 220 V charger?

Posted: Tue May 25, 2010 7:32 pm
by mitch672
That's the million $ question, no one knows yet, there are no Leafs, no one has charged one yet with a meter on the EVSE to measure KwH consumption yet, and we probably won't be able to until some production Leafs are delivered, or Nissan releases the information.

Re: What is the efficiency factor for the 220 V charger?

Posted: Tue May 25, 2010 7:40 pm
by garygid
During charging, some energy (perhaps 5%) is lost (mostly as heat) in the battery.

The charger might lose as little as 2%, but 5% might be more typical. Less sophisticated chargers (less expensive) will tend to lose more, up to 10% or even 20%.

The LEAF's built-in 110/250v charger ... who knows.

So, guess 10% loss for now?

The EVSE itself will lose very little power.

Re: What is the efficiency factor for the 220 V charger?

Posted: Tue May 25, 2010 9:25 pm
by darelldd
Yeah, the smart money is on a 10% overall charging loss. That's a good rule of thumb for a properly designed battery/charging system. And for the record, it is about what the Toyota Rav4EV demonstrates. To get much better than that, you start spending a lot of money and getting diminishing returns. 10% is the sweet spot.

All bets are off in a hot climate where lots of battery cooling is going on.

Re: What is the efficiency factor for the 220 V charger?

Posted: Tue May 25, 2010 11:31 pm
by garygid
There should be no "cooling power" losses while charging the LEAF, apparently.
At least it seems to have no battery cooling.

Possible charger cooling, but probably not, with only 3.3 kW (or 6.6) x 5% = 165 (or 330) watts heating (or double that) in the charger, and a similar amount in the whole (huge) battery pack.

Re: What is the efficiency factor for the 220 V charger?

Posted: Wed May 26, 2010 12:28 am
by planet4ever
garygid wrote:The EVSE itself will lose very little power.
:lol: Now that sounds like a safe statement. But if you nose the Leaf up close to the EVSE and have a long cord coiled up between them, you might lose a measurable amount in the cord, no?

Re: What is the efficiency factor for the 220 V charger?

Posted: Wed May 26, 2010 7:15 am
by garygid
If the supplied cord has "properly" sized power conductors (for the 40-amp circuit), the power (IxIxR) losses in the cord, though certainly measurable, should be fairly insignificant.

Most installations will have cords much shorter than 50 feet, I suspect. I have no answer yet (from AV) on what the "available" cord lengths will be. I would guess that 15 to 25 feet would be more typical.

However, there are limited-access cases, like mine, where at least 30 feet will be needed, and 50 feet would help.

Also, the cable might be detachable from the home-version of the EVSE box (as a simple way of meeting the strain-relief safety requirement on the EVSE), so a short cord might be supplied for "typical" use, with the option to buy an "expensive" interchangeable longer cord.

Re: What is the efficiency factor for the 220 V charger?

Posted: Wed May 26, 2010 8:42 am
by DeaneG
I looked into this as part of trying to understand my future electricity bill. I found online info that a Tesla roadster has a charging efficiency of 0.8, and a Mini-E 0.8 to 0.85. This is the ratio of AC power in that you have to pay for from your utility provider, to the DC power out of the battery during driving. I think this efficiency factor improves with slower charging rates - Level I would be better than Level II, etc, for the same reasons that a light touch on the accelerator will improve range - smaller losses in the battery, copper, etc.

I'll try to find the web references I found for this. The first was a technical blog by one of Tesla's founders. The other was a technical test and measurement of a Mini-E prototype's performance in a couple of different driving scenarios.

Re: What is the efficiency factor for the 220 V charger?

Posted: Wed May 26, 2010 11:50 am
by darelldd
garygid wrote:There should be no "cooling power" losses while charging the LEAF, apparently.
At least it seems to have no battery cooling.
Not even fans to move air? Wow.

Re: What is the efficiency factor for the 220 V charger?

Posted: Wed May 26, 2010 11:52 am
by darelldd
DeaneG wrote:I looked into this as part of trying to understand my future electricity bill. I found online info that a Tesla roadster has a charging efficiency of 0.8, and a Mini-E 0.8 to 0.85.
Check which iteration of the Tesla that is. The battery management has been significantly improved over the years. And please note that the Tesla has some serious battery temp controls in place!