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Old 05-23-2016, 02:02 PM   #41
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Someone else did the experiments for me:

http://avt.inel.gov/pdf/fsev/SteadyS...on2015Leaf.pdf
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Old 05-23-2016, 02:45 PM   #42
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Quote:
Originally Posted by TromboneAl View Post
Someone else did the experiments for me:

http://avt.inel.gov/pdf/fsev/SteadyS...on2015Leaf.pdf
The 120 V charging eff% is pretty low - 62% - 78% through the cycle, and pretty linear?

220V is ~ 81% ~ 91% , and looks to reach high 80's pretty quickly (a good thing).

Gotta use the right denominator, an average ~ 70% loss @ 120V means you need 1.43x the kWh from the socket to end up with 1 kWh in the battery.

Power factors were surprisingly high, very near unity.

But unless you meter the socket, you'd still be trying to use these generalized factors against the car monitors, and the accuracy of those are questionable. If I were buying an EV for the fun and tech side of things, I'd just have to have a meter on that socket! But that's just me (and a bunch of people on the EV forums who report their numbers).

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Old 05-24-2016, 05:35 PM   #43
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The trickle charging is less efficient. There's a baseline usage of 300 watts, so having the charger on for 18 hours means you pay more for a charge.

Also, with Time of Use electricity, our low rate starts at 9 PM. With a trickle, you may need 20 hours of charging, so if you want the car ready at 7 AM, you're going to need to do some charging at 26 and 38 cents per KwH.

7.41c/kWH, wow!
Not knowing about the hardware inside the chargers, I was surprised to learn that there's such a large difference in efficiency between low-power (Level 1) and high-power (Level 2) charging.

If the loss is entirely due to the conversion of power from AC to DC, then perhaps that is because of the inferior design of the Level 1 charger that is meant to be used only as a backup charger (same as a spare tire not being of the same quality as a normal tire to save cost).

Regarding the lower off-peak price of 7.41c/kWh in my area, I forgot to mention that the peak rate is 22.26c/kWh for the summer. In the winter, the peak rate is 10.20c/kWh.

I can also choose a fixed price plan of 8.03c in the winter, and 13.31c in the summer.
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Old 05-24-2016, 09:04 PM   #44
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Not knowing about the hardware inside the chargers, I was surprised to learn that there's such a large difference in efficiency between low-power (Level 1) and high-power (Level 2) charging.

If the loss is entirely due to the conversion of power from AC to DC, then perhaps that is because of the inferior design of the Level 1 charger that is meant to be used only as a backup charger (same as a spare tire not being of the same quality as a normal tire to save cost). ...
It did seem odd, but I think T-Al's comment on 300 W baseline is the key.

It sounds like there is some fixed wattage just to keep the battery charger systems up and running and monitoring during charging? Those fixed amount of watts would be a larger % of the Level 1 charge.

The table in that pdf shows that the efficiency of Level 2 at its lowest charge rate of 1.41 kW is pretty close to the Level 1 charger at its max charge rate of 1.38 kWh -- 81.5% (L2) versus 78.4% (L1).

(I assume it auto-adjusts to battery conditions, slowing down as it nears completion?)

The lowest wattage loss is at L2 low current, 81.5% of 1.41 kW is 261 watts wasted, and L1 wattage losses are only a little higher (287 and 298 watts). I'm not motivated enough right now, but I think a pretty good estimate could be made of the fixed and variable losses there, and I'd eyeball the baseline ~ 130 Watts (assuming the L2 low current mode would be near 92% eff without the fixed part, that cuts the 260 Watt loss to 130 W), my next step would be to plug that in to the L2 high current rate, to see how it fits, but not now!

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Old 05-24-2016, 09:17 PM   #45
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300W is a lot of "overhead" power to waste, if it is the power that the charger dissipates even if the battery is not taking in any. What do they do? Have a big heater in there? What could it be that uses that much power just idling?
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Old 05-24-2016, 09:35 PM   #46
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Yes, but my eyeball estimate says it is maybe 130 watts, not 300. There is less than 300 watts of total waste in some of the charger modes, so the fixed waste is only a portion of that. And it may be even less than my 130 watt guestimate.

Still,the power of a 100 watt light bulb is not just a little monitoring going on. Maybe the Leaf forums have more detail?

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Old 05-24-2016, 10:36 PM   #47
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Here's how my usage has gone up. Got the car on 5/18/2016:

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