4 ms·

One of the dirty secrets of li-ion is that in order to use it for cars, you need high voltage batteries, and if your charging source isn't similarly high voltag

One of the dirty secrets of li-ion is that in order to use it for cars, you need high voltage batteries, and if your charging source isn't similarly high voltage, your charging efficiency tanks because you spend 30-40% of your energy stepping your voltage up to a level that will charge your batteries. For example, if you charge your Tesla with a 120v AC power supply, you're looking at 58% charge efficiency, which will put your end to end efficiency at the same level: ~50%.

Baeocystin 5y ago
The numbers from my friends' Leaf point to a charging efficiency loss of 110V vs. higher rates at around 10%. FWIW. [edit] From https://www.mynissanleaf.com/viewtopic.php?f=31&p=545335#p545318 https://www.mynissanleaf.com/viewtopic.php?f=31&p=545335#p54... >Level 1 (120v, 12 amps): 78% efficient >Level 2 (240v, 16 amps): 91% efficient >Level 2 (208v, 30 amps): 91% efficient >CHAdeMO (500v DC, ~100 amps): 93% efficient
- darksaints 5y ago
  Yeah, that's because of the lower nominal voltage of the battery: 350v vs Tesla's 450v. So you get higher charge efficiency, but you'll get lower motor efficency with it. Not sure if it comes out ahead in end to end efficiency.
avidiax 5y ago
Why is it so hard to step up voltage efficiently? 120VAC is already AC, so a simple transformer can boost it to e.g. 480VAC easily, and then you have the same AC to DC problem that a native 480VAC charger would have. At least for li-ion, the infrastructure problem isn't too terrible, as most cars will have an endpoint with high-voltage, i.e. the workplace.
- addaon 5y ago
  The size of a high-power 60 Hz transformer is prohibitive in weight, both directly (where are you going to put it?) and in impact on price (shipping, amount of metal). It ends up lighter, cheaper, and not much less efficient to do a high-frequency conversion instead, either as a boost directly from the 120V AC or as a DC-DC in the secondary.
- iamgopal 5y ago
  To reduce cost ( improve volumetric efficiency of transformers) such voltage conversion are done at much higher frequency. Side effect is lots of switching losses. Diamond based semiconductor are coming but that will take time.
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Baeocystin 5y ago

The numbers from my friends' Leaf point to a charging efficiency loss of 110V vs. higher rates at around 10%. FWIW. [edit] From https://www.mynissanleaf.com/viewtopic.php?f=31&p=545335#p545318 https://www.mynissanleaf.com/viewtopic.php?f=31&p=545335#p54... >Level 1 (120v, 12 amps): 78% efficient >Level 2 (240v, 16 amps): 91% efficient >Level 2 (208v, 30 amps): 91% efficient >CHAdeMO (500v DC, ~100 amps): 93% efficient

darksaints 5y ago
Yeah, that's because of the lower nominal voltage of the battery: 350v vs Tesla's 450v. So you get higher charge efficiency, but you'll get lower motor efficency with it. Not sure if it comes out ahead in end to end efficiency.

avidiax 5y ago

Why is it so hard to step up voltage efficiently? 120VAC is already AC, so a simple transformer can boost it to e.g. 480VAC easily, and then you have the same AC to DC problem that a native 480VAC charger would have. At least for li-ion, the infrastructure problem isn't too terrible, as most cars will have an endpoint with high-voltage, i.e. the workplace.

addaon 5y ago
The size of a high-power 60 Hz transformer is prohibitive in weight, both directly (where are you going to put it?) and in impact on price (shipping, amount of metal). It ends up lighter, cheaper, and not much less efficient to do a high-frequency conversion instead, either as a boost directly from the 120V AC or as a DC-DC in the secondary.
iamgopal 5y ago
To reduce cost ( improve volumetric efficiency of transformers) such voltage conversion are done at much higher frequency. Side effect is lots of switching losses. Diamond based semiconductor are coming but that will take time.

deleted 5y ago

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