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The article repeatedly states that DC chargers can deliver more power than AC chargers, but I don't see how that could be a thing. Is it some limitation with th

The article repeatedly states that DC chargers can deliver more power than AC chargers, but I don't see how that could be a thing. Is it some limitation with the onboard power supplies? It's my (limited, third-party) understanding that dual chargers on a Tesla will gladly saturate a 240V 80A J1772, while a single charger will take 48A off a NEMA 14-50 @ 240V.

lazyjones 9y ago
> Is it some limitation with the onboard power supplies? I'm pretty sure it's a limitation of the rectifier circuit in the charger.
gwbas1c 9y ago
It's a limitation in the car. When you have an AC based charger, the conversion and step up to battery voltage happens inside the car itself. This process generates waste heat, which must be vented. At level 1, (wall outlet,) and level 2, (oven outlet,) it's not a big deal. When rapid charging, the heat dissipation is huge. The AC to DC converters that can handle rapid charging are physically huge and There's no practical way to put that inside the car itself. I suggest learning the basics about how charging a battery works. You need to apply a DC voltage directly to the battery. Electric vehicle batteries are in the hundreds of volts. What these systems do is the car and the charger communicate, and the car ends up telling the external charger how to charge its battery. That's why there's a lot of competition among standards.
- microcolonel 9y ago
  > The AC to DC converters that can handle rapid charging are physically huge and There's no practical way to put that inside the car itself. Ahh, that makes more sense now that I think about it. Because of the cross sectional area required to efficiently rectify and transform such high currents, the equipment is either very large (and thus expensive) and heavy (and thus inappropriate for a motor vehicle), or very inefficient (requiring considerable active cooling, and costing a lot more dosh).
NotSammyHagar 9y ago
It's a limitation of the ac/dc transformer in the car. The batteries actually take dc to charge. Another way that Tesla innovated was having much bigger transformers in their cars. Charging capacity is in kw. batteries are hours of that (kwh). A regular us outlet has 1.44 kw charging capacity (120v * 12 amps). A high power car like a tesla has 85kwh or 100kwh of capacity, so 100kwh/1.44 = 69 hours, so it's not practical to drive 250 miles in a day and charge again; for that you need higher power chargers. A leaf is only 3.3 kwh (unless they increased it in the new models), tesla model s were 11 kwh or 22 kwh. Details The on board transformer has a limited capacity to charge the battery. If you only charge 120v you only need 1.44kw charger. But you'll never be able to charge faster. 220v 12 amps is 2.64 kw. Original tesla model s had either 11 kwh or double chargers, 22 kw. The model x split the difference with 11 or 17kw. 40 amp power is commonly available, 40 amp * 220 v = 8.8 kw, 71 amp * 220 = 15.6kw, 100 amps * 220 = 22kwh, the max that tesla has onboard. Did you know, a tesla supercharger is just a bank of regular car transformers that are combined to make the high power 140 kw charging power of top end superchargers (used to be around 90kw, they have kept increasing the top end, but the same plug). This page gives a nice breakdown of different models and shows the anemic charging limits of most non-teslas. https://www.clippercreek.com/three-things-determine-ev-charge-time/ https://www.clippercreek.com/three-things-determine-ev-charg...
- microcolonel 9y ago
  > The batteries actually take dc to charge. Yeah, I'm aware of that; I guess I didn't think that charging the battery in pulses (direct from a beefy rectifier, followed by a the DC transformer) would be incorrect or unreasonable. I'm guessing it's harder than I thought to build a high-rated rectifier.

lazyjones 9y ago

> Is it some limitation with the onboard power supplies? I'm pretty sure it's a limitation of the rectifier circuit in the charger.

gwbas1c 9y ago

It's a limitation in the car. When you have an AC based charger, the conversion and step up to battery voltage happens inside the car itself. This process generates waste heat, which must be vented. At level 1, (wall outlet,) and level 2, (oven outlet,) it's not a big deal. When rapid charging, the heat dissipation is huge. The AC to DC converters that can handle rapid charging are physically huge and There's no practical way to put that inside the car itself. I suggest learning the basics about how charging a battery works. You need to apply a DC voltage directly to the battery. Electric vehicle batteries are in the hundreds of volts. What these systems do is the car and the charger communicate, and the car ends up telling the external charger how to charge its battery. That's why there's a lot of competition among standards.

microcolonel 9y ago
> The AC to DC converters that can handle rapid charging are physically huge and There's no practical way to put that inside the car itself. Ahh, that makes more sense now that I think about it. Because of the cross sectional area required to efficiently rectify and transform such high currents, the equipment is either very large (and thus expensive) and heavy (and thus inappropriate for a motor vehicle), or very inefficient (requiring considerable active cooling, and costing a lot more dosh).

NotSammyHagar 9y ago

It's a limitation of the ac/dc transformer in the car. The batteries actually take dc to charge. Another way that Tesla innovated was having much bigger transformers in their cars. Charging capacity is in kw. batteries are hours of that (kwh). A regular us outlet has 1.44 kw charging capacity (120v * 12 amps). A high power car like a tesla has 85kwh or 100kwh of capacity, so 100kwh/1.44 = 69 hours, so it's not practical to drive 250 miles in a day and charge again; for that you need higher power chargers. A leaf is only 3.3 kwh (unless they increased it in the new models), tesla model s were 11 kwh or 22 kwh. Details The on board transformer has a limited capacity to charge the battery. If you only charge 120v you only need 1.44kw charger. But you'll never be able to charge faster. 220v 12 amps is 2.64 kw. Original tesla model s had either 11 kwh or double chargers, 22 kw. The model x split the difference with 11 or 17kw. 40 amp power is commonly available, 40 amp * 220 v = 8.8 kw, 71 amp * 220 = 15.6kw, 100 amps * 220 = 22kwh, the max that tesla has onboard. Did you know, a tesla supercharger is just a bank of regular car transformers that are combined to make the high power 140 kw charging power of top end superchargers (used to be around 90kw, they have kept increasing the top end, but the same plug). This page gives a nice breakdown of different models and shows the anemic charging limits of most non-teslas. https://www.clippercreek.com/three-things-determine-ev-charge-time/ https://www.clippercreek.com/three-things-determine-ev-charg...

microcolonel 9y ago
> The batteries actually take dc to charge. Yeah, I'm aware of that; I guess I didn't think that charging the battery in pulses (direct from a beefy rectifier, followed by a the DC transformer) would be incorrect or unreasonable. I'm guessing it's harder than I thought to build a high-rated rectifier.