deonb
Active Member
Sure, but a 208V 50A breaker is uncommon (i.e. NEMA 18-50 outlets are fairly uncommon. Most 3 phase connectors are 30A or 60A).
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Charging at 208v
- Thread starter siatacars
- Start date
Sure, but a 208V 50A breaker is uncommon (i.e. NEMA 18-50 outlets are fairly uncommon. Most 3 phase connectors are 30A or 60A).
If you've got a 60amp circuit and outlet, then I'd still suggest installing a hardwired EVSE is a better option than the similar expense stepping the voltage up... you don't gain anything other than being able to use your UMC, which I'd say is less convenient than a permanent charging station.
Are there actually 208 to 240 step up transformers capable of 40A on the secondary? Given that it has to handle 10K Watts, it would have to be a majorly beefy affair. Plus, on a 50A breaker you would be running well above 80% continuous so the NEC police (big brothers to the pillow tag police) will get you.
And, I agree wrt the over engineering comment.
And, I agree wrt the over engineering comment.
You would need to have a 60A circuit on the primary side of the transformer, because it will be drawing 46A when the car draws 40A. There's no free lunch - the power has to come from somewhere! The transformer itself will also have to be rated for that current.
Again, you're talking about charging 15% faster. It's really not worth the trouble. If you want fast, get an HPWC and twin chargers, and you'll charge 100% faster.
Again, you're talking about charging 15% faster. It's really not worth the trouble. If you want fast, get an HPWC and twin chargers, and you'll charge 100% faster.
TonyWilliams
Active Member
Welll... as a guy who just drove 3500 miles with a 40 amp charger... I disagree that it's "not worth the trouble". At 150 miles per charge event requiring 5 hours of charging, 3500 / 150 = 23 full charge events * 5 hours = 115 hours of JUST_CHARGING. Since the typical public 208 volt / 30 amp J1772 choice is almost 40% slower, for instance, that's a good chunk of my life watching the birds chirp.
But, even at 208 volts with a full 40 amps still would have added (using your 15% increase in time) 17 hours to my two week trip. No thanks.
By the way, I did carry a 40 amp / 40 volt step up transformer with me. Plus a method to pull two J1772 together to ensure 240-250 volts * 40 amps.
TonyWilliams
Active Member
Well, sure, but that's really for another thread. They are exactly that... in addition to my Roadster adapter, every kind of plug know to mankind (even a CS6365), numerous EVSE's including Model S UMC, a 2013 Nissan LEAF "UMC" modified to a variable 6 - 25 amp / 100 - 250 volt unit, my Clipper Creek CS-50, extension cords, etc.
It's all part of the long distance EV "sport".
Sure, every extra kW is useful on a road trip. But what you were doing ain't exactly in accordance with the electrical code!
Don't try this at home, folks. I guess you weren't at home so it's okay? :tongue:
Yes, I get it, as I have most standard adapters myself along with a dual TT-30/NEMA 5-20 adapter, but I would still like to understand what you have better. Could you answer my questions? I don't understand the utility of a 40A, 40V transformer, and I'm curious whether your dual J1772 adapter was to increase amperage, or increase voltage, and what are the specs of your dual J1772 adapter.
TonyWilliams
Active Member
Nope, not at home, but if I was, it's entirely likely that I could have met every NEC. I neither specified how or what I was doing, nor suggested anybody do those unspecified things.
So, folks, try anything you want. Just don't burn down the house and blame it on me.
When you're out on the road, except for overnight charges, you want the fastest charge speed you can acquire.
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TonyWilliams
Active Member
The utility of the step up transformer is maximizing the power into your car's charger. if your charger can take 10kW, wouldn't you like to have 10kW?
So, anytime the voltage is below 250 volts, your charger is not receiving the full 10kW, since the amperage is limited to 40. If we increase voltage above 250, the amperage will drop to not allow the charger to draw more than 10kW. Max voltage is 277 for the charger.
So, the 40 volt step-up transformer will bring the 208 volts that is commonly available in public commercial areas to 248 volts so that the full 10kW car be available to the charger. The transformer is rated at 40 amps to match the need of the charger.
If you were using this with a Roadster 70 amp or Model S twin charger 80 amp unit, you would want a 40 volt / 80 amp transformer to get the maximum charge rate at 208 volts.
The purpose for dual J1772 is so that the two 30 amp charging stations can provide 40 amps to my car (or 60 amps to a Roadster or Model S twin charger).
TonyWilliams
Active Member
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