240 volt charging issue

[FlasherZ]

Thank you @sefs! That is exactly what I was referring to. Most people don't realize that for boost-buck configurations, the iron/copper of the transformer is only carrying the "difference" kVA, here 32Vx40A or 1.3 kVA.

Still, is it worth $500+ to increase charging speed from 24 to 28 mph?

Note that I'm not talking about establishing a boost transformer - I can pretty much guarantee that won't be worth it, given the difference in benefits vs. cost, maintenance, that nasty hum, and heat. But if there's an opportunity to get the power company to offer a distribution transformer change that would take you from 120V/208Y service to 120/240 service, take advantage. Never hurts to ask.

 

[miimura]

If the boost transformer is dedicated only to charging, why stop at 240V? Why not set it up to provide 250V? It's an incremental solution, so why not take incrementally more benefit?

 

[Cosmacelf]

You could set it for 250v, but then you would run the risk of pushing too much power through the UMC, cable and adapters which could result in too much heat build up. IMHO, those components are at their limit already.

 

[Cottonwood]

It only current through the UMC, etc, that causes power dissipation. Raising the Voltage will not increase power and heat build up there.

The real problem is a tolerance one and how high a Voltage is too high for the car. Let's take a hypothetical. Assume that the typical Voltage at your garage is 200 Volts on a nominal 208 Volte connection. If you put in the correct boost transformer(s) to get the car's connection to 250 Volts, that would provide 4% from making up the nominal and an additional 4% from going to the limit of 250V.

Now what if the utility changed a tap on its transformer, the feed wire was upgraded, or other users just stopped drawing current and the feed went back to 208 Volts? That would ripple through the boost transformers and take the car to 260 Volts. If the utility went a little over 208 V, then the problem would be even worse.

We know that the charging modules are used in Superchargers at 277 Volts; are those specially built units or is every charging module good to 277 Volts.

This is not an over-Voltage risk that I would like to take with my MS.

 

[stoneskid]

It depends - they might change / reconfigure the transformer for free, never hurts to ask - depends on the circumstances.

Is this a single-family dwelling? or a commercial setting?

Its a commercial property that I have owned for 20 years. It's not a big deal cause if I need a quick charge I can head down the road and supercharge.

 

[FlasherZ]

You could set it for 250v, but then you would run the risk of pushing too much power through the UMC, cable and adapters which could result in too much heat build up. IMHO, those components are at their limit already.

My transformer at home is set to 249V... to compensate, the car stops at 79A.

 

[Cosmacelf]

Why am I not surprised that FlasherZ somehow manages to get a higher boost voltage from the power company

 

[FlasherZ]

Co-ops are far easier to work with. Many distribution transformers are adjustable, so when they put the new transformer in, I asked them to set it just under 250V. As it turns out, it doesn't make that big of a difference because the car will limit to 79A with the higher voltage. At my home the UMC charging maxes at 39A while at my lodge it goes full 40A (236V there).

 

[davewill]

Co-ops are far easier to work with. Many distribution transformers are adjustable, so when they put the new transformer in, I asked them to set it just under 250V. As it turns out, it doesn't make that big of a difference because the car will limit to 79A with the higher voltage. At my home the UMC charging maxes at 39A while at my lodge it goes full 40A (236V there).

Interesting. The 79a makes sense figuring that the max power the two chargers can handle is very close to 19.2kW. On the 39a, I guess the car must be maxing out one charger @ 9.6kW. The logic is probably 40a and below, one charger, then the charger separately stops at it's power limit. I'm fairly confident the UMC isn't smart enough to be the one doing it.

 

[miimura]

The chargers in the car will limit to 10kW each when the voltage is over 250V. Normally they limit to 40A each.

 

[mknox]

Co-ops are far easier to work with. Many distribution transformers are adjustable, so when they put the new transformer in, I asked them to set it just under 250V.

Muni's aren't so bad either :wink:

I assume the distribution transformer is dedicated to your service alone. Typically, when we install transformers we set the taps to provide as close to the nominal 240 volts at the end of the secondary bus under normal loading conditions. High voltage complaints can be just as common as low voltage among utility customers.

 

[FlasherZ]

The chargers in the car will limit to 10kW each when the voltage is over 250V. Normally they limit to 40A each.

It's not over 250V. The car leaves some headroom for EVSE electronics and such.

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Muni's aren't so bad either :wink:

I assume the distribution transformer is dedicated to your service alone. Typically, when we install transformers we set the taps to provide as close to the nominal 240 volts at the end of the secondary bus under normal loading conditions. High voltage complaints can be just as common as low voltage among utility customers.

Your assumption is correct, I live about 1/10th mile from my nearest neighbor.