EV Charger Voltage Range

[Ravenvalor]

Hello,

Thanks for all the great help with my daily questions.

Do you think that #1 THWN is large enough to feed most electric car chargers that use 40-amp, 240-volts? The breaker will be 50-amps, the receptacle will be NEMA 14-50R, the voltage is 208-volts, the distance is 400', the conduit is 2" PVC in the ground, there won't be any other circuits in the conduit so there will be 3 - #1 THWNs and a #6 THWN ground. Once the circuit reaches its destination it will feed a spa panel with a 50-amp GFCI breaker and then the receptacle.

The Southwire Voltage drop calculator predicts 2.86% voltage drop so 2.86% from 208-volts is 199-volts. Looks rather low for a 240-volt circuit.

Thanks again.

 

[retirede]

EVSEs I’m familiar with don’t care about undervoltage. The charger in the car might. The most likely effect is a bit slower charging.

I know that most car dealerships (especially the bigger ones) have 208V services and their L2 EVSEs work just fine.

 

[Ravenvalor]

Good to know. I guess unlike electronics protecting a motor which won't start due to undervoltage, electronics protecting a car charger is just charging a battery.
What if someone tried to plug a RV into that receptacle? Do you suppose there may be start up issues with some of the motors in the RV?

Thanks,

 

[MD Automation]

Agree with Retirede, likely the only effect of ~200 VAC would be slower charging.

I charge my Chevy Bolt at my shop on 208 all the time with no trouble - and the long home run from the receptacle to the panel at the shop here (w/ #12s) probably gets my voltage to the EVSE down to ~ 200, especially in the summer. Again, no problem except for slower charging.

One option for you might be a small buck boost transformer. Would help get the voltage at the end up to something like 225 pretty easily. Probably something like a 1.5 kVA would work.

I use a 0.75 kVA sometimes at the shop and also at my family home in Brooklyn when I travel there (ConEd runs buried 3 phase 208 down the street and feeds all the homes w/ 2 legs of that). So I can boost that 208 to 230 and charge around 10% faster. Here is that little buck boost in Bklyn feeding the EVSE...



A downside to the boosted voltage would be uneven L-N voltages. The EVSE and charger in my Bolt does not care. Most don't use the neutral for anything. They only care about L-L. But maybe that's a problem for something else plugged into that 14-50R?

 

[Ravenvalor]

One option for you might be a small buck boost transformer. Would help get the voltage at the end up to something like 225 pretty easily. Probably something like a 1.5 kVA would work.

I use a 0.75 kVA sometimes at the shop and also at my family home in Brooklyn when I travel there (ConEd runs buried 3 phase 208 down the street and feeds all the homes w/ 2 legs of that). So I can boost that 208 to 230 and charge around 10% faster.

 

[LarryFine]

A downside to the boosted voltage would be uneven L-N voltages. The EVSE and charger in my Bolt does not care. Most don't use the neutral for anything. They only care about L-L. But maybe that's a problem for something else plugged into that 14-50R?

Some time ago, I suggested that, if you select a unit so the secondaries will be connected in series, they could be wired to opposite ends of the primary, maintaining equal voltages to the neutral.

For example, looking at the boost diagram below, separate the secondaries and wire X3-X4 to the H4 end, and X1-X2 to the H1 end.



In other words, wire it like you would an open-delta setup, but with only one transformer, and no neutral connection to the transformer.

It would basically look like this diagram, but with one winding in each place where this diagram shows two (and there would be no "neutral" or B phase connection to the unit):

 

[MD Automation]

Some time ago, I suggested that, if you select a unit so the secondaries will be connected in series, they could be wired to opposite ends of the primary, maintaining equal voltages to the neutral.

Larry, that's a great idea. I wonder why the typical wiring diagrams don't want you to wire things that way?

I'll have to try that here in the shop this week, would totally expect it to work just fine. Almost all buck boost transformers have a set of windings on the primary (like 120x240) and secondary (like 12x24) to let you do what you propose.

 

[LarryFine]

Larry, that's a great idea. I wonder why the typical wiring diagrams don't want you to wire things that way?

I'll have to try that here in the shop this week, would totally expect it to work just fine. Almost all buck boost transformers have a set of windings on the primary (like 120x240) and secondary (like 12x24) to let you do what you propose.

Exactly. A 240v primary with a 12/24v secondary on 208v will develop a 20.8v boost, for a 228.8v output.

A 16/32v secondary on 208v will develop a 27.7v boost, for a 235.7v output. (all numbers theoretical).

What makes my suggestion "radical" is splitting up the secondaries to maintain equal L-N voltages.

I don't know why B-B transformer makers don't suggest this. Maybe we should ask if it's a good idea.

 

[hillbilly1]

Good to know. I guess unlike electronics protecting a motor which won't start due to undervoltage, electronics protecting a car charger is just charging a battery.
What if someone tried to plug a RV into that receptacle? Do you suppose there may be start up issues with some of the motors in the RV?

Thanks,

The majority of RV’s have 120 volt loads only, even with the 50 amp plugs. It’s just distributed between the legs.

 

[Ravenvalor]

The majority of RV’s have 120 volt loads only, even with the 50 amp plugs. It’s just distributed between the legs.

Thanks for the info. I will quote 1/0 just to be safe.

 

[LarryFine]

The majority of RV’s have 120 volt loads only, even with the 50 amp plugs. It’s just distributed between the legs.

"Are you sure?!"


I know the 30a supplies are only 120v, but every 50a one I've done had a 120/240v 4-wire cord.

 

[hillbilly1]

"Are you sure?!"
View attachment 2559123

I know the 30a supplies are only 120v, but every 50a one I've done had a 120/240v 4-wire cord.

Positive. A/C’s are 120, water heater if it has an electric option. I’ve owned quite a few over the years including a 36’ Class A sitting next to the house right now. They make a 30 to 50 amp dog bone that jumpers the hots together if both legs are not available. A built in energy management system regulates the loads if both legs are not available, 120 between legs instead of 240 or 208. (Alternates the front and rear A/C’s) a few super coaches have 240 dryers and water heaters, but are very high end. But the majority do not. Just because 240 volts is available, only 120 volts is used.