75A OpenEVSE Testing with the Tesla Model S w/twin chargers

[waidy]

Just want to clarify, that the 75Amp Open EVSE has a maximum throughout of 18KW (240V*75Amp). The breaker should be a 100Amp breaker and 3 legs of 3Awg copper wires + 1 leg of 8Awg ground wire. Appreciate your confirmation.

Also, the length of the 3awg wire from the breaker to the 75Amp Open EVSE location is 77 feet. Should the wire size be up-sized to count for "long distance" transmission lost? Please advise.

 

[mitch672]

Just want to clarify, that the 75Amp Open EVSE has a maximum throughout of 18KW (240V*75Amp). The breaker should be a 100Amp breaker and 3 legs of 3Awg copper wires + 1 leg of 8Awg ground wire. Appreciate your confirmation.

Also, the length of the 3awg wire from the breaker to the 75Amp Open EVSE location is 77 feet. Should the wire size be up-sized to count for "long distance" transmission lost? Please advise.

I used (2) #3 THHN copper (for each 120V leg), and (1) #6 THHN copper for ground. No third wire (neutral) is required, everything runs on 240V. Yes, I used a 100A 2-pole breaker on a 125A subpanel... I don't think the wire length will be an issue.
I bought #3 copper because I found a good price for it at "Stayonline" (.75 per foot, they even have multiple colors, I used red and black), here is a link: 600 Volt THHN

They only ship va FedEx (FedEx ground isn't too bad), so factor that into your decision as well.

 

[waidy]

@mitch672: Thanks for your clarification and advise.

 

[milotron]

Thanks for the clarity guys.

So, it looks like an inexpensive step up or autotransformer might get the extra kW out of the charger, if I can maintain the voltage at 250VAC. ( electrical code issues aside for using the autotransformer..) Especially considering the voltage drop at the end of the circuits and long service conductors, and the utility standard voltage of 240VAC, it may get a little extra power out of it. I am an electrician and electrical engineer with lots of stuff on hand to try this out. Just need my car to arrive. Depending on what the loaded voltage drops to, that extra 10-25 volts gets almost another kw of power being delivered.

 

[FlasherZ]

Just want to clarify, that the 75Amp Open EVSE has a maximum throughout of 18KW (240V*75Amp). The breaker should be a 100Amp breaker and 3 legs of 3Awg copper wires + 1 leg of 8Awg ground wire. Appreciate your confirmation.

Also, the length of the 3awg wire from the breaker to the 75Amp Open EVSE location is 77 feet. Should the wire size be up-sized to count for "long distance" transmission lost? Please advise.

Yes, 100A breaker is required. THHN/THWN can use #3 for this, minimum ground size should be #8 CU.

Wire length is not an issue unless voltage drop will be an issue for you (unlikely but could affect charge rate very slightly.) My vendor's calculation chart shows a 3v drop over 80 ft. of #3 THHN @ 75A. You're good to about 400 ft with 6% max drop.

- - - Updated - - -

Thanks for the clarity guys.

So, it looks like an inexpensive step up or autotransformer might get the extra kW out of the charger, if I can maintain the voltage at 250VAC. ( electrical code issues aside for using the autotransformer..) Especially considering the voltage drop at the end of the circuits and long service conductors, and the utility standard voltage of 240VAC, it may get a little extra power out of it. I am an electrician and electrical engineer with lots of stuff on hand to try this out. Just need my car to arrive. Depending on what the loaded voltage drops to, that extra 10-25 volts gets almost another kw of power being delivered.

For the most part, you're going to find that the few extra volts aren't going to be a big deal when you compare it to the complexity of an autotransformer, if you're already near 240v. I'd only consider an autotransformer if I had 208Y/120 service. 220v instead of 240v results in a reduction of about 2.5 miles per hour of charge.

 

[bluetinc]

Hey Mitch672,

Have you traced down where you are loosing that much voltage. When I run at 75A, I see about a 10V drop, half of which is in my lines inside the house to the car, the other half from the street transformer to the main input lines into my main panel. It might be good to understand why you are seeing almost 10%, especially if that is all occurring inside your home.

Peter

I use my OpenEVSE daily, but I have dual chargers. Even with dual chargers, I am seeing it draw 74/75 Amps, the voltage collapses from 239 to 220-221 at that load, the maximum rate I've seen so far is 43 miles/hour, but it's very cold here, and I'm sure that's affecting the rate as well (as some energy is going into heating the pack). As FlasherZ stated, the 14-50 outlet will provide the full 40A a single charger is capable of using, I doubt you will gain anything by providing 75A to a single charger Model S.

 

[mitch672]

Hey Mitch672,

Have you traced down where you are loosing that much voltage. When I run at 75A, I see about a 10V drop, half of which is in my lines inside the house to the car, the other half from the street transformer to the main input lines into my main panel. It might be good to understand why you are seeing almost 10%, especially if that is all occurring inside your home.

Peter

It's mostly on the utility, the sag occurs at or before the service entrance to the house. The service was just final inspected last week for the 150A to 200A upgrade that was completed 11/2011 (don't ask). Need to give the utility some time before I start complaining about the 18V drop at heavy loads.

 

[smorgasbord]

I haven't seen 220V in quite some time.

220, 221 - whatever it takes.


Sorry, couldn't resist the Mr. Mom quotation.

 

[FlasherZ]

220, 221 - whatever it takes.

Sorry, couldn't resist the Mr. Mom quotation.

Yup. I make that reference all the time. Usually creates a groan or two.