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Generating 220V from 110V on the go or in a host garage overnight
- Thread starter greencharge
- Start date
My understanding is that the power supplied won't be any different. Actually, it might be less because there will be a small loss during the conversion. The only reason to use something like that is if what you are powering can't use 110V.
What jerry33 said.
You can safely pull 12 amps from 120 volt outlet on a 15 amp circuit. 12 amps * 120 volts = 1440 watts, so that's the most power you will get out of that outlet. You can convert voltages, but that lowers the current and the power stays the same.
Additionally, that transformer linked above can only handle 100 watts, so that's a tiny fraction of the power that the car can draw directly from a 120 volt outlet. If you plugged your car into it, best case is it would trigger the transformer's built in over-current protection. Worst case it starts a fire. I think you probably cannot convince the car car to charge at such a slow rate, and if you could, it would be so slow as to be useless.
You can safely pull 12 amps from 120 volt outlet on a 15 amp circuit. 12 amps * 120 volts = 1440 watts, so that's the most power you will get out of that outlet. You can convert voltages, but that lowers the current and the power stays the same.
Additionally, that transformer linked above can only handle 100 watts, so that's a tiny fraction of the power that the car can draw directly from a 120 volt outlet. If you plugged your car into it, best case is it would trigger the transformer's built in over-current protection. Worst case it starts a fire. I think you probably cannot convince the car car to charge at such a slow rate, and if you could, it would be so slow as to be useless.
No need if the car can handle it. The only reason you might want that is if you had a version of it that ran at more than 20A (>2400W), because the car limits 120V charging to 20A. But that's another whole ball of wax.
The only way this would work, is if you could find 2 different 120V outlets that are on different legs of the 240V feed. Then, if you had an adaptor that plugged into both 120V outlets you could pull 240V X 12A or 2880 Amps. You would have to use a 240V plug from Tesla and make sure that you set the charging rate to 12 Amps. This could get you 6 miles/hour charging rate.
roblab
Active Member
I just wire in a 50 amp circuit breaker to the breaker box (for instance, at my brother's house) with 6-3 w/ground cable to a 14-50 outlet, and plug in at 40 amps. 2 hot wires, 2 ground wires (yeah, ground and neutral to same buss bar) seems to be a lot simpler than looking for two legs of 120 in separate parts of the house and charging at 1/3 the rate with a combiner plug. (I about have him talked into doing a permanent outlet.)
I always carry a half dozen brands of breakers and call ahead to people I'm going to visit to find out what their brand of box is, so I can charge at 40 amps most everywhere. So far have only done this at three homes.
Puyallup Bill
Member
I sure hope you included some protection, maybe relays, so that if one plug is unplugged it is not "hot" through the UMC to the other leg hot. Especially important when away from home using someone else's circuits where some one, for what ever reason, might unplug one cord.
For safety, you should never set it to more than 12.
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Ground and neutral to the same bus bar only if you are working in the service panel. If you're working with a subpanel (including in Northern California where the service equipment is outside and the home panel is generally a subpanel) you must ensure ground and neutral are separated (2005 or newer code cycle).
Oh, does this really happen through the UMC? I guess a circuit is made between the two hots. I guess you would provide protection by having two relays, each 120v hot energizing a relay that would allow current to flow for the other hot. So if one of the 120v plugs got unplugged, it would break the connection for the other hot and thus nothing would be connected to the UMC. This would require the neutrals be used for each 120v receptacle to energize the relays. And here I thought making a 2x120v adapter would be easy!
If only one cord gets unplugged, the car won't charge. It is easy to make a 2x120V adapter, the difficulty is in finding the two opposite-leg outlets that have available ampacity with appropriately-sized extension cords (12 AWG for 50-100 ft, 10 AWG for > 100 ft). The neutrals aren't used - the UMC will ignore them.
Now, if someone wired a receptacle backwards (found frequently in older homes), watch out! you'll end up with a dead short when the two cords are plugged in.
What Puyallup Bill was referring to was an electrical shock danger if only one plug is plugged in. If the UMC is plugged into the adapter and into the car, it is possible that the unplugged plug will see 120v hot on its hot blade coming from the other plugged in plug through the UMC and car charger electronics. I haven't verified this myself, but I could see how it could happen. Anyone know for sure?
Puyallup Bill
Member
If a person builds one, USE THE RELAYS. I can not speak for the Tesla UMC, but with the Nissan unit, the exposed plug will be hot if the relays are not used and one plug is unplugged while the EVSE is plugged into the box. Makes no difference if the EVSE is plugged into the car or not. Can't see why it would be different with the Tesla unit.
I can not verify the Tesla set up, as my box has the relays and I don't care to disable them for a test.
Yes, the using the relays is the way to go. I was hoping that I could build one that only needed 10/2 wire instead of 10/3 ( since I might as well build one that works with TT-30 and 5-20 plugs for a possible 24 amp draw) but the relays will need a neutral wire, and then a box to house everything. But I agree, you need the shock protection.
No, because the contactor will not be energized on the UMC, so the car won't ever see the voltage.
NEC article 625 requires interlock, meaning that the car's coupling cannot be energized until everything is safely connected. For this to occur, the EVSE requires voltage to generate the pilot signal (which wouldn't be there with one plug disconnected); the EV would then modify that voltage and signal the EVSE to close the contactor and provide charging voltage; then the EVSE requires power to close the contactor and connect the mains to the coupling end.
That said, you will see the voltage presented from the other hot leg through the transformer for the control logic on the EVSE. And yes, while the current possibility won't be high, it's still enough to kill, so protect yourself.
Another reason you need relays / indicators / etc. is to avoid issues associated with reversed "polarity" at an outlet, or an issue where the two different neutrals have differences in their potential (because they come from two different distribution sources, or something), so that you don't create a significant current through your cords, or a dead short.
These types of problems are why a "quick 220" or "easy 240" or whatever violate NEC and are not recommended.
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Well, FlasherZ and Puyallup Bill, I had to see for myself. So built a quick and dirty 2x120V adapter with no protection. I found two 120V non-GFCI circuits on different legs. Checked to make sure there was 240V across the hots of my adapter. Plugged in the UMC. Green lights, it was happy. Dialed down the car charging screen to 12A. Plugged in the UMC into the car. Car starts charging and I'm getting between 6 and 7 miles per hour charge, 12A at 234V. Unplugged one of the 120V plugs at the wall. A double beep comes from the car, the UMC lights go out, charging stops. I test to see if there is now voltage across the ground and hot of the plug I just unplugged. Gulp, it reads 120V. Well, maybe it won't be much current? So I touch them. Ouch. Definitely enough current to not do that test again 
So yes, I've confirmed that with the Tesla UMC you DEFINITELY need protection to protect against a shock hazard should one of the two 120V plugs be unplugged. 120V relays here I come!
So yes, I've confirmed that with the Tesla UMC you DEFINITELY need protection to protect against a shock hazard should one of the two 120V plugs be unplugged. 120V relays here I come!
Yes I found the same thing. This is defiantly a big boy toy! Think danger like a fuel nozzle and sparks. You must be careful! Or hook up relays. I'm thinking at a buddy's house no kids, work, motel. It's an easy way to push range out. P.s I wired a one of these across the hots. It lights up when you hit the opposite hot. I hold the second plug in my hand until I remove the first plug so I don't forget it live.
