Do It Yourself: 240v from two 120v sources

I built this circuit. Using a Nema 6-50 outlet. It works perfectly unless I plug it into GFCI outlets. They trip as soon as the charging adaptor is plugged in. Is there a way around this?

I plan on taking a trip in a week. Most all hotel outdoor outlets are GFCI so I need it to work with GFCI outlets. Is that possible?

Thanks in advance.


Ray

mrrjm said:

I built this circuit. Using a Nema 6-50 outlet. It works perfectly unless I plug it into GFCI outlets. They trip as soon as the charging adaptor is plugged in. Is there a way around this?

I plan on taking a trip in a week. Most all hotel outdoor outlets are GFCI so I need it to work with GFCI outlets. Is that possible?

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GFCI outlets sense the difference in current between the Hot and Neutral legs, assuming that if there is a difference, then the excess current is going to ground. This protects someone even when there is no ground connected to their device or outlet. Unfortunately, you can't do a anything about this since the 240 is generated by drawing current from the 2 hot sides and no current is flowing through the neutral and thus causing an imbalance between the hot and neutral which causes the GFCI to trip.

Alex is right. The whole concept is fundamentally incompatible with GFI protected outlets. There's no workaround other than using a different outlet.

It's possible to combine two 120v outlets that are GFCI'd (or on the same leg for that matter), but not using anything like the simple adapter most have made. Basically you need an isolation transformer (go back to page 24 of this thread.) Another option would be to use a second charger.

An isolation transformer that would handle an EVSE's 30 amps - or even 15 - would be a monster.

What I might do if I had to charge and there was not other option is try to bypass the GFCI. Of course if the panel breaker is GFCI then that won't work

nsayer said:

An isolation transformer that would handle an EVSE's 30 amps - or even 15 - would be a monster.

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Did you look at the discussion on page 24? We're talking about 12 amps (maybe up to 16) from two 120v outlets, and apparently you only need a transformer sized for the power from one outlet. ~2 kva should do. Still not something I'd like to carry around in my trunk all the time, but definitely not too big to carry if there was a definite need.

actually there might be a way. use a small transformer to make a circulating current through both neutrals exactly equal to the current through the line. It could be done. It would be a high current, but just enough voltage to drive the current through the neutral wires and the bus bar of the panel.

I don't think that will work. You're still pulling current from the hot line that you're not returning to the neutral. That will always trip a GFI.

mrrjm said:

What I might do if I had to charge and there was not other option is try to bypass the GFCI. Of course if the panel breaker is GFCI then that won't work

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What sort of hotel are you going to? I can't imagine most hotels would sanction you removing the faceplates from their outdoor outlets to defeat their safety protections. Also, what makes you think there will be multiple outdoor outlets within reach on different circuits? I'd think it fairly likely that many or all of the outdoor outlets would be on the same circuit anyway, in which case you're not going to be upping the power you can draw no matter what you can do.

Anyway, if you're driving a Leaf the battery's so small you're probably fine just charging on 120v anyway, so why go to all this trouble? And have you ruled out finding any public charging stations nearby on plugshare if you absolutely need to charge faster? Most hotels have shuttles available that can drop you off and pick you up from somewhere nearby with a charging station.

nsayer said:

I don't think that will work. You're still pulling current from the hot line that you're not returning to the neutral. That will always trip a GFI.

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As far as I know a GFCI can only sense whether there's an imbalance of current between hot and neutral - it has no way of knowing whether the currents on the two wires are actually from different circuits. The idea certainly seems like it'd work in theory, but I have no idea how one could exactly match the current in practice.

I'm driving a Tesla. Sorry to jump on the Leaf forum. This would be a last ditch effort if I was stranded (unlikely) but possible. Yes we are only talking 12 amps. 15 amps if the outlets are 20 amp. I wouldn't even consider bypassing a GFI unless my only other option was to tow the car. Even then I'm sure I could find Non GFI outlets.

fooljoe said:

nsayer said:

I don't think that will work. You're still pulling current from the hot line that you're not returning to the neutral. That will always trip a GFI.

Click to expand...

As far as I know a GFCI can only sense whether there's an imbalance of current between hot and neutral - it has no way of knowing whether the currents on the two wires are actually from different circuits. The idea certainly seems like it'd work in theory, but I have no idea how one could exactly match the current in practice.

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But that begs the question. How would you pull current from somewhere else that you could feed back into the GFI neutral without unbalancing *that* source's GFI? And if that source doesn't have a GFI, then why not just use *it* for the quick-220 instead of the GFI source?

nsayer said:

But that begs the question. How would you pull current from somewhere else that you could feed back into the GFI neutral without unbalancing *that* source's GFI? And if that source doesn't have a GFI, then why not just use *it* for the quick-220 instead of the GFI source?

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You're not "pulling current from somewhere else", you're siphoning off some power from the existing 2 hots (assuming they're on different legs), stepping the voltage way down, and (somehow) dynamically adjusting the current in this low-voltage "neutral to neutral" circuit so that it matches the current in the high-voltage "hot to hot" circuit that you're using for charging. Of course whether and how you can perform this dynamic adjustment precisely enough and quickly enough not to trip the GFCIs is the big question.

Oh, I see. You're counting on the GFI not noticing a voltage difference in the returns.

I don't see why that wouldn't work right offhand, but the whole thing is already a Rube Goldberg machine even before you start down that road...

Oh, and the current between the two hots is not static. Your "compensator" would need to vary the return current to keep the two GFIs happy.

EDIT: Oh you said that already. Yeah.

I have my doubts on the 'quick enough' part.

A typical GFI is just a CT coil with the hot and neutral running through it. Any time the current on the CT exceeds the trip current divided by the Te of the coil, the GFI will trip. I can't envision a reaction time fast enough to overcome that arrangement.

how could the current between the two hots be different... the neutral is not connected. where are the electrons involved going to/coming from?

[oops - erase erase erase]

johnrhansen said:

how could the current between the two hots be different... the neutral is not connected. where are the electrons involved going to/coming from?

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No, no, it's that the current from one hot to the other will vary over time, and the current going into each neutral must *exactly* balance it at any given instant.

That's going to be tough to arrange.

This past April I posted about EMW's creation which sold for $49 I think. Here's the link: http://www.mynissanleaf.com/viewtopic.php?f=26&t=4330&p=361604#p361604" onclick="window.open(this.href);return false; Thank goodness the forum response to this device prompted EMW to remove it from it's for sale list. However, there are still these devices in the wild. A friend from the Orange County LEAF gatherings had this device for use with his EMW juice box. Again this is not for the faint of heart...

Yeah, that is just a stunningly bad idea.

I'm building another of my version of this device for some friends who have a (non EV) need for one. I personally would never consider using anything less than the "3 relay" circuit. And that circuit, all built, actually winds up being well north of $100 once you buy all of the parts.