Generating 220V from 110V on the go or in a host garage overnight

[Cosmacelf]

The problem is what happens when only one plug is plugged in? This is the "normal" state of affairs that occurs every time you use the unit. With one plug plugged in and the other one just sitting there, you might feel current if you grab hold of the second plug, because you if you touch the hot and the neutral or ground on the exposed plug, you are completing the circuit of the relay coil through your fingers. I don't think this is safe.

BTW, presumably you are going to box this up? Your description sounded like it was all open...

 

[mrrjm]

The problem is what happens when only one plug is plugged in? This is the "normal" state of affairs that occurs every time you use the unit. With one plug plugged in and the other one just sitting there, you might feel current if you grab hold of the second plug, because you if you touch the hot and the neutral or ground on the exposed plug, you are completing the circuit of the relay coil through your fingers. I don't think this is safe.

BTW, presumably you are going to box this up? Your description sounded like it was all open...

Yes it will be boxed up. This is the beauty of using the 240 volt relays and not the 120v relays. The control side of the relays are powered by the "hots". So if one of the plugs are disconnected then both relays are off. No current/voltage on the open plug. The neutrals are NOT used.

I plan on using a tester first but I don't know what would happen if the hot and neutral were reversed. I assume both relays would be off.

If I can figure out how to post a picture I'll draw a schematic.

Thanks

Ray

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This is just a test circuit

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guess I didn't need all the jumpers

 

[FlasherZ]

This is the beauty of using the 240 volt relays and not the 120v relays. The control side of the relays are powered by the "hots". So if one of the plugs are disconnected then both relays are off. No current/voltage on the open plug. The neutrals are NOT used.

Your second plug will have its hot prong at 120V relative to earth when unplugged and the first plug is plugged in. The second plug's hot prong will have 120V supplied via plug 1, through the two relay coils. If you also joined the grounds, grabbing plug 2, touching ground and hot together will give you a good shock as you will experience the 120V from plug1hot---coil1---coil2---plug2hot---you---plug2ground---plug1ground. While the relays are open as you say, there is still a path through both relay's coils that will present 120V to you. While neutrals are disconnected, remember that in the service panel, neutral is bonded to ground. Therefore, one leg's hot is roughly at the same potential as ground.

Even if you didn't connect grounds, you would still have a safety hazard because plug 2's hot prong would be at 120V relative to any other earth. If you touched plug 2's hot prong while barefoot on concrete, or touching a pipe or a grounded frame of another appliance you'd feel it.

 

[mrrjm]

Yep you're right. I see it now. If I use the circuit in post #28 with 2 120v relays that solves this correct?

Thanks again for the help.

 

[FlasherZ]

Yep you're right. I see it now. If I use the circuit in post #28 with 2 120v relays that solves this correct?

Thanks again for the help.

It makes it safer. There is one problem that is difficult to escape, and it has to do with ground handling and certain types of installations. It's more of an issue at campgrounds and older, more questionable infrastructure, but it's still a concern -- see post 33 for a description of the failure scenario. This is more common of a scenario than you might think - I ran across a broken neutral just about 2 weeks ago at a campground near me. An RV owner warned me not to use the pedestal, telling me that his appliances were acting very strangely while plugged into it. I plugged in and charged fine -- he asked me how I managed to charge the Tesla, and knew immediately it was a broken neutral.

You can't easily escape this situation without creating a problem for other failure scenarios. This is why the NEC forbids these types of arrangements.