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TonyWilliams
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Re: Do It Yourself: 240v from two 120v sources

Sat Jun 14, 2014 3:56 pm

nsayer wrote:Let's not forget, a hot-neutral swap will cause a two-relay design to present 120 volts to a 240 volt device. That may not be unsafe from a hazard to life perspective, but it may result in equipment damage.
Yes, I think everybody gets that. The contention was the "safety" aspect, and again, I don't see Phil's design (which I built long ago) as unsafe. Yours is more "complete", and may save some unpleasantness to some component, but Phil's is not unsafe to humans.

nsayer
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Re: Do It Yourself: 240v from two 120v sources

Sat Jun 14, 2014 4:02 pm

Phil's prevents the virtual neutral problem.

I'm not sure I'm willing to concede that that is the only danger to humans that is worthy of prevention. But I'm content to agree to disagree.

And besides, "safety" encompasses not just injury prevention, but damage to property as well.

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Ingineer
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Re: Do It Yourself: 240v from two 120v sources

Sat Jun 14, 2014 5:22 pm

If you are using this on an EVSE, there is no risk of equipment damage should it run on 120v. It's also highly unlikely that low voltage could damage ANY equipment.

People: Do not subscribe to the FUD, there is nothing wrong with your 2-relay design, and no need to change it. There's been quite a few of these built and thousands sold of a similar design (Quick220) that passed UL testing procedures. Most UL tests are quite stringent!

You should never open any electrical equipment until ALL connections are disconnected. Nsayer's "corner case" wouldn't even apply.

The design of safety systems is to protect uninformed public, not a qualified professional. If you consider yourself such and you start working on equipment still energized, then you are definitely not!

-Phil
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nsayer
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Re: Do It Yourself: 240v from two 120v sources

Sat Jun 14, 2014 5:50 pm

Ingineer wrote:If you are using this on an EVSE, there is no risk of equipment damage should it run on 120v. It's also highly unlikely that low voltage could damage ANY equipment.

People: Do not subscribe to the FUD, there is nothing wrong with your 2-relay design, and no need to change it. There's been quite a few of these built and thousands sold of a similar design (Quick220) that passed UL testing procedures. Most UL tests are quite stringent!

You should never open any electrical equipment until ALL connections are disconnected. Nsayer's "corner case" wouldn't even apply.

The design of safety systems is to protect uninformed public, not a qualified professional. If you consider yourself such and you start working on equipment still energized, then you are definitely not!

-Phil
Go look at the Quick220 patent. It's not the same design as yours. Saying that their UL approval has anything at all to do with your design is disingenuous at best.

Suggesting that qualified professionals don't need or use safety systems (as opposed to the "uninformed public") is downright laughable.

No qualified professional would knowingly work on energized equipment. Safety systems are designed to prevent hazardous ambiguities. And it's defense in depth - something that is easily worth the extra $15.

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TonyWilliams
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Re: Do It Yourself: 240v from two 120v sources

Sat Jun 14, 2014 6:43 pm

nsayer wrote:Go look at the Quick220 patent.
What are the particulars of that one?

nsayer
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Re: Do It Yourself: 240v from two 120v sources

Sat Jun 14, 2014 6:54 pm

It was a few pages back.

https://www.google.com/patents/US5977658" onclick="window.open(this.href);return false;

Their design is a single 208/240 relay wired the same way as the "third" relay of my design.

I designed mine before I discovered their design. The only weakness is that they're not testing the neutrals. You can argue that that's not necessary. I don't have nearly as good a rebuttal for that, except that if the neutral is not working there may be other problems hiding.

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TonyWilliams
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Re: Do It Yourself: 240v from two 120v sources

Sat Jun 14, 2014 8:28 pm

nsayer wrote: I don't have nearly as good a rebuttal for that, except that if the neutral is not working there may be other problems hiding.
Fair enough.

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Re: Do It Yourself: 240v from two 120v sources

Sat Jun 14, 2014 8:37 pm

I took a moment to read the Quick220 patent. Even they called out the same objection I did:
If, the user proceeds as in the previous paragraph, but connects the second input plug 10B to another 120-volt receptacle (not shown) that is wired to the same end of secondary winding 38 of distribution transformer 36 as is first receptacle 44A, the resulting voltage between line voltage conductors 12A and 12B and, hence, control terminals 20A and 20B will be zero. The switching device 18 will not close, and the line voltage conductors 12A and 12B will remain electrically isolated from output conductors 24A and 24B. Similarly, if there is line voltage on either of conductor 24A or 24B, but not on the other, switching device 18 will not close, and the line voltage 12A and 12B will remain electrically isolated from output conductors 24A and 24B. This isolation is a desirable feature of the invention: power is isolated from the output receptacle 28 and the electrical load 46 until input plugs 10A and 10B are properly connected to appropriate 120-volt conductors which are 180 degrees out of phase, producing the desired 240-volt output. This eliminates potential equipment damage or electrical shock to the user, which may happen if either output conductor 24A or 24B is electrically connected to power and the other is not.
Q.E.D.

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Re: Do It Yourself: 240v from two 120v sources

Sun Jun 15, 2014 6:16 am

nsayer: I would be interested if you would comment on the advisability of:

1) On a regular basis using any device like yours in an area which would definitely benefit from GFCI protection at either the two receptacles used (e.g. a concrete floored basement garage that is prone to becoming damp when it rains)?

2) On a regular basis using any plug-in EVSE on a single non-GFCI protected receptacle in a similarly hazardous area?

nsayer
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Re: Do It Yourself: 240v from two 120v sources

Sun Jun 15, 2014 7:58 am

MikeD wrote:nsayer: I would be interested if you would comment on the advisability of:

1) On a regular basis using any device like yours in an area which would definitely benefit from GFCI protection at either the two receptacles used (e.g. a concrete floored basement garage that is prone to becoming damp when it rains)?

2) On a regular basis using any plug-in EVSE on a single non-GFCI protected receptacle in a similarly hazardous area?
Well, you can't use this device on GFI outlets. I would advise against removing GFI protection from outlets so that you can use this device.

I don't believe they sell GFI equipped 220 outlets. They do make GFI equipped ganged circuit breakers. You could use that to add GFI protection to this device. Remember that the GFI only protects in the downstream direction. It won't offer any proaction from malfunctions upstream. That's why building codes call for GFI outlets in bathrooms, kitchens and garages, where damp conditions are expected. The concern is plugging and unplugging the 120 cables of the "quick220" device itself when you're standing on a damp floor. There can be no GFI protection for that operation, because the device is incompatible with GFI outlets.

EVSEs are required by the J1772 specification to include their own GFI circuitry. So EVSEs are safe to use in all weather, HOWEVER, the GFI typically only protects from the J1772 cable to the car. You must follow the manufacturer's/builder's recommendation as to how to treat the chassis of the device and its electrical connection, as those are outside the scope of GFI protection. That said, standing on a wet floor and manipulating a 240 volt plug is not a great idea. If you had to do so you would be well advised to shut off the breaker and/or unplug the "quick220" device first.

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