Combining two 120V into a 240V connector

[widodh]

IF, again IF you were able to do so, this power still has to come from your main distribution panel.

The first thing that you should check out what the amperage is of your main fuse. If that is high enough you should preferably run a dedicated line for charging your Model S, with it's own breaker in the main distribution panel.

Don't start playing with random wires in your house. 40A or 80A is a lot of power which can kill!

Like the people above me already said, get an electrician. It will cost you a bit, but you'll sleep much better

 

[dhrivnak]

I have been trying to do this, unsuccessfully i might add, to join two j1772 circuits to get 60 amps. So far no luck as i have not been able to find balanced legs in the wild.

 

[hcsharp]

Edit: When this thread was merged with another it became ambiguous which question I was answering. Personally I would not have merged the threads because each one requires an entirely different discussion. Below is my response to n00b's question:

>How about doubling the amperage instead of voltage? Is it possible to combine two 120V @ 12A to provide 120V @ 24A of charging, or two 240V @ 24A into a 240V @ 48A? Could this reduce the charging time by 50%?

You can do it in theory. Should you? Hmmm... Probably not for several reasons. Even if you are an electrical engineer or electrician I wouldn't do it because of all the obstacles. You will need a pilot signal generator to signal the car that 24A are available at 120v. You have to test to make sure both circuits are on the same phase but not on the same breaker. Both circuits have to draw the same amperage and the only reasonable way to do that is with self-balancing. To achieve that, you have to be able to ascertain that the house wiring to both outlets is roughly the same length and gauge. You have to be certain that no other loads are operating on either circuit. The cords that you use to your combiner box have to be the same length. Your combiner box will need to be equipped with safety devices to prevent one plug from becoming hot while you plug the other one in among other things. When you consider all these requirements, it pretty much becomes virtually impossible to do. I routinely combine two opposite phase outlets to get 16A 240v but that is far, far easier and safer. And it charges more efficiently at 240v.

There are people who have combined NEMA 14-50 outlets at campgrounds to draw 35A off of each one to charge their Roadster at 70A 240V but that's a very different ballgame.

 

[n00b]

Edit: When this thread was merged with another it became ambiguous which question I was answering. Personally I would not have merged the threads because each one requires an entirely different discussion. Below is my response to n00b's question:

>How about doubling the amperage instead of voltage? Is it possible to combine two 120V @ 12A to provide 120V @ 24A of charging, or two 240V @ 24A into a 240V @ 48A? Could this reduce the charging time by 50%?

You can do it in theory. Should you? Hmmm... Probably not for several reasons. Even if you are an electrical engineer or electrician I wouldn't do it because of all the obstacles. You will need a pilot signal generator to signal the car that 24A are available at 120v. You have to test to make sure both circuits are on the same phase but not on the same breaker. Both circuits have to draw the same amperage and the only reasonable way to do that is with self-balancing. To achieve that, you have to be able to ascertain that the house wiring to both outlets is roughly the same length and gauge. You have to be certain that no other loads are operating on either circuit. The cords that you use to your combiner box have to be the same length. Your combiner box will need to be equipped with safety devices to prevent one plug from becoming hot while you plug the other one in among other things. When you consider all these requirements, it pretty much becomes virtually impossible to do. I routinely combine two opposite phase outlets to get 16A 240v but that is far, far easier and safer. And it charges more efficiently at 240v.

There are people who have combined NEMA 14-50 outlets at campgrounds to draw 35A off of each one to charge their Roadster at 70A 240V but that's a very different ballgame.

Thank you for the detailed explanation that's clear to someone who is not an electrical engineer. It sounds like it's way easier to just rewire with a thicker wire to double the current draw
What do you mean when you said it's something entirely different when people combine two NEMA 14-50 outlets to double the amperage?


p.s. I agree the thread should not have been merged as they are two distinct discussions. Mods, could you please un-merge the threads? Thanks.

 

[hcsharp]

Thank you for the detailed explanation that's clear to someone who is not an electrical engineer. It sounds like it's way easier to just rewire with a thicker wire to double the current draw
What do you mean when you said it's something entirely different when people combine two NEMA 14-50 outlets to double the amperage?

You can be reasonably certain that outlets in two adjacent campground sites have similar lengths of cable running to the outlet. You can be reasonably certain that there are no other loads on each circuit/breaker. You can be reasonably certain that you're not going to burn your house down if something goes wrong. You have to provide your own pilot signal anyway so not that much more of a hurdle to add the necessary safety features into the device. Overall it's far less effort to achieve far greater benefit. Charging at 120v is inefficient at any amperage.

p.s. I agree the thread should not have been merged as they are two distinct discussions. Mods, could you please un-merge the threads? Thanks.

I hate to be critical of the mods cuz it's a labor of love for them and they generally do a great job but it would have made much more sense to combine with the thread on charging from two J1772 outlets that dhrivnak has contributed to here. That thread also has info on doubling amps from two NEMA 14-50 outlets.

 

[NigelM]

Mod Note: The threads were merged because they both started from a similar premise. It's still a relatively short thread and apart from 1 comment on J1772, there didn't seem much point to move it to a J1772 discussion. If you're worried about the ambiguity of which question or post you're responding to please use the quote function and that will help keep things clear.

Caveat: Doug is much more technically savvy than me and he's the boss so if he wants to move it anyway, I have no problem with that.

Combining two 120V into a 240V connector

I was wondering if someone more electrically inclined could figure out some type of device that would combine two 120V outlets and turn it into a 240V so that you could charge faster.

What I'm imagining is if I went to a friends house or somewhere that didn't have a high power charger. I could use 2 extension cords and plug in two 120V plugs into a small device that would combine it to make a 240V. The extension cords would have to be plugged into different breakers since most house breakers have a 15 amp capacity.

Is this possible?

Combining Two Lines to Double the Amperaage

From reading the forum it appears combining two 120V into a 240V requires finding two outlets that are out of phase. How about doubling the amperage instead of voltage? Is it possible to combine two 120V @ 12A to provide 120V @ 24A of charging, or two 240V @ 24A into a 240V @ 48A? Could this reduce the charging time by 50%?

 

[hcsharp]

Mod Note: The threads were merged because they both started from a similar premise.

Not really. One is doubling the amperage. The other is doubling the voltage. They are two very different conversations with very little in common. Look at the responses and you'll see what I mean.

It's still a relatively short thread and apart from 1 comment on J1772, there didn't seem much point to move it to a J1772 discussion.

The other thread wasn't much of a J1772 discussion as much as a technical discussion about doubling amps from two sources which is partly why it moved on to discuss doubling amps from NEMA 14-50 outlets. To some extent you're right, which is why n00b's thread should probably have stayed by itself.

If you're worried about the ambiguity of which question or post you're responding to please use the quote function and that will help keep things clear.

In retrospect that's easy to say, but it was unnecessary until the threads were merged. Sometimes you have to strike a balance between too much bandwidth and shorter posts that can be read more quickly without quotes if they aren't needed.

Caveat: Doug is much more technically savvy than me and he's the boss so if he wants to move it anyway, I have no problem with that.

Please don't take my comments the wrong way. I'm only trying to provide some feedback that might be helpful. TMC is a great place to hang on the 'net partly because of the people it attracts, which not coincidentally is the product of a lot of hard work by you and the other moderators. I appreciate the time and effort you put into this. Since I'm not volunteering to be a moderator, I'll trust your judgement as to what to do in this case. Thanks.

 

[nsayer]

It may be a mistake to resurrect this thread, but I thought I would chime in with my two cents.

You cannot combine two circuits to increase the amperage. Running two circuit breakers in parallel is a really bad idea.

BUT you can take two 120 volt outlets and use the hot lines from each to make a 240 volt circuit, but doing so has a rather lengthy list of caveats:

1. You cannot use a circuit protected by a GFI for either leg. GFIs will trip if every milliamp that leaves the hot line doesn't return on the neutral, and doing this completely defeats that. Newer houses have GFIs outdoors and in the garage, which means now you're going to need to start using beefy extension cords to get inside... it all turns very iffy.

2. You must be extremely careful not to over-draw. The outlets you use will not be dedicated, so you cannot draw the full breaker power - and not even after the continuous duty 20% derate. I would, in fact, not draw more than 12 amps with such a system. At 240 volts, that's 2.8 kW. Still twice as good as L1, but really it's only meaningful for folks taking Volts on road trips or the like.

3. You MUST NOT just hack apart a pair of cords and splice them into a receptacle. If you don't do this with a proper, safe design, you raise the possibility of an unplugged 120 volt plug turning into a virtual neutral line - which would make it a very dangerous shock hazard.

I've designed and built a box that does this, but it uses 3 DPST relays and I went to a lot of extra trouble to insure that everything is disconnected from the receptacle unless the plugs are plugged in in precisely the correct configuration. Anything less, IMHO, is not something I would be comfortable recommending.

 

[FlasherZ]

It may be a mistake to resurrect this thread, but I thought I would chime in with my two cents.

I discuss this pretty thoroughly in the FAQ (see my signature below the post). It's just a bad idea all the way around, and comes with insurance and liability implications (and even in some jurisdictions could be criminal, where knowingly violating the NEC is a misdemeanor).

 

[nsayer]

I discuss this pretty thoroughly in the FAQ (see my signature below the post). It's just a bad idea all the way around, and comes with insurance and liability implications (and even in some jurisdictions could be criminal, where knowingly violating the NEC is a misdemeanor).

Quite simply, the NEC has no scope over things plugged into outlets. After all, a building inspection is not required to plug something in.

Doing it poorly is a bad idea. That much is quite true. But that fact does not preclude any possibility of it being done properly. The commercial Quick220 product is UL approved, FWIW.

 

[FlasherZ]

Doing it poorly is a bad idea. That much is quite true. But that fact does not preclude any possibility of it being done properly. The commercial Quick220 product is UL approved, FWIW.

UL approved doesn't mean anything unless you know the category in which it is UL approved. It is UL approved as a power supply device, like a power brick.

The question of whether NEC has scope over things plugged into outlets is a gray area - there are cases out there where the NEC's prohibition on cords running through doors and windows was upheld, and that contradicts the notion that anything plugged in isn't under jurisdiction of NEC. In addition, that same argument would seem to preclude any plug-in EVSE equipment, yet most manufacturers properly follow the guidelines. Remember, the NEC doesn't give itself jurisdiction, it only spells out its intent. It's codified by law - and when a jurisdiction says "the NEC shall be followed" without any limitations on its scope, those measures are accepted as law whether you're making an appliance argument or infrastructure argument.

I have seen insurance companies decline to pay for a loss based on a violation of NEC which included plugs in outlets (running several extension cords to an outbuilding from outlets on the side of a house to power garage doors and lights).

Could you make a technicality argument that would be accepted? Perhaps. Do you want to risk it? Up to you. Others before you lost a lot of time and their home for years trying to fight it. In addition, there is no safe way to treat multiple grounds from multiple circuits in a single device without creating some risk in failure scenarios -- failure scenarios that are entirely possible and have occurred in campgrounds.

If it's a risk you're willing to take, then that's fine, but I will never suggest to anyone else (especially those without electrical experience - or even worse, those who think they have infrastructure/building electrical experience because of a degree but don't) that they should violate code without a full understanding of the situation.

 

[nsayer]

Well, that's just plain FUD.

You can't get something UL approved by mailing in box tops. I'm fairly confident that UL knew damn well what the Quick220 was and how it was to be used. They have a blanket ban on certifying turkey fryers, but apparently had no problems with passing this device.

Is there anything I posted in my reply earlier that is untrue?

Is there anything specific about how the commercial "Quick220" works that is unsafe (their patent has a schematic: Patent US5977658 - Voltage doubling alternating current power supply - Google Patents )?

I'll say it once again: the fact that something can be (perhaps even often is) done poorly or unsafely does not in and of itself preclude any possibility of it being done properly.