Dual-circuit wall-plug charger

[GSP]

I've known people who have done this (split current of the same phase through two wires, have done it myself for non-EV needs; and also in the US get 240v from different 120 outlets)
but definitely it's the sort of thing you should do only if you have EE knowledge, in general, and about your specific setup... and can't fool-proof for others to "re-use". You seem to be informed enough to know how to tackle it.

Combining two 120 volt outlets to get two "hot" wires in series for a 240 V supply is totally different than combining two 220 volt schuko outlets in parallel to draw twice the current at 220 volts.

The former is relatively safe when done correctly, but there could be multiple safety problems with the latter. I am not an expert, but I don't think US code allows paralleling AC circuits.

GSP

 

[GarrickS]

I know this has been talked to death at this point, but I didn't see the simple guidance. In parallel, only the voltage is added, not the amperage.

A "quick 220" with two 120v 20A circuits gives you a 240v 20A circuit. NEMA does not have an applicable socket for 240v 20A. If you want to stick with this route, you have to stick to two 120v sockets. You must also replace the 20A breakers with double-pole single-throw (the handles are linked together) so that a fault on either side will trip both.

Now, you _could_ wire those circuits to a 15-30 or 15-40 socket, but you are really crossing a line of safety and code violation. At the very least, you _must_ label the socket for its actual limits.

That said, all this *sugar* is wonky and you should just do it properly to avoid burning down your house.

 

[AB4EJ]

NEMA 14-50 is split phase, is it not? You have two separate out-of-sync 120V phases, with a net 240V difference between the phases, power flowing from one live to the other during half the cycle and reversed on the other. So you have little to no power returning through the neutral line then; unless I'm mistaken, the neutral is only for dealing with imbalances, or when you want 120V and tap only one of the phases vs. the neutral. If you have little to no current flowing through the neutral, that's of course going to trigger GFCI.

In my case however I'm talking single phase. Two live wires, in-phase, joined together, and two neutrals, joined together (and of course grounds joined). We don't do the whole split-phase thing to get 220V in Iceland

Just for info, in the US, the two different sides of a 220v outlet are in phase, not out of sync. The only difference between them is the voltage, which is being pulled off 2 different taps on the same transformer. The two taps are 120v to neutral (each) but across them it is 240v.

The only way you have circuits with phases "out of sync" is if you have 3-phase service, which is generally not installed in a residence. It is used mainly for commercial power.

 

[KarenRei]

Just for info, in the US, the two different sides of a 220v outlet are in phase, not out of sync. The only difference between them is the voltage, which is being pulled off 2 different taps on the same transformer. The two taps are 120v to neutral (each) but across them it is 240v.

That's only possible if they're 180° out of sync.

 

[AB4EJ]

That's only possible if they're 180° out of sync.

No, it doesn't work that way. Here is the circuit:

They are both in the same phase, just taking different number of turns on the transformer, where the center tap is connected to neutral (shown as ground in the figure). Take it from me. (I actually got 100% on the final exam where we studied this stuff). (BS, Electrical Engineering, Virginia Tech).

 

[KarenRei]

No, it doesn't work that way. Here is the circuit:

View attachment 240126

They are both in the same phase, just taking different number of turns on the transformer, where the center tap is connected to neutral (shown as ground in the figure). Take it from me. (I actually got 100% on the final exam where we studied this stuff). (BS, Electrical Engineering, Virginia Tech).

I appreciate that, but I'm not the one making these graphics:

That said, I understand the confusion here. You're describe them as in-phase because they're additive. I'm describing them (as are those making the graphics) as out of phase because if you put two oscilloscopes' ground taps on the neutral and one of each of the probes on the lives, the waveforms would be out of sync with each other.

 

[AB4EJ]

I appreciate that, but I'm not the one making these graphics:

That said, I understand the confusion here. You're describe them as in-phase because they're additive. I'm describing them (as are those making the graphics) as out of phase because if you put two oscilloscopes' ground taps on the neutral and one of each of the probes on the lives, the waveforms would be out of sync with each other.

Man, that is really weird, the way they show that; generally, when you add two identical waves together that are 180 deg out of phase, what you end up with is zero; they perfectly cancel each other out. I think it depends on how you hook up the scope... and also how the transformer is wound... anyway, it is very interesting to see it shown that way.

 

[Garlan Garner]

Well, who knows what is 'code' in Iceland... In the US, there is a device (I don't have a link for it this second) that does exactly that, plugs into two outlets/circuits. The problem is that it can't use circuits on ground-fault breakers (as I recall), and most garage circuits are. So, you need to run extension cords everywhere.

Somewhere with true two-phase and that doesn't have that requirement may have a better chance of doing something like that, but, local electrical code needs to be checked.

Most locations in the US use two phases, 180 degrees out of sync, called split-phase. Either phase to neutral is a 'normal' 120 VAC circuit. The two 'hot' leads to each other is used to get 240 VAC for stoves, water heaters, Tesla Wall Connectors etc.

Iceland? You live in the US. What's the concern for Iceland about?

 

[boaterva]

Iceland? You live in the US. What's the concern for Iceland about?

Lol, that's where KarenRei lives...

And for the comment about 'neutral' in a 14-50, there isn't one. Just two hots and a ground.

 

[jkn]

Man, that is really weird, the way they show that; generally, when you add two identical waves together that are 180 deg out of phase, what you end up with is zero; they perfectly cancel each other out. I think it depends on how you hook up the scope... and also how the transformer is wound... anyway, it is very interesting to see it shown that way.

You connect two identical waves together, that are 180 deg out of phase, through your load. Your load sees double voltage.

 

[Cosmacelf]

Going back to the original question, isn't the biggest problem potentially plugging into two different receptacles that happen to be on the same breaker? I'm guessing that in Iceland, each receptacle doesn't necessarily have their own breaker? One breaker can serve multiple receptacles? If so, how are you going to know whether or not you are doubly overloading a breaker when you accidentally plug your device into the same breaker circuit?

In the US, a 240V combiner doesn't have this problem since if you were to plug into the same breaker circuit, both receptacles would be in phase and thus a properly constructed device wouldn't work (in the US, you use relays in your combiner device for both shock safety and to make sure no electricity is shown on the output unless conditions are correct).

 

[AB4EJ]

Going back to the original question, isn't the biggest problem potentially plugging into two different receptacles that happen to be on the same breaker? I'm guessing that in Iceland, each receptacle doesn't necessarily have their own breaker? One breaker can serve multiple receptacles? If so, how are you going to know whether or not you are doubly overloading a breaker when you accidentally plug your device into the same breaker circuit?

In the US, a 240V combiner doesn't have this problem since if you were to plug into the same breaker circuit, both receptacles would be in phase and thus a properly constructed device wouldn't work (in the US, you use relays in your combiner device for both shock safety and to make sure no electricity is shown on the output unless conditions are correct).

You can determine this as follows - if you connect to the hot side of two different outlets and measure (using an isolated voltmeter) the voltage between the two hot wires - if they are in different sides of the transformer, you'll get 240 v; if they are both on the same side of the transformer, you'll get zero volts.

In any case, are you sure you really have to do this? It is not the safe way to set up for charging...

 

[AB4EJ]

You connect two identical waves together, that are 180 deg out of phase, through your load. Your load sees double voltage.

Begging a thousand pardons, I see how this works now. The trick is that the center tap of the transformer is grounded. and I hadn't thought about the effect of that....

 

[Cosmacelf]

AB4EJ, unless I am missing something, you have missed that Iceland is single phase 240V, so your measurement idea to determine whether or not two receptacles are on the same breaker or not won't work.

 

[KarenRei]

Today I decided to buy some hardware to prototype this concept... and I found a problem, although not one that's been discussed here before!

I got a 30A female, 2 16A male schuko plugs (our local home standard), some 3x2,5mm wire, and a junction box. I started wiring up the first schuko, connected the ground, then went to connect the neutral.... hmm, which pole to connect to... oh yeah, I forgot, schuko is symmetric. It doesn't define which one is live and neutral, and you can plug in a cord either way (and thus it can be wired either way on the wall end). So for what I was thinking of implementing, when you plugged in there's no way to know whether you'd be connecting live to live/neutral to neutral (and thus having two parallel paths at approximately half the current each), or live to neutral/neutral to live (and immediately throwing the breakers on both circuits). :Þ

Thanks a bunch, Albert Büttner, for such a brilliant design :Þ Well, there goes that idea...

 

[miimura]

Today I decided to buy some hardware to prototype this concept... and I found a problem, although not one that's been discussed here before!

I got a 30A female, 2 16A male schuko plugs (our local home standard), some 3x2,5mm wire, and a junction box. I started wiring up the first schuko, connected the ground, then went to connect the neutral.... hmm, which pole to connect to... oh yeah, I forgot, schuko is symmetric. It doesn't define which one is live and neutral, and you can plug in a cord either way (and thus it can be wired either way on the wall end). So for what I was thinking of implementing, when you plugged in there's no way to know whether you'd be connecting live to live/neutral to neutral (and thus having two parallel paths at approximately half the current each), or live to neutral/neutral to live (and immediately throwing the breakers on both circuits). :Þ

Thanks a bunch, Albert Büttner, for such a brilliant design :Þ Well, there goes that idea...

If you study the Quick220 device designed for North America, you can apply the same methodology to detect the polarity and use lights to indicate the polarity of each plug when everything is plugged in without popping any breakers. The basic idea is to use some sensing devices in a combiner box before the box actually connect anything together.

Even though there is a solution to your current problem, I still think this is generally a bad idea.

 

[AB4EJ]

Can someone please explain to me, why there is so much interest in doing 220v charging "on the cheap" -? This is something that can set your house on fire or electrocute someone if not done exactly right... I mean, I just don't see how you can justify the risk simply to avoid a few hundred bucks for an electrician to do it right....

 

[KarenRei]

Can someone please explain to me, why there is so much interest in doing 220v charging "on the cheap" -? This is something that can set your house on fire or electrocute someone if not done exactly right... I mean, I just don't see how you can justify the risk simply to avoid a few hundred bucks for an electrician to do it right....

Once again (how many times does this have to be repeated?), this is not about trying to avoid having to install a home charger. This is because:

1) Not everybody has the right to have the wiring in their residence redone (for example, if they're not the owner)
2) Nobody has the right to redo someone else's wiring (for example, if they're visiting a friend or other random destination).

Why would you assume that anybody would want to hack together two circuits if there was an easy way to avoid it? Do you think that people who use Quick220s do so because that's the "best" way to get 220V? No, they use them because, for their particular situation, that's the only way they can.

It must be nice living in a place where there are chargers and superchargers everywhere so you never have to think about improvised solutions. That is not Iceland. Go enjoy your infrastructure which we don't have. And if you have the privilege to have your wiring redone, again, enjoy that privilege and don't complain to those who don't.

 

[AB4EJ]

Good rant.

 

[jkn]

Today I decided to buy some hardware to prototype this concept... and I found a problem, although not one that's been discussed here before!

I got a 30A female, 2 16A male schuko plugs (our local home standard), some 3x2,5mm wire, and a junction box. I started wiring up the first schuko, connected the ground, then went to connect the neutral.... hmm, which pole to connect to... oh yeah, I forgot, schuko is symmetric. It doesn't define which one is live and neutral, and you can plug in a cord either way (and thus it can be wired either way on the wall end). So for what I was thinking of implementing, when you plugged in there's no way to know whether you'd be connecting live to live/neutral to neutral (and thus having two parallel paths at approximately half the current each), or live to neutral/neutral to live (and immediately throwing the breakers on both circuits). :Þ

Thanks a bunch, Albert Büttner, for such a brilliant design :Þ Well, there goes that idea...

I can imagine automatic solution for problem caused by symmetric plugs. It is rather simple, but with electricity there is always possibility of deadly mistake.

Perhaps you should instead buy an EV with double range, so that you don't need to recharge away from home.