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I've never tried this because I assumed the current would not split evenly. In fact I'm a little surprised it works! A warmer cable will conduct more current. No? So why would it be self-correcting? I would have thought one cable would keep getting warmer taking progressively more current than the cooler one.
Eberhard you misunderstood his idea. He suggested first rectifying the 3 phase power and then feeding it into a single phase inverter to charge the Roadster. You, myself, and others have thought about this idea for a long time.:smile:it will not work on different phases on a 3-phase grid, because of 120° phase shift.
I think you got it the wrong way 'round. Copper has positive thermo-electric resistance coefficient. IOW the hotter cable in that pair increases its resistance, evening out the difference in current with the colder one.
If "twin charging" meant hogging TWO charging stations in a parking lot, you can bet that there will be a number of unhappy fellow electric car owners expecting to charge up their car, only to be thwarted by someone so thoughtless as to claim "more than their fair share" of recharging resources.
Whether its true or not, that's the perception we would see on Fox 11 news pieces.
-- Ardie
I do plan to add a lable saying feel free to disconnect if you need to charge. Right now I see many chanrging stations, many with 3-6 plugs and it is RARE I see someone using one. While I hope this becomes a problem I think we have some time before this develops.
Well my first test combining two J-1772 circuits did not go well. I carefully checked the phase on both input circuits and when I tried to combine both charging stations had a ground fault. If anyone has a suggestion on how to get around ground faults please let me know.
I assume the circuit had 3 phase power as it was showing 212V and if I charge the car it drops to 207 volts. To check between phases I have two 220V lights and a 30 amp DPDT switch I can use to change polarity. I assume if the lights are on then I have voltage between the phases. Both phases with voltage then I assume I am good and can turn on the curcuit breakers. I realize this may not always work on 3 phase power but I figure I have a 2 out of 3 chance of it working. On two phase power I thought it would always work
I left off the switches to turn on the J-1772 circuits. I do this with resistors going to ground from the signaling wire on the J1772 plugs.
I realize I may need signaling to tell the car I can charge at above 30 amps but I was taking this a step at a time.
Now that I look at the wiring diagram I should probably wire my signaling lights between the phases such that if they are both off, then the phases are the same flow.
Three phase is definately a problem. I tried two different stations tonight and they both appeared to be different 3 phase legs. With most charging stations being on 3 phase power there may be very few places I can use this. I will keep testing but as of today things are not looking hopeful.
The second challenge is GFI protection. If the GFCI detects more than a 4 mili-amp difference in legs it will trip. So if the two circuits do not have the exact same wire length and connection impedance the GFCI trips.