Dual-circuit wall-plug charger

[KarenRei]

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.

For $9k (probably $11k European prices) you might as well request that I build public charging stations. Seriously, that's more than a quarter the price of the entire car. Without actually solving the problem on the far end ("And when I drive even further?" - this isn't a small country, the Ring Road alone is 1332km), while doing absolutely nothing on the near end.

And what solution are you thinking of?

 

[jkn]

For $9k (probably $11k European prices) you might as well request that I build public charging stations. Seriously, that's more than a quarter the price of the entire car. Without actually solving the problem on the far end ("And when I drive even further?" - this isn't a small country, the Ring Road alone is 1332km), while doing absolutely nothing on the near end.

And what solution are you thinking of?

I expect somebody to build public charging network. Government?

Do you promise that electrician checks your connections? I'm not electrician, so check is needed.

 

[KarenRei]

I expect somebody to build public charging network. Government?

"Expecting someone to build it" will do a fat lot of good for my M3 until it actually exists.

Do you promise that electrician checks your connections?

What connections? If you're talking about wiring connections, I know how to use a screw connector - I'm not a moron.

 

[eladts]

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.

NEMA does have a socket for 240V 20A, the NEMA 6-20. These sockets are very common in motels for connecting the AC units. The Model 3 UMC even has an adapter for it available. There is no need to improvise.

 

[jkn]

"Expecting someone to build it" will do a fat lot of good for my M3 until it actually exists.



What connections? If you're talking about wiring connections, I know how to use a screw connector - I'm not a moron.

M3, so we have at least a year before you have it.

I found more serious problem: Assuming you want to pull total 20 A from 2 wires. If one wire has 1.0 ohm resistance and another 0.1 ohm, you will get 1.82 A from first and 18.18 A from second. I cannot imagine practical solution for this. Transformer might work, but a 230 V 8 kW isolation transformer weights 42 kg. Not practical. Electronic device could pull equal current from two sources, but it is too difficult (=expensive) to make.

Smallest (=cheapest) electrical connection available here is 3*230V*25A = 17 kW

 

[KarenRei]

I found more serious problem: Assuming you want to pull total 20 A from 2 wires. If one wire has 1.0 ohm resistance and another 0.1 ohm, you will get 1.82 A from first and 18.18 A from second.

This is not a new problem; it's been discussed earlier in the thread (the worst case, of infinitely more resistance on one path than the other, means your max charge rate is no better than one socket). The effect of imbalanced resistance in the wall is reduced (although not eliminated) by 1) using identical extension cords (which act as identical inline resistors), and 2) the fact that Tesla automatically ramps back charge currents if the total voltage drop is too excessive (voltage drop will increase the greater the resistance in a given path). Technically one could tune the resistance on each path to be equal, but that's complicating things. The more the voltage drop in the extension cords exceeds the voltage drop in the wall (so long as it's not excessive), the more equal the flow will be.

Now, if there was an imbalance between the resistance in the different wires on a given circuit then that would be a problem, as live and neutral currents wouldn't be equal and it should throw a breaker. But that shouldn't happen unless the wiring is bad.

Smallest (=cheapest) electrical connection available here is 3*230V*25A = 17 kW

Once again people keep diverting to the topic of rewiring the main panel and installing new hardware, as if everyone has the right to rewire where they live, or as if anyone has the right to rewire when they visit another place. Can we please stop with the red herring?

 

[KarenRei]

Even just minor thinking about the variable resistance presents simple solutions. E.g. dual-line (live+neural) variable resistor (dimmer / voltage regulator / thermostat, etc, rated for 30+A at up to 250VAC) and a LCD ammeter on each line. Set charge current to ~15A with resistance at minimum (if on 16A breaker - ours are rated to 100%, not 80% like in the US), balance the resistance so that the ammeters read equal on both lines, then boost the charge current to 30.

Or even simpler: forget the ammeters and just use a voltage regulator on each line set to the same value, with said value being slightly below the minimum normal wall voltage measurement.

But again, resistance isn't the issue that concerns me. It's the symmetric plugs that are the problem. Connecting live/neutral and neutral/live is a Bad Thing.

 

[jkn]

Even just minor thinking about the variable resistance presents simple solutions. E.g. dual-line (live+neural) variable resistor (dimmer / voltage regulator / thermostat, etc, rated for 30+A at up to 250VAC) and a LCD ammeter on each line. Set charge current to ~15A with resistance at minimum (if on 16A breaker - ours are rated to 100%, not 80% like in the US), balance the resistance so that the ammeters read equal on both lines, then boost the charge current to 30.

Or even simpler: forget the ammeters and just use a voltage regulator on each line set to the same value, with said value being slightly below the minimum normal wall voltage measurement.

But again, resistance isn't the issue that concerns me. It's the symmetric plugs that are the problem. Connecting live/neutral and neutral/live is a Bad Thing.

Current will split itself so that voltage loss is same on both routes. So I don't see how you could use voltage regulators. You need two regulators set up to provide constant current. I doubt those exist for 230 VAC. Even worse: It is easy to avoid connecting neutral to live, but my solution does not tell which is live. That information is needed for regulator. (To protect fuses you need to regulate live, not neutral current.)

Normally if neutral line is disconnected, device stops operating. In this case if one neutral line is disconnected, another carries double current. There is small possibility that it overheats and starts a fire. So I guess you need to regulate neutral current also...


I doubt Tesla ramping back charge current is sensitive enough to help. In my example voltage drop would be only 1.82 V. Current would go mainly through better wire. Your system would need fast fuses in both live and neutral lines to protect house circuits. Slow 15 A fuse does not protect fast 16 A one.

I made test with a 2 kW heater. 9 V drop measured from same extension cord. 6 V drop measured from 3phase connector (different fuse, not used by heater). So most resistance is before last fuse box! Only 0.35 ohm after fuse, 0.7 ohm before it (main fuses, electricity meter, line to transformer)!

I repeat my example with 0.2 ohm cables added. Resistances, after fuses are 0.3 ohm and 1.2 ohm. Combined resistance 0.24 ohm, V drop with 30 A is 7.2 V.
In 0.3 ohm route current is 24 A, in 1.2 ohm route 6.0 A. Identical extension cords will help, but not enough.

 

[wycolo]

> why there is so much interest in doing 220v charging?

Same current @ 2x voltage = twice the kw. So twice the power into your EV battery using the same wires/same current.

Test the circuit you plan to use by plugging in a toaster and timing it. If there is a poor connection somewhere, typically in a wire nut, the surge of current often will melt the poor connection in the wire nut and the circuit goes dead. In that case you have to track down and fix. If the toaster works normal compared to running it on your kitchen counter then you are all set to use this new circuit for whatever. If you install new wiring always test with a heavy load like a toaster; a voltmeter or LED tester does not test for current carrying capacity.
--

 

[KarenRei]

Even worse: It is easy to avoid connecting neutral to live, but my solution does not tell which is live. That information is needed for regulator. (To protect fuses you need to regulate live, not neutral current.)

You've mentioned your solution several times, but not actually mentioned what it was.

I made test with a 2 kW heater. 9 V drop measured from same extension cord. 6 V drop measured from 3phase connector (different fuse, not used by heater). So most resistance is before last fuse box! Only 0.35 ohm after fuse, 0.7 ohm before it (main fuses, electricity meter, line to transformer)!

The breakers themselves have some measurable resistance as well. Haven't measured personally, but I understand it's usually something like 0,1-0,2 ohm or so.

Identical extension cords will help, but not enough.

Well, if you're comparing a normal house socket with some high power 3-phase socket, of course you're going to get a huge resistance difference. Either way, I see nothing wrong with tuning the resistance via variable resistors and ammeters. Do you? So long as they're rated for the voltage and current, and the resistors adjust both the live and neutral (a quick search reveals such parts for sale on ebay)

 

[KarenRei]

> why there is so much interest in doing 220v charging?

Same current @ 2x voltage = twice the kw. So twice the power into your EV battery using the same wires/same current.

And it's even more extreme than that. With low power charging, you can lose a good bit of power to overhead, leaving less left over for charging. If you have to do heating as well, the problem gets much worse. MS for example, when heating can draw 6kW for the cabin heater and 6kW for the pack. Good luck getting anything close to that over a schuko. :Þ

Test the circuit you plan to use by plugging in a toaster and timing it.

Indeed - I was actually thinking about using a heat gun or a couple blow driers, but the effect is the same. Testing with cheap hardware first.

 

[ccdisce]

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...

Awwww go easy on the uncle Albert.

You should be able to easily identify which wires should be connected together using a working lamp or a hair dryer or if possible a digital voltmeter.
If you connect one lead of the lamp to one wire from the first pair .... any wire and any wire from the second pair the possible outcomes are::

lamp ON .......the lamp is across 240V don't let the wires touch

lamp OFF ........ the lamp is across 2 wires in phase so it should be ''safe'' to hook them together
and so for the other 2 wires
I you move to another 2 outlets you will have to redo the test.

You could use a 240VAC DPDT relay to do the detection and if it gets activated it would flip the wires around however a heavy duty switch or a relay will have to be added in series with one of the pairs prior to connecting them together.

remember one hand behind your back, thick rubber boots on a dry surface and stay safe.

 

[jkn]

You've mentioned your solution several times, but not actually mentioned what it was.



The breakers themselves have some measurable resistance as well. Haven't measured personally, but I understand it's usually something like 0,1-0,2 ohm or so.



Well, if you're comparing a normal house socket with some high power 3-phase socket, of course you're going to get a huge resistance difference. Either way, I see nothing wrong with tuning the resistance via variable resistors and ammeters. Do you? So long as they're rated for the voltage and current, and the resistors adjust both the live and neutral (a quick search reveals such parts for sale on ebay)

I'm not certain you can do this safely, so wanted you to contact an electrician. I was also curious if anybody else figures this. ccdisce got close, but I would use two relays and I don't see any need for any other switch. Relays need perhaps 12 VDC to operate, so not very simple.

This is an old house, so real fuses instead of breakers. That 3-phase connector is protected by 10 A fuses, so it is not very high power. Exactly same type of fuse than nearby 1-phase connector I measured resistance. I did not measure resistance of 3-phase connector. I used it to get voltage drop (resistance) common to all connectors in the house. Remaining 0.35 ohm is specific to that 1-phase connection + extension cord. New 16 A line would probably have lower resistance. Single poor connection could increase resistance and send majority of current other route. In worst case this would send 30 A current through wire meant for 16 A.

If you add 1 ohm via variable resistor with 15 A current, you get 15*15 = 225 W heat in that resistor. Can you find tunable resistor for that? I you are certain differences are always less than 0.2 ohm you still need 15A*15A*0.2ohm = 45.0 W resistor. A problem remains one connector could have extra resistance in live wire another in ground wire. Unbalanced ground current could over heat wire. Not very likely, because current will go mainly through better wire. Since result could be fire, even small probability must be taken seriously.

Situation can suddenly change, so you must have circuit breakers on all 4 wires.

 

[ccdisce]

I'm not certain you can do this safely, so wanted you to contact an electrician. I was also curious if anybody else figures this. ccdisce got close, but I would use two relays and I don't see any need for any other switch. Relays need perhaps 12 VDC to operate, so not very simple.

This is an old house, so real fuses instead of breakers. That 3-phase connector is protected by 10 A fuses, so it is not very high power. Exactly same type of fuse than nearby 1-phase connector I measured resistance. I did not measure resistance of 3-phase connector. I used it to get voltage drop (resistance) common to all connectors in the house. Remaining 0.35 ohm is specific to that 1-phase connection + extension cord. New 16 A line would probably have lower resistance. Single poor connection could increase resistance and send majority of current other route. In worst case this would send 30 A current through wire meant for 16 A.

If you add 1 ohm via variable resistor with 15 A current, you get 15*15 = 225 W heat in that resistor. Can you find tunable resistor for that? I you are certain differences are always less than 0.2 ohm you still need 15A*15A*0.2ohm = 45.0 W resistor. A problem remains one connector could have extra resistance in live wire another in ground wire. Unbalanced ground current could over heat wire. Not very likely, because current will go mainly through better wire. Since result could be fire, even small probability must be taken seriously.

Situation can suddenly change, so you must have circuit breakers on all 4 wires.

jkt,

You are correct as providing 12VDC to activate the relay would be a real pain to supply in a 240VAC environment, however
I did mention above that you would need 1 240VAC double pole double throw relay to function as a tester/sensor and 1 switch to 'automatically' switch over both wires of the second pair if they are out of phase relative to the first pair. The switch ( starting from the OFF position )mentioned is a separate device gives the relay time to switch thus preventing a transient short circuit which could be caused by the relay needing time to flip the second pair of wires over to the normally open contacts of the relay.

In the unpowered state the normally open contacts of the relay will be wired over to the other pair via this switch which should be set to the open state just in case the relay needs to switch over the wires.
The thought experiment I did was what if ;

a. The breakers are OFF and both inputs to this box are plugged in simultaneously.....no problem
b. Both breakers are turned on:
1. If the switch is ON and the relay is required to activate you will have a short circuit for about the time that the relay takes to switch about 100mS which may or may not trip the breakers, the moment the breakers trip the relay would go back to the state you do not want to be in.
2. If the switch is OFF the relay would switch and give you a green light indicating that it is now OK to throw that Switch.

As you pointed out the disparity in the impedances of the 2 fused circuits we are dealing with here pose a problem and I would at least replace the fuses with new ones.

 

[KarenRei]

You are correct as providing 12VDC to activate the relay would be a real pain to supply in a 240VAC environment

Dual-coil latching relay and diodes? Current on one route = latch, current on the other route = unlatch. Resistors to bring it down to the operating voltage. Should probably diagram it to see if it'd be that simple or not...

a. The breakers are OFF and both inputs to this box are plugged in simultaneously.....no problem
b. Both breakers are turned on:
1. If the switch is ON and the relay is required to activate you will have a short circuit for about the time that the relay takes to switch about 100mS which may or may not trip the breakers, the moment the breakers trip the relay would go back to the state you do not want to be in.
2. If the switch is OFF the relay would switch and give you a green light indicating that it is now OK to throw that Switch.

What about , instead of a switch, a slow DPST after the DPDT to eliminate the possibility of user error? Same latching mechanism as above perhaps?

If you add 1 ohm via variable resistor with 15 A current, you get 15*15 = 225 W heat in that resistor. Can you find tunable resistor for that?

Something like these? Though they seem to be ~10 ohms, might be hard to make fine adjustments:

AC power rheostat 110-220VAC 4000W open frame ACD-O220-4000
AC power rheostat with bias 110-220VAC 4000W with enclosure ACD-E220-4000L | eBay

They also mention "proper cooling", although don't define at what level of resistance you need what level of cooling. Clearly there's some point at which the heat sink alone would be sufficient, and some transition point where you'd need a fan.

A problem remains one connector could have extra resistance in live wire another in ground wire.

I assume you mean neutral, not ground. In theory that shouldn't happen, but yes, breakers on all four wires is quite reasonable. Ideally I'd not want some gigantic breaker box-style breakers. I found these pushbutton ones:

AC 125V/250V 16A Red Reset Button Overload Protector Circuit Breaker 2Pcs | eBay

... but the trip times are awfully slow. I'd hate to have to use fuses and need to replace them if something goes wrong. Found some 15A ones that aren't slow, such as:

https://www.amazon.com/Zephyr-Circu...90665&sr=8-3&keywords=push+button+breaker+15a

There's also the issue that technically there's no requirement that all sockets be on 16A circuits. That said, "normal" sockets here generally are, and high-power appliances often assume that they are. For example, in my place, the only schukos not on 16A are in the kitchen (13A). And it's easy enough to check just by looking at the breaker panel.

 

[ccdisce]

I think I have a 120VAC relay here an maybe a suitable switch to build a prototype or maybe I can use an optical relay...... hmmm.
I have a couple of extension cords, one is pretty bad and can be used to simulate one feed being more ' resistive' than the other, not as bad as totally resistive as in open cct.

I have gone ahead and started to draw up an Eagle Schematic . Do you have Eagle loaded on your PC? as I could send you the .sch file.

 

[KarenRei]

I'm a Linux user; I had actually started diagramming the circuit in KTechLab before realizing that KTechLab doesn't have relay support :Þ Turns out I was wrong, Eagle actually is available for Linux. Downloading now

ED: Installed, and seems to work. Have never used Eagle before, but shouldn't be too hard to figure out

 

[jkn]

Dual-coil latching relay and diodes? Current on one route = latch, current on the other route = unlatch. Resistors to bring it down to the operating voltage. Should probably diagram it to see if it'd be that simple or not...



What about , instead of a switch, a slow DPST after the DPDT to eliminate the possibility of user error? Same latching mechanism as above perhaps?



Something like these? Though they seem to be ~10 ohms, might be hard to make fine adjustments:

AC power rheostat 110-220VAC 4000W open frame ACD-O220-4000
AC power rheostat with bias 110-220VAC 4000W with enclosure ACD-E220-4000L | eBay

They also mention "proper cooling", although don't define at what level of resistance you need what level of cooling. Clearly there's some point at which the heat sink alone would be sufficient, and some transition point where you'd need a fan.



I assume you mean neutral, not ground. In theory that shouldn't happen, but yes, breakers on all four wires is quite reasonable. Ideally I'd not want some gigantic breaker box-style breakers. I found these pushbutton ones:

AC 125V/250V 16A Red Reset Button Overload Protector Circuit Breaker 2Pcs | eBay

... but the trip times are awfully slow. I'd hate to have to use fuses and need to replace them if something goes wrong. Found some 15A ones that aren't slow, such as:

https://www.amazon.com/Zephyr-Circu...90665&sr=8-3&keywords=push+button+breaker+15a

There's also the issue that technically there's no requirement that all sockets be on 16A circuits. That said, "normal" sockets here generally are, and high-power appliances often assume that they are. For example, in my place, the only schukos not on 16A are in the kitchen (13A). And it's easy enough to check just by looking at the breaker panel.

Because rheostat is so small, it cannot convert extra voltage (*current) to heat as resistor does. It limits current by switching it on/off rapidly. What does Tesla charger do, when it sees this kind of input? LC filter after rheostat might help.


ccdisce's polarity switch need only one 12 VDC supply. (I understand it now Mine needs 2, but does not need delay:

You have plug A with wires A1 & A2 and B with B1 & B2.

Relay 1:
Voltage between A1 & B1 is converted to 12 VDC and used to close relay connecting A1 with B2 and A2 with B1. If there is no voltage difference between A1 & B1, it does nothing.

Relay 2:
Voltage between A1 & B2 is converted to 12 VDC and used to close relay connecting A1 with B1 and A2 with B2. If there is no voltage difference between A1 & B2, it does nothing.

 

[jkn]

I'm a Linux user; I had actually started diagramming the circuit in KTechLab before realizing that KTechLab doesn't have relay support :Þ Turns out I was wrong, Eagle actually is available for Linux. Downloading now

ED: Installed, and seems to work. Have never used Eagle before, but shouldn't be too hard to figure out

Does Tesla charging station make AC to DC conversion? If so, 3-phase charging station could have 3 single phase converters in parallel. Perhaps it could be used with 2 (or 3) single phase circuits (perhaps with modifications). This does not produce as good DC as 3-phase, because zero points in 3-phase don't happen at same time.


gnuplot
plot sin(x), sin(x+pi*2/3), sin(x+pi*4/3) #3phase
plot abs(sin(x)), abs(sin(x))+abs(sin(x+pi*2/3))+abs(sin(x+pi*4/3)) #DC current from single phase and 3phase