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Extension cord for supercharger help

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geordi

Mr Fusion V.1
Jun 14, 2022
805
584
Connecticut
Because of the amount of traveling that I do with a tool tray on the back of the car, I wanted to try and get an extension cord for supercharger use. Not looking for anything crazy just only need about 2 to 3 feet which is ridiculous how short these stupid cables are.

I managed to get all of the components including a complete Brand New cable off of a supercharger pedestal so I know the wiring is more than capable of handling the slower charge speed that my car has. Wired it up as a straight through cable, and when I connect up the cable to the supercharger first, my cord will activate the charging door. But for reasons I do not understand, it will not actually enable and start charging. It is straight through, every wire connects directly to the same pin at the other end. Does anyone have a suggestion on what I’m missing?
 
How big is your tool tray that you can't back into a charge spot? I have a bike rack and can still reach the port without an extension with my bike on the back. Might not always be easy but it's doable. Can't imagine you'll get much traction in helping with this as it seems sketchy.
 
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I suspect the Supercharger checks for any small unexpected voltage drop, similar to how AC charging is also monitored. Adding an extension would add some resistance that could be easily detected by a voltage drop that shouldn't occur. If this is true, the SC prevents charging as any small voltage drop could indicate a damaged cable or connector.
 
I’m sure everyone here is so incredibly concerned about my safety as to provide Snark rather than any individual information. But to calm your concerns, I’ve worked as a master electrician in film and television working with 400+ volts and three phase power coming from generators, feeding 8/0 cables running for hundreds of feet.

I’m using their exact same cables from a 250 KW supercharger that is connecting to a car that is limited to just 120 maximum charge rate because of the age. So the cable is more than capable. It’s also only 3 feet long, so the possibility of voltage drop being detectable in that short range is just about nonexistent.

You are correct there a supercharger monitors what is going on, but part of that and most of what it is monitoring is only the temperature in the plug. The cables are being utilized far beyond what the national electric code says they should be. Inside of a super charger cable is either parallel runs of one gauge cable, or multiple parallel runs of 10 gauge which is considerably smaller. This is what Tesla is pushing 400 V and 250kW through. That level of power creates significant heat in the wire, which is why you can feel it heating up when charging in the summer.

As for my ability to park within range of the charger, it is not guaranteed. Most locations have chosen to put a post right in the middle of the parking space right at the curb, while sitting back the charger at least a foot. That’s wasted room that when I am 2+ feet forward because of the tray, the cord does not want to reach. With an actual trailer, it is completely impossible. I know for a fact that I am not the only person using my Tesla with a trailer, this is not an unusual problem and there are zero suppliers that offer an extension cord that are in stock. I have been searching. I would happily buy one if I could. If you've got an option, feel free to link it and guarantee that they are in stock, with a $20 bet.
 
I’m sure everyone here is so incredibly concerned about my safety as to provide Snark rather than any individual information. But to calm your concerns, I’ve worked as a master electrician in film and television working with 400+ volts and three phase power coming from generators, feeding 8/0 cables running for hundreds of feet.

I’m using their exact same cables from a 250 KW supercharger that is connecting to a car that is limited to just 120 maximum charge rate because of the age. So the cable is more than capable. It’s also only 3 feet long, so the possibility of voltage drop being detectable in that short range is just about nonexistent.

You are correct there a supercharger monitors what is going on, but part of that and most of what it is monitoring is only the temperature in the plug. The cables are being utilized far beyond what the national electric code says they should be. Inside of a super charger cable is either parallel runs of one gauge cable, or multiple parallel runs of 10 gauge which is considerably smaller. This is what Tesla is pushing 400 V and 250kW through. That level of power creates significant heat in the wire, which is why you can feel it heating up when charging in the summer.

As for my ability to park within range of the charger, it is not guaranteed. Most locations have chosen to put a post right in the middle of the parking space right at the curb, while sitting back the charger at least a foot. That’s wasted room that when I am 2+ feet forward because of the tray, the cord does not want to reach. With an actual trailer, it is completely impossible. I know for a fact that I am not the only person using my Tesla with a trailer, this is not an unusual problem and there are zero suppliers that offer an extension cord that are in stock. I have been searching. I would happily buy one if I could. If you've got an option, feel free to link it and guarantee that they are in stock, with a $20 bet.
My post was not entirely snark. It was mostly warning. I've seen posts where people were way in over their heads - things like "I bought a salvaged car, how do I get it working again?" with a follow-up question of "What does 'root access' mean?". It's also not hard to find pictures of charred charging equipment.
Anyway, I wish you luck.
 
What does the female end of your apparatus look like, and how did you create it? Pictures of this frankenbeast are definitely in order.

I’m wondering if there’s some sort of continuity check or other sensor in the head of the SC cable that isn’t getting the signal it needs from your extension.

Should be possible, EVSEadapters sells one…

 
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EVSE hasn't been in stock for months. Nobody has them.

The female end is a socket I scavenged from a Lectron J1772 / Tesla adapter that allows J1772 cars to charge from a Tesla mobile connector or HPWC.
Originally there was one pin (one of the two smaller pins) that was not connected. I found the matching wire in the harness from the Supercharger end (IIRC it was the proximity wire) and soldered it to that open pin. All the others are connected one to one, straight through.

For anyone wondering - the J1772 spec and the Tesla spec are only a shape change different. The "normal" J1772 is only capable of up to 12kw, yet Tesla runs the same connectors to 250kw. The difference is whether you allow higher temperatures from the power transfer.
 
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...You are correct there a supercharger monitors what is going on, but part of that and most of what it is monitoring is only the temperature in the plug. ...
I would find it hard to believe Tesla doesn't also monitor the voltage and current at the Supercharger. They clearly measure the voltage in the car, so it would be very easy to check the voltage drop if both the car and Supercharger are monitoring voltages. It might even be self-calibrating - i.e. with multiple cars, it can easily determine the normal voltage drop. When an extension is added, under current, it should be easy to detect the difference. All hypothetical, but since it doesn't work, seems like a possible cause. One test would be to make a 2" extension and see if that works. If so, then my theory seems more likely with a 3-foot extension.
In various diagnostic screens, Tesla shows voltages to 5 places, suggesting a 16-bit A/D measurement. For 500V, this would provide about 7mV resolution. It would seem the standard cable would have a lot more than 7mV drop, as might your extension too.
 
@vcor - I didn't know that it would show the voltage to that resolution, so maybe... BUT there are also a lot of reasons that the voltage might be different than expected, dirt / corrosion in the plug as one plausible reason. I don't have the math skills to calculate the drop across a 3 foot cable, but just trying to do an ohm check on it, I wasn't reading anything on the highest resolution of my probe.

I did voltage drop calculations for a solar installation (used an online system though) and for the system I built of 130 volts and 8 amps, the loss for a 12 gauge cable at 40 feet was about .1 volts. For shorter cables (like from the controller to the battery and at only 12v)... The drop was less than the calculator could tell me.
 
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@vcor - I didn't know that it would show the voltage to that resolution, so maybe... BUT there are also a lot of reasons that the voltage might be different than expected, dirt / corrosion in the plug as one plausible reason. I don't have the math skills to calculate the drop across a 3 foot cable, but just trying to do an ohm check on it, I wasn't reading anything on the highest resolution of my probe.

I did voltage drop calculations for a solar installation (used an online system though) and for the system I built of 130 volts and 8 amps, the loss for a 12 gauge cable at 40 feet was about .1 volts. For shorter cables (like from the controller to the battery and at only 12v)... The drop was less than the calculator could tell me.

I agree. If superchargers refused to work due to a cabling/resistance discrepancy measured in millivolts, the user experience at stations would be abysmal. That’s clearly not the case. This idea is a dead end.
 
@vcor - I didn't know that it would show the voltage to that resolution, so maybe... BUT there are also a lot of reasons that the voltage might be different than expected, dirt / corrosion in the plug as one plausible reason. I don't have the math skills to calculate the drop across a 3 foot cable, but just trying to do an ohm check on it, I wasn't reading anything on the highest resolution of my probe.

I did voltage drop calculations for a solar installation (used an online system though) and for the system I built of 130 volts and 8 amps, the loss for a 12 gauge cable at 40 feet was about .1 volts. For shorter cables (like from the controller to the battery and at only 12v)... The drop was less than the calculator could tell me.

Dirt and corrosion I would think would be the most likely thing. A good connection makes an amazing difference. Some of the older 85s have seen quite a drop in supercharging speed from simply having dirty connectors. But I would think with your experience you would have checked that. So I'm still wondering. I do want to know if you get this resolved! Please let us know.
 
Dirt and corrosion I would think would be the most likely thing. A good connection makes an amazing difference. Some of the older 85s have seen quite a drop in supercharging speed from simply having dirty connectors. But I would think with your experience you would have checked that. So I'm still wondering. I do want to know if you get this resolved! Please let us know.

The cable / supercharger handle that I got was new / unused, so there shouldn't be any issue with corrosion there. The handle was definitely not bashed around and scratched up from usage in lots of cars.

Did you try changing the order you plug things in?

I believe I did, the car will recognize an un-energized cable insertion and not be happy about that... But I don't believe it triggers the SC end to power up. I will try that again a little later today just to be sure.
 
In general I would suggest you look for and use a Supercharger stall that allows for pull in parking rather than back in. I think most recent Superchargers have at least one stall like this for people with trailers so they don't have to disconnect the trailer to charge. Maybe it isn't available in all Superchargers depending on the layout of the parking lot.

I would not be surprised if what you are trying to do is going to be tricky or impossible. For example, I think some of the Supercharger cables are liquid cooled based on the high current they are running and an extension cable wouldn't be able to handle it without heating up and having increased resistance. The Supercharger probably has all sorts of failsafe checks to make sure some odd faults do not occur that might detect an extension cable as a fault.
 
For anyone wondering - the J1772 spec and the Tesla spec are only a shape change different. The "normal" J1772 is only capable of up to 12kw, yet Tesla runs the same connectors to 250kw. The difference is whether you allow higher temperatures from the power transfer.

I know very little about this subject matter so please take this with an appropriately sized grain of salt. I am not 100% sure this is true as the Tesla to J1772 adapter will work for destination/wall chargers but does not work at superchargers. There has to be something different being done with the supercharger that is not being accounted for in the standard/traditional Tesla to J1772 adapter.

Perhaps see if you can locate the pinouts for a Tesla NACS adapter (their new adapter which enables supercharging to non-Tesla vehicles).
 
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