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DIY UMC gen 2 extension, how many wires?

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Since extension cords are out of stock everywhere, I’m looking for a way to do it myself. I found a few cords on eBay that are cut off from other UMC chargers, but they have either 5 wires or 8 wires. This video shows that the cable has 7 pins
. Does that mean the cord on ebay is not genuine or it’s from another old connector? Should I just buy another UMC and cut off the cable from that one?
 
While it's usually not recommended to use an AC extension cord with a mobile connector, I find it just on this side of wholly unacceptable for somebody to construct a DIY extension cord for the Tesla Proprietary Connector. EVSEadapters.com has those extensions in their catalog, but as you say, they are out of stock for every one if the listed lengths they sell. I would contact them and enquire how many wires they have in their extensions cords if you insist on proceeding with this project.

It would be much safer and infinitely easier to accomplish the extension by using an AC cord. Find one which has a large enough gauge wire for whatever outlet you are using (14-50, 10-30, etc.). Those are easy enough to find on Amazon. You may be circumventing a safety circuit that is built into the Tesla NEMA adapter; there's a temperature sensor in those adapters which monitors the heat of the outlet. Using an extension cord places that sensor away from the source outlet.
 
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While it's usually not recommended to use an AC extension cord with a mobile connector, I find it just on this side of wholly unacceptable for somebody to construct a DIY extension cord for the Tesla Proprietary Connector. EVSEadapters.com has those extensions in their catalog, but as you say, they are out of stock for every one if the listed lengths they sell. I would contact them and enquire how many wires they have in their extensions cords if you insist on proceeding with this project.

It would be much safer and infinitely easier to accomplish the extension by using an AC cord. Find one which has a large enough gauge wire for whatever outlet you are using (14-50, 10-30, etc.). Those are easy enough to find on Amazon. You may be circumventing a safety circuit that is built into the Tesla NEMA adapter; there's a temperature sensor in those adapters which monitors the heat of the outlet. Using an extension cord places that sensor away from the source outlet.
An AC extension cord would put the UMC unit outside under the sun in my situation. QCcharge is a company that used to do this kind of extension but they said they don’t have any more cord. I think just extending the wire itself is ….. I don’t wanna say safer….. but less janky than the extension cord they have on EVSAadapters.org. But still, I understand it’s not ideal regardless.
 
An AC extension cord would put the UMC unit outside under the sun in my situation. QCcharge is a company that used to do this kind of extension but they said they don’t have any more cord. I think just extending the wire itself is ….. I don’t wanna say safer….. but less janky than the extension cord they have on EVSAadapters.org. But still, I understand it’s not ideal regardless.
I was going to say that the EVSEadapter.com Tesla extension cord looks pretty professional (photos on their web site; I've not seen one in person) but reading one of the reviews a person said it wasn't as pictured and what was received looked like a prototype. The QCcharge cord has a slightly different design for the receptacle but again, looks like a good implementation.
 
I was going to say that the EVSEadapter.com Tesla extension cord looks pretty professional (photos on their web site; I've not seen one in person) but reading one of the reviews a person said it wasn't as pictured and what was received looked like a prototype. The QCcharge cord has a slightly different design for the receptacle but again, looks like a good implementation.
They make a similar extension, but you can also send your umc in and they will splice and extend it the way I’m trying to do
 
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Been thinking about doing this myself and grabbed the screen above from a YouTube teardown of the Gen2 UMC. In addition to the standard J1772 wires, I believe there's a 3.3V source for the handle open button and handle temperature sensor wire.

To the naysayers, the reason I'd want to do it this way is actually for safety. Extending after the UMC provides GFI and keeps the cable in an unpowered state until plugged into the car. This is inherently much safer than running an always hot non-GFCI protected extension cable to the UMC and then leaving the UMC sit somewhere exposed to the elements.
 
Been thinking about doing this myself and grabbed the screen above from a YouTube teardown of the Gen2 UMC. In addition to the standard J1772 wires, I believe there's a 3.3V source for the handle open button and handle temperature sensor wire.

To the naysayers, the reason I'd want to do it this way is actually for safety. Extending after the UMC provides GFI and keeps the cable in an unpowered state until plugged into the car. This is inherently much safer than running an always hot non-GFCI protected extension cable to the UMC and then leaving the UMC sit somewhere exposed to the elements.
The ones arguing safety on the other side is because there are plenty of proven safe pre-manufactured extension cords for 240V outlets that can be purchased outright. Maybe you are skilled enough, but I would not trust any random person to be able to safely construct a extension cord on the TPC side, and there are more points of possible failure, and some failure modes that are much harder for the user to detect (for example the signal wires) vs a dumb extension cord.
 
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View attachment 839488

View attachment 839489

Data point: had my Leviton 6-50 outlet melt on me recently. I haven't seen many recommendations for heavier duty 6-50 outlets. Any suggestions?

Note that I was pulling the full 40 amps from a Gen1 UMC. Honestly it seems like 32 amps is just a safer way to go unless you hardwire a wall connector given how hard it is to find a decent 50 amp receptacle. Also, was using a 6 gauge 6-50 extension cord which explains why things melted instead of the UMC derating.

Above (from thread here) is an example of what can happen using "proven safe" pre-manufactured extension cords. The UMC has a temperature sensor in the plug itself which allows it to sense if the plug or receptacle is getting too hot and start reducing power. In theory, 50 amp rated cords and outlets should be able to handle 40 amps continuous. In practice, this is often not the case.
 
Above (from thread here) is an example of what can happen using "proven safe" pre-manufactured extension cords. The UMC has a temperature sensor in the plug itself which allows it to sense if the plug or receptacle is getting too hot and start reducing power. In theory, 50 amp rated cords and outlets should be able to handle 40 amps continuous. In practice, this is often not the case.
Leviton is the common outlet that fails because it is not industrial rated (which is what Tesla calls for) and as mentioned it only has half a contact point that other outlets have. Yes, as others mentioned you do defeat the temp sensor on the outlet side if you use an extension. However, regardless, anyone can easily buy an industrial rated outlet and an industrial cord with beefier conductors.

The same can't be said of anyone making their own TPC extension cord, it's not nearly as straight forward as that (which is why OP has to ask). As I said, if you are a skilled enough DIYer, you can probably do it (even without instructions), but I don't trust any average person to be able to do it.
 
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I have zero issues using a quality extension cord going to my MC with my non-limited NEMA 14-50 to NEMA 5-15/20 custom made adapter. My Terrabloom 14awg SJOOW cord is super pliable, has quality nickel plated connectors on each end, 105°C rated insulation, lighted receptacle end that supports 240V use, and can sustain 24A of charing indefinitely without rising above 80°C. But if that not warm and fuzzy enough for some, this is how you solve the extension problem:

Cut the NACS handle off the end of of your MC (but leave 4" of the coord on and ship it to me to experiment with - i'll pay for the costs :) ). Grab a second used MC (FB Marketplace, NextDoor, LetGo, CL, eBay, etc), and cut the coord off tight at the relay box side (again, leaving 4" and send to me :), then splice both cords in the center using high quality compression fittings for every wire (do NOT use solder anywhere). To secure the splice "nodule" that is now in the middle of the cord, thinly cover it with hot glue, then slip high-quality 3M heat shrink tubing over it. When you heat the tubing to shrink it, the hot glue will re-melt and squish out the ends of the heat shrink tubing along with all the air inside, creating a dependable water seal. Trim excess hot glue and you're in business with a 38' long MC.
 
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