I have heard this said before (that car does not care about voltage level - only charge rate amps) though it surprises me a little. I would think that Tesla might use a "hint" about expected voltages for a given plug style as part of their safety mechanisms to cut off charging if voltage is too low (i.e. loose connections or other issues). But yes, based on what I have read I suspect you are right. [...] Does the Tesla have any concept of various voltages around the world (what nominal is), or does it just assume whatever the voltage is when you plug in to be "nominal" and it monitors the change to that value over the charging session for safety purposes?
You did answer your own question there. Weak or loose connections in the wiring will show themselves as a very resistive point in the circuit. To detect that, you won't see it if you just put a multimeter on it to read the voltage with no load on it. It will still say 120V or 240V with no current flowing. But then as you ramp up more and more current, it causes that resistive point to show a big voltage drop across it. So yes, that is what the car reads. It compares the initial voltage reading to the voltage when it increases the current. If the voltage sags a lot from that initlal no-load value, that shows the problem. And yes, the car does have a safety system where if it sees that voltage drop, it will try again at a much lower current to see if it's better. But as long as it stays steady near the initial value, it isn't going to matter whether that is 120 or 208 or 240.
Part of my concern about building random adapters is what might happen in the wrong hands... While building an adapter to allow you to plug in your car to a TT-30 receptacle but using a Tesla charging "tip" that was a 240v style plug could cause an adapter to exist that would be dangerous in other situations. Like a 240v motor that then gets plugged into 120v and pulls too many amps due to the lower voltage...
Yes, most people do highly recommend that you put some kind of marking label around these pigtail adapter cords that say "FOR TESLA CHARGING ONLY" or the like. It's for a very specific purpose, and you wouldn't just want to leave them around in a drawer for someone to find and misuse.
If you just have the NEMA 14-50 tip that comes with the car and you wanted to adapt that to TT-30 to plugin at a campground (and naturally you would need to limit the charging current manually in the car which is not great from a safety standpoint),
I already mentioned in my previous comment, why I
highly recommend to
only do these adapters from the same amp levels, so the car will always set the amps correctly without people having to remember to do it. I was on a trip and arrived really late at night, so I was kind of tired, and as I hooked up my setup of 14-50 to a 10-30 dryer outlet, it started to ramp up the current, and then I remembered right then that I needed to lower it, and quickly did so, but that can be easy to forget. What I am going to do to fix that is to cut the Neutral pin off of my Tesla 14-30 adapter so that it can fit into the pigtail adapter cords I have which have 14-50 receptacles on them. That way I will be appropriately using 14-30 to 10-30 or TT-30, so the amps will always be correct. So now, that was a great segue to your next question about what to do with Neutral.
Moreover, I have wondered about making adapters what to do with Neutral. If you just have the NEMA 14-50 tip that comes with the car and you wanted to adapt that to TT-30 to plugin at a campground (and naturally you would need to limit the charging current manually in the car which is not great from a safety standpoint), what would you tie the neutral in the adapter to? You are going from a four prong plug to a three prong plug. Leaving neutral connected to nothing could create a DANGEROUS situation if someone used the adapter for anything other than a Tesla. I guess the logical thing to do would be to tie Ground to Ground, Neutral to Neutral, one of the Hots to Hot, and the other Hot to Neutral. That way the Tesla would see 120v from Hot to Hot and then any other un-intended user of the adapter would see 120v from hot to neutral on one leg, and 0v from the other hot to neutral on the other leg. They would see only 120v from hot to hot (which is bad) but not perhaps as bad as having a floating neutral or seeing 240v from a hot to neutral...
Yes, that is an interesting thought. What is going on with a 4 prong to 3 prong conversion? Well, here is the secret. On all of those Tesla UMC adapter plugs they have, which have four prongs on them, like 14-50 or 14-30, one of them is a dummy that isn't connected to anything. It doesn't need anything but two pins for a voltage difference and a ground. Real outlets of that type are intended to have both 120V and 240V supplies available for use. But for charging a car, it only wants the highest voltage it can get. If there's 240V on two of the pins, it has no need for anything lower. So for making any of these converter pigtails, you never need to hook anything up to the Neutral pin of the 14-50 receptacle side, because the Tesla plug side is going to have no connection there anyway.
So for any of these 120 to 240 conversion examples, the 120V outlet source has its voltage coming from a Hot wire and a Neutral wire. So to make this work for the Tesla to see it, you need to take those two wires and connect them as if they were on the 240V pins of Hot1 and Hot2. And yes, obviously missing Neutral wires are a terrible idea and can blow things up if you try to plug a mobile home into it, so don't ever do that and mark your adapters "FOR TESLA CHARGING ONLY".
Do you know if anyone has published specs on the resistor values for various different available charge currents for the various adapters Tesla sells? I would like to learn more about what available steppings are!
Yes, here's a comment that lists them.
Any Solutions for 30/24 amp charging?
But really, making these homemade pigtail adapters are now kind of a "ye olden dayes" thing, now that the 2nd generation Tesla UMC is out. For one thing, Tesla makes a LOT more adapters for it now, so you can usually just buy the one you want, instead of needing to make one. Plus, third party places are now making authentic-ish adapters that plug right into the UMC for the some of these outlets that Tesla doesn't sell adapters for, like TT-30. EVSEAdapters.com is one of the most well known places for this. Here are some of their adapters for TT-30, 6-30, and L6-20. These will signal the car with the proper current limit automatically.
Tesla Model S / X / 3 Gen 2 Charging Adapters
So this building adapters stuff isn't really needed anymore.
