120 v. or 240 v.?

[WileyTheMan]

I would say either method puts stress on the car's charging system, quick high voltage or slow charging at low(er) voltage, so you might as well make it more convenient.

I charged my TM3 for the first year of ownership exclusively with a 120v/15a circuit (circuit is about 12 years old so not old construction, and charged consistently at 111v/12a) before finally getting a 240v/60a circuit installed with a Tesla WC. Here are my nutshell experiences:

Convenience was compromised with 120v charging. I knew that if I had to use the car for anything other than my daily commute, I was charging at a net loss overnight (I couldn't make up the energy used from an overnight charge). This meant more careful planning and was frankly a pain to deal with. There were times I had to leave the car plugged in the whole weekend, and could only use the car if I had no other choice.

It eventually fried my 120v plug. To be clear: I was forced to use a heavy gauge extension cord in order to charge and I know it's not recommended, but the nearest plug was just too far away. I would have to have hired an electrician to locate a plug closer, and at the time I could not afford deal with potential revised building requirements that might be required in order to get my permit for the work. And if I was going that route, I might as well wait to install something faster. Anyway, the cord would get warm while charging and eventually burned out the plug itself (not the circuit) within nine months. I didn't learn until later that the mobile charger has a thermal safety feature that prevents that from happening, but it won't work on an extension cord, apparently.

I am incredibly happy with the 240v circuit I had installed, and do not regret it at all. It addresses all my negative experiences with 120v charging. I can finally relegate the mobile charger back to what it was made for: Backup charging when you have no other sources.

 

[Kirby64]

This is a good callout. Assuming that the circuit is 20a with 12 gauge wire (this is not a given - I have seen a lot of houses with 15a circuits in the garage as I don't know that 20a is a requirement) then if you are just using the NEMA 5-15 adapter (likely because the receptacles are not even 5-20 capable even if the circuit is) then you still have 5a (4a continuous) of available headroom for "other" stuff.

I would say though that if you are charging at 16a continuous (using a 5-20 adapter) then that circuit is *100%* utilized. It is not that you still have 4a remaining for other stuff. That capacity is burned by the continuous load nature of the EV. So in the example of drawing 12a on the 20a circuit above, that 12a counts as 15a. So you have 5a remaining (or only 4a if you want to connect another "continuous" load).

I'm aware of the 16A cont. technically means the circuit is at full utilization and nothing else should be pulled from it... that being said, assuming (as I mentioned) that other loads are minor then limiting current on the UMC to 15A gives you enough headroom to use whatever else you want. Stuff like cordless drill battery chargers and lights. Obviously this assumes no large loads. Also this assumes 20a breaker/12ga wire/etc... It's a lot of ifs, I suppose.

That being said, 20A in a garage circuit is pretty easy to confirm. If that's the case, and the OP isn't driving hardly at all (like he says), 120V/12A will probably do him just fine.

At the same current, 240V charges nearly 3x faster than 120V; due to static overhead as pointed out by @SSedan above. Off the top of my head, this brings up 2 issues.
1) 120V is much less efficient. Even if you don't need to charge faster, if you have any aversion to waste then avoid it. (I hate unreasonable waste.)
2) Your car's on-board charger (and other vehicle systems that would otherwise be idle) will be in use 3x longer; tripling wear. In the short-term, this wouldn't be an issue; but over years of this kind of use, that wear will add up.

The 3x faster charging thing everyone quotes is a myth. At 15A (12A real), 240V charges at 11mph (according to Tesla). The actual charge rate of 120V-12A is ~5mph. Tesla's website is just flat out wrong. The delta is even less at 20A. 240V is 15mph, and actual from 120V-20A is 7mph (vs. 4mph as their website says).

Also, I'm not sure we have any conclusive evidence that charging for a longer period of time actually accelerates wear. These are electronics; they don't wear out like an engine or other mechanical components in the same fashion. People keep saying that, but I don't know of anyone that has any evidence that 120V charging is going to kill your car's inverter faster or something. It's just FUD.

 

[eprosenx]

The 3x faster charging thing everyone quotes is a myth. At 15A (12A real), 240V charges at 11mph (according to Tesla). The actual charge rate of 120V-12A is ~5mph. Tesla's website is just flat out wrong. The delta is even less at 20A. 240V is 15mph, and actual from 120V-20A is 7mph (vs. 4mph as their website says).

Also, I'm not sure we have any conclusive evidence that charging for a longer period of time actually accelerates wear. These are electronics; they don't wear out like an engine or other mechanical components in the same fashion. People keep saying that, but I don't know of anyone that has any evidence that 120V charging is going to kill your car's inverter faster or something. It's just FUD.

I think to have a rational conversation we need to either compare Tesla posted rates against Tesla posted rates, OR real world rates (with the same car, battery temperature and conditions, etc...) against real world rates. We should not cross those streams since it is apples to oranges.

When a Tesla says 5 mph on the screen, I think that can actually be 4.5 mph under the hood, while 3.49 miles per hour may just display 3 mph. So it is not granular enough to have this conversation accurately without more data.

I generally agree with you that total runtime on electronics is probably the wrong metric to look at. It really is probably more heat/cool cycles we are worried about since that is what puts stress on things (so total # of charge cycles).

But running a cooling pump is a mechanical device and so running it puts wear on it, so shorter runtimes are not a bad deal for the cooling pump (presuming it runs the whole time during charging?).

 

[M3BlueGeorgia]

If you are running wire, run 6 gauge wire, even if you only end up with 120v/20A, which IMHO is the minimum you should routinely charge off.

That way, if you subsequently choose to upgrade to 240v/50A, it just requires a change to the breaker and to the socket, without the considerable expense of re-running the wiring.

 

[daniel]

Again, thanks to everyone for all the information

The Model 3 doesn't have this limitation. Everything runs properly even if charging off 120V/12A.

Okay, thanks for that. I'm definitely going to have 240 v put in because it just seems like it should be available.

Do you need to utilize the power at the exact time it is generated (i.e. "no export" to the grid allowed), or does the power company let you export power during the sunny times and then pull it back later at a 1:1 trade, so while they won't "pay" you for overages, they allow you to time shift using the grid as a battery? I ask because if you need to utilize the power at the instant it is generated then you may want larger charging ability so you can have the car charge at just the right time of day. (are you going to have storage like Tesla Powerwall's or something?)

The Maui Electric Utility is already fully-subscribed for buy-back power. They will not buy my electricity. I told the contractor that in that case I'd be happy to just give them the electricity for the sake of the environment. But they will not take it. So I'll have 32 panels and two Powerwalls. Once my PowerWalls are full, the panels will only generate what the house is using. That's a waste of capacity, but so many people have solar on Maui now that the grid cannot accept more. I'm willing to accept this situation because I've wanted solar for so long and could never have it where I lived before.

Note that I'm living on a small island. There's no realistic situation where I'd ever need a full charge overnight.

 

[wycolo]

Consider cooling the garage passively by painting roof silver, placing foil thermal reflective layers in amongst the trusses, etc.
--

 

[EVDRVN]

The Model 3 doesn't have this limitation. Everything runs properly even if charging off 120V/12A. That being said, a 240V outlet is probably wise anyways assuming it's cheap enough to do. If it ends up costing you $500++ in conduit and wiring... maybe not worth it. As others have mentioned, 240V is going to be more efficient, but if the cost is going to be 100s of dollars you won't ever make up the difference in efficiency gains.



Assuming you have a properly wired outlet, 120V isn't inherently unsafe. With 12ga wiring and a 20A breaker backing it, you should be fine pulling 12A out of a multi-ganged outlet. If your concern is that it could be connected to 100 things in the house... well, that's a separate problem. I personally would see no issues with a 20A breaker servicing an entire garage (multiple outlets) being used to charge a Tesla at 12A. Hell, if you don't have a fridge or some other relatively high current draw device that is going to suck a bunch of power, you could charge at 16A. There's a reason for that 80% derating...

EVSE units should never to be on a shared circuit, they are not toasters or hair dryers. Since an EVSE uses the full capacity of a 15A outlet and near capacity of a 20A outlet for extended periods it is an exception device. A 20A circuit is preferred and code in some areas since 120V outlets are not designed for continuous loads for long periods of time. I have been in this industry for more than 15 years and can tell you that 120V charging is a bad idea because the vast majority of 120V circuits are compromised in some way or are on shared circuits and many breakers are worn or faulty. In addition continuous loads loosen breaker wires and outlet connection on 120V circuits. Installing a 20A 120C circuit is senseless as you can just do a 6-20 instead if 20A is your max bandwidth. 120V outlets wear fast, are removed more often, oxidize and create more resistance and then heat which causes cascading effects, I see this all the time. We could go on for a while about the issues of 120V charging without even considering the efficiency and other drawbacks. It is never a good idea to advocate against safety and unless you have a very good dedicated 20A circuit it makes no sense to put one in. Lastly a large number of "20A" outlets are on 15A breakers and even 14G wire as a result of lazy electrical work or ignorant home owners.

 

[Kirby64]

EVSE units should never to be on a shared circuit, they are not toasters or hair dryers. Since an EVSE uses the full capacity of a 15A outlet and near capacity of a 20A outlet for extended periods it is an exception device. A 20A circuit is preferred and code in some areas since 120V outlets are not designed for continuous loads for long periods of time. I have been in this industry for more than 15 years and can tell you that 120V charging is a bad idea because the vast majority of 120V circuits are compromised in some way or are on shared circuits and many breakers are worn or faulty. In addition continuous loads loosen breaker wires and outlet connection on 120V circuits. Installing a 20A 120C circuit is senseless as you can just do a 6-20 instead if 20A is your max bandwidth. 120V outlets wear fast, are removed more often, oxidize and create more resistance and then heat which causes cascading effects, I see this all the time. We could go on for a while about the issues of 120V charging without even considering the efficiency and other drawbacks. It is never a good idea to advocate against safety and unless you have a very good dedicated 20A circuit it makes no sense to put one in. Lastly a large number of "20A" outlets are on 15A breakers and even 14G wire as a result of lazy electrical work or ignorant home owners.

I'm not going to argue there aren't cases of shoddy workmanship or bad installations where 120V charging isn't a great idea, but you're arguing against strawman here. IF the backing is 14ga wire, and IF it's only a 15A breaker, and IF it's a multi-ganged outlet... then it's a bad idea. Well, no duh. You'd be exceeding max load of the circuit in that case... so it's not OK.

NEMA 14-50 circuits can have the exact same problems you present about oxidizing connectors, wearing spring clips, and faulty breakers. Literally the only thing that is better for a NEMA 14-50 is that the outlet itself should have far fewer plug/unplugs. If someone is seriously concerned about that, a $6 heavy duty 5-15 outlet for a 120V system is a single trip to Home Depot away and you can use a fresh new outlet. The same exact problems with undersized wiring and wrong breakers apply to larger circuits as well, you probably just don't see them as often because they're far less common.

Assuming a house was wired properly and is of relatively modern vintage (or the wiring is of modern vintage), what's the actual issue here? You seem to be advocating for a NEMA 6-20, which has every single issue you complain about except for the lack of shared circuit.

Also, an EVSE already derates itself to comply with continuous load. That's the whole point of 16A vs. 20A (or 12A vs. 15A). I'm not saying best judgment shouldn't be applied here in determining if your circuit is capable of handling the load, but you're making it sound like a 120V EVSE is going to always cause a house fire.

 

[efusco]

Daniel, I think, ultimately, it will be a good call to go with the 240v. Cost should be minimal since they're already working on the electical with the solar install. The location (Maui), certainly makes this a more interesting question because my 'gut' says 'always go 240v', but it is likely with the warm weather and limited driving distances that it will never be absolutely necessary.

As an aside, I'll be in the Islands in July (no plans for Maui right now though) in case you wanna meet for a drink somewhere.

 

[EVDRVN]

I'm not going to argue there aren't cases of shoddy workmanship or bad installations where 120V charging isn't a great idea, but you're arguing against strawman here. IF the backing is 14ga wire, and IF it's only a 15A breaker, and IF it's a multi-ganged outlet... then it's a bad idea. Well, no duh. You'd be exceeding max load of the circuit in that case... so it's not OK.

NEMA 14-50 circuits can have the exact same problems you present about oxidizing connectors, wearing spring clips, and faulty breakers. Literally the only thing that is better for a NEMA 14-50 is that the outlet itself should have far fewer plug/unplugs. If someone is seriously concerned about that, a $6 heavy duty 5-15 outlet for a 120V system is a single trip to Home Depot away and you can use a fresh new outlet. The same exact problems with undersized wiring and wrong breakers apply to larger circuits as well, you probably just don't see them as often because they're far less common.

Assuming a house was wired properly and is of relatively modern vintage (or the wiring is of modern vintage), what's the actual issue here? You seem to be advocating for a NEMA 6-20, which has every single issue you complain about except for the lack of shared circuit.

Also, an EVSE already derates itself to comply with continuous load. That's the whole point of 16A vs. 20A (or 12A vs. 15A). I'm not saying best judgment shouldn't be applied here in determining if your circuit is capable of hanling the load, but you're making it sound like a 120V EVSE is going to always cause a house fire.

An EVSE does not do any derating it tells the charger to honor the pilot signal. The assumption is that the outlet it is plugged into is installed properly. Yes there are issues with all outlets yet most 14-50's are properly installed not most 120V outlets. If you note in my posts I note that it is pointless to install a new 120V outlet and most existing have high probability of issues. In addition most 14-50 or 10-30 etc residential outlets do not see high cycles of unplugging and plugging in, 120V outlets do as a general rule. A large number of consumers do not know how to inspect or evaluate a proper circuit, even many "electricians", I know I have spoken to hundreds that should not be doing wiring and do not know what NEMA means. If any one has a proper 120V outlet to charge an EVSE then they can do 240V. Unless you are relegated to 120V then there is no point to using it regularly and if you must the things I outlined hold true.

 

[daniel]

Consider cooling the garage passively by painting roof silver, placing foil thermal reflective layers in amongst the trusses, etc.
--

Thanks for the thought, but my garage is part of the house. I'll have a contractor advise me on three options: 1. Install a duct from the house A/C into the garage; 2. Install a small A/C unit in the garage to cool it a few degrees; or 3. Do nothing and accept that the garage will always be war.

Daniel, I think, ultimately, it will be a good call to go with the 240v. Cost should be minimal since they're already working on the electical with the solar install. The location (Maui), certainly makes this a more interesting question because my 'gut' says 'always go 240v', but it is likely with the warm weather and limited driving distances that it will never be absolutely necessary.

As an aside, I'll be in the Islands in July (no plans for Maui right now though) in case you wanna meet for a drink somewhere.

Hi Evan. I'd love to get together for a drink (non-alcoholic for me) or lunch if you find yourself on Maui. And I'll invite you to come out on the water paddling an outrigger canoe as my guest. We'd meet at Maui Canoe Club at about 6:50 a.m. any morning Monday through Friday. Or you could be at my house at 6:30 and we'd walk over together along the beach, mostly. Canoes launch at 7:30 and stay out for an hour.

I don't know if you're still on PriusChat. I was going to post a question about my Prius over there a little while ago (an error message on the MFD) but I found the answer without having to post. And now that my Tesla Model 3 has arrived here, I've sold the 14-year-old Prius. I kept it as a second car when I was driving the Zap Xebra, which only had a 40-mile range, and when I was driving the Roadster (which was too small for about 1% of my driving) and I shipped it here for the winter because the condo didn't have a plug. And now I don't need it any more so I sold it. The end of an era. It was an awfully advanced system in 2004, but now it just seems like another gas-guzzler.

I've definitely decided on 240 v. The way I drive, 120 v. would be plenty fast enough, but after reading all the comments above, I'm going with 240 v. And thanks to everyone for all the help.