As a backup, I would like to use a generator to charge my Tesla 3. First thing was to get an adapter for the 240 plug to fit into the 240 outlet of the generator. Done. However, when trying to charge (reducing the charge rate to 24V to ensure no problems or breaker trips), the warning light came on that the plug is not grounded. Since I have a ground nut on the generator I bought a lightening rod (solid copper) and connected it with the recommended wire weight, but this still did not work. Now I am looking into a "ground to neutral" plug to insert into the generator. Does anyone have any suggestions? Has anyone done this?
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Using a generator to Charge Tesla 3 in a pinch
- Thread starter ChileKid
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Make sure it’s an inverter type generator. Like many Honda’s. The non inverter types are just horrible sine waves. They are way off of 60 hz , way off on voltage and often square wave.
There was another thread recently that the Wall Connector checks for seeing 120V hot to ground. If it does not see that it will not charge. Not sure if UMC has the same Check.
Most (portable) generators 240V output is NOT a true split phase and will not have 120V to ground on each hot.
Does the generator have neutral on the 240 plug. Try measuring both hot to neutral and both hot to ground.
Large permanent generators probably emulate a true split phase. I don’t know when that transition happens. My cheap 4000 watt el-cheopo POS Genrac had 240 volt but was not split phase.
I would charge at 120V. You can go up to 20A. Maybe even higher if you trick it. That alone is 2400 watts continuous. Which a good amount on a portable generator.
I assume you meant lowered to 24A not 24V. 24A 240 is 6000 watts continuous. Most generators are labeled by there peak wattage. That would be like an 8000 watt generator. To handle 6000 watts continuous. How big is the generator your using?
There was another thread recently that the Wall Connector checks for seeing 120V hot to ground. If it does not see that it will not charge. Not sure if UMC has the same Check.
Most (portable) generators 240V output is NOT a true split phase and will not have 120V to ground on each hot.
Does the generator have neutral on the 240 plug. Try measuring both hot to neutral and both hot to ground.
Large permanent generators probably emulate a true split phase. I don’t know when that transition happens. My cheap 4000 watt el-cheopo POS Genrac had 240 volt but was not split phase.
I would charge at 120V. You can go up to 20A. Maybe even higher if you trick it. That alone is 2400 watts continuous. Which a good amount on a portable generator.
I assume you meant lowered to 24A not 24V. 24A 240 is 6000 watts continuous. Most generators are labeled by there peak wattage. That would be like an 8000 watt generator. To handle 6000 watts continuous. How big is the generator your using?
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eprosenx
Active Member
Yup.
I built an adapter for my Honda EU2000i that ties neutral to ground. I plug it in to one receptacle on the generator while running things that care about the neutral to ground bond (like a Tesla) to the other receptacle.
I have a picture somewhere.
eprosenx
Active Member
So I would tweak a few things here:
Tesla does not recommend charging off a generator, but I suspect that is mostly due to wanting to avoid tech support calls and perhaps safety hazards. Safety wise, you should probably technically have the generator solidly grounded to earth, and neutral bonded to ground, and a GFCI since by definition you are running it outside.
From a practical standpoint, I don’t see a lot of issues with generators. Yeah, the Tesla will test to make sure neutral and ground are bonded, but it actually can’t tell if it is connected to earth at all.
I disagree that the sine wave would be a square wave. Square waves occur when you have crappy inverters changing DC to AC. A traditional generator is purely an analog device and so the wave is created by the magnets spinning. So the waveform should be not that bad (though I suppose loads placed on the generator could distort it).
Portable generators *are* split phase and should be 120v to neutral from either hot. This is a function of the windings in the generator. There will be an equal number of windings on both “hot” legs out from the neutral. I have never seen a portable generator that offered 240v but not 120v/240v split phase.
I absolutely would not charge a car off 120v from a generator if I had the option. That would be only loading half the windings in the generator and it would be less efficient. No reason to off balance the genny that way.
Teslas are kind of a best case load for a portable generator since they ramp up slowly (so the throttle has time to react) and they have no major surge current or anything. A Tesla is just a big rectifier load. Rectifiers are generally pretty tolerant to voltage and frequency variations, so I am not convinced a generator would be that bad for them.
eprosenx
Active Member
It is only rated for 1600 watts continuous which is a little over 13 amps.
If it is cold out you might get a little more out of it if you are lucky, but it will overload it and cause it to kick off eventually or if it is hot out.
We charge a friends solar battery system off a EU2000i sometimes and we have even had to set it down to 12 amps on hot summer days (generator has a lot of hours on it).
Yes indeed. I can usually get around 25min out of mine at 16A. I should have been more clear. I usually set it to 12A for sustained operation.
I have a (newer model) Honda EU2200i generator. I also needed/have a homemade neutral to ground (bonding) pigtail occupying one of the 120V outlets when using it to charge the M3. The M3 eats the true sine wave from the Honda just fine. In moderate temperatures (~75 degF) I have used it to test charge my M3 at 15A using the Tesla 5-20 Gen2 UMC charging adapter for 1 hour, without a hiccup. The 2200i is rated at 1800 watts continuous, which is 15A, and it already has 20 amp 5-20 outlets, so you don't even need a 5-15 to 5-20 'cheater' plug. I get 6 mph from this configuration. Honda is known for conservatively rating their small generators & I might try upping the charge current to 16A, which is the upper limit on the UMC 5-20 adapter, anyway. You can tell the little Honda gen is working pretty hard to crank out 15A continuously. Not a particularly efficient use of gasoline & not something you'd want to do routinely, but in a pinch.
Honda makes a bonded version of this generator, the EU2200b, which doesn't need a ground to neutral bonding plug. It's not real common to find this model, however.
You can also use the Companion model of this generator, which has a 3-pin 30 amp TT-30 (RV) outlet, together with a correctly wired non-standard TT-30 cable and TT-30 to 14-50 adapter, mated to the 14-50 charging adapter which (used to, anyway) comes with the Model 3. You could then parallel two of the Honda generators to double the charge current.
Honda makes a bonded version of this generator, the EU2200b, which doesn't need a ground to neutral bonding plug. It's not real common to find this model, however.
You can also use the Companion model of this generator, which has a 3-pin 30 amp TT-30 (RV) outlet, together with a correctly wired non-standard TT-30 cable and TT-30 to 14-50 adapter, mated to the 14-50 charging adapter which (used to, anyway) comes with the Model 3. You could then parallel two of the Honda generators to double the charge current.
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eprosenx
Active Member
Good callout on the EU2200i! I am jealous, I wish I had the new model now since it is a couple hundred more peak and running watts.
Note that the "Companion" model genny comes with a L5-30 receptacle I think, NOT TT-30. Though I have an adapter to TT-30 and another (properly / improperly) wired adapter to take TT-30 to 14-50 (which then the Tesla 14-50 adapter for the UMC will accept). I have not actually tried this combo yet, but it should work. I am sure there is a single adapter out there that could be used from L5-30 to something the UMC can digest.
FWIW, I would not run the generator at over 15a continuous as I just don't think it is very nice on the motor or electronics. It might do it, but in general, it would not be worth the concern to me.
Though I do think the Tesla's draw about a half amp less than what you set them to, so perhaps 15.5a total actual draw would be just fine...
Yes, the 30 amp outlet on the 'Companion' model is an L5-30. It takes a $10 adapter to get to a TT-30.
Uncle Paul
Well-Known Member
If it was me, I would contact Tesla directly to determine the feasability and specifications for charging my specific Tesla with a generator.
I know that you will try anyway, but you will find that it isn’t worth it
A 2000 W generator, if you can get it to work, will be at max capacity and burning a LOT of gas and still take over 24 hours to charge.
That means that nothing else in the house is getting power
Also you will find that most generators don’t have the duty cycle to run that hard for that long. You’ll want to be prepared to change the oil around 12 hours and probably need at least 20 g of gas.
I’ve got a 30kW whole house generator, that I don’t expect to charge the car with.
Moral of story: Big storm = charge to 100% and leave it there.
If you can’t get out to go elsewhere to charge, then you really shouldn’t be getting out
A 2000 W generator, if you can get it to work, will be at max capacity and burning a LOT of gas and still take over 24 hours to charge.
That means that nothing else in the house is getting power
Also you will find that most generators don’t have the duty cycle to run that hard for that long. You’ll want to be prepared to change the oil around 12 hours and probably need at least 20 g of gas.
I’ve got a 30kW whole house generator, that I don’t expect to charge the car with.
Moral of story: Big storm = charge to 100% and leave it there.
If you can’t get out to go elsewhere to charge, then you really shouldn’t be getting out
If this is a real concern you are better off picking up a really cheap used gas car or motorcycle.
In a real emergency, tow the Tesla behind a willing pickup truck driver using a long tow strap.
The built-in regen capability of the car will charge harder and faster than any generator, and probably more efficiently - so less gas money paid to the truck driver.
Towing the car around will be like an anchor on the truck and that strap won't go slack unless he needs to slam on the brakes.
If you were pulled for about a half hour you'd be up nearly 50%.
That's only a 15 minute drive away turn around and 15 more minutes and you're home.
For the time you're hooked-up, your Tesla paired to the truck makes a through-the-ground mechanically linked hybrid vehicle system.
The built-in regen capability of the car will charge harder and faster than any generator, and probably more efficiently - so less gas money paid to the truck driver.
Towing the car around will be like an anchor on the truck and that strap won't go slack unless he needs to slam on the brakes.
If you were pulled for about a half hour you'd be up nearly 50%.
That's only a 15 minute drive away turn around and 15 more minutes and you're home.
For the time you're hooked-up, your Tesla paired to the truck makes a through-the-ground mechanically linked hybrid vehicle system.
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I doubt that most of us posting on this thread treat this as a real concern. It's not to me, but just the same, the knowledge that I can do it is tucked neatly away. For any significant power outage, my generators will be powering my refrigerators, freezers, furnace fans, a few lights, and those of my neighbors.
seattlite2004
Active Member
+1. I have a Honda EU6500. Predates my S and is housed in a shed built for that pupose behind my house (shed is on concrete footers and is vented, and I do not run it inside, just keep it there along with fuel). Impractical to connect to car because of distance to garage, and potentially problematic as @ewoodrick suggested. When I got my 1st S, I had the electrician who did the wiring in my garage, also install a regular outlet next to the 240v. And connect the regular one to the subpanel that I feed the generator into. That will allow me to maintain my charge level for the likely length of an outage. The EUs are great generators. Inverter, governor to lengthen run time. Depending on load I can get 14 hrs on 4.7 gal of gas. Very reliable. Very quiet - 53db
I have a small one as well to power my aquarium, but I know it won't help me on the car side.
Really good stuff eprosenx. I have a 20 kw whole house generator with an automatic transfer switch. I’m curious if I could charge my 3 in a pinch paying close attention to other loads. I use a NEMA 14-50 outlet on a 50 amp breaker which charges at 32 amps max. No dryer no oven no dishwasher. There is a 100 amp breaker on the generator itself. Thanks in advance for your thoughts.
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