Emergency charging from a portable generator

[Febtober]

I've got a 23 MYLR that I usually charge on a 60amp circuit via the wall connector outside my garage. I have the mobile connector, and I usually just keep it in my car. Now I'm interested in being prepared in the event of an extended power outage in my area. When I first bought my house, I also purchased this portable gas generator. It's never been used and is still in the box.

I've been trying to figure out if it's possible to charge the Tesla from this, but I'm finding lots of conflicting information. Some sources say it can only be done from an inverter generator (not what I have), some say it can be done but I'll need a ground bonding plug, some say yes I'll just need some sort of adapter.

The highest power outlet on this generator is an L14-30 twist lock outlet at 240v. I found this adapter, which to my untrained eyes appears to be what I'd need to connect to the mobile connector and charge. But I'd like to make sure this is correct before I spend the money on it.

 

[ucmndd]

Yes, that adapter will work, assuming you can get the thing charging in the first place.

The mobile connector does perform a ground test before allowing charging. You may need to properly ground the generator via a grounding rod.

Best advice would be: Try it before you need it and see what happens. You don't want to be figuring this out in an actual emergency. Get the generator out of the box and fire it up.

Try it on a regular 120v plug first - that will give you an idea if the car will accept a charge, what else you might need, etc. before investing in the 14-30 pigtail for the mobile connector.

 

[Cosmacelf]

Also, you have to exercise those generators. They have a bad habit of not starting when you need them.

 

[dgpcolorado]

To use EVSEs that do a ground check on a generator you can use a plug that connects the ground to neutral. You can do this with a regular NEMA 5-15 plug that has jumper wire between neutral and ground and put that in the extra outlet on the generator. That will allow the generator to pass the EVSE ground check. Whether this will also work when you use a 240V outlet on a generator, I couldn't say — my generator had only 120V NEMA 5-15 outlets on it.

Years ago I did this by putting two 110 kOhm resistors between the two blades and the ground, as you can see from the pictures below. However, a simple wire jumper between the neutral and ground should work as well. This jumper plug is then placed in the extra 5-15 receptacle on the generator and the EVSE plugged into the other. Again, not sure this will work for using the 240V plug.

 

[jcanoe]

Bottom line - The Tesla Gen2 Mobile Connector manual includes a Caution against using the Mobile Connector with a private power generator.

If you search on YouTube there are videos created by Tesla owners that cover using portable gas powered generators to charge their Tesla vehicle.

You an also find videos that demonstrate charging the Tesla vehicle using a ~1kW portable power station and a small bank of 100W solar panels.

 

[Rocky_H]

I've been trying to figure out if it's possible to charge the Tesla from this, but I'm finding lots of conflicting information. Some sources say it can only be done from an inverter generator (not what I have), some say it can be done but I'll need a ground bonding plug, some say yes I'll just need some sort of adapter.

Well...yeah. That's why you're getting a lot of conflicting information. This is such a crap shoot of unpredictability of whether or not any given model of generator will be able to work or not and what kind of extra modification it might need, etc. that we can't just give you an answer ahead of time for a generator that's still in the box that you haven't tried. As @ucmndd said, you'll have to try a couple of things with it to see if you can figure out a way that it will work.

 

[Big Earl]

Charging on a diesel generator at our old house.

 

[ATPMSD]

I also purchased this portable gas generator. It's never been used and is still in the box.

This will not work. Tesla needs high quality AC power with a “pure” sinewave, hence you need an Inverter Generator. The key is it must have a Total Harmonic Distortion (THD) of <5%, preferable <3%.

Proper grounding is also an issue.

 

[outdoors]

As a reference I am installing a propane 7kW to power my system in the event of total failure, yet I run it through my inverter battery setup. I am traveling so can't link now. Pouring a pad, or something. Permeant.

Portable could work in a system such as mine with proper hookups, but nobody does it. Would have to be the correct sizing etc... I also just gave it away. Couldn't stand to hear it in pristine wilderness.

Direct to the car. Would say not recommended. God they are loud of you are talking about really charging the car.

 

[Cosmacelf]

Yeah portable generators like that are soooo loud. Only portables that aren’t are Honda and they are 2x the price.

 

[Big Earl]

Yeah portable generators like that are soooo loud. Only portables that aren’t are Honda and they are 2x the price.

Hondas can get pretty loud once you load them up and they increase the revs.

Speaking of generator noise, anyone looking to do a home backup generator should seriously consider spending the extra money for an 1,800 RPM unit over a 3,600 RPM unit. The former will usually be a 4 or 6 cylinder engine like a car or a truck, while the latter will likely be a twin cylinder engine like you’d find in a large riding lawn mower. The noise and longevity differences between the two cannot be overstated - totally worth the extra expense, in my opinion.

Best options are propane and diesel, with my favored fuel being diesel - no fuel pressure loss in extreme cold weather (propane phase shift from liquid to gas), a bit less maintenance, more readily-available fuel that you can pour into the tank yourself, more energy density that requires a smaller tank for similar run time.

Sorry, I know that’s off topic for a portable generator thread.

 

[Cosmacelf]

Hondas can get pretty loud once you load them up and they increase the revs.

Speaking of generator noise, anyone looking to do a home backup generator should seriously consider spending the extra money for an 1,800 RPM unit over a 3,600 RPM unit. The former will usually be a 4 or 6 cylinder engine like a car or a truck, while the latter will likely be a twin cylinder engine like you’d find in a large riding lawn mower. The noise and longevity differences between the two cannot be overstated - totally worth the extra expense, in my opinion.

Best options are propane and diesel, with my favored fuel being diesel - no fuel pressure loss in extreme cold weather (propane phase shift from liquid to gas), a bit less maintenance, more readily-available fuel that you can pour into the tank yourself, more energy density that requires a smaller tank for similar run time.

Sorry, I know that’s off topic for a portable generator thread.

I’ll second the 1800 rpm. The best fuel is natural gas if you have it of course.

 

[Eric33432]

My 60 KW Generac works fine. Liquid cooled, 4 cyl turbo charged, 3,600 RPM. I would think small portable generators might give mixed results.

In 2023 this replaced an older 60 KW 6 cyl (V6) normally aspirated gen set, also 3,600 RPM which became unreliable after 20+ years. The power it produced also worked fine for charging Tessies.

Runs from town gas.

 

[Big Earl]

60 kW is a big unit. I don’t think you can find an 1,800 RPM version unless you go with diesel. Very nice setup you hav there. Is your home 400 or 600 amp service?

 

[tga]

Every portable generator that I've ever seen bonds the ground and neutral. If you connect them to your house with a transfer panel/switch, you are supposed to disconnect the bonding at the generator (NEC only allows 1 neutral/ground bond at the service entrance), but most people don't. If you do, you're supposed to re-connect the bonding at the generator (or use a ground/neutral shorting plug) for standalone service.

The mobile connector does perform a ground test before allowing charging. You may need to properly ground the generator via a grounding rod.

Technically, the GFCI test is just verifying that the UMC can detect a mis-match in current flow between the hot and neutral (or both hots). It does this by leaking a small amount of current between the hot and ground and making sure the GFCI circuit detects it.

This test will pass if the ground conductor is a valid current return path, which only requires the neutral and ground to be bonded. It does not require the ground conductor to actually be connected to ground (earth bonded), so a ground rod shouldn't be necessary.

Years ago I did this by putting two 110 kOhm resistors between the two blades and the ground, as you can see from the pictures below. However, a simple wire jumper between the neutral and ground should work as well. This jumper plug is then placed in the extra 5-15 receptacle on the generator and the EVSE plugged into the other. Again, not sure this will work for using the 240V plug.

Why did you connect the hot? The ground pin is now floating at 60VAC?

Best options are propane and diesel, with my favored fuel being diesel - no fuel pressure loss in extreme cold weather (propane phase shift from liquid to gas), a bit less maintenance, more readily-available fuel that you can pour into the tank yourself, more energy density that requires a smaller tank for similar run time.

In theory diesel has cold weather problems as well (gelling), but I've never had an issue starting my tractor in the dead of winter (usually using left over summer diesel from mowing season). FWIW, I've never have any problems with my propane fired furnace and above ground tank, even down to -20F.

 

[fhteagle]

I've successfully charged a 2023 MYLR from a no name gasoline generator, via an OpenEVSE. Had to disable the GFCI test on the OpenEVSE of course. I did verify a valid ground via the L14-30 to the metal frame foot of the generator. But no neutral-ground bond anywhere in the system.

I started at 2 amps max via the car touchscreen, and slowly worked it up. Indicated volts went rather unstable by 7 or 8A, so I was really only pulling ~1600W from a 5000W nameplate generator.

Same test with an old ClipperCreek built portable EVSE failed, probably at the GFCI check phase.

 

[jcanoe]

I've successfully charged a 2023 MYLR from a no name gasoline generator, via an OpenEVSE. Had to disable the GFCI test on the OpenEVSE of course. I did verify a valid ground via the L14-30 to the metal frame foot of the generator. But no neutral-ground bond anywhere in the system.

I started at 2 amps max via the car touchscreen, and slowly worked it up. Indicated volts went rather unstable by 7 or 8A, so I was really only pulling ~1600W from a 5000W nameplate generator.

Same test with an old ClipperCreek built portable EVSE failed, probably at the GFCI check phase.

ClipperCreek (CC) EVSEs were designed, built to strictly conform to all EVSE specifications. My CC LCS-20 would display a ground fault anytime I used my corded leaf blower no matter the 120V circuit I used with the leaf blower. CC customer support was super helpful. CC suggested that there was a small amount of voltage or amperage leakage within the motor of the leaf blower from hot to ground. It was enough to trigger the CC fault. The CC would automatically reset after ~17 minutes (another EVSE spec.)

 

[Eric33432]

60 kW is a big unit. I don’t think you can find an 1,800 RPM version unless you go with diesel. Very nice setup you hav there. Is your home 400 or 600 amp service?

Class 480 meter which some people might call 600 amp service. Three 200 amp transfer switches which double as main disconnects as they contain 200 amp breakers.

I had an 1,800 RPM ONAN 85 KW unit at my last house. That one had a Ford V10 truck engine in it, converted to work on town gas. Much better quality than Generac.

 

[Midnightsun]

I wired ours independent of our whole house generator. Why? I have a standard Kohler 20KW unit, does the whole house no problem. Have a 200a inlet with a 200a transfer switch wired to the main panel. A 20kw is only good for around 85a or about 65a continuous. In the 8 years of running our home not once has the generator stumbled due to too high demand. I have baseboards in the basement, garage and shed however the house is heated/cooled via heat pump (3T) or gas depending on how cold it gets. Also have 2 water heaters and a spa running not to mention 2 refridgerators, 2 freezers and 4 small wine coolers.

My concern was tripping the breaker if the car decides to charge at 48a which would require someone to be at home to reset the generator breaker. I have piece of mind by not supplying the wall connector. One could reduce the output of the wall connector however that also requires intervention in case of a power failure. When on vacation we simply leave the car plugged into a 120v receptacle in the garage which does get power from the generator.

 

[Midnightsun]

Just to add to the above post. A soft start unit installed on the AC or heat pump makes a really big difference in start up draw from the generator/grid and will also fix those dimming lights when the compressor kicks in whether you be on generator power or city power. Well worth the small investment of sub $400.