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How to Charge a Tesla with a Portable Generator

Many have tried to charge their Tesla (or other electric vehicle) with a portable generator. Most have failed. Is it a fool’s errand, or can it be done?

To be honest, I’ve never actually considered the option until I’ve stumbled upon this topic on the internet. There are a few guides and suggestions on charging EVs with a generator on various forums and YouTube. Still, the most reported outcome is failure.

Since I deem myself to be somewhat of an expert on portable generators and there seems to be in principle nothing preventing you from charging your Tesla with a generator, I decided to give it a shot.

I will go through all the details necessary, including the requirements given by Tesla, choosing the right device for the task, some tips on how to go about setting up your crazy experiment and what outcomes to expect.

For the Love of God, Why?

Charging an electric car with a portable generator seems, and in most cases is, a pretty dumb idea. After all, it defeats the whole point of having an electric car in the first place – to replace the combustion engine by a sustainable power source.

Photo of a Tesla car charging from a portable generator on the side of a road

Someone charging their car on the side of a road with the Honda EU3000iS
Source: reddit (opens in a new tab)

In fact, using a generator to charge your car is probably even less effective than using a gasoline-powered vehicle. Instead of using gasoline in an efficient car engine which converts its output directly into kinetic energy, you are first using a generator to transfer gas into kinetic energy and that into electricity, which then flows into your electric vehicle and is used to create kinetic energy again.

Since each node of transfer will result in some loss of efficacy, you end up with a pretty non-efficient sequence. However, this method of charging may be useful under some circumstances. Consider the following.

Once an electric vehicle runs out of power, you’re done. Even if you find a good friend who’d be willing to rescue you, he can’t exactly bring you a spare battery, and he sure ain’t moving that Tesla unless he runs a towing business. However, any car can fit a generator! Therefore, it would come in handy if you could simply recharge your car with one and move along to the closest power station.

Other scenarios in which you may find charging your EV with a generator handy include:

  • Needing to charge your electric vehicle during a blackout.
  • Getting stranded in a campsite, which is off the grid.
  • Running a silly experiment.

However, this is in no way a practical, reasonable, efficient or an intelligent way of charging your car. Even Tesla Motors themselves discourage you from doing so in their own user manual.

However, in case of an emergency, here’s how to go about it.

Standard charging conditions

Since Tesla’s are the most popular and discussed electric vehicles at the time of writing this article, we will limit ourselves to them. Other EVs may have their own specifics.

Charging Equipment

Picture of the Tesla Gen 2 Mobile Connector in its storage bag

The Tesla Gen 2 Mobile Connector only comes with a NEMA 5-15 adapter

Tesla’s use their unique power outlets. These are adaptable to NEMA outlets using a so-called mobile connector. Until 2018, the mobile adapter which came with each purchase featured a 5-15 and a 14-50 connection (Gen 1). Newer models can only be connected with a 5-15 outlet (Gen 2) out of the box.

However, both generations offer a wide selection of adapters, which will come in handy and will most likely be required.

In addition, the power source used for charging must:

So, how do generators square up to these requirements?

Using a Generator to Charge an EV

Sine Wave

By requiring a clean sine wave, Tesla has limited us to inverter generators. Before going for one, check if the generator truly provides an unmodified, clean sine wave (as opposed to e.g., square waves).

Grounding

The generator must also be grounded – the neutral bond to the frame of many generators is usually sufficient, but grounding issues may arise.

Many inverter generators have a floating neutral – Such devices are apparently rejected as ungrounded by the Tesla’s internal software. To solve this issue, we suggest either to convert to a bonded neutral, or trying, at your own risk, a so-called bonding plug, such as the one from Southwire that you can find on Amazon (opens in a new tab).

If grounding still remains an issue, the only option left is to ground your generator the old-fashioned way.

Outlets and Power

Note that portable inverter generators are equipped with a combination of NEMA 5-20, 14-30 and 14-50 outlets. Unless you have a generator with a NEMA 14-50 outlet and own a Gen 1 mobile adapter, ALL will require you to buy a separate Tesla mobile NEMA adapter! You can get these adapters from the Tesla Online Shop (opens in a new tab).

There are 3 limiting factors to the final charging power. Firstly, the outlet type, which is designed to carry a current only up to a certain value of amps. Secondly, what Tesla actually draws from the outlet (which is always less). Lastly, the power limitations of the generator itself.

Outlet Types

Picture of the A-iPower SUA8000iSF

The A-iPower SUA8000iSF is one of the few inverter generators with a NEMA 14-50R receptacle

Most inverter generators are rated for roughly 2000 W and are therefore only equipped with NEMA 5-20 outlets, which are rated for a maximum of 120 V and 20 A, 2400 W. You can probably get a few miles out of them to get you to the nearest power station, but they are far from sufficient during a serious black out, when you have to rely on your generator’s power for up to several days.

NEMA 14-30 outlets are less common but can be found in many generators as well. They are rated for a maximum of 240 V and 30 A, 7200 W. These will be able to charge your car in a far from optimal, but still quite reasonable amount of time.

NEMA 14-50 outlets are far less common among inverter generators and can only be found in some of the more expensive models. They are rated for a maximum of 240 V and 50 A, 12000 W. However, they do exist and may be a viable option for recharging your car in case of a blackout, or more generally, when you need to recharge a significant portion of your battery in a reasonable amount of time.

Tesla’s Limits

As already mentioned, your TESLA WILL NOT draw the maximum available wattage when charging.

For summary, the table below shows the max amps and watts drawn by each adapter.

Table 1: Max amps and watts drawn by each adapter, according to the generation
AdapterMax ampsMax watts
Gen 1Gen 2Gen 1Gen 2
5-2016A16A1920W1920W
14-3024A24A5760W5760W
14-5040A32A9600W7680W

As a result, charge times will differ by mobile adapter generation, outlet, and, since not all Teslas are equal, also the Tesla model.

For summary, the tables below show the max mileage per hour of charge for each adapter and mobile connector generation, by car.

Table 2: Max mileage per hour of charge by outlet for Gen 1 mobile adapters
Adapter
(Gen 1)
Max mileage per hour of charge
Model SModel X
5-2043
14-301714
14-502925
Table 3: Max mileage per hour of charge by outlet for Gen 2 mobile adapters
Adapter
(Gen 2)
Max mileage per hour of charge
Model SModel 3Model XModel Y
5-204434
14-3017221421
14-5023302029

Available Generators

Lastly, the FINAL wattage limit is given by the generator itself. At the time of writing, the most powerful inverter generator is rated for 7000 W (29 A). Both numbers fall below the max value of 7680 W (32 A) for Gen 2 NEMA 14-50 mobile adapters. The same will apply for the numerous 3000-5000 W generators and their NEMA L14-30R outlets, or 1000 W generators and their NEMA 5-20R outlets.

For this reason, YOU WILL RARELY REACH THE MAXIMUM WATTAGE/AMPS/MILEAGE (values in Table 1, 2 and 3) when charging your Tesla electric car with a portable generator, especially with 14-50R outlets, since they are currently not unachievable with inverter generators.

What to Expect

Most importantly, as I have mentioned previously – grounding issues. I have yet to see a single case of charging an electric vehicle with a generator that is not complicated by grounding issues. Solving them has been explained above. The following video may also be of some assistance.

It will take a while. The generator must be warmed up first. When charging a Tesla, the amps must be set to the lowest possible setting using the dashboard monitor and only gradually brought up to the maximum amps. During this process, your generator may die on you if you up the amps too quickly.

After doing so, given that you are using an inverter generator and therefore, most likely a NEMA 5-20R outlet, you are limited to a recharge speed of 4 miles per hour, which coincidentally, is pretty close to the average walking speed of a human. Therefore, you should consider if it’s even worth your time. If it is, expect to spend the next few hours reading your favorite book and refilling your fuel tank repeatedly.

Lastly – failure. The internet is full of them. While many have successfully charged their Tesla using a generator, there seems to be an equal amount of those who have tried and failed, without ever managing to resolve the fault. If you are going to rely on a backup generator for your electric vehicle, we suggest you try it out several times to check if it will actually work beforehand.

Conclusion

In summary, we have found out that it is in fact possible to recharge your Tesla and possibly any other electrical vehicle, using a generator. However, only a few inverter generators with a clean sine wave will be suitable for the job, you will most likely run into grounding issues and if all of the above is solved, you will still have to wait several hours to get any significant mileage.

Have you tried and successfully charged your EV or Tesla with a portable generator? Which model of generator did you use and how did it go? Let us know in the comments below!

Paul

Paul

Manager & Editor of generatorbible.com. Early retired from the OPE industry, living in South Carolina. He now mostly spends his time traveling and taking care of his wife and grand-children.

1 Comment
  1. Thanks for the read! I have a 2016 VW eGolf. It has a maximum power draw of 7200W (240V x 30A). I bought a 9500W (peak, 12000W) generator, thinking it would work in a pinch. Unfortunately, the voltage seems to drop to about 210V when I run it with the charger, pushing the current to 34+A and causing my charger (rated to 32A) to trip, resetting the process. It charges fine when limited to 13A of current. I haven’t tried the warm-up, increasing the current max slowly — I’ll give that a try to the extent possible with the eGolf (you can only choose 5A, 10A, 13A, and maximum on the car).

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