9000W Generator in the Frunk of my Rivian R1S… Can I charge while driving?

So, I’m adding a 9000W generator for off-grid camping (boondocking) purposes, not really to charge while driving, but it’s got me thinking… I know people have discussed this before, but I haven’t seen anyone actually try it on a production EV. If I wanted to charge while driving, could I somehow hook it up through the regen system of the motor? Or could it go directly to the battery? How would you make this work in theory, to extend your range past the vehicle’s limit without stopping to charge?

Sounds a bit like the BMW i3 REX, doesn’t it?

Randy said:
Sounds a bit like the BMW i3 REX, doesn’t it?

Yeah, similar to that and also the Chevy Volt or the upcoming Ramcharger.

Imani said:

Randy said:
Sounds a bit like the BMW i3 REX, doesn’t it?

Yeah, similar to that and also the Chevy Volt or the upcoming Ramcharger.

I thought the Volt had both electric and gas motors connected to the transmission? The REX just had a small generator charging the battery, right?

@Randy
Actually, the Volt has an all-electric drivetrain with a 4-cylinder generator that kicks in when the battery’s dead. The gas engine doesn’t directly connect to the transmission. The i3 REX had a smaller generator, and while it helped extend the range, it wasn’t strong enough to fully power the car once the battery drained.

Trains have been using this setup for a long time—diesel engines running generators that power electric motors. It’s not a new concept and it works well.

@Amelia
Actually, the Volt could run as both a series hybrid (like you described) and a parallel hybrid when it made sense for efficiency. The second-generation Volt added more flexibility, but even the first gen could operate as a parallel hybrid in certain situations.

@Randy
Yeah, you’re right, it did change between Gen 1 and Gen 2. I think the Ramcharger’s more like the i3, though.

Randy said:
Sounds a bit like the BMW i3 REX, doesn’t it?

Honestly, the REX and Volt designs were super practical for their time. It’s too bad they didn’t put those drivetrains in bigger vehicles. A small battery with a generator that gets good fuel efficiency would cover the needs of most people and eliminate range anxiety.

You could try connecting a generator to the high voltage lines… but then you’d probably only need one car, because you’d be… well, toasty forever.

Thomas said:
You could try connecting a generator to the high voltage lines… but then you’d probably only need one car, because you’d be… well, toasty forever.

Not sure you’d be toasty forever… just long enough for someone to collect what’s left of you and your Rivian!

There’s a guy who actually did something similar, but I wouldn’t recommend trying it unless you’re okay with the possibility of ruining your Rivian. For one, you’d want the generator bolted down properly—definitely don’t want it rolling around. Also, getting power into the battery pack directly is tricky, especially since it’s high voltage (around 400V). The system can charge while driving (regen), but tampering with the battery pack isn’t something to take lightly.

Here’s a video of someone who tried it: https://www.youtube.com/watch?v=hHhf223jGIE

9000W for off-grid camping? What are you powering out there? Also, where do you need 700 miles of range? Arctic expedition or something?

It hasn’t been done because there are real challenges! The motors in EVs have around 400V going to their controllers (some use 800V), so there aren’t any ‘regen’ wires to tap into. As for charging directly to the battery, that’s more plausible, but it would require software modifications. You’d need to hook the generator up to the vehicle’s charging port and then hack the software to activate the onboard chargers while driving.

Alternatively, you could try to make your own AC to high-voltage DC charger and connect it directly to the battery, but you’d better hope the car doesn’t freak out and shut down due to unexpected power flow!

@Jason
The BMW i3 REx is probably laughing at this!

Even if you somehow connect to the battery without frying anything, the car’s software might throw a fit when it detects power coming from an unexpected source. It could easily make the vehicle inoperable. Even tapping into the low-voltage DC systems can cause problems in cars like Teslas, and I imagine Rivians are similar.

Tapping into the motor for regen sounds equally risky. You’d essentially be turning your car into a hybrid by feeding power directly to the motor instead of the battery, but that’s a complex and potentially dangerous job. Plus, if done wrong, it could mess with the car’s traction control.

A safer route would be creating an auto-charging system. You could set up a 5-10kWh LFP battery pack in the frunk, charge that with the generator, and then feed the power into the car’s AC charging port. You could even charge the car during long stops like at red lights. It’s not perfect but it might give you a little extra range in stop-and-go traffic.

What you’re describing is basically a series hybrid, like what BMW did with the i3 years ago. They added a small 650cc engine as a range extender because the battery tech wasn’t quite there yet. As the batteries improved, they stopped offering the REX version. Nissan is now doing something similar with their new Qashqai hybrid.

So, 9kW? That’s like 5% of a typical fast charger. You’d add about 30 miles per hour of charging. That’s basically like using a slow Level 2 home charger.

Running it while you’re driving wouldn’t really help much. 9kW isn’t that much power for a big truck. You’d get maybe 2 miles of range per hour if you’re driving on the highway. To make a real difference, you’d need a much larger generator, like the 600+ hp one they’re putting in the upcoming Ramcharger EREV.