Slide-in REX engines for electric cars stopped by government regulations

Surely every electric car driver has had this idea – why not carry a portable gasoline powered generator so you can charge your car in a pinch? I’ve spent quite a bit of time weighing this idea back and forth, because it’s so simple. The BMW i3 even gets ever so tantalizingly close to this because of how the REX engine is installed, but we’ll get back to that in a minute. William Kemp, the author of the Zero Carbon Car, even built a DIY EV conversion that incorporated a biodiesel powered diesel generator. However, what we have before us is the sort of DIY hack nearly anybody would try, recharging a BMW i3 off a portable generator, and the guys at GadgetReview had partial success.

What these guys did is take a trip to Home Depot where they rented a 3000 watt portable (er.. luggable) gasoline generator as well as some tubing to try and run the generator while driving. The first stage was – as you see – to simply plug the portable charging unit into the generator, and charge the car. After charging for half an hour the car had gained 4 miles range, for a minuscule 8 miles range gained per hour of charging.

Anybody can do this, and it’s pretty trivial to set this up. However, it doesn’t provide much range boost. However in this trial setup they hampered themselves by using the 120 volt level 1 charging unit, limited to a 1.5 kilowatt charging rate. The genset is rated for 3000 watts, and has a 240 volt outlet. That means a portable level 2 charging unit would have given them 8-10 miles range in that half hour.

This worked fine so long as they were stationary with the genset located outside the car. Their next step was to pop the genset in the trunk, run some hose from the generators exhaust port out a window, and leave the charging unit plugged in and charging. This failed in two very expected ways – the car wouldn’t move, because it was charging – the cabin quickly filled with exhaust fumes.

Modern electric car charging systems have interlocks so that the car cannot be driven while charging. This is to prevent drive-off’s at the charging station – that is, driving away while the charging station cord is attached to the car. This happens at gasoline stations all the time, apparently. It’s a safety thing.

The issue with exhaust fumes should stop everyone trying to do this. It’s possible to bypass the safety systems (I think) and enable charging while driving – but will you be able to build this so that it’s safe? Can you ensure you capture all the exhaust fumes and make sure none of them escape into the passenger cabin? Probably not. So don’t even try.

Or if you do, read carefully what William Kemp did with his car. He didn’t get any old genset, he got a very compact 10 kilowatt marine diesel generator interfacing it smartly with his car.

But let’s get back to what could happen, if only the car companies were wise enough. And the BMW i3 is ever so tantalizingly close to this idea.

What if electric cars were designed so a small gasoline engine could be installed when needed, and removed when not needed?

The BEV version of the BMW i3 has this empty space in the rear of the car where the REX engine would sit. Both the BEV and REX i3’s are the same, but that the REX version has that gasoline engine.

BMW could do some more work on the design, making it simple and easy to slide the REX engine in and out. It could be offered as a rentable widget BMW has in stock at dealerships. The BMW i3 owner wouldn’t have to debate whether to spend the $4000 ahead of time for the REX option. They could rent it as needed, instead.

There isn’t a technical or commercial/retail reason to not do this. Any of the automakers could design an electric car with easily removable range extender engine. The automakers have more ability than DIY hackers at home to safely bypass the charging system interlocks, and safely route the exhaust fumes. This isn’t rocket science, and I think it’s pretty clear some electric car owners would respond positively.

The hurdle would be regulatory. In California a BEV vehicle is awarded a white HOV sticker, while the PHEV’s (like the BMW i3 REX) are awarded green HOV stickers. But would a BEV in which a REX engine has been installed still qualify for the white HOV sticker? Nope. Likewise a BEV with a REX engine installed, even if temporarily, needs to be counted in a different emissions class than a regular BEV with no REX engine. That is, a BEV with REX engine installed has become a PHEV.

The EPA and other emissions regulation agencies need to know about that mobile source of emissions. These agencies are tasked with tracking emissions reduction targets, and a BEV with REX engine installed throws off the calculations.

Before one of you pseudo-libertarians starts taking umbrage at government intrusion on an individual car owners right to do as they wish, let’s ponder a few things. The atmosphere is a shared resource, and it’s obvious not everyone is trying to limit the harmful crap they pour into the atmosphere. Therefore the government has a long standing well entrenched system of emissions testing, and emissions regulation. Ever get your gasoline car smog checked? That’s the government doing its job protecting our shared resource, the atmosphere.

Therefore, what stops us from having slide-in REX’s for BEV’s is government regulations which have yet to be written.

On the other hand there’s something else BMW (or any automaker) could do. Instead of a slide-in REX engine, why not a slide-in battery pack? This wouldn’t require any government regulation stuff – no emissions to regulate.

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About David Herron

David Herron is a writer and software engineer living in Silicon Valley. He primarily writes about electric vehicles, clean energy systems, climate change, peak oil and related issues. When not writing he indulges in software projects and is sometimes employed as a software engineer. David has written for sites like PlugInCars and TorqueNews, and worked for companies like Sun Microsystems and Yahoo.