Dear Readers,
My article last week on the range of electric vehicles while towing had a few interesting comments and questions. In fact, I get direct emails every week with the same basic question: Can I run a small generator in the back of my EV truck to help recharge it while driving or towing a trailer? Â
UPDATE: Read Part 2 of this article where I answer more of your questions and discuss (self) charging EV possibilities. Click HERE
Here’s one such question from last week’s article
“I always wonder why can’t a gas generator recharge at the same time that you are driving? If this could happen, then even if it can’t totally keep up with the demand, at least it could get you farther down the road. Also, even though it wouldn’t be totally independent of fossil fuels, it would be way better using a small one- or two-cylinder engine than the V-10 or V-8 that’s in there now. Why don’t we ever hear about an option like this? This is what I think of when I think about a hybrid, and my motorhome has plenty of room to set something like this up on it.”
The numbers don’t add up…
Yup, that’s true. If you look at the actual kWh of energy needed by an EV driving down the road and compare it to the energy output of any reasonable-sized generator, you’ll soon see that you’ll only be adding 10 percent (at best) to your driving range.
Just the facts, ma’am…
Here are the basic facts. A typical EV such as the Volkswagen ID.4 has a 75 kWh battery that allows it to drive about 275 miles on a single charge. That works out to around 3.5 miles of range per 1 kWh of charge. Now let’s assume you have a 2.2kW generator that can output 1,800 watts continuously. If you ran the generator for 4 hours, it would produce around 7 kWh of energy. Now, that’s assuming 100% transfer efficiency, etc. So, in 4 hours of driving, it could possibly add maybe 24 miles of range. But things being not 100% efficient, it would be lucky to add perhaps 15 to 20 miles of range to a 250-mile trip.
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And it won’t work, anyway…
Also, every EV I’ve looked at locks the vehicle in park while charging, so you can’t drive away from the charging station with the cord plugged in. It would require a major modification to the EV’s charging system to make this even possible.
Yes, I’ve tried this myself
I’ve actually done this with a Class-1 charger that output 1,000 watts and calculated it would take around 75 hours of continuous generator running of a Honda EU2000is generator to completely recharge the 75 kWh battery in my ID.4 EV. So that’s even worse.
I did calculate that my Honda EU7000is generator could recharge an ID.4 in maybe 10 hours. But that’s a 240-pound beast that would burn through 5 gallons of gasoline doing this stunt. So, while it’s certainly possible, these are not practical solutions.
What about an EV truck towing a trailer?
Well, the numbers will be much worse for that situation. In that case, you’ll likely have a 150 kWh battery and a reduced towing range of perhaps 200 miles. So, even if you put a 7,000-watt generator in the bed of the truck, my numbers show it would take perhaps two times as long to restore half the mileage range. Not a great (or even good) option.
How about those Top Gear guys?
Yes, I know that the wacky guys from Top Gear showed this sort of thing on one of their television episodes a few years ago. They had a generator strapped to the back of a small electric vehicle and thought the generator would charge the battery enough to keep the traction motors propelling the car forward. But it failed miserably, which was one of the jokes in the show.
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Isn’t that how hybrid cars and trucks work?
Yes, it is. But the F-150 PowerBoost truck I reviewed last summer had a 3.5L turbo boost V6 engine plus a 35kW drive motor it could use in various combinations. So, the gasoline engine was directly connected to the drive wheels most of the time, and the 35kW drive motor also acts as the generator power source for the 7.2kW on-board inverter.
The advantage of that setup is that the truck could drive for a few miles around town on the 1.5kW traction battery alone, or use the V6 and electric motor at the same time for a big boost while accelerating. And many plug-in hybrid cars have a much larger traction battery allowing them to drive maybe 75 to 100 miles on battery power alone before needing to power up the gasoline engine.
If you really wanted to extend the mileage enough to restore the lost range while towing a trailer, you would need something like a 25kW generator running in the bed of the truck. And that’s just not a practical solution by anyone’s calculations.
So the numbers are not there, just yet. But don’t count out electric RV’s just yet. There’s some exciting developments in the near that could change how EVs operate. I can’t wait to see if they work…
Let’s play safe out there….
Send your questions to me at my new RVelectricity forum here.
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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##RVT1052
A Chevy Volt is perfect for our use case 60 miles of electric and 10 gallons at 37 mpg. We add gas avery 6 months around town and crush it on road trips. The engine is a generator only. I can see how the Dodge pickup will be popular as it functions the same. A 450-500 mile Chevy or Tesla truck will be fine 90% of the time too. If you are camping or towing you will have to work around charging infrastructure until its more accessable. A 13kwh Duromax dual fuel generator with a couple lp tanks would add 30 miles/hour charge while stopped for lunch, exploring or over night to fill in the gaps between supercharging. The volt gets 3.1 miles /kwh, Model 3, 3.5-4.1 and the trucks 2.5/kwh
Seems like the best approach would be a version of regen braking as part of the travel trailer. The TV is pulling it anyway, if you could send back the power to the TV to charge the batteries then you should be able to get longer range.
I like your logic and math. The failing Honda generator takes way too much time, but maybe it gets close to 250 miles out of 5 gallons? Not bad.
25kW generator? I am a fan of Mazda including the rotary engine the RX-3 I had. I am anxious to hear reviews of an upcoming production MX-30 PHEV with a rotary generator that is probably about 25 kW. Supposedly operating under high constant RPM as supposedly the best case for a Wankel. What are you thoughts on the Range Extender application? And it is a practical size to tow.
Looking at your ID4 and 7KW genny, you get 275miles on full charge, which takes about 5 hours to exhaust again. Running your 7KW, you’ve added 1/2 a charge again, so you go another 150mi/2.5 hours. 75mi, 1:15, etc… Yes, you obviously will run out, but you DO go 400 miles on maybe 5 gallons of 87octane (minus random inefficiencies, yeah yeah)? Now, if you subtitute a 10KW diesel, you probably burn half the fuel and add 33% more power… seems like it COULD work (to add range to a modest range car, NOT to commute every day this way).
I really liked testing the Ford F-150 PowerBoost Hybrid truck with the built-in 7.2kW inverter generator that can easily power a 240-volt 50-amp RV or two 120-volt 30-amp RV trailers. It also has a 35kW traction motor that lets you drive it around town on just the battery without the gasoline engine starting at all. However, I really wish it had a traction battery larger than 1.5kWh since that’s only 5 or 6 miles of driving around town on battery power. If they added a 20kWh battery in the bed with a 50 mile electric range, and increased the weight rating a bit, this would be a real winner for towing small/medium size RV trailers.
What to buy? Get the right vehicle for your driving needs. Towing a heavy trailer long distances?…Get a ICE tow vehicle or prepare to suffer inconvenience and waste time.
Just taking lots of short trips around town? EV or hybrid do those jobs well, reducing trips to the gas station (but raising your electric bill). No free lunch unless, perhaps, you have a big expensive solar installation at your place.
What NOT to buy? Don’t buy the BS that you are “saving the planet” with your EV. You are simply moving your “footprint” elsewhere. But maybe your circle of friends will get smaller if you don’t drive one like they do…along with their thinking and opinions. Your choice!
We all choose what BS we want to believe.
I “like” EVs as commuters, but I constantly have to point out that you do NOT buy an EV to save the planet. The CO2 footprint of manufacturing an EV vs ICE, muxxed with the CO2 saved by then driving on grid power thereafter, places the breakeven at 130K miles before you have “saved” a gram of CO2. And then there are the hazmat concerns mining and for disposal of GIANT batteries than (currently) are not recycled well at all. Maybe tech will improve, but right now EVs are almost certainly harming the planet more than helping. I’m still looking to buy a new one, just to play the government strong-arm game and save $$$… but it isn’t for the planet.
Seems like the mostly electric vehicle with a small gas engine or EV with generator might be most useful where there is no charging station. Even if it takes many hours
It’s a reasonable backup plan if you get stuck in the woods somewhere without a charging source nearby. But I would hate for it to become a regular thing…
Add a 2nd battery from a battery rental service when going on your 2 week rv hoiday.
I”ve wondered about exactly this concept…. “On demand range.” I’m looking at EVs for almost-always short range, and buying a hyper-range battery is stupid… but if I could “rent some range” at a reasonable cost, it might be attractive.
Hi Mike. everything is dependent on batteries these days. I think strip out the batteries all together and go more direct. Run the ev or what ever electric vehicle it is with just a generator. It can’t be that hard and it would be cheaper than having to keep changing it up, And hanging around waiting and see how that works out
Regards kelvin
THe main reason trains work and cars don’t is that trains don’t have to stop nearly as often… they can run “steady state” and therefore efficiently. For a car, you HAVE to have regenerative braking into a battery, and WANT to have some range without revving up the generator. So, that’s called a hybrid and you’ve seen those. To power the car “realtime” from the generator, the engine is as big as ICE-only equivalent, and you’ve lost a little efficiency FROM there by going electric and back. Better torque probably, but not a win for range.
Hyliion semi truck’s already use this technology. They have a hybrid system which uses a generator to extend their EV range. Granted it is a larger vehicle but in time it should be able to be scaled down.
I remember 10 years ago when Volkswagen had a diesel/electric hybrid Rabbit that they claimed would get 70 mpg. I still think a smaller diesel engine with a substantial electric motor and a 30 to 50 kWh battery would be a great combination for SUVs.
These EV vehicles should of came with self charging devices like others have on the braking and running of the wheels. Just think of the times all four wheels rotate and have a small alternator type recharging system on each. Then you have no worries of running out of power.
Most people on this board are smart enough to understand perpetual motion. But thanks for trying.
Some of us don’t drive a ton of miles and rarely are more than 100 miles from home. In the winter, I work from home and drive maybe 50 miles a week. 5 months out of the year, I drive 250 miles a week. I’m considering getting an ev for business, as I make 50-60 stops a day, 2 days a week and fuel economy is terrible. If I go on vacation, I just rent a car, because mine is junk, and rather not have any issues on a trip. As long as I can get an ev with 125 miles range, that will cover 95% of my driving needs.
Small generators may not have the power, but what about a tow behind unit you could rent for a couple days for a long trip?
The BMW i3 Rex has exactly this solution.
The Chevy Volt has entered the chat…
A portable generator won’t have a catalytic converter or any other emission controls, so it will create a lot more pollution than any modern vehicle engine.
Great points, One item not mentioned is if the goal is a carbon free footprint then gas generators defeat the purpose of an EV. Better to stay with gas or diesel motors until technology improves and one can achieve a carbon free footprint.
Probably going to be quit sometime before an EV will have a zero carbon footprint, it can’t happen until we are free of fossil fuels to generate electricity. I think for the time being it would make sense to produce gas combustion engines that get higher gas mileage, they’ve had the technology for years to get 100 plus mpg.
Report of a guy getting 26 miles on a pint (over 200mpg) of gas with a 1936 Ford flathead V8 stock except for the vapor carburetor patented by Charles Pogue a couple years before. We’ve made a lot of NON progress since then.
Proof or it didn’t happen
How many years have we been hearing about the miracle gas mileage device that’s being kept from us?
Have you seen the guy who used a lawnmower carb on his Ford Maverick v8 302 and was getting like 40+mpg? I mean there’s video. And he shows the adaptor he 3d printed to make it work. And he explains everything. Maybe not a miracle or 200mpg, but that 70’s V8 getting 40+mpg is pretty impressive.
I never believe stories that cover magic carburetors and spark plugs doubling mpg in a gasoline engine. There’s a lot more involved in solving this issue.
My Chevy Volt does exactly that. A high compression 1.4L internal combustion engine is a generator/range extenter.
BMW i3s also work with a BMW motorcycle engine in the truck as a generator. Ford patented a generator that can be added to the bed of a lightening
EVs are not going to be the vehicle of the future. I believe if they are to change it will be a nuclear powered vehicle that requires no driver. But for his to happen a lot more accurate gps data needs to be collected- including lots of off road data.
I don’t think that a nuclear-powered vehicle is a practical idea due to the radiation hazard that would result from any wreck. But it’s a cool retro idea from the ’60s…😎
For sure. But I keep reading how nuclear technology has made huge advances (along with all other technology) in terms of safety, efficiency and size. After all the US Navy has utilized small nuclear power plants in many of its ships and submarines for many decades, and some have suggested that these small scale plants have applications as local power plants. But currently the only realistic option for providing all the extra electricity to charge up EVs is to simply burn more coal – which is ironic considering how most EV drivers thinking they are driving “green”.
As it becomes more widely recognized that current renewable sources (wind and solar) are extremely costly, inconsistent, unreliable and cannot produce stored energy – these are not realistic solutions towards reducing the burning of fossil fuels for power. It’s time for realistic assessments of current state Nuclear plants to become part of a higher output, lower cost and wider range of our electrical generating plants.
Ok Mike, you made my day “Just the facts, ma’am…” Brought back memories of Jack Webb as Joe Friday in Dragnet. Thanks for all your well-informed information!
Snoopy
And how is this electricity produced to supply all these charging stations. So much for saving the planet plus our infrastructure is so outdated.
The two biggest renewable energy contenders are solar and wind, with solar being more practical right now. As far as the power infrastructure, we basically are using a 100-year-old distribution system that desperately needs updating anyway. I believe the time is now.