Towable Generators

How about this one:

Honda Power Equipment - EB11000

You would need to build a small trailer around it, but it shouldn't be too difficult, or expensive.

All the best,

Chris H.

I would imagine that out on the highway the noise wouldn't be too much of an issue, but in a downtown area, it might be a different matter...

Dry Weight: 403 lbs
AC Output: 120/240V 10,500W max. (87.5/43.8A 9500W rated (79.2/39.6A)

A little on the high side of weight and on the lower side of power.

Half the weight, twice the power at similar dimensions then it will start getting interesting.

Hi there--I'm new to this forum. Just joined tonight. Excuse my ignorance, but just how big of a generator would you need to operate the electric motor?

dtaschacht said:

Hi there--I'm new to this forum. Just joined tonight. Excuse my ignorance, but just how big of a generator would you need to operate the electric motor?

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Welcome to the forum!

It'll vary depending on how you plan to use it of course, but according to this wikipedia entry it takes a generator with about 15-20kW of output to maintain highway speeds for a midsized car. For a larger car it's 30kW or more. Genset trailer - Wikipedia, the free encyclopedia

Sounds about right if you convert it to hp, since it takes 10-20hp to maintain 60mph and 20kW is about 27hp. Of course this is assuming the generator is mainly being used to maintain highway speeds (probably the way it's going to be used since it'll mainly be used for long trips on highways).

Generally speaking you would want a generator to recharge a battery pack. Autos have intermittent and variable power demands so better to let the generator give it an even slow charge, and let the electric motor draw bursts of power as needed.

Size depends on how much "range extension" you need. If you wanted to drive on generator power alone when the batteries were near empty then you would probably need a fairly large (e.g.: 75kW / 100hp ) generator.

So is what you pictured there a 75Kw generator?

I love the idea of a towable Genset for long trips and then just plug in at night every night at home. Especially for the Model S.

Required generator power depends on what you want from it.

If you want it to provide all the power you could ever need, than it has to be pretty powerful - over 150kW or very close to motor max power or even over it, because of losses in wires and PEM. This makes little sense though. Get an ICE car and avoid the middleman.

If you want to have practicaly unlimited range (with gas refuels ofcourse) than it has to provide for average highway requirements or around 30kW. This sounds reasonable but it really isn't. We humans have our own constraints and have to sleep amongst other things ie. we have to take brakes. Generator doesn't and can keep running overnight.

So, it could be of lower power.

If it is only 10kW then your max range would double from 250 miles to somewhere around 500 miles when the car would switch into "very limited power mode" - you would only have those 10kW of power left. Enough for slow acceleration and about 30mph max speed. But after those 10 hours of driving your would be well advised to take a brake and maybe get some sleep. You could leave the generator running to charge up the batteries though. It would do that in some 6 hours. 10kW generator looks usable.

So what would your range increase to using a 30KW Genset at highway speeds - say an average of 50-60 mph (which is really a highway speed of around 70 mph figuring in stops etc..) I don't think any reasonable person would ever expect to travel more than 720 miles a day (60 mph x 12 hours). That would effectively be unlimited mileage. And then on top of that you could charge all night while you sleep and start fresh the next day.

Steve Hawkins' Long Ranger

RXT-G 3-Phase AC
AC-150 70kW configured for 7,200rpm 70a
continuous output of 24kW.
Drivetrain: Kawasaki Ninja EX-500 powered ACP AC-150 converted to a generator system.

ACP specs

See also this other thread about REEVs since the power requirements are similar. (Though usage may be different since you're likely starting with a lower capacity battery.)
http://www.teslamotorsclub.com/technical/2189-reev-concerns.html.

Be sure not to confuse power and energy.

Kevin Harney said:

So what would your range increase to using a 30KW Genset at highway speeds - say an average of 50-60 mph

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According to data from Roadster Efficiency and Range, Roadster needs about 15kW for constant 60mph.
With 30 kW gen-set your range would become practically limitless at that speed. Things could change with many stop 'n' goes, climbing hills etc.

30 kW is overkill. We should be aware that engines capable of 30kW of CONSTANT power output are very heavy. very loud, very big (think truck or bus engine). That genset linked above with 24kW output would have very short lifetime (a year max) as it is using a bike engine. Bike engines see very low average power (under 10kW) so they can afford to be light and still have high max power. They are very high-maintenance things though.

Gen-set could have normal operating mode at say 5kW with low noise and high durability and performance mode for times you really need that extra energy and are willing to sacrifice some durability.

doug said:

See also this other thread about REEVs since the power requirements are similar. (Though usage may be different since you're likely starting with a lower capacity battery.)
http://www.teslamotorsclub.com/technical/2189-reev-concerns.html.

Be sure not to confuse power and energy.

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The REEVs are definitely related, only difference is what you mentioned and also that they have internal generators.

However, it seems right now the REEVs have "range extenders" which are intended to be the primary source of power after the battery is depleted while minimizing the need to draw power from the battery (since presumably it is near depleted or has reach a threshold level where you don't want to deplete much further). For this application then the 75kW that TEG mentioned will be more appropriate. This is because the generator also has to provide power for acceleration (so it needs more peak power).

In a towable generator, the intention is mostly to maintain highway speeds for long distance travel, with the battery providing power for other situations, so the power requirements are much lower (though it has to be continuous power rather than just peak).

yes but that genset being towed would only be used a couple times a year max and even then only for a couple days at a time maybe. I think it would be ideal to rent one for vacations just as one rents say a uhaul trailer.

Kevin Harney said:

yes but that genset being towed would only be used a couple times a year max and even then only for a couple days at a time maybe. I think it would be ideal to rent one for vacations just as one rents say a uhaul trailer.

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Yes that would be ideal, but it seems like there is no one who is working on this idea and making some rentable genset trailers. Genset trailers in the mean time would be a lot more practical, cheaper, and easier to implement than other alternatives like rapid charging or battery swapping.

REEVs seem to get a lot more attention.

Of course the market for towable gensets right now would probably be very small, so it might get more attention after all the promised EVs get released.

There is a simple reason that the REEVs get more attention from others ..... The others have a range of ONLY 40-50 miles!!!!!! You would have to tow a trailer ALL THE TIME with that mileage With a 200+ mileage range you would only need the trailer for long trips.

I have pondered many of these same questions I found in this and other related threads. But so far all it appears to be is theoretical discussions. Questions I still have are:

1) Has anyone actually tried interfacing a towable generator to the Roadster?

2) Is there a less conspicuous pigtail cable that can be added to tether the generator instead of connecting to the side mounted power receptacle?

3) Does the car's firmware even allow the batteries to be charged while the car is driven?

Under normal conditions I would likely never have the need but I would like the ability to take it on long trips from time to time, without a flatbed.

ZeroFossilFuel said:

I have pondered many of these same questions I found in this and other related threads. But so far all it appears to be is theoretical discussions. Questions I still have are:

1) Has anyone actually tried interfacing a towable generator to the Roadster?

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I have never seen such a thing done. I assume you saw the ACP gen trailer for the TZero and Rav4EV early in this topic though...

2) Is there a less conspicuous pigtail cable that can be added to tether the generator instead of connecting to the side mounted power receptacle?

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The car may put itself in "park" when off/charging. The reductive charging might not work right if you tried to plug a charger in while the vehicle is in motion. Just speculation, but I bet you would have trouble trying to add charge to the vehicle while it is in motion. (The gearbox always turns the motor when the vehicle moves... no clutch to disengage it). I have never seen a Roadster charge from any connection other than the one under the charge cover.

3) Does the car's firmware even allow the batteries to be charged while the car is driven?

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Well technically that is what regen is doing. A long time ago I inquired about the idea of having the Roadster charge itself when towed behind an RV. Somewhere along the way someone made a comment that such a thing is possible. So I suppose you could hook up a tow hitch between the front of the Roadster and an RV, turn on the Roadster and then start towing it and the battery would start charging based on regen.

Under normal conditions I would likely never have the need but I would like the ability to take it on long trips from time to time, without a flatbed.

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This is a question many have pondered. The usual "solution" ideas are quick charge and pack swap. Neither seem to be reality now. Better Place suggests that they will have both technologies ready on a mass scale someday soon. Tesla more or less said they are considering it for Model S. Time will tell.