VW wagon EV with charging trailer...thoughts?

[alohaspirit]

Originally Posted by ai4kk

I don't think 1 or 2 KW would do it for a car on the open road.

you dont?

then get a bigger generator

[Frank Lee]

I like aloha's idea. So maybe it's too small to meet the on-the-go needs. Pull over, have a burger, let her charge up while you relax.

[Piwoslaw]

Remember that the generator doesn't have to charge the batteries in 30 minutes. If the 2kW gennie is on for the whole trip, plus stops, then it will let the batteries discharge more slowly.

BTW: How much power is needed to keep a vehicle with reasonably small CdA at 50mph?

[ai4kk]

That was kind of the point behind using the ICE from the donor car and the bigger motor from the forklift

Seriously, roughly how many KWs does it take to maintain 65 in a reasonably slippery car? What would that equate to in HP? I realize that we have to factor in efficiency losses but that is a starting point.

My only real concerns about the original ICE is that A) it may be heavier than needed.....but not sure if a smaller industrial diesel would really be any lighter. and B) if the engine's most efficient output range can't be matched to the generator's best speed whether through a chain drive or whatever. The weight can be dealt with possibly by looking for the smallest automotive diesel I can find, and the speed rating can at worst case be solved by using a bigger generator that can efficiently use all of the ICE's power at best RPM....and then shut it down when it is not needed.

Considering that unless you're a traveling salesperson most cars spend a fraction of their time on long road trips, I can accept a small trade-off in highway efficiency if it makes the car practical to use in daily driving as a primary / only car.

[luvit]

a honda 2000W is plenty. the charging would use no more than 1800W at 15amp current.

there may be some cars that would require 2500W generators, but that depends if a car's charging cable would need to be 20amp current.

[Piwoslaw]

Originally Posted by luvit

a honda 2000 KW is plenty. the charging would use no more than 1800 KW at 15amp current.

there may be some cars that would require 2500 KW generators, but that depends if a car's charging cable would need to be 20amp current.

Wow, dude, I think you meant 2000 W, or 2 kW, not 2000 kW!!!. That's more than 2680hp, enough to pull a train. So yeah, 2000 kW is plenty.

I used EcoModder's calculator to see how much power is required to keep a certain speed (not accelerate). I used the default numbers, exept Cd=0.26. 2 kW would keep you rolling at just under 35mph (35mph requires 2,148W), while to go 55mph you'd need 5,982W. That's really not much. Changing to Cd=0.32 gives 6,993W @ 55mph.

So, in the first case (Cd=0.26), exactly 1/3 of your power would come from the 2kW generator, extending your battery life by that much. If you count in "burger&pee" stops, coasting and regenerative braking, subtract acceleration, then you could probably extend your range by 50%-60%. A 5kW gennie would be more than enough if you stay below 50mph.

So ai4kk: once you get your wagon converted and aeromodded, use the calculator to see how big a generator you'd need. You'll see that the engine from the donor car will be way too big.

[luvit]

Originally Posted by Piwoslaw

Wow, dude, I think you meant 2000 W, or 2 kW, not 2000 kW!!!. That's more than 2680hp, enough to pull a train. So yeah, 2000 kW is plenty..

lol. yeah, i meant 1800W or 1.8KW / 2000W/2.5KW
i edited my post, but forgot to drop the K. *fixed*

[ai4kk]

So in keeping with the theme of reusing as much as possible from the original donor vehicles (VW Fox diesel and electric forklift), if the combination of the VW 1.6l diesel (tuned perhaps to operate more efficiently at a lower RPM) and the large motor from the Frankenswift forklift, what effect would a lower duty cycle have on overall efficiency? Would keeping the ICE warm enough be a problem? How much power would it take to spin an electric motor like that at max reliable/efficient RPM with a sizable load (charging and propulsion) on it?

It seems that if the generator combo is too big, reducing the duty cycle would solve that....kind of like pulse and coast. Run it till it's charged, then turn it off till the voltage drops a certain amount. I don't think physical size and weight would be too big of an issue considering that an automotive diesel is pretty compact to start with compared to an industrial diesel.....and the 1.6 is about as small as we can easily find over here in a car. If someone knows of a suitable alternative, that would be great, but I bet it won't be as cheap as the engine that came in the car.

[Silveredwings]

See Jerry Halstead's excellent EV calculator

[Piwoslaw]

Originally Posted by ai4kk

It seems that if the generator combo is too big, reducing the duty cycle would solve that....kind of like pulse and coast. Run it till it's charged, then turn it off till the voltage drops a certain amount.

Batteries have a max current for charging, above that you're either wasting energy or destroying the battery. It's better to charge longer with less current. (I hope I'm not lying, any EV owners help if I am.)
The ICE/generator's most efficient rpm may produce more "juice" than the drivetrain+batteries can handle at the moment. All of this will have to be sorted out once you know your battery parameters.

Originally Posted by ai4kk

I don't think physical size and weight would be too big of an issue considering that an automotive diesel is pretty compact to start with compared to an industrial diesel.....and the 1.6 is about as small as we can easily find over here in a car. If someone knows of a suitable alternative, that would be great, but I bet it won't be as cheap as the engine that came in the car.

The smallest automotive diesel I know of is in the Smart ForTwo. It's a 0.8 liter, direct injection, commonrail turbodiesel (=very new and high-tech). Its 54hp is more than enough to serve as a gennie, plus it weighs less than 200lbs. Here's more info. I don't think the ForTwo had that engine as an option in North America, but in Europe it can be found in scrapyards (I found two at a local auction for the equivalent of US$700 each). There is also the 1.2 liter TDI from the 3L versions of VW's Lupo and Audi's A2, but that's just more eye candy for America with EPA emissions

Also, Christ found a diesel engine. I'm not sure if he's found a use for it, but it's heavy!