View Single Post
Old 07-18-2013, 11:21 AM   #238 (permalink)
NachtRitter's Avatar
Join Date: Dec 2008
Location: Placerville, CA
Posts: 1,594

RippinRoo - '05 Subaru Legacy Wagon 2.5 GT
90 day: 21.16 mpg (US)

Helga - '00 Volkswagen Jetta TDI
90 day: 53.91 mpg (US)

Olga - '03 Volkswagen Jetta Wagon
90 day: 46.24 mpg (US)
Thanks: 303
Thanked 311 Times in 186 Posts
Originally Posted by RedDevil View Post
So we're ditching the genset option because the Leaf's max charge rate is not high enough?
It does not have to charge the battery, right? It just can feed the EV's engine directly.

We accept that converting a car to an ICE pusher trailer with all the controls is feasible.
Circumventing the max 'charge' limitation to match the power used under load should not be harder that that imho. With twice the power generated the problem disappears.
Then the range is limited only by the generator's tank size.
OK, let's assume that. Recall that the Leaf in my example consumes 16 - 21kWH at 65mph (without a trailer). Granted, that's taking into account the losses from charger to battery and back out from battery through controller to motor... so there would be fewer losses going direct to controller and then to motor, but as has been said the whole path is pretty efficient already so we're not saving all that much, right? And again, we haven't accounted for the additional drag of the trailer, so using "best case" numbers wouldn't pass the snicker test.

Assuming a 21kW genset (where the 21kW is peak and continuous is 20kW, such as this one: Mobile Isuzu 21 kW Diesel Generator (Note that this one is already on a trailer, and weight is already at 1875lbs)), consumption is 1.8gph. Does that beat the theoretical pusher's "worst" of 1.2gph? Nope.

The problem is that the ~21kWH consumption is steady-state flat cruise consuming the 0.33kWH/mile... That's not real world... In the real world, a driver has to accelerate, slow down, climb grades, descend grades, etc... if your going to depend on the genset to drive the motors directly, then it has to be sized to handle the peak power draw of the worst case portion of the trip. For that kind of worst case, the 21kW genset isn't gonna cut it, and a bigger generator is gonna consume more fuel.

Granted, it might be possible to have the controller pull from the battery pack when the motor draw exceeds the rating of the genset, though to me that sounds complicated... and the EV's battery isn't getting recharged, so if regen (which is also lossy) from downhills & deceleration can't keep the battery charged, then eventually battery pack will be drained and the "just right-sized" genset won't be able to get the EV going from a stop or get it up a hill anymore. How soon that happens depends entirely on the route.

Bottom line: even if you sized the genset to drive the electric motors directly for steady state 65mph cruise, the fuel consumption is higher than the pusher...

Last edited by NachtRitter; 07-18-2013 at 11:31 AM.. Reason: wording fixes
  Reply With Quote