MetroMPG.com: Electric pusher trailer

[MetroMPG]

Wow. It's been 2 years since I daydreamed up the topic for a December 2005 MetroMPG.com article called "All I want for Christmas is a plug-in hybrid pusher trailer".

In that post, I mused out loud about "hybridizing" the Blackfly ... not by tinkering under the hood, but by adding a 3rd pair of wheels!

My idea was the reverse of something I'd seen a couple of creative EV owners tackle to extend the range of their 100% battery-powered cars:

(from MetroMPG.com - All I want for Christmas is a plug-in hybrid pusher trailer)

The Porsche in this photo is a pure EV. Its trailer is a fully functional front half of an early 80's VW Rabbit: ICE-powered (Internal Combustion Engine), automatic transmission. The Porsche owner installed a simple set of controls to "drive" the pusher trailer: an ignition/starter switch and throttle control.

The owner claims this setup is completely stable in all driving conditions.

The idea for the Metro was the mirror image: an electrically-driven trailer for around town use. Since most of my city trips are low speed/short distance, I figured I could pull it off technically, and end up with something like this:

(from MetroMPG.com - All I want for Christmas is a plug-in hybrid pusher trailer)

Having successfully built the ForkenSwift, I still think about this idea.

I really think it could work - and it would get around the issues of owning two vehicles (parking, insurance, maintenance) - an EV for town use, and an ICE for longer trips.

And obviously, other people do too. I still get mail on the subject. I'll post one reader's response in a few minutes.

[MetroMPG]

A reader recently wrote:

I need an electric pusher unit like yours that has possibly 30-60 hp for an electric assist on a 25 ft motorhome. It could be set for one cruising speed like 65 mph, I could turn it on when going down hill or up hill with my cruise control on. This should increase my mpg. I could also charge the batteries when going down hill.

First of all, you're absolutely right. A pusher trailer would increase your motorhome's MPG.

Unfortunately, beyond that I don't have any more good news for you. It's not really a practical approach, because you'd have to spend a boatload of money on high tech batteries to make it work.

It's a question of the energy content of the batteries: it takes about 700 lbs. of lead acid batteries to equal the energy content of one gallon of gasoline. How far would a pusher trailer with 700 lbs of batteries get you at highway speeds?

My electric car - the ForkenSwift - with its 8 golf cart batteries (520 lbs worth) has as much energy on board as 3/4 of a gallon of gas. (Actually that's when they were new. Half dead as they are now, they probably have half that much power again - so 1/3 of a gallon of gas).

Of course you could use batteries with more energy density: nickel batteries (NIMH or NICAD) are better, and lithium batteries are better still. But you'll have to sell the motorhome to afford an advanced battery pack that's able to push it any distance

You can see why EV technology is used mainly for low power/low speed applications. Or why hybrid gas-electric cars are designed to use electric assist at low speeds in the city, rather than for extended periods on the highway.

It's all about the batteries.

[lectruck]

A pusher trailer would be great, you would have to figure out which gear to put the transmission in or get a direct drive motor. Could you get the motor to charge the batteries when not using the electric drive? Probably only with a regen AC system!

[Intrigued]

Boy, that Porsche setup is cool but weird looking!!! The first question in my mind is: "Where did he put the gas tank???"

I know it's been mentioned before, but something like the pictured Metro trailer, with a biodiesel generator in it, would sure help with EV range. I'll have to surf around to see what the arguments were against that...

[NiHaoMike]

Originally Posted by MetroMPG

A reader recently wrote:

First of all, you're absolutely right. A pusher trailer would increase your motorhome's MPG.

Unfortunately, beyond that I don't have any more good news for you. It's not really a practical approach, because you'd have to spend a boatload of money on high tech batteries to make it work.

There's a simpler solution: DWL the motorhome! Most basic implementation is free, more advanced implementation requires some relatively cheap instrumentation equipment.

[bennelson]

Having some experience with towing an electric vehicle (the Electro-Metro) with a gasoline vehicle (Chevy S10), I can tell you that it is completely possible to push the gasser around from behind with the electric.

Several times this winter, I was towing the day after a snowstorm, and my (two-wheel drive) truck is pretty poor on snow.

One time, my truck tire got off the really smooth plowed part of the road just enough to start slipping, and I got stuck.

No problem, I put the truck in neutral, hopped in the attached Electro-Metro, flipped it on, and easily used the Metro to push the S10 right back into the clear part of the road. It was great!

I am not sure exactly how steering of a gas car would be effected while being pushed from behind from an electric though in general driving.

Another great "pusher-trailer" to take a look at is Mr Sharkey's. It's pretty slick and features a couple different ways to be used.

[mattW]

Hmmm I still think your way is a little backward metro. Around town is when you would have more difficulty parking and thus not want a trailer, compared to highway where a trailer is a relatively non issue. Also the majority of your driving would probably be in town so you carry the extra weight and rolling resistance for a greater proportion of your km.

It makes much more sense to have a light easy to park EV for the majority of your driving around town and to use the ICE pusher when you occasionally need to go highway. What is the advantage of the reverse?

[MazdaMatt]

The electric pusher is great for anybody who knows how to drive with a trailer.

[Intrigued]

Originally Posted by mattW

Hmmm I still think your way is a little backward metro. Around town is when you would have more difficulty parking and thus not want a trailer, ...
It makes much more sense to have a light easy to park EV for the majority of your driving around town and to use the ICE pusher when you occasionally need to go highway. What is the advantage of the reverse?

Huh?

[EDIT] Oh, I get it. I was thinking you were both trying to say the same thing. It would be neat to reverse-hybridize the Flea to help it's fuel mileage even more!!! Batteries will move you more efficiently, but can't take you far enough outside of the city.

[MazdaMatt]

Read the thread again... his pusher idea is a battery-powered trailer, not a gas one like the porsche.

Just a thought regarding the motor-home guy. I don't think that he needs to have a pusher that can carry his entire motorhome at highway speeds. I think he just needs a high-geared electric drive that takes some of the load off of the engine. Heck, he could only turn it on to accelerate... Would even be able to tie the pusher throttle to the motorhome's "load" and give it an "idle load" and allow it to provide power to try to get it down to "idle load". "idle load" would be set according to his standard highway cruising load.