MetroMPG.com: Electric pusher trailer
 

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:

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.

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.

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!

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...

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

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.

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?

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

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. :)

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.

Sorry 'bout all that... I'm finally getting on Daylight Savings Time here...

I edited my last post. I do think that would be kind of the ultimate fuel-mileage boost to help your in-town driving by hybridizing with an electric system!!!

Personally I like the idea of having an all electric car and then using the trailer as a serial hybrid setup for longer trips. The trailer could even be used to expand the cargo capacity of the vehicle for traveling longer distances. The trailer setup could be standardized so that it could be used with different vehicles that were capable of using the setup. It could also be marketed as a backup generator for a home as well.

Ooohhh! I LIKE it!!! :thumbup: A (biodiesel :D) range extender/ generator/ charger/ power backup unit! Handy as a button on a shirt!!!

Why does this thread keep dying? I'm going to look at a junker crx seller is asking $450 for. Auto! Should be a good donor for such a project. Not sure I'll make my Rex elec but maybe freeway cruise with a 10-20 HP engine... I do have a 45 minute freeway commute that could payoff quickly.

I was also thinking about ditching the trailer and just adding a mini bike type solution. Briggsnstratton/Honda horizontal shaft with a sprocket on a swing arm with a motorcycle wheel. The setup could hangout in your boat tail then air shock to the ground at cruising speed.

I also like the idea of a range extender for an EV.
It has been mentioned in other threads.

I am hoping to mount an off the shelf generator to a section of box steel tubing that will slip into the box section on my tow bar. The tow bar gives a nice solid mounting point.
Using this method attaching and removing the generator should only take seconds. A tow bar lock can be added to prevent somebody liberating the generator from the EV.

I realise that the generator will not provide enough power to provide continuous driving but it should increase the range.

I would use such a set up maybe once or twice a month, the rest of the time the generator would sit on a shelf in the shed.

I will try and do some math. :eek:

For a long trip i would expect a speed in the high sixties (mph).
Would 20kWh per 100 miles be about right (5 miles per kWh)?

Miles are not my native language :D

So a 20kWh battery pack gets you 80 miles at 80% DOD. Or about 1 hour 20 minutes travel time. At 60 miles per hour you would need a 12kWh supply to keep going indefinitely.

If you had say a 4kWh generator running for the whole trip assuming a 90% charging efficency. You get 4kWh x 1.333hours x 0.9 efficency = ~4.8kWh That's an extra 24 miles or 24 minutes travel time. During that 24 minutes your generator adds another 1.44kWh getting you another 7.2 miles or 7.2 minutes travel time.
7.2 minutes gets another 2.16 miles or minutes.
2.16 minutes gets another 0.6 miles... And so on.

So roughly 35 miles of extra range (guestimate). Just a bit under 44% extra range.

I am sure there is a nice formula that will give the accurate figure but maths isn't my passion. :o

So there is no way i am going to be able to fit a 13.3kWh (including charging losses) generator on a small hatchback car. But a 4kWh generator is definitely doable.
It is definitely cheaper than increasing my battery pack size by 44%.

Does this sound correct? My math is probably as bad as my assumptions. :o

This also gives me a generator that can be used for other purposes.

• Emergency power for the house (limited number of devices, mainly fridge and tv)
• Power supply when camping.
• Portable power for power tools etc.
• An emergency charging source if the EV gets stranded somewhere away from utility power.

I think of the small generator as more like "emergency use". The "other purposes" stuff is a bit of a red-herring if the main purpose is range extension.

But a homebrew series hybrid is going to be very inefficient, and the number of charging stations is growing daily PlugShare - EV Charging Station Map - Find a place to charge your car!

It just makes more sense to have a beater (possibly as backup) if an ev doesn't meet your driving needs IMHO.

I suppose because it's a pretty big project.

I've seen one person create an electric pusher trailer since this thread was originally posted. Let me see if I can find it...

http://ecomodder.com/imgs/pusher-trailer.jpg

From: http://ecomodder.com/forum/showthrea...html#post33586

I took the ForkenSwift off the road last year due to extensive underbody rust. At the time, I actually had everything I needed to make this...

http://ecomodder.com/forum/attachmen...1&d=1422372375

But and have since sold the EV parts from the blue car. Why? After much soul searching, I realized it's a big project, and I've already got TMFP! (Too Many ... Projects!)

Unfortunately the yearly registration and insurance here in Australia is more than the cheapest cars are worth.
Reg and insurance is $757.70 annually compared to my EV conversion donor car purchase cost of $400.

That plug share site shows only one available charge site on my monthly long distance route. Unfortunately it is located about 2% into my trip so it wouldn't make much difference charging there or before i left. Also it is at a car dealership, there is only one charge point and it would most likely be in use by the cars being serviced. The dealer isn't even the same make of car as mine.

If the generator can extend my range enough to safely get to my destination where i know there are available charge facilities. Then that would be preferable to me. Maybe soon there will be extra charge stations added along the route and i could feel more confident of getting a mid trip top up.

This does lead me to think about what the social conventions around charge points are. At a petrol station there are lots of pumps and once you fill up you are expected to pay and move away from the pumps.

But with an EV the charge time is longish so people would be likely to grab a bite to eat while they wait. But what about when somebody decides to have an hour long lunch while their EV blocks the only charge point? Do the charge points make some sort of attention getting display to attract the attention of the owner when they complete the charge?

What about somebody that commutes to work, parks their EV at a charge point, then goes into work leaving their car all day in the charge point parking spot?

Same for shopping centre car parks, the charging stations there could be blocked for hours by drivers that park there to get their free top up. The top up may only take minutes if they are local yet they could spend hours shopping.

I am hoping for something like a subtle flashing light or beeping sound for say the first 5 minutes after the charge completes but that slowly escalates to a car alarm intensity if the charge cable isn't removed. :D

I like your maths Astro; it should work out roughly the way you figured it. The problem I see is charging the vehicle while operating it. My PiP will not allow the vehicle to be driven while plugged in, and I'm sure all cars are designed this way.

The first problem to tackle is having an over-ride mode that allows the car to charge and drive at the same time.

Once that is figured out, I'm sure a generator could be added to extend range.

I too like the idea of making things modular and versatile. A generator that can perform all of the tasks above makes it much more valuable.

I'd like to see batteries become more modular so that individual banks can be added/removed from a car, and added/removed to a motorcycle, lawn mower, leaf blower, chain saw, etc. The cost of ownership of all these items would be greatly reduced if the same power source could be utilized.

A generator only makes sense as a range extender if it's also used for other purposes. If the only purpose is to extend range, then a gas pusher makes more sense.

6 kWh generator
http://www.generatorsales.com/reflect143.jpg

Well a conversion can cost a lot also, have you looked at how long your commute is and speeds, and figured out how much battery you would need? And how much motor/controller you need? It is tempting to rely on a generator but you have to have an EV to attach it too, and have determined the energy requirements before you can sort out how/if to augment the main pack.

Part of it may be that this isn't the hybrid section of the forum.

The EV will be my daily commute vehicle and the battery pack will be sized to deal with that daily trip plus some local trips to the supermarket, etc.

Adding another say 50% to the battery pack size for just that one long trip each month would mean i would be carrying around that extra weight every day and not getting any benefit from it.
I could look at making the extra battery pack capacity removable but the size, weight and cost of that extra battery capacity would be quite high compared to a small generator.

I have to register and insure the EV but if the generator can increase my range enough to deal with my long trip then it saves me at least $757 dollars a year as i don't have to pay the registration and insurance on a second car (not to mention the maintenance) that would only be driven 12 times a year. Also the EV gets a $100 dollar discount on it's registration for being eco friendly. :)

Then if later on a charging station opens up near the mid point of my trip then the EV would be able to make the trip without assistance. And i would only be left with a useful generator rather than a surplus and costly second car.

The generator would only be an interim solution until the charging network improved and it would save me having an extra, seldom used ICE vehicle.

With the car being a conversion rather than a factory electric such a mod would be fairly straight forward. I imagine the lockout on driving whilst charging is to prevent somebody driving off when the charger is still plugged in.
Even if i can't charge whilst driving and have to plan on a one hour rest and recharge around the mid point of the trip that could be done.

It is annoying to have each device have its own unique battery pack configuration.
If there was some standardisation then the number of battery packs i would need would be greatly reduced as i don't run every device simultaneously. Also when a device fails (as they tend to do) the battery pack could be salvaged and re-purposed to another device.
I have seen that a few of the power tool manufacturers have released power tool ranges that share the same battery. Still quite expensive. Also they seem to be compromising on capacity. Picking an average capacity that leaves the more power hungry power tools lacking performance. The more power hungry tools really need to have provision for two standard battery packs. Then the average sized battery pack would make sense.

It really isn't unused, the less you cycle your pack the longer it lasts, the more capacity the less you cycle. Plus you have more power available if you want to have some "fun". You can upsize the motor and controller for better acceleration/top speed. It works for tesla.

How many miles are we talking about here, commute vs once/month?

I have both a generator trailer and a pusher trailer (based on an aircooled VW). The pusher is great for long highway trips, but on sub-100 mile journeys where it would only serve to prevent one fast-charge session in my i-MiEV, it is on balance, impractical. Driving the pusher is fun- it turns the MiEV into a vehicle with some serious passing power on the highway, having doubled the power available! I'm working on refinements, as binary control (WOT vs lugging a dead engine at speeds under 30 mph and when stopping/starting) is inefficient and yeilds a a blended city/hwy mpg of only 20.
My genset trailer charges the Karmann Eclectric at 4 kW, which only extends highway range by about 15 minutes/15 miles, but it does enable continuous recharging while crawling through traffic or stopped somewhere that has no EV charging options...

An automatic-transmission Metro drivetrain could make a very good EV pusher, but I built with what I know best and had on hand.

Simple answer.
35.4 miles versus 54.7 miles.
So an increase in range of 54% is required.

More involved answer.
There are two different routes i can take in my commute.
Route 1 is a 57km (35.4 miles) round trip at 60mph.
Route 2 is a 42km (26 miles) round trip at an average speed of 30mph.
Route1 is via a freeway so almost the entire trip at freeway speeds with only 6 sets of traffic lights. However the wind resistance will be quite high and it has tolls so an extra $10 per day.
Route2 is a shorter distance and at lower speeds however it has 34 sets of traffic lights. So significantly less wind resistance but more stop and go. My drive system will have regen so i will win back a small amount of the stop go energy.

I gave the round trip figures for the commute as i have not secured any sort of charging at work so i have to do the round trip on a single charge. Whereas the once a month trip has charging available at the destination.

The once a month trip is 88km (54.7 miles) one way all at freeway speeds.

If i can secure charging at work then i will be using a 6kWh battery pack and no hope of doing the once a month long trip even with generator assistance. If i can't charge at work then it will be a 12kWh pack which makes the long trip feasible with generator assistance.

So my build is a 6kWh battery pack with provision to add another 6kWh.

It's never simple is it. :)

You'd be better off with an econobox 5 speed and good technique. The plug in prius 4.4kwh battery is only good for 11 epa miles, and it is well engineered. I don't think your commute is a good fit for a budget "ev", and you will get crummy hybrid efficiency if you don't know exactly what you are doing.

The Prius is nearly 400kg heavier than my vehicle.
I would also imagine a hybrid vehicle would have many compromises in it's design to allow for the dual power systems.

Even the most efficient gas guzzler still guzzles gas.
Electricity is cheaper and can be cleaner. Some of the electricity will come from my solar panels so cheaper still.
I am quite hopeful of my EV being able to cope with my daily commute.
Worst case scenario is it will require further expansion of the battery pack.
There are few problems in the world that can't be solved by throwing large sums of money at it. :D

Ah, you have a build thread, and you live in OZ :) If I thought the EPA (or the DMV) wouldn't pown me, I would definately entertain a hitch mounted small diesel chained to a wheel on a swingarm (with raising/lowering perhaps). Just one speed to help at higher speeds.

edit, like this but with a small diesel:
http://99mpg.com/getimage.asp?id=/Pr...van.jpg&mode=0
http://99mpg.com/getimage.asp?id=/Pr...old.jpg&mode=0

pusher trailer update
 

General update- I took my longest trip yet with the pusher trailer this week. 353 miles total in the i-MiEV with a single quick charge and one L2 charge en route. Otherwise, it was all hillbilly-hybrid! There were two 145 mile highway legs and 63 in-town miles in-between, during which I was towing around the dormant pusher.

Pusher control is still binary- meaning it's either running at wide open throttle, or not... This is enough power from the salvaged 1600cc aircooled VW engine to average 65 mph on hilly interstate, using the electric drive to boost power up the hills, and scrubbing off speed with regen on the way down (though I also slowed to 60 mph uphill and sped to 70+ downhill). That is 'charge sustaining' mode, in which I maintained SOC within two bars over more than 100 miles.
In this charge sustaining mode, I once again hit 19.5 mpg. BUT, throwing in the around-town errands at my destination, the trip averaged 29 mpg overall. Not great, but about 7 mpg better than I could have expected with the family minivan. A whopping 3.88 gallons of fuel saved.

Economically, I would've been better off with a borrowed pass to the West Coast Electric Highway, as I refuse to pay Aerovironment's $7.50/session DCFC fee for non-subscribers, and it was logistically very helpful to not spend almost four extra hours waiting on charging sessions... The approximate $32.32 I spent on gas and $10.10 I spent on EVSE come out to 12 cents per mile, which is a lot more than MR BEAN's long term average of 2.4 cents, but equals the fuel-only cost in our minivan, and after all, I did save 3.88 gallons and about 73 lbs of CO2, given that I was recharging mainly on hydro and my home solar array. NOx and HCO, unburnt hydrocarbons, etc.. are another question.....

SO in summary, no better-than-OEM hybrid mpg numbers or great financial savings to report, but enough to continue refining the pusher, perhaps with a tune-up and throttle control.
:roll:

The maneuverability of an i towing a trailer is compromised ONLY by parking stalls, and that's not bad when the tongue length is tuned to allow a full 90 degree parking angle between car and trailer (especially for an i at charging stations). Otherwise it can still go anywhere.

jray3, do you have pics posted of your pusher setup? A dedicated thread about it would be fun.