Range Trailers

Thought this topic deserved it's own thread as it'll keep popping up. FYI, range trailers are a supplemental power source pulled on a trailer. That power source can be anything, be it a genset, battery, fuel cell, engine-driven axle, microturbine, jet engine, propeller, the sky's the limit.

Here's the latest company to troll for funding, and their animation uses an iMiEV / CZero.
http://www.gizmag.com/ebuggy-ev-battery-trailers/24202/

Here's some previous/existing versions.
http://www.facebook.com/pages/The-Range-Trailer/257589060955815
http://tzev.com/2001_rxt-g_.html
http://www.evalbum.com/1713
http://tzev.com/1993_tevan_RXT-B.html
http://www.evalbum.com/753
http://www.evalbum.com/304
http://www.karmanneclectric.blogspot.com/2012/02/byov-build-yer-own-volt.html

Yeah, I saw the eBuggy site a few weeks ago, but I wasn't aware there were so many others trying this idea.

So how does my 66bhp i-MiEV haul this battery trailer up a freeway-grade hill at 65 mph? It seems to me this is a fatal flaw. The only way I see around it would be to put some sort of smart motor assist in the trailer, turning it into a crude mini-EV in its own right - and incidentally raising the trailer cost by quite a bit, one would imagine, since I think it would have to be pretty smart to be safe enough for public roads.

For their part, eBuggy seemed pretty vague about details of this sort; I posted this question to their facebook page and got no reply, which deepened my skepticism.

Any other thoughts on this?

Well, our battery packs only have 150 kg (330 lb) of cells, and a (Harbor Freight) steel trailer that could carry two of those packs only weighs 70 lb! So, add some hardware, and a realistic weight for an iMiEV battery trailer to haul a second pack should be 450 lb. Going through that effort, I'd build it for a double pack (still under 800 lb total), and add the second one as funding and/or salvaged pack availability allows!
Towing a small trailer that fits in the wind shadow of a vehicle consumes very little extra energy on the flats, and at least our cars would make up for some of the uphill penalty with regen on the way down! My buddy who build a 200 AH range trailer for his factory S-10 EV and drove it from Seattle to the Mexican border and back reports tremendous regen recovery on the long downslopes, so much so that he had to consider the upcoming terrain and sometimes cut short his charging stops. Since our i has the power to push air aside at 82 mph, I'm sure it could tow at 65, perhaps slower on the hills. At any rate, I'd bet that it could make it up hills better than the 35 mph semis that I often pass as they struggle up a local highway. (My conversion can maintain 70 mph and surge to 75 mph up that hill while towing the genset trailer, but I don't recall the energy draw- it can pull up to 170 kW!)

I haven't added instrumentation to measure exact amperage yet, but will try to go ahead and record the readouts when pulling my smallest trailer, as well as total consumption over a mixed driving route. One I've already recorded comparing my conversion to the iMiEV consumption.

One other item to mention is that a battery trailer can be used to provide power for the first and last legs of a round trip. Imagine driving 45+ miles on trailer power before dropping your trailer at a charging station, then proceeding another 30+ miles before turning around, and then you pick up the charged trailer on the way home. That's a round trip of 105+ miles without any charging stops for the car, only for the trailer as you run your other errands. I have a buddy who did this with a 'drop pack' on his electric motorcycle conversion as his daily commute! :ugeek: He charged at work and had a friend's house halfway where the drop pack was recharged during the work day. He's since converted a roundtrip-capable pickup truck .

Of course, a 105+ mile day is quite feasible with Level II charging stops, (I did a 110 mile round trip on Sunday at 65 mph speeds), and a few of our members could hypermile it without charging, but a range trailer could reduce the logistical calisthenics required, especially in most of the country where there is no public EVSE.

It sounds like the 32Kw trailer must have one very large (or two smaller) chargers built on board, if you can 'drop it' to recharge and then pick it up later - Even a pair of the cars OEM chargers/BMS systems will require 4 or 5 hours to recharge the two packs. Of course you'd need an enclosure of some sort to make it all weatherproof. it might be hard to keep it under 800 pounds . . . . maybe you could add the drivetrain from a wrecked iMiEV to the trailer to push it along??

*IF* you could pick up a pair of battery packs/BMS systems/chargers from a couple of wrecked iMiEV's really cheap (like $2K or less each) this might prove to be a workable solution for longer trips, but unless you really needed to go that far on a regular basis, this sounds like a lot of trouble and money for relatively little gain . . . . you'd still have probably $5K in the project and you'd only be using it for those longer trips

It's an interesting propositon though . . . . post pics of your project as you build it please and I'm sure we'll all be interested to hear how the final thing works in actual use. The range gain of the final product will be pretty hard to predict I think, especially in hilly country

Personally, I'm a big fan of buying technology which was engineered for your intended usage - If I regularly needed to make longer trips I would get a plug in hybrid of one sort or another . . . . plug it in whenever/wherever you can and live with 50 MPG when you can't, as opposed to spending big $$$ to be able to temporarily increase the range of a pure EV. The money you'll have in your trailer would buy the gas for a PHEV on those long trips for years and years

Don

Oh Don, why do you have to bring practical considerations to bear on these discussions!
EVs are my primary hobby, so I like to do things to 'em just because it hasn't been done before (or could be done better). My non trailer-mounted surplus computer server UPS already puts a steady 2200 Watts into my conversion, and it can also keep the iMiEV onboard charger maxed out at 1900W on 120V through my SPX EVSE. Throw that puppy in the boot or on a small trailer, and we'd gain six miles of range per hour of fun time (err typo, meant RUN time). I haven't found the right 240V output UPS yet with a low input V pack requirement for portable use... The only mod that should require would be a cleaner path for AC input than having the J1772 handle stick out while underway, and a bypass of the safety that prevents charging while underway (and perhaps some grounding issues). Ideally, that bypass would only be in effect while using the added inlet, while use of the OEM J1772 charging inlet still prevents one from driving away while plugged in!
Of course, patching in a parallel 330V pack of Headways or LiPo cells would probably be easier and perhaps even lighter, but I like cheap creativity!

I think everything you and all the other long term EV'ers do to these and other cars is really cool - It's the 'what if' thinking that's got things to where they are today and we 'Johnny Come Lately' guys owe you a tremendous debt of gratitude

I just don't think the idea of 'range trailers' will catch on with too many of us though. They're expensive for what you get (50 or 75 miles of extra range once or twice per week) too 'techy' for most of us to feel comfortable with and how many people really enjoy towing trailers . . . . I guess they're OK until you need to back up, but I sure wouldn't let my wife out the door towing one . . . . she wouldn't do it anyway

For the 90% of us who don't have your abilities, the car as it sits will probably have to do. My 'contribution' to the EV community so far has been not to overstate the cars capabilities - I'd hate to see anyone buy it thinking it's an acceptable replacement for a car someone needs to drive 100 or 150 miles per day, so I tell them that's not too practical unless that mileage represents 2 or 3 different trips from home, leaving with a fully charged car each time, or if it's a 50 mile trip to work where they can recharge before heading home. You West Coast guys are kinda spoiled in this regard, since you do have recharging capabilities all over town, so as long as you can take a long lunch stop, you can go most anywhere - Not so down here. We're really lucky in that just about every place we need to go is well within the cars range

I lived in Tacoma for 2 or 3 years when I was stationed at McChord - The traffic back then though wasn't half of what it is today

Keep up the good work - Everyone of these projects you guys build really interest me . . . . sometimes they even motivate me to get off the couch and build something of my own

Don

I agree that the range trailer as a standard appliance to keep parked in your garage is probably not the best idea. If you actually used it often enough to make it worth the cost and the space, I think you probably bought the wrong car given current realities. Like Don (I think), I'm uncomfortable with answering the question "What's its range?" with "You can drive it 200 miles a day." I think that's a) slightly disingenuous, and b) likely to make the car sound initially attractive to someone who really shouldn't be buying it. As things stand today in most parts of the country, assumptions about an EV's suitability need to be based on charging at home in the owner's garage. People who depend on "opportunity charging" in areas that lack public chargers (i.e., probably way over 80% of the population) will soon develop a reputation as geeky pests, if not moochers.

Range trailers may be one way of breaking out of these constraints, but their practicality, if they prove feasible, lies in renting them for occasional use, not buying to own. Say you'd like to take your i-MiEV to the shore for a beach vacation, but that's a 130 mile drive down the interstate. So you stop at the first service plaza, pick up a 32kWh range trailer, drop that off at the last service plaza before Beachville, then head into town, presumably to park in a designated slot at your EV-friendly resort hotel. If the whole EV business scales up a bit, that's an entirely plausible "infrastructure" scenario. All assuming, of course, that towing several hundred pounds of battery up and down hills at freeway speeds isn't somewhat abusive of the drive train - a point on which I remain a bit skeptical without the manufacturer's engineers weighing in.

Don and Vike, I agree with you both- with a couple of qualifiers. There's plenty of folks who spend good money on a large genset 'just in case'- or in Don's case, WHEN the big storm comes. EV hobbyists are already sitting on a big energy reserve with much greater surge capacity than any consumer grade genset (49 kw, anyone?). A snowbird neighbor near here forgot to disconnect his genset when he left last winter, and the darn thing 'stuck on' after a brief outage and ran nonstop for almost a week (inside a padlocked enclosure) before it's big propane tank ran dry...
That wouldn't have been an issue with a proper UPS/EV setup.

I'm building a (pusher engine style) range trailer primarily for my drag-racing conversion, to prove a point and engage in creative recycling and desigh, and then realized it may offer even more utility for the iMiEV. I'd love to be able to keep a small, light and affordable battery pack in the racer, but not have to tow it to distant EVents with a big rig. Additionally, I think that if done right, a pusher trailer would make a distance run in the iMiEV less stressful than (60 mile)distance run in stock form, and significantly less stressful than CHAdeMO recharging is on the pack. A well-balanced pusher makes the EV feel like you're just coasting down an endless hill, reducing gear and motor loads for more miles than it adds load to them..
A generator or battery trailer, yep, no debate that it'll add stress to the gearbox on both sides of a hill. How much that'll matter should take quite some time to determine... I can't think of a more durable setup than a fixed-gear rear wheel drivetrain with no driveshaft, and one that's designed for significant torque both coming and going, while a low-inertia motor rotor and gentle controller rampup ensures that shock loading is kept to a minimum. (unless perhaps, say one was regularly rattling over rutted desert dirt roads to the point of actually needing a spare tire)