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Electric Motorhome thoughts


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Old 05-28-2009, 09:10 AM
FEF FEF is offline
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Default Electric Motorhome thoughts

All,

I'm trying to find a way to convert a very light motorhome to electric power. I've been in involved in a few conversions, and I don't think it's absolutely possible, but I thought I'd try ask a few questions and start a discussion, on the off chance I missed something. I'd really like to make this happen, but I don't see how under $20K-30K. I'd really like to buy used parts to keep cost down (assuming it's feasible)

Vehicle:
- 1972 Revcon 250
- GVW of 10,000 lbs, with a combined weight (towing) of 20,000lbs
- FWD Toronado drivetrain with Olds 455/TH425
- Right now, with the engine out, it weighs about 3800 lbs

Assumptions:
- Electrical and mechanical skills are not an issue.
- Used parts and pieces will be used whenever possible

I see 2 main issues, the drive system and the charging system.

Drive system:
Can it be done? I think so. Motor/controller choice will be key. AC, or DC... I'm not sure I care, though DC appears to be a lot cheaper then AC at this time.

While cost may be an issue, I've seen 2 Kostov motors do a heck of alot of work. But I don't know much about what's required to control them. Can they run from 1 controller? I wouldn't think so. If not do they need to be sync'd? Some links would help here.

Charging system:
I'm pretty sure I can get the motorhome across town a few times, but this is where it starts to look impossible. Home generators (which I need anyway) can be put on a small trailer (or maybe in the engine bay - It's a HUGE area). This adds more tire friction and weight. Once I find out what kind of controllers I need, I can calculate power required to opperate and charge times.

Can any of you point me to successful full-size truck conversion links? That would help a lot. It's a great dream, but I'm not sure the technology exists for "the average guy".

Thanks in advance,


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Old 05-28-2009, 04:20 PM
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What kind of range and speed are you hoping for?

I mean... you can totally bolt on any standard electric motor and just feed it power until you move... It's a question of how fast and how far you want to go. If you're hoping to retain the original range of a motorhome... well... That doesn't really seem feasible... Except that as you mentioned, motorhomes generally have a spot for a generator... So you can drive a little, charge a little. If you're only looking to go around town (in your motorhome?) then it seems a bit more feasible.

What are your goals / reasons for this project?


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Old 05-28-2009, 08:58 PM
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Well what you are running up against is pure physics. You can certainly put a motor and battery to make it move, but to have it go fast enough over a realistic distance will be almost impossible at this weight class. For light weight transportation (something like a Honda Civic size) you can make car that will go up to 200 miles with breathtaking acceleration and high speeds. In fact it has already been done and you can buy one today from Telsa Motors

Motor and control technology is already here, it is the battery and the battery weight that is going to kill you. Telsa uses a 3-phase 375 volt AC induction air-cooled electric motor with variable frequency drive. Output is 248 peak horsepower (185kW) and 276 ft/lbs (375 nm) of torque. Redline 14,000 rpm. Drivetrain is single speed fixed gear. It has a 40 Kwh battery capacity weighing 992 pounds with 177 miles/kwh affords 220 mile range. Total vehicle weight is about 2800 pounds.


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Old 05-29-2009, 08:53 AM
FEF FEF is offline
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Right. As we say, "it's not in the math", as far as I can tell.

As for the reason, While the Olds 455 is a GREAT engine, it's not the most efficient engine. I was converting to diesel power (and still may) but having issues putting a hole in the oil pan for the front axles to pass through. It can be done, but truth be told, I'd rather have the grunt of an electric motor.

The criteria I'm trying to shoot for should be fairly simple by motor vehicle standards. I only need a top speed of 70mph. I've gone cross-country in a vehicle with a top speed of 60 (30mph on some hills), so 70mph would be awesome. However, none of it will work if I can't get the system to run from a diesel gen-set.

This is where the math is troubling. We know generators are rated in KW/H (generally). Only as an example, if I cruising at 60 burns 500A, then I'll need a 72K generator on a 100% duty cycle for 8-10 hours a day. I'm looking at about 1000 of generator, plus the batteries/electronics/motor. It's still possible with the gen-set on the car trailer, but what kind of current would a full-size truck pull at 60-70mph?

I was planning to keep the torque converter, too. That's good and bad, because it can double the torque, but it won't lock-up with the TH400.

This has got to be why diesel locomotives are so large. That generator in there must be massive.


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Old 05-29-2009, 08:16 PM
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Quote:
Originally Posted by FEF View Post
This has got to be why diesel locomotives are so large. That generator in there must be massive.
OK please do not be offended but 70 MPH is not realistic.

You had a good idea with a diesel engine as they are far more efficient and cleaner than gas burning ICE, not too mention much higher torque needed to pull heavy loads.

Ok the generator idea is just for lack of better words is dumb because of all the energy loss in conversions from liquid fuel > mechanical > electrical. Generators at best are only 80% efficient but only when running at maximum capacity, Much lower a less than full capacity.

The reason trains use diesel engines (16 cylinder 6000 HP) to turn a generator to power traction motors is two fold:

There is no clutch man could make to withstand the forces.
Electric motors have extremely flat and high torque from 0 RPM up to red line RPMís.


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Old 05-29-2009, 11:33 PM
FEF FEF is offline
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Offended, no. A bit sad, ya. Even the lighter motorhome is just not in the math. I knew running off a generator with a battery buffer was virtually impossible (today), but I was hoping to pull a rabbit out of the hat.

That said, if I think some more, I may be able to get a 100 mile range. This leads to the idea of a duty cycle. Do you have any links on quick charging? I think Optima has information on their site. I don't see how a wet cell battery would work, though. I don't think this will work either, but it's a good discussion at least.


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Old 05-29-2009, 11:49 PM
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I've found interesting information. Some batteries can go from 30% to 95% in 3 hours. I understand that the details are tricky, but if you had a 2 pack system, one battery pack could be charged while the other is running. This means something like a 66% cycle, but you could get somewhere if you're not in too much of a hurry.

It's a very interesting topic for me, but I may be better off developing a dry sump oil system for the domestic diesel engines.


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Old 05-30-2009, 10:34 AM
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Again we make full circle back to physics. And unfortunately you cannot break the law of physics no matter how hard you try

The stumbling block for EVís is the batteries and the power density limitations of Wh/kg and punching through the 200 Wh/kg barrier. Todayís lithium-Ion comes close to the 200 WH/kg, but those that do like Cobalt that have 170 Wh/kg are limited to 1C discharge rates which is useless for EVís that need very high C rates of 30C or more. Those Lithium technologies that do have high C rates are low density of around 130 Wh/kg and short cycle life meaning only 100 to 300 charge cycles before capacity is completely down to 0%.

What is needed is a battery with 1000 or more charge cycles without degrading, power density of 200 Wh/kg, or more, and 30+ C rates. To date there is no battery out there that can do that. Till that happens EVís are road blocked from becoming mainstream. Now with that said I believe we will see this happen in the next 5 years as there is a lot of R&D to build such a battery, when it happens, EVís will be a reality for light transportation. In the meantime we as a country should be building out the electrical generation and transmission to meet the demands by building nuclear power plants to meet the power requirements.

As for most medium and heavy transportation, only liquid fuels can supply the energy density needed for those applications. There are some exceptions like light rail for public transportation using overhead lines, but rail is not practical in the USA. As just about every city would have to be bull dozed and reconfigured as a hub and spoke configuration where all biz is in the center of town.


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Old 08-07-2009, 05:17 PM
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man you guys make me register and everything just so i can tell some of you how much i hate you..

What makes you think this is impossible? Only problem i see is cost. If you want to move anything as big as an RV youll need a lot of power. If your rich enough to drop $200k then it CAN be done with some work.

There's a few ways to do this but one way to do this is youll need to drive something like 4 wheels independently. Meaning something like having an AC motor on each of the wheels. On top of that you might need some way to gear up when you need to. Maybe a 2 speed gearbox that you can control electronically. This alone will be pretty hard to do. If this is somehow done successfully you'll be set. Rest is much easier.

Then you'll need 4 separate battery banks for each of the motors. Get as high of AH batteries as you can with enough voltage to power the AC motors. (ac usually requires more voltage) Also with an AC motor you can utilize regenerative braking easier/more efficiently.

Then your mostly done. Rest that's needed is a way to control each of the 4 controllers at the same time. Try to removed any extra weight that just doesnt need to be there. Lightening up your ride is very important because you just added at least 2k lbs more weight. However removing your gas engine should have removed a lot of weight. Oil, coolant, gas, exhaust piping, radiators and etc.


Depending on how much your total weight is you should now have a good chance to get some range. They key is never give up. expand your range of thinking and it can be done.


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Old 11-01-2010, 10:41 PM
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If this thread were a hot chick with big boobs & a propensity for cooking, I'd marry it. Just bought a 74 Revcon last month & itching to mod that sucker out & convert. As we all know, technological innovation increases exponentially, while the price ALWAYS drops rapidly. With that in mind, here's some brainstorming. I'm not an expert on anything so feel free to correct me. I reserve the right to be wrong about everything...

Reducing weight & drag are big factors for speed & range. *Revcons are Aluminum, so that's lightweight... but carbon fiber, sold in sheets, could replace body panels, etc. & shave some serious weight.

Since your 72 is a flat nose ("Square Stream"), drag reduction is a big opportunity. I google image searched helicopter canopies & if you could graft one on to the front of the 'Con, I'd think you'd have a sweet drag coefficient. *I don't know where helicopters go to die, but I'm sure there's a junkyard full, somewhere.

Sunking's post on batteries was pretty informative. Thanks, Sunking. Silver oxide cells are new & spendy now but I think they're high density/low weight. Don't know about the Cs but somebody does. Doubt they're practical now but with all the capital flowing into EV tech, that's gotta change, rapido.

Googled on it awhile & found EV & hybrid trucks in the works. An EV RV can't be too far behind. *You could always convert the Olds 455 to CNG or swap a diesel & run it on fry grease.

Or you could convert it to steam, like the old Sentinel buses of the '30s:

Get that done & you could add some compressed air tanks for a steam/air hybrid. Check out the size of this motor:

Not sure what I'm gonna do with my Revcon yet, but I haven't ruled out a U-Haul, chock full of high amp hour Yellow Tops.*

Or some horses.*


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