Electric Motorhome thoughts

Conversion Kits
1

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,

2

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?

3

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.

4

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. :slight_smile: 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. :frowning:

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

5

[QUOTE=FEF;6563]
This has got to be why diesel locomotives are so large. That generator in there must be massive.[/QUOTE]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 RPM’s.

6

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.

7

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.

8

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 EV’s is the batteries and the power density limitations of Wh/kg and punching through the 200 Wh/kg barrier. Today’s 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 EV’s 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 EV’s 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, EV’s 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.

9

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. :whistle:

10

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:
[ame=http://www.youtube.com/watch?v=S1NhY1PZBWw&feature=youtube_gdata_player]YouTube - (HD) GT2827 Steam Bus in Whitby[/ame]

Get that done & you could add some compressed air tanks for a steam/air hybrid. Check out the size of this motor:
[ame=http://www.youtube.com/watch?v=Dq8aZVLpf-c&feature=youtube_gdata_player]YouTube - Air Car (2 of 2) from Australia[/ame]

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.*

11

First, I would lose the automatic transmission. It is far to large for the torque you will need. The automatic also wastes power, which is why automatics of that era especially got lower fuel milage. I remember reading that a TH350 consumes 27 HP at full load. Consider the smallest aluminum case manual that will meet the torque needs of the new motor. Think of other ways to reduce the weight of the vehicle. Power steering could also be eliminated. Using a generator will extend the range, but you will need a DC generator that matches the battery voltage as well as a way to charge from line power. A battery this large would best be charged from 240 volt line power, which will limit where the vehicle can be charged. Even the largest 120 volt chargers will require long charging times. Also, consider the vehicle’s GVW as well as weight distribution when planning the size and distribution of your batteries. Too much weight in the wrong place will make the vehicle unsafe to drive.

Daniel

12

Just a quick thought: If the conversion is being made to electric (with wheel hub motors), wouldn’t a “transmission” be a moot point anyway? And if the conversion is being made to a hybrid, why not consider a hydraulic hybrid such as some large industrial vehicles (like garbage trucks) use? While most efficient in repetitive stop-and-go city driving, it would certainly help ease the battery drain during initial acceleration, and the hydraulic cylinders take up minimal weight and space under the vehicle.

George

13

[QUOTE=FEF;6555]All,

I’m trying to find a way to convert a very light motorhome to electric power.
…

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.
[/QUOTE]

I have also thought about this, but as many other posters have pointed out, using PbA batteries with an already heavy vehicle will lead to limited range and low top speeds. (Along with large power demands). Lithium batteries would make it almost practicable from an energy/range standpoint, but the cost wold be terribly prohibitive.

The ONLY benefit I could see is if you are already planning on paying to park in an RV/Motorhome park every night, where they provide electricity (20-50amp circuits!) as part of your normal fee. (So you would get nightly fill ups included in costs you were already going to pay.) However, you would only be able to drive 20-60 miles between RV parks each day without other generators, etc. So this may work for people who stay in RV parks all/most of the time, and live in an area with high density of RV parks (i.e.not the midwest/southeast).

The other option is to have a very large PV array on the roof and move your motorhome 20-30 miles once every 2-3 weeks (parking in the sun between moves) but that size of PV system will greatly increase your costs.

Another plus of an EV motorhome…your “house battery” would be able to support just about anything ;>
Jay

14

[QUOTE=FEF;6563]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. :).[/QUOTE]

My Thoughts are simple - You can compare the Tesla Roadsters Energy use to it’s sibling the Lotus Elise Fuel Consumption [6.14 litres / 100km (46 mpg)].
Wikipedia Says Tesla uses 135 Wh/km

Direct Discussion comparing these two cars energy Use (Blog)

My Electric Firefly (Geo Metro) uses a bit more at ~140 Wh/Km on the Highway at 100 Kph, and can range from 67-100 Wh/Km best, to 277-285 Wh/km Worst The Gas Power Firefly was rated at ~5.5 L/100 Km.

An Extra Link from Tesla Motors on Efficiency

Don’t forget to compare vehicles fuel consumption with converted cars on EV Album (EV Photo Album: Our Electric Cars on the Web)

So - you take the current burn of your motor home, and compare it to some samples of other vehicles that you see converted to electric, and what their have in the battery pack will give you a clue as to the possibility of performance.

On the Other Hand - to reduce fuel burn, you could consider a hybrid add-in like EMIS from Net Gain Motors. There are other Hybrid Retrofits available apparently too!

XL Hybrids: Lincoln Town Car - Story

Poulsen Hybred: Make My Car into a Prius Hybrid Plug-in Kit - Story

For battery research - check out my own website’s white papers at Electricfly - MyElectricfly.com Click ‘Whitepapers’ down at the bottom of the menu on the left, there are two papers, a two page, and a four page, to give you some battery choice thoughts.

Ultimately - the key question is your investment cost, Desire to save money in ROI terms, or your goal to shift your energy use partly or totally to non Liquid Fuel operations.

Robert

15

[QUOTE=Sunking;6572]The stumbling block for EV’s is the batteries and the power density limitations of Wh/kg and punching through the 200 Wh/kg barrier. Today’s 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 EV’s 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 EV’s 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, EV’s 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.[/QUOTE]

Interesting - if you use cells with a 1C Capability - when you have the power you need - you will naturally get a larger range, by the vary definition of ‘C’ meaning essentially - ‘Compared to an hour’ since a 1C Rating means delivering the rated power in 1 hour. Lead Acid Batteries are actually rated at 0.05C or 1/20C. (20 Hour Rating)

Oh - by the way - the A123 Cells with the 30C Capability - can do 1000 Cycles at 100% Depth of Discharge (DOD), and most LiFePO4 cells can do 2000 Cycles at 80% DOD. See My White Papers, and see if I am out to lunch!

If you need - for example - 750 Amps to accelerate, and you used 1C Cells - you would need a 750 Ah Pack Minimum, Maybe a bit more for line and connection losses - so maybe an 850 Ah Pack capacity. If you consider an 80% Depth of Discharge - that gives you some 680 Ah usable. Most any highway rated vehicle will be at least 120 Volts, so 680 Ah x 120 Volts = 81,600 Watt Hours. (81+ kWh). Wait - that’s about the size of the 300 mile Tesla Model S Pack!

Don’t Forget - running any pack at a constant 30C by definition means two minutes (2) of run time since 60 / 30 = 2. Great for the Drag Strip, but a bit overkill for highway driving - even for city driving, in most Cities!

Ideally - Cells with about a continuous 10C - 15C capability - but a better Energy Density is the goal. My own Electric Firefly - has a power consumption range from best to worst of about a factor of 4; where driving like a mad man uses about 4X as much energy as being really nice does!

Wanting the ability to Drive an Electric Vehicle for 1 hour continuous means that you need a packs energy of about 125% of what you will use, to keep the Depth of Discharge to no more than 80%. If you have a 10C capable Pack - your accelerations most likely will not be battery, but controller limited. At a 3C Cell limit - you would need a larger pack, but that would net you a longer range!

A Volkswagen Beetle using 3C Cells drove from [B]UBC in Vancouver, to Halifax, Nova Scotia in the summer of 2010![/B] Without any standard Charging Infrastructure available! They Spent the Day in Toronto - August 31st, 2010. Also See: Travelling across Canada in an e-car - Photo Taken While I Watched, just after breakfast! got Question? Contact the Club, or Neil Roberts.

Agreed - better energy density is important, but with all the work going on with Zinc-Air, and Lithium-Air, I expect by the time your Nissan Leaf or Tesla Model S battery is toast - there will be major improvements in the Box!

Enjoy the Rid! Robert

16

AC Propulsion (http://www.acpropulsion.com) is the company who designed the battery pack, electronics and charging system for Tesla Motors. They are in San Dimas, CA, north of Ontario, CA. I believe that two of their systems, tuned properly, can power an RV up to 40 feet. With solar panels on the roof, or two HJ systems in lower storage, you can stay on the road for 400 miles and have a recharge time of two hours. All you need is the propane system for cooking (I don’t like electric cooking). Also, the quiet HJ systems will run your AC all night long and not take energy from your batteries. I wouldn’t travel without a generator though.