# design questions- 8000 lb RV, with regnen,



## major (Apr 4, 2008)

hertfordnc said:


> I have 1972 Revcon.
> It is one of the lightest coaches of its size- 25 feet, 7800 lb empty.
> 
> It's all aluminum, front wheel drive, only four tires (no duals)


Hi hert,

I would be concerned that the addition of several tons of batteries and electric drive would overload your chassis. When doing large vehicles like buses and RVs, it would be wise to start with a heavy duty platform.

Regards,

major


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## aeroscott (Jan 5, 2008)

Thats very light , are windshield's available . I've been thinking along these lines for my 6000 lbs Dodge Cummings 4x4 . I just posted on ac vers dc motor efficiency about drive line losses . A Prius drive trans hocked up to a small diesel would make a great generator perm magnet for max eff. and simple regulation (engine speed ) . Then use 2 or 4 modified Prius drives powering each wheel . These unites can modded with extra cooling to handle much higher power , but how much moding is needed for the gears and drive chain . With 4 units sharing power you would have a better power to weight ratio then a Prius (1 for each wheel) .


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## hertfordnc (Jul 30, 2008)

I can't really address the "tons of batteries" question until i have some sense of the power requirements. 

I figure in the coming years batteries will become available from salvaging hybrids. 

I understand these batteries are often scrapped because of one bad cell. Cottage industries are already turning up rebuilding batteries. 

I'm thinking the Tahoe system will provide a lot of components. 

Is that misguided? I have a civic hybrid. i figure if it had three battery packs and a bigger electric motor it could be all EV. and the regen system would still do its job. 


I need to know;

- How much motor / amps will it take to move this thing at 65 MPH ?

- How much battery will it take ?

- how can i adapt some kind of regen ? 

- How much can I put back in from a diesel genset? 

This is a five year plan. 


?? 


Windshields are $1000 delivered 

I keep my eyes open for a donor. They come up cheap and unwanted pretty regularly.


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## Tesseract (Sep 27, 2008)

hertfordnc said:


> I can't really address the "tons of batteries" question until i have some sense of the power requirements.
> ...
> I need to know;
> 
> ...


1. An average conversion uses 350Wh/mi at 65mph. A small truck uses 450-500Wh/mi. I'm guessing your RV will use something like 1kWh-2kWh/mi.

2. Multiply your desired range by the Wh/mi figure to get Wh. E.g., 200mi x 1.5kWh/mi = 300kWh of battery. Somewhere around a quarter million dollars worth of battery, give or take a couple regular conversions worth.

3. Not sure what you are asking... How can you get regen, perhaps? There are many ways to get regen, but practically speaking you need to go with an AC drive system. At least 200kW/300hp of sustainable power to move something that big and heavy without taking too much longer than the original engine.

3. My WAG is that you will need 30kW of continuous power to maintain 65mph in an RV. So your genset needs to be able to deliver that much power (plus what is needed to overcome losses elsewhere) to be able to drive indefinitely. Say 50kW. That's a big genset.


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## hertfordnc (Jul 30, 2008)

Tesseract said:


> 3. My WAG is that you will need 30kW of continuous power to maintain 65mph in an RV. So your genset needs to be able to deliver that much power (plus what is needed to overcome losses elsewhere) to be able to drive indefinitely. Say 50kW. That's a big genset.


That's exactly what I was looking for. A 30KW Kubota genset burns less than 3 gph so that would be 20 mpg or better. 

I've googled around a little and I'm not finding any good examples of bigger EV. But someone must have done and I've seen lots of fleet trucks and vans on ebay.


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## icec0o1 (Sep 3, 2009)

RV's are for long distance trips. Having a $50k lifepo4 battery for 200 miles is a complete waste in my opinion. You can only justify a lifepo4 pack if you put it in a daily driver and can rack up at least 100k miles on it over 10 years. Otherwise, you're better off paying even $5 per galon at the pump. 

Unless you RV a LOT, you'll definately spend more money on the conversion than you'd save on gas. But if you do RV a lot and do believe gas will hit $5 a galon (which I do), then I'd suggest finding a nice, efficient generator, supercaps or just enough A123 high discharge lifepo4 cells to provide max power (around 200kw min) for 1-2 mins, and the cheapest DC controller/motor setup you can find for sustained 60KW and max of 300kw+.

Btw, forget about regen completely. Regen is only worthy of any consideration if most trips are primarily in stop and go city traffic. I doubt you'll be driving your RV through cities that much.


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## tomofreno (Mar 3, 2009)

> Btw, forget about regen completely. Regen is only worthy of any consideration if most trips are primarily in stop and go city traffic. I doubt you'll be driving your RV through cities that much.


 Good point on the mostly highway driving. Plus an AC motor/controller of the power you need will cost a fortune. I think way more compared to a comparable power series DC motor than you could begin to rationalize in the small amount of energy you will get back through regen with mainly highway driving.


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## nimblemotors (Oct 1, 2010)

Some time ago I put forward a story about the EV RV that travelled the country, transporting salvage batteries from place to place. It would pick up a big set of lead batteries and delivery them to a recycling plant in another state, where it acquired a new set to delivery in another state.
This way, it could travel far distances providing a service. It used a solar array to charge when the batteries where drained, so you'd just camp out for days until recharged. This would be a nice fictional book story placed in 2029 after the world economy has collapsed and oil was $500 barrel...

An RV should be converted to run on natural gas, like a UPS truck, it is clean and cheap and the tank weight isn't an issue for an RV.



hertfordnc said:


> I can't really address the "tons of batteries" question until i have some sense of the power requirements.
> 
> I figure in the coming years batteries will become available from salvaging hybrids.
> 
> ...


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## hertfordnc (Jul 30, 2008)

In response to several comments above;

- I realize this is impractical in the current environment but I happen to have a very light RV which i intent to keep for a long time. The power requirement to move it down the road are not going to change so it's just a matter of when alternative energy options become available. For now I just want to know what the goal is.

- I don't agree that regen is only for traffic. I drive a civic hybrid. Regen takes place constantly. Roads are not flat and the battery charges on every downhill or deceleration. 

- In some ways an RV is an excellent platform. In a hot climate you're already driving with a generator running. At the end of the day you pay for an unlimited electrical hookup

- I believe batteries are cheap to make. Compared to the ICE manufacturing costs will plummet in the coming years as more EV's and hybrids come to market 


Obviously there is a lot I don't understand about this but it ain't rocket science. 

thanks


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## T1 Terry (Jan 29, 2011)

What size and KW output is the motor that is in the bus at the moment? This will tell you have big the electric motor will need to be.
I'd be looking at an AC motor set up for sure, with that much weigh regen is a guaranteed thing.
I am looking at a hybrid drive/regen braking set up for my 10 tonne 36 ft motorhome conversion and the costs aren't that outrageous. I've even thought along the same lines as you regarding a direct electric drive and gas fuel genset to assist the 1 kw of solar I already have. The big battery bank means you can free camp for ages as well, a big bonus over here.
The unlimited power at the van parks means virtually free fuel as a bonus.
The major issue with regen is the capacity of the batteries to accept the high rate of charge so this will be the real determining factor of the battery bank capacity. Even if the battery bank had the capacity for 100 miles and the generator/charger and solar could recover half of that in the 1 1/2 hr travelling it just means more stopping and checking out the sights along the way while the batteries top up. No point arriving at the van park with the batteries fully charged is there 

T1 Terry


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## ElectriCar (Jun 15, 2008)

Regarding weight alone and the wh/mile others are getting, I think it would take around 1200-1500 wh/mile, depending on the aerodynamics and frontal area. Motor wise I think you could move it quite well with two ADC 9" in parallel but of course you'd have to mate it up to the transmission. Not confident an 11" would do the job alone but I don't know what's out there larger other than industrial motors. Soon though I expect there to be many more options with the price of fuel as it is.

I think you would need about 300kw pack to take you close to 200 miles. At today's battery pricing and energy densities, you're looking at about $120,000 for that pack using large prismatics. Considering the price of RV's these days that's not way out of line. Then the question becomes can you fit 500 cells in that thing? Mine are about 3.75" x 10" by 7" for a 200Ah cell. With 500 of them you'd be close to your mileage mark, plus or minus a little. Maybe A123 or similar cells would be better suited to this task due to their small size and energy density, not sure about this option.


For builds that require lots of energy, ie over the road trucks, my F250 diesel truck with a 15,000lb camper behind it and builds like yours, three things need to happen. One, fast charge infrastructure needs to be developed to enable rapid recharging. This is the easiest to implement as the technology is here now. When this happens we can get by with smaller packs at the expense of more frequent stops. Two, batteries or super caps need to make a large jump in capacity to allow smaller packs. Three, batteries need to be much more affordable.

When these thing happen electric propulsion will then become mainstream for all vehicles. Due to world wide government support for battery development, there's been lots of recent development with drastic improvements in capacity and charge/discharge rates. That said, I'm expecting that by five years or so the size of batteries will shrink considerably and hopefully become more affordable.


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