[mperrotta]

hello to everyone. I'm completely new to this forum and very new to ev builds as well. i am a mechanical engineering student that will soon graduate and have been wanting to do an electric project car for a long time. i really want to build a fun car with an electric drive train that will make use of recovery processes to extend the range. my idea is to take a small compact for the base. possibly something similar in size to a civic. from what research iv done, i sounds like regenerative breaking is easier with an AC induction motor. im still doing research but i want to include a solar panel. I have found a panel that could possibly be integrated into either the hood or the roof of the car that ways only 35-40lbs and generate 240 watt ( although that is a nominal value for a spacific angle). i have also toyed with the idea of a sterling engine running an alternator or generator to recharge the battery using heat from the motor. i do want something sporty but i also want range to be good. im hoping that the solar panel and the sterling engine may be a way to increase range and possibly reduce the battery size needed. as a stated before im new to this and would love some direction to where i should go next. thanks in adavnced for any help with this

[Ziggythewiz]

It's a fun project, and you'll learn lots. The first thing to learn is there isn't much energy to recover. Regen can get you 10-30%, and solar and a stirling engine running a generator might get you 1-3% ea.

[dougingraham]

Originally Posted by mperrotta

im still doing research but i want to include a solar panel. I have found a panel that could possibly be integrated into either the hood or the roof of the car that ways only 35-40lbs and generate 240 watt ( although that is a nominal value for a spacific angle). i have also toyed with the idea of a sterling engine running an alternator or generator to recharge the battery using heat from the motor. i do want something sporty but i also want range to be good. im hoping that the solar panel and the sterling engine may be a way to increase range and possibly reduce the battery size needed. as a stated before im new to this and would love some direction to where i should go next. thanks in adavnced for any help with this

Welcome! Small and lightweight cars make for good conversion candidates.

For a small and efficient car you will get something between 200 and 300 watt hours per mile traveled. What this means is that your 240 watt panel will extend your range by about 1 mile per hour if putting out full power. In the continental US the solar insolation value is between 3 and 5 hours per day so in places like Arizona you might get 5 miles of range per day from the solar panel. The estimated $250 that panel will cost could buy approximately 10000 miles of electricity. An average daily output of the panel might be 6 miles making the break even point about 4.5 years if you exclude the cost of the special charger and losses it would impose. I would estimate it would be closer to 15 years assuming you are in a really sunny place. Far better would be to put the panels on your residence and offset the electricity use of car that way. You don't want to carry around anything you don't have to.

If you are talking about the heat from the electric motor there is not enough of that to make it worth trying to use it to recharge the batteries. If you are 90% efficient on the motor and using that average of 250watt hours per mile and running at 60mph your waste heat is going to be about 1500 watts spread out over the motor and motor controller. If you could capture all of it you would extend your range by 10%. It is very difficult to get the heat out of the motor with the kind of temperature differential you need to operate a Sterling engine + generator + charge controller. For the additional cost, weight and complexity you would better off just offsetting the weight savings with extra batteries.

With Regenerative Braking you can extend your range somewhat but the amount varies greatly with the kind of driving done. If you have stop and go traffic and lots of hills you get something back. If you have nothing but constant speed it extends your range not at all. The OEM's all include it because they all use some sort of AC motor and it basically is free to add in that situation. Don't get fixated on regen as it probably wont extend your range by more than a few percent.

There is lots of info to be found here. Check out the FAQ's. Use the search function.

[McRat]

I'm building a solar cell motorcycle (if I can't balance it, it will become a 3 wheeler.

OK, the amount of panel area you need for 1 hp is stunning. 50 sqft? My array is 4 foot by 20 foot (long, long motorcycle) and makes about 1000w at 18vdc.

You probably don't want glass panels, they are heavy. Mine are on a sheet of stainless steel with a polymer coating, so they are thin and slightly flexible. 65lb for 1000w. To get 1000w with glass panels is over 160lb. The extra weight almost chews up all the power.

If you have the patience, you buy the solar chips, and you make your own array, then coat it with that polymer to protect them. They are fragile like butterfly wings.

There is another technology (look on Ebay for flexible solar 128w) that you can even walk on, and is super flexible. But it takes 100sqft for 1 hp. And it weighs more than the stainless panels.

Even at 100% efficiency (the best cells are about 40%, the ones me and you can afford are 18%), it would still be 10sqft per HP, so a normal car could only make 3-4 hp.

A huge drawback of solar is that if you block the light (or break) 1 cell in a panel, the output falls 90%. ie - If I put my thumb in the right place on my 100w panel, it turns into a 10w panel. Since you hook the panels in series for the most part, it affects the whole series. For cars, you'd want to go just single panels in parallel.

When you spend hundreds of thousands of dollars, and hundreds of hours in a wind tunnel, you can make a solar car that can run almost like a good bicycle.

[mperrotta]

thanks for the reply(s). sounds like i need to skip the solar panles. what is the general consensus for adding an engine (maybe something like a small motorcycle engine) to extend range. my questions is about the weight of the batteries compare to the weight of the gas and motor. i seem to remeber the energy density of gas to be about 8 times higher than electricity on batteries.

a second idea on the styling engine would be to build a highly thermaly conductive hood to create heat or if a gas motor was used as a suppliment perhaps use the exhaust heat from that.

my next question is about motors for my project. every thread on this sight seems to suggest using DC motors where as AC induction motors seem capable of greator power and possible longer range. im guessing im missing some information about what the advantages and disadvantages for each are. im also unsure of where to start looking for motors in terms of manufactures

[EVEngineeer]

How much money are you willing to spend? Or do you not care how long this project takes and therefore will spend money over a very long period of time?
You should check out http://www.diyelectriccar.com/wiki/ because you may find interesting facts there.

[ricklearned]

Originally Posted by mperrotta

thanks for the reply(s). ...... every thread on this sight seems to suggest using DC motors where as AC induction motors seem capable of greator power and possible longer range. im guessing im missing some information about what the advantages and disadvantages for each are. im also unsure of where to start looking for motors in terms of manufactures

Not everyone has a DC motor. I have an AC35 in my VW. I live in a hilly beach town and I love seeing the amps I get from Regenerative Braking. There is no question that DC is simpler and probably cheaper, but we live in a great country that gives us many choices. Do your research, define your goals and pick the one that works for you.

Remember what the Dahli Lama said when asked about what was the best religion. His response was, "Whatever religion you have picked for yourself is the best religion."

[Qer]

Originally Posted by mperrotta

what is the general consensus for adding an engine (maybe something like a small motorcycle engine) to extend range. my questions is about the weight of the batteries compare to the weight of the gas and motor. i seem to remeber the energy density of gas to be about 8 times higher than electricity on batteries.

That sounds about right. I once calculated the number to about 10, but that was a few years ago and batteries are slowly getting better. There's no question that we're still far off from the day when a fully charged electric car can compete with a comparable car with an ICE and a full tank when it comes to range.

You're talking about doing a hybrid and yes, it's possible. It's also possible to get better MPG than a stock ICE car since you can select a smaller engine (that covers your average load rather than the peaks) and run it at optimal RPM. Definitely possible but there's probably a lot of interesting challenges working out all the kinks...

Originally Posted by mperrotta

my next question is about motors for my project. every thread on this sight seems to suggest using DC motors where as AC induction motors seem capable of greator power and possible longer range. im guessing im missing some information about what the advantages and disadvantages for each are. im also unsure of where to start looking for motors in terms of manufactures

I've said it before and I say it again; you have to compare systems rather than technologies. It's probably true that you won't be able to buy a DC-system that can regen (it's not impossible, for example old Renault Clios use SepEx but I don't know of any manufacturer that sell regen-capable DC-systems atm) but as has already been said, regen is only useful if you have the right driving pattern.

Also, AC is usually both more expensive and heavier (again, this is a general observation, YMMV) so it might be worth it to spend some more money/weight on batteries to get that extra range instead.

But as I said; you have to compare SYSTEMS. Pick out a few motor/controller combinations (AC, DC, BLDC, whatever), compare prices, performance, weight, other peoples experiences etc and don't get hung up on how they work "under the hood". When the car's ready and driveable it really won't matter anyway. The only thing that will matter is if it's up to your expectations and how well it fills your needs.

Oh, and KISS. Sounds great to have all the plans now to add this and that etc, but don't build a mountain you can't climb. Start with finishing a car that works, then you can either improve that later or build a better one when you've realised all the mistakes you did with the first...

[Duncan]

Just a quick comment about using waste heat
Any heat engine's efficiency is dependent on the input temperature and the output temperature
Max possible efficiency = (Tin - Tout) / Tin - Temperature in Kelvin (absolute)

That is Max possible - small motors normally get less than 25% of max possible

[dougingraham]

Originally Posted by mperrotta

what is the general consensus for adding an engine (maybe something like a small motorcycle engine) to extend range. my questions is about the weight of the batteries compare to the weight of the gas and motor. i seem to remeber the energy density of gas to be about 8 times higher than electricity on batteries.

If you assume you need 250wh per mile at 60mph this means you would need at least 15000 watts to maintain speed. SInce your charger would be about 85% efficient and your generator is about the same that means the motor would need to put out about 21000 watts which is 28 horsepower. That is a healthy motor generator set. And that would be able to just maintain speed on a level road. To work going up hills it needs to be twice this size and then you need to oversize it more in case you are in the mountains at 10k feet. And this is why the Volt has a 63kw (84hp) motor generator. Could you get by with less? A little, yes.

My problem with a Hybrid is that you now have the worst aspects of internal combustion to deal with. You need a gas tank and a radiator and a muffler. And as GM is so pleased to point out in the commercials the last couple of weeks people almost never use it. Remove all that stuff and add batteries back in for the weight savings and your range goes from 40 miles to 80 miles and almost nobody needs that much range for a daily driver.

I don't know if there is a consensus but if I could rent a motor generator set on a little trailer to pull behind my car when I went on trips I would do that. I sure wouldn't drag it around all the time when I almost never would use it. So the Volt is a really good crossover to get people used to not having a 300 mile range which they almost never use.