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puddleglum 04-06-2013 02:19 AM

Planning a budget EV build
I've been dreaming of building an electric car for years now (and probably will for a few years more till I can complete one) but I took a first step and put in a offer on an old Datsun forklift. They want more than I offered, but still reasonable. The drive and pump motors are both 11" 48 volt 10kw motors. I couldn't drive it much, but it did drive and wasn't making any funny noises so I think they should be okay. As near as I can tell, the drive motor is about the same size and weight as a Warp11(not as efficient I'm sure) so a little heavy for a commuter car, but isn't too big better than too small? I found one other guy using the same motor at 144 volts in a pickup. I would appreciate any thoughts as to whether I'm on the right track in buying this.
Since my driving needs are different than a lot of people, I spent the last six months tracking all my in town trips to see what I would really need in an EV. My must have's are: a 4dr vehicle that seats 4 adults comfortably and/or 3 adults with at least a full grocery cart's worth of stuff; a 15 mile min. range, but 25 miles would be better; a top speed of 60mph, cruise at 40-50mph and have normal acceleration to 45mph; it must be easy to drive, comfortable and reliable so my wife will drive it. If it was fast off the line that would be a bonus, I would like to have a little fun factor.

Ryland 04-06-2013 09:20 AM

Only draw back of a motor that big is getting it to fit in some smaller cars, but if you want a 4 door car that shouldn't be a problem, a motor that size should give great performance.
My parents EV is a converted VW Golf, the person that built it didn't sink the rear battery box in to the floor where the gas tank was, so the rear battery box comes up to the rear glass, but it doesn't impede on the passenger compartment at all so 2 adults or 3 kids can sit in the back seat, the rest of the batteries are under the hood and they have a 20 mile range with lead AGM batteries.

When their current pack wears out I'm pretty sure they are going to switch to lithium batteries, there are people doing group/bulk buys and getting the price down to $0.34 per watt hour, where my lead acid batteries cost about $0.20 per watt hour, so lithium batteries don't have to cost even twice as much as lead and you will get more range because the batteries have better discharge curves and are lighter.

Daox 04-06-2013 10:51 AM

Rylands tips are great. The problem will likely be your axle shaft clearance (cause your motor is so large) if there is a problem.

25 miles is a lot of lead though. 15 isn't so bad. Lithium really is the way to go, it'll last so much longer, weigh so much less, and just be less hassle in the long run. I'd highly recommend it if you can swing it.

mechman600 04-06-2013 12:58 PM

+1 on lithium. Unless you can get lead batteries at wholesale price (like I was able to), lithium is the way. A realistic 25 mile lead car will weigh too much to be safe (in my opinion).

If you can make it fit, your 11" motor should be quite efficient.

puddleglum 04-06-2013 08:36 PM

Thanks guys, I really want to go with lithium right from the start as well, but it will mean that I have wait a little longer to bring this to reality. I've thought about trying to go with lead to start, but I hate doing things twice and I really don't like the idea of doing battery maintenance on floodies. I know it will cost more in the long run to do a lead conversion and then change it all over to lithium as well. I'm thinking it would be better to start with a small lithium pack and then add a second pack later to upgrade performance and/or range. Does that seem reasonable? Looking at EV calculators, 100ah of lithium will give about the same range as 180ah of lead, because of it's lower weight and deeper discharge abilities. Does that seem about right? If so, that would make AGM's almost as much as lithium.
If I were to do a build with a small lithium pack and planned to enlarge it later, which would be better? Should I start with the voltage I want and low ah cells or the ah cells I want but lower voltage? I understand the range vs performance tradeoff, but which would be an easier upgrade?

Ryland 04-07-2013 02:17 AM

It can be hard to wrap your brain around... going with one voltage now and adding more batteries for a higher voltage later will give you greater performance as you upgrade for a sporty off the line feel and you will get less line loss so you will increase range by just a little bit, but it will also require either a higher voltage controller now or one later and it will either require a charger that can be adjusted or buying two...

voltage gives you speed, amperage gives you range, so figure out your speed you want and then increase your range as you can... maybe?

Some people say you can piggy back battery management systems by pairing cells up to give higher amp hours, the risk is if you go with cheap cells, a cheap battery management system or have something fail! if you choose to pair up cells to later get more amp hours then plan in adding fuses and either a meter or an LED system that tells you if you have a single cell go bad, it might seem silly now, but people do have cells go bad and the more you push them the greater that risk is, have new and old cells mixed is pushing what they can do, same with undersizing the pack.
If you want to spend the money and have two battery management systems, one for the first string of batteries you buy and one for the 2n string you buy, then you can save your self a bit of trouble, still having a meter between the two packs to tell you if one is laging is a good idea, but the BMS (battery management system) should keep everything safe and keep one pack from killing the other, the draw back is an over all higher cost compared to paring up cells to share a BMS.

You can of course buy lead acid batteries, but the first set of lead acid batteries is going to be the quickest for a new EV owner to kill, so in 3 years you are going to be buying a new set, at that point you will have paid as much as you would have for lithium and your car is not going to have as good of performance.
Most people I talk to say that when they switch from lead to lithium they see at least a 50% increase in range with the same labeled capacity, with fewer watt hours per mile.

puddleglum 04-07-2013 02:10 PM

Yes, I have a lot to wrap my head around before this becomes a reality.

I have another question that is more important in the short term. How much stuff would be worth keeping off the forklift once I get it? I plan on keeping the drive and pump motors and any accessible couplings and cables for sure. Would there be any possible reason to keep the controller and contactors or the steer motor?

Ryland 04-07-2013 07:40 PM

Contactors might be worth keeping, higher voltage contactors open faster and with more force to make sure they don't get welded closed, but what are on there might still be ok to use.

Hydraulics are fun to have around if you want to make a log spliter or something.

Huge battery is useful to power your house for a day or two if the power goes out.

Solid rubber wheels?

MetroMPG 04-07-2013 08:44 PM

I used the forklift contactors in the ForkenSwift.

I kept the steering motor, but haven't used it for anything (after abandoning my electric boat motor conversion).

Also kept the forklift controller, but again, haven't used it for anything.

The scrap value of the parts is probably the best direction to take. :)

puddleglum 04-08-2013 12:31 AM

Thanks, I don't get the battery with the forklift, but it is there for now so I can use it to test run things. I plan on taking most of it to the scrap but i don't want to throw away something that would be worth using or selling separately. I don't think I want to deal with hyd. parts too. I have too much stuff around already that I'm not doing anything with.

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