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Discussion Starter · #1 ·
I want (need) to convert a vehicle for financial reasons as well as green reasons. I need to be able to do this conversion on a very strict low dollar budget. I am trying to source a donor vehicle for as close to free as I can get. I have located a salvage yard with thousands of electric motors (they have no markings and I can't distinguish between a DC and an AC motor). I am already broke, and since I can't and won't borrow from anyone, I really want to make this project out of as much recycled material as possible. This is my green side. I have experience in parts fabrication, but I lack electrical knowledge. I haven't read as many threads as I probably should have by now, but my time is limited. Forgive me if this question is completely ridiculous. If I use capacitors to help run the motor and recharge the batteries, will I get better range? Please don't yell too much. Like I said, I'm not an electric engineer. I can fabricate parts using mills, lathes, drills, grinders, sanders, and files, just don't ask me to rewire your car or house with a schematic (I can't read them). Any advice you can give me would be a help (just don't ask me to give up).

Admin: 'one of many'
4,838 Posts
Tell us what you need the vehicle to do. How many occupants and luggage, speed you need to get up to, distance you need to travel. All this would help.

As for cheap, a chap here negotiated with a salvage yard to find all their batteries of the same type, he got mostly Optima red tops I think. The deal was that he took the ones he tested as ok and paid $3 each for them and the yard bought them back at $2 each when they were no good. A near endless supply of $1 batteries. It suited him as he didn't need to rely on the vehicle and it was only a short commute.

3 Posts
Discussion Starter · #3 ·
I need this vehicle to shuttle around and possibly some moderate travel. It will have four occupants totalling about 450lbs with at most 500lbs luggage. The speed limit around here is 65, but we have some long, steep hills, so speed should go up to 90 or 95 just to compensate (this is from driving some older gutless cars). I know that this may be far reaching, but if I don't at least try, I'll never know. I'm trying to get something like a Hyundai or Subaru station wagon. Something in the mid-sized range should suffice, although it may be a bit cumbersome. I hope this helps.

Admin: 'one of many'
4,838 Posts
I need this vehicle to shuttle around and possibly some moderate travel.
Range is an important aspect.
Moderate travel to a person in a city like London UK could be 5-10 miles. Someone in Coober Pedy, South Australia could see 500 miles as moderate given their nearest neighbour is 300 miles away.

Anyway, what you want can be done but it all comes down to efficiency. Your vehicle needs to be light weigh, aerodynamic and with little rolling resistance. Then you will need an effective motor, ie just enough for the power you require. You will need to weigh up how much you spend to how efficient your motor can be, you may be lucky and find a great motor for free or you may need to spend out for a rebuild or a new WarP9.

Lead acid batteries are cheap but will limit your range and speed considerably due to their capacity and discharge rates and their weight. You could get better batteries but it will cost.

You say that you need to do this for financial reasons and that you have a ver low budget and that you also haven't time to read all the threads that may help you.

Perhaps a cheap to buy and cheap to run ICE small car would be better for you until things get easier?

I am on a budget, have a quick look at how my conversion started, the link is in my sig. I have no budget at all. I am a part time teacher and I get no pay from June to end of September. I have no savings and any part time income I get just covers the bills so there really is no money at all. But I will put the time in to read everything round the clock while I can. It is 2.50am and I am still up reading.

My conversion will cost a fair bit.
I am moving myself and a soft bag on a 70 mile round trip commute at up to 60mph for most of the journey 3 days a week school time.
Car £450
Motor £400-£1600?
Controller £800?
LiFePO4 Batteries £4-5000?
Charger £600?
Misc bits and tooling £1000?

How low budget do you want? I am sure that there are folks who will come along as say I could do the whole thing for half the cost if I could do more of it myself like making a controller and charger and using lead acids and recharging at work.

It is worth reading the threads on motors, batteries, people's projects, etc and getting a feel for what folks are able to achieve and see how much of it you can achieve for your needs.

You could start by working out how much power you need to move the vehicle at your required speed to get a Wh/mile figure. That will help determine how much motor you need and how much battery capacity.

Admin: 'one of many'
4,838 Posts
Here's a little worked example I posted on this thread:
Maximum speed will be dependent on how much power your motor can produce and how fast it can run and what the gear ratio is.

Firstly, though, you will need to know how much power is needed to push your vehicle up to your maximum speed.

This will depend on [wiki=6646]Rolling Resistance[/wiki] and air resistance and how much power you need to overcome it.

For example (all figures must be in SI units):
Power to overcome [wiki=6646]Rolling Resistance[/wiki]

Pr = Crr x M x V

Pr is the power required in Watts
Crr is the [wiki=6646]Rolling Resistance[/wiki] of the tyres to the road surface
M is the mass of the vehicle in Newtons
V is the velocity in metres per second

So for example
Crr = 0.03 ordinary tyre on aspalt
M = 1200kg (11760N) a guess at how heavy your vehicle may be
V = 65mph (29.1m/s)

Pr = 0.03 x 29.1 x 11760
Pr = 10525Watts

Power to overcome air resistance:

Pa = Rho x V3 x A x Cd

Pa is power required in Watts
Rho is the air density
V3 is the velocity cubed
A is the frontal area of the vehicle in metres squared
Cd is the drag coefficient of the vehicle

So continuing the example
Rho = 1.29 at 0c
V3 = 24534.6m/s
A = 2 metres squared - random figure based on a guess of how big your vehicle is
Cd = 0.3 average nice car figure

Pa= 1.29 x 24534.6 x 2 x .03
Pa= 9495Watts

Total power, P = Pr+Pa
P = 19746Watts
P = 19.746Kw

1 hp = 746 Watts

Therefore you need 26.47hp to attain 65mph in this example.

Now, having that power won't get you up to 65mph unless your motor can be geared to produce that power at 65mph.
If the motor has 27hp at 5000rpm then you need to ensure that the transmission allows 65mph at 5000rpm.

Now the other figure you will find quoted is the Watt hour per mile (wh/mile) figure.
You can get this from total power/speed in mph.
In this case you will get 303.8Wh/mile at 65mph.
If you reduce speed you will see that your Wh/mile decreases and your range increases.
This is all on flat ground in still air and based on lots of assumptions for the figures used. It also does not take into account any mechanical losses of efficiency.

I hope this helps you get an idea of how much motor and battery capacity you may need.

1,704 Posts
very nicely written woodsmith.

weasel, I too encourage you to read as much as possible, as it will help you make wiser more informed decisions.

DIY EVs at this point are pretty much restricted to shuttling around the battery tech isn't really at the level where we can "travel" per

I would stick with the cheaper option of lead has batteries for a good can get forklift motors form junkyards for hundreds of dollars...a curtis 144V 500A controller would do you proper... (1500$ though) there are other controllers that are cheaper im sure..have you checked the classified section of this forum for people selling parts...etc..

I think the idea of a small lightweight import car is your best bet, go with lightest weight possible and then trip out as much as you dont need....also look at for tips and tricks to lower the drag on the car, e.g. underbody tray, front grill blockers, low rolling resistance tires, etc.
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