Thread: Electric Yugo
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Old 03-07-2012, 11:32 AM   #17 (permalink)
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First, thanks for the replies!

Just to clarify the plan at the moment is:
1. Obtain and install new controller and batteries
2. Test to see if motor is up to the job, add cooling or replace with larger motor if it isn't
3. Find some sort of instrumentation to measure the draw on the battery pack at any given point.
4. Do A-B-A testing on modifications to try to lighten the load on the battery pack

The only reason for bringing up the aeromods at this point is just that I was thinking about them and figured I'd share. Maybe I should have posted that in the aerodynamics section.

I'll make sure to build the system to the max voltage the motor can take, if it's still too weak I'll rewire the batteries to the voltage of the new motor.

Tracking down mpg information was harder than expected. I've seen numbers from 30-45mpg. Probably a lot of this is due to variation in driving technique.

Looking at Greg Coleman's page, the wh/mi numbers seem off. He reports having "6 Deka MK Power M24SLDGFT 12 Volt GEL 73.4AH, 12.00 Volt, Lead-Acid, Gel" 6*12V*73.4Ah is 5,284wh. So even if he used 100% of the capacity to get 15 miles that's still just 350wh/mi not the 440wh/mi there or 500wh/mi. Several of the wh/mi figures seem to be off on that site. I saw a Honda Crx that said it used 18,000wh/mi (Michael Brooks' 1986 Honda CRX). This was most likely the impulse reading for watts at speed considering he has a 33mi range. At the same time there are other crx's that report 240wh/mi (Allen Grvoer 's 1986 Honda CRX) and 70miles range using lead acid (Victor Tikhonov's 1991 Honda CRX). Now the Yugo isn't as aerodynamic as a Honda crx, but it sure is more than a pick up truck.

The calculations I did before included cruising speed, as well as energy to get up to speed as if it were completely wasted at a stop (no cruising), which seems overly harsh to me. That would be as if somebody accelerated full out to speed then maintained that until just before each stop and slammed on friction brakes, wasting all the kinetic energy. On the other hand the 99mile range would be as if you could start out cruising with no slopes, crosswind, wipers, lights, etc. I did try to also take a margin of error on all my figures for size, weight, Cd, motor efficiency, etc.

Is there something else that would cause draw on the battery that I'm forgetting?

To clarify some of what I said before. I'm trying to build the battery pack so that the rate of draw is less than what the batteries are rated at. For example if they have a 115 min capacity at 75amps then I want to make sure that the draw is less that 0.5 C on the battery pack. That means it needs to have at least 2 hours of driving time. Now this doesn't have to be two useable hours of driving time, as I'm only looking at the rate. So if I have at least two hours of driving range, in order to prolong battery life I'd limit myself to just one hour of driving per charge. So if the full charge would give me something like 80miles of driving range, I'd limit my own range to 40mi, unless I ran out unexpectedly, in which case the extra buffer would be there even if it damaged the batteries to do so. Now my understanding of lead acid is that the more slowly you draw current from it the more charge you can use, and the longer they last. This is why my first priority would be to limit the rate of draw from the batteries, and then to limit the depth of discharge. I would actually normally drive less than 20miles in a day, but I figure if I could achieve 80 miles of range, and limit the current draw then the battery pack should last much much longer than one which depletes it self down in a matter of a few minutes of driving.

I'll try to find the specs on the golf cart motor to see what voltage it is. If it's less than 72 volts should I just abandon it and look for something that can take a higher voltage?

Also, I would be interested in making a lithium pack. I just don't know where to get lithium batteries with a BMS for anywhere near the price of lead acid. Now on the one hand I shouldn't need as many, and they should last much longer, but on the other hand the price is so high on everything I've seen. If you could point me to a good source I'd be glad to check it out.

I just saw your new comment Daox. Yeah it rarely gets cold here at all. It does rain for a few minutes at a time here and there though. Headlights shouldn't be too big of a draw because I'd be doing mostly daytime driving, but even so I'd gladly look into making some LED ones. A lot of places have to worry about the batteries being too cold and losing capacity because of this, but with temps over 100 in the summer I'd be more worried about keeping the motor and batteries sufficiently cooled.

P.S. found this here on Ecomodder about a guy with an electric Yugo. It's not extremely detailed as to what batteries, range, etc but I thought it was cool.
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