# MIata conversion



## TheSGC (Nov 15, 2007)

48 volts is not enough to get 40-45 MPH. You would need at least 72 volts to do those speeds with acceptable performance. I would say 72 volts using 8 volt batteries would give you the range and speed in the Miata.

You could use a forklift motor if it could run at those voltages. As for the controller, Kelly Controller sells 72 volt controllers at decent prices, and search eBay to see if anything comes up.


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## JRK5150 (May 18, 2008)

I originally planned for 72 volts with 6 12v batteries. The cost of the new controller was prohibitive though, so I started looking at cheaper 48v systems. I just looked into the Kelly controller, thanks to TheSGC!New prices don't look too bad, I just didn't like the thought of paying 700 bucks or more. Do you think the 72v 200amp kelly would be enough? As for the 8v batts, do you think I could get away with 6 12volts instead to reach the bottom end of my range reqirement?


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## frodus (Apr 12, 2008)

If you're talking about the 200A max controller, no, that won't work very well. A 200A continuous might be fine, but getting that car rolling without it feeling like a snail, is going to take higher currents. 

Plan on some very large 12V batteries if you're going that route. Since you need 30-40, lets say 35miles range, at say 250Wh/mile (good starting point for small car)... that ends up being 8750Wh pack required, at 72V that works out to be around 125Ah 12V batteries. They're large, and you need at least 125Ah bats to get that range at that voltage. You'll also need something more along the lines of a 500-600A max kelly controller and a decent size motor. Call Jim Husted with Hi-Torque electric about a motor. Otherwise its going to accelerate like poo... I mean, I know you just want to go 45, but you also need it to accelerate better than a 3 cylinder Geo Metro. Just backing the Sparrow up an incline out a garage, it takes 200A. Thats going somewhat slow without accelerating. Just think what it'd take with a large hill and trying to keep at 35mph.

Also, how are you going to remove power brakes? I was under the impression that hydraulic brakes used on cars were pretty much required. Not sure how you plan on doing that while keeping the brakes functional. Removing the power steering isn't a big deal on smaller cars.... lots of autoX guys do that.


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## TheSGC (Nov 15, 2007)

I think you would need at least the 400 amp controller because any hills will uses a lot of amps, and acceleration would be extremely slow at 200 amps.

My next question is how hilly is your area? You could use the Trojan T1275 12 volt 150 Ah batteries and they should give you around a 30 mile range. But if you have large hills, those 12 volts will deplete rather quickly.

Ah=Range. Usually you want at least 12KWh of power for 35 miles at 40 MPH, and 72*150=10.8 KWh. 

The 8 volt batteries are 170 Ah, so 72*170 = 12.24KWh


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## JRK5150 (May 18, 2008)

Alright, it looks like a used 400 amp controller will be on my parts list as well as 6 Trojan t1275s. BTW, I live in Florida, so big hills are not a problem! Frodus, I will not be removing the hydraulic brakes, only the vacuum assist brake booster. I will replace it with a non power assisted master cylinder. If I didn't do this I would have to use a vacuum pump while I drive to have proper brake function. Since I'm trying to keep the weight down, I won't need the extra power assist. Any other suggestions or tips? Thanks for all the help, it's GREATLY appreciated!


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## TheSGC (Nov 15, 2007)

If you don't have any hills, those T1275 could take you as far as 45 miles per charge at 72 volts. (If you are nice to them!) 

You should use the EV Caclulator to help you choose parts.
http://www.evconvert.com/tools/evcalc/


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## JRK5150 (May 18, 2008)

Alright, this is very cool! I now know exactly which batteries I need as well as controller size. Now it looks like I'll need to more closely read over the threads on selecting a proper forklift motor and go hunting.


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## EV-propulsion.com (Jun 1, 2009)

Hi,
The miata makes for a nice electric car, but it is definitely not the easiest conversion to do. We have developed a kit to do this conversion (or seperate parts) if anyone is interested at www.EV-propulsion.com
thanks,
Mike


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