Build your own cheap electric car? These guys did

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Permalink Reply by SJC on October 28, 2009 at 2:13pm

There is a program on cable called "Electrified" that showed a Porsche 911 converted to an EV. People have been converting cars to EVs in the SFO Bay area for decades. They are not "cheap" however, it can cost more than $30,000 to make a good conversion.

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Permalink Reply by neil cox on October 30, 2009 at 3:48pm

Cheap electric car maybe, State of the art no, unless you can steal the batteries and wheel motors. Except for the slight possibility of dumb luck, the car won't work well without considerable know how.
My guess is, you can add 1000 pounds of cheap lead acid deep cycle batteries = about $1200 to a $500 used 5 speed car with a bad gasoline motor, but otherwise good condition. If you connect the electric motor to the motor end of the manual transmission, some of the 5 gear choices will likely be usable. Range will likely be less than 100 miles, with sluggish acceleration, and a top speed of 70 miles per hour down hill. You need a dc series motor designed for about 115 volts dc rated several horsepower. Possibly it will survive 200 volts if you have enough batteries to produce 200 volts. A small separate field winding will give you fine speed control, perhaps too fine in some of the 5 gears. Ac motors greatly complicate your design problems, unless you can buy a kit for several thousand dollars..The kit may not work well (either) as there are lots of scam artists out there. I think 3 phase synchronous electric motors rated about 300 volts are typically used with variable frequency ac for speed control.
A simple one diode battery charger will charge your batteries if they total about 160 volts directly from the 120 volt power plug. A two diode voltage doubler with a 320 volt center taped battery will work The diodes should be rated about 50 amps and they need a good heat sink. If the battery voltage is much less than 155 volts or 310 volts you will need a 3000 watt resistor to limit the charging current. Two 1500 watt electric heaters in parallel may work well. !3 fully charged batteries rated 12 volts are about 169 volts, so 12 batteries may be correct for fast charging.Your circuit breaker should be 30 amps or more. Over charging will shorten the life of the batteries so you need to stop charging when the first battery is over 13 volts without charging current. Possibly the charging voltage will be only slightly higher than the not charging voltage when the batteries are new. You can possibly bring up the the batteries that are only about 12.5 volts individually with a 12 volt charger. New batteries all the same brand and model number should show close to the same voltage.
You possibly need 2 extra 12 volt batteries for the field winding speed control and other auxiliary devices, such as head lights. These two can possibly be the two poorer batteries removed from the main battery bank. These can be charged with a 24 volt battery charger such as used for most electric scooters or large trucks, if you want fast charge. Lead acid batteries last longer if you never discharge them below about 12.5 volts. Neil.

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