So you don’t make the mistakes we did and end up disappointed with the range
and performance of your do it yourself electric car, here are sample answers to the basic performance questions on the previous page:
1. Estimated driving range 15 miles one way - 30 miles round trip
2. Car weight 2,000 lbs before batteries, 3,300 with battery pack
3. Top cruising speed needed, 60 mph
4. Yes, I want performance from my EV
5. There are a lot of stops and starts
6. Somewhere with a real winter, it hits zero in the winter
7. It gets hot, but not blazing
8. There are plenty of hills: total vertical of 1,500 ft along a typical drive
9. Yes, it gets windy
10. The electric car is mostly for one person, sometimes two
11. I want power brakes, power steering, heating, and AC
12. I want regenerative braking
13. There is maybe a plug in the garage where I work
14. I’ll mostly charge at home in a garage
15. I’ll just use an onboard charger
Here is an explanation of the basic performance items to check:
15 miles range one way x 2 = 30 miles total miles range. Taking the energy usage average from a number of cars in the 3-3,500 lb range, we get 300 watt hr/mi as a conservative average energy usage. As an average starting point then: 30 miles x 300 watt hr/ mile = 9000 watts or 9.0 kWh energy.
The problem is that the average case is never met in real life. Practically, your do it yourself electric car will always need more energy. This is because the other questions on the list all draw more power except the regenerative braking and the recharging.
Next if you want to accelerate from a stop to 60 mph, it will use about ½ the energy it will take to go one mile. To accelerate to 45 is about half that again.
If you are driving through the city there will be stops. So, if you accelerate to 45 mph from 15 stop lights in 30 miles, you have used 75 kWh x 15 = 1,125 watts or 1.13 kWh right there.
Most batteries still perform the best at around 65 degrees or so. When temperatures are elevated or lowered as in the real world, storage declines a LOT. This is something not advertised too much, but happens even with new cars like the Mitsubishi i Miev.
Hills are another battery drain. If you plan to be pulling your do it yourself electric car up many hills, your batteries will feel it. If you are pulling hills at speed, they will really feel it. This is another item often skimmed over in EV information brochures as “range depends on driving style” and stuff like that. Then people wonder why they are not getting the range advertised.
Wind and added weight are additional EV concerns. Wind resistance can be considerable, as can additional weight. You will need to plan accordingly.
Brakes: One of the main requirements for the do it yourself electric car builder is the brakes. Electric motors do not make any vacuum like the intake manifolds of gas powered cars. You will want to install a 12V booster pump and vacuum reservoir. Hot rodders sometimes use this setup, and some older Cadillacs and other cars have it too. You can find the pumps in scrap yards with a little looking. If junkyards are not your thing, there are plenty of kits.
The brake setup will pull a few hundred watts. You will need more power for an electric steering pump that might draw 12v x 60 amps or 720 watts.
The do it yourself electric car also needs heat. It will be electric. They have little $29.95 US, 12v x 12.5 amp (150 watt) heaters that might defrost a window on a warm day, but not a driver. Try for a 300 Watt heater at a minimum.
If you can swing it, regenerative braking can return 10-15% or so of your stopping energy back to your battery pack. It can offset some of the energy losses above.
Finally, you want to think through how you will charge your car. Where exactly are you going to plug it in? Can you rig up to 220V - the car will charge a lot faster. Is the garage heated?
There are a number of onboard smart chargers you can get at a reasonable price considering what they do. Get a pretty good charger capable of balancing all the batteries in your pack. Battery balance is key to a top performing pack.
After going through the performance needs of your do it yourself electric car,
it’s time to look at some of the key components to make it happen. These are the components that form the heart of the electric car conversion.
Here is a list of parts we used in the example and our do it yourself
electric car:
9" Series wound DC Motor
Motor to Transmission Adapter (Retains Clutch)
Motor Mount
Controller Heat Sink and Mounting Plate
Curtis 1221C Motor Controller
Curtis Style PB6 Pot Box
Russco Battery Charger
30 amp DC/DC Converter
Main Contactor
500 amp Main Fuse
0-500 amp Meter or eMeter
Shunt
Main Breaker
Manual Disconnect Cable
2/0 Battery Cable - varies minimum 2 gauge wire
Battery Cable Ends - varies
Fuel Gauge or eMeter (extra cost for the eMeter)
Misc. Wire crimps, covers and connections as required
