Step 6: Batteries
The motor won't do you any good, unless you have some batteries to power it with.
This car uses 6 x 12V batteries, for a 72V system.
These are Deka Dominator true Gel-Cell batteries. They can not leak or spill acid, nor do they require watering.
I was fortunate enough to be able to get these batteries, slightly used, for $12 each - essentially scrap metal prices!
One downside of these batteries is that they are picky about charging voltage. I was finally able to find a 72V charger designed for these batteries, and got it used for $200.
If I had used the more typical deep-cycle flooded batteries, I could have used a different charger, or even 6 12V chargers, one on each battery.
Four batteries are in the cargo compartment of the car, and two are in front, where the radiator used to be.
For the rear batteries, I cut two pieces of bed frame to lay across the spare tire well, and ran a bolt through the end of each piece down into the frame of the car.
For the front batteries, a few friends came over and helped me weld in a metal tray for the two batteries to sit on. Then I cut two short pieces of unistrut, and ran threaded rod through holes in the tray to bolt the batteries down. I then insulated the front batteries with rigid styrofoam and re-installed the front bumper.
I went to the boat store and bought a "battery charger power inlet". This is a male electrical connection with a rubber cover. Since the gas tank was already removed, I installed the power inlet where the gasoline used to go in.
I added an additional circuit in my garage, just for the car, and have a 25' 12 gauge yellow extension cord with power indicator light in the end, just for plugging the car in with.
Plug it in at night, and it's charged the next morning, automatically.
Update! I later played around with more batteries. With a motor controller that supports higher voltage, I was able to run up to 144V (12x 12V batteries.) At that voltage, the top speed of the car was at least 73 mph, but I really had no cargo space.
Just so you know, Ford Ranger front coil springs fit the back of a Geo Metro, but you have to shorten them.
This car uses 6 x 12V batteries, for a 72V system.
These are Deka Dominator true Gel-Cell batteries. They can not leak or spill acid, nor do they require watering.
I was fortunate enough to be able to get these batteries, slightly used, for $12 each - essentially scrap metal prices!
One downside of these batteries is that they are picky about charging voltage. I was finally able to find a 72V charger designed for these batteries, and got it used for $200.
If I had used the more typical deep-cycle flooded batteries, I could have used a different charger, or even 6 12V chargers, one on each battery.
Four batteries are in the cargo compartment of the car, and two are in front, where the radiator used to be.
For the rear batteries, I cut two pieces of bed frame to lay across the spare tire well, and ran a bolt through the end of each piece down into the frame of the car.
For the front batteries, a few friends came over and helped me weld in a metal tray for the two batteries to sit on. Then I cut two short pieces of unistrut, and ran threaded rod through holes in the tray to bolt the batteries down. I then insulated the front batteries with rigid styrofoam and re-installed the front bumper.
I went to the boat store and bought a "battery charger power inlet". This is a male electrical connection with a rubber cover. Since the gas tank was already removed, I installed the power inlet where the gasoline used to go in.
I added an additional circuit in my garage, just for the car, and have a 25' 12 gauge yellow extension cord with power indicator light in the end, just for plugging the car in with.
Plug it in at night, and it's charged the next morning, automatically.
Update! I later played around with more batteries. With a motor controller that supports higher voltage, I was able to run up to 144V (12x 12V batteries.) At that voltage, the top speed of the car was at least 73 mph, but I really had no cargo space.
Just so you know, Ford Ranger front coil springs fit the back of a Geo Metro, but you have to shorten them.
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If there was a way to leave the clutch you could shift gears while running. The electric motor was designed for slow heavy use not hwy speeds?
Shifting without a clutch really isn't a problem. It's a very different thing having an electric motor that comes to a complete stop when you do (rather than an engine that has to idle) The electric motor has been working great.
First, when you say the peak horsepower in 96.5 hp, this peak horsepower occurs when the gas peddle is fully compressed and not the constant horsepower correct?
Second, how can you be pulling 500 amps from the batteries when the capacity of the batteries is only 100 AH? Does the controller amplify the amps?
Third, how did you figure that your cars uses about 300 WH per mile? what calculations did you do? I am trying to understand all the calculations involved in this type of project.
Thank you
How many watts or horsepower a motor uses depends on which gear you are in, the weight of the car, if you are accelerating or not, etc. When you are at a stop, you use 0 watts.
For the batteries, AMPS is a rate of energy flow. AH or Amp-Hours is a CAPACITY. It's a bit like comparing miles-per-gallon to how many gallons a gas tank is - they are two different things.
To figure how many watt-hours per mile, a simple way is to reset the car's trip odometer, go for a drive, and return home. Plug in the car's charger through a device that tracks energy usage. I use one called a "Kill-A-Watt". When the charge cycle is complete, divide the watt-hours used to charge the car by the number of miles on the trip odometer to get watt-hours per mile.
HP = torque x RPM / 5252.
The acceleration of the car then depends on the horsepower or watts produced by the engine, and the other forces on the car (drag and friction and gravity if going up or down a hill) which depend on the speed, the weight etc. Is this not correct?
For the batteries, I guess I worded in a bad way. 100 AH tells us that we can pull 100 amps for one hour or 1 amp for 100 hours correct? So pulling 500 amps would only allow the batteries to run for 12 min or 1/5 and hour if they were fully discharged, right? (500 amps X 1/5 hour = 100 AH)
Since I am doing a feasibility project, checking the possibility of turning a truck into an electric truck, I do not have any equipment to check the watt-hours per mile and need to do an estimate based off numbers and calculations. Do you happen to know how to do this?
You are correct in that gears do NOT create power (horsepower) they only swap torque and speed. A typical gas car uses the transmission to match the engine to the road in terms of speed (usually upshifting) and torque requirements (usually downshifting) Many electric cars use fewer gears because they have a larger range of torque than a gas engine car. For batteries, you have that about right, exept that it is a tad more complicated than that once you figure in the Peukert effect
You can do a rough estimate of of how many horsepower/amps/volts you will need with an online EV Calculator. You can find one HERE.
MPH = RPM *Circumference / gear ratio * 0.000947 for converting from inches per minute to miles per hour.
Using a motor performance graph you can then find the torque and amp at any rpm and thus any speed. Using the torque you are able to figure out acceleration and using the amps helps you determine the range. When engineering a car you determine the gear ratios based off what gives you the best performance. Since I already have a transmission the process I described allows you to estimate your performance. Is this correct?
I never did any of that though.
In my case, I had never built an electric car, and was really looking for just an "around town vehicle". I have another (internal combustion) vehicle that would be dedicated to long trips.
I simply found an electric motor that looked plenty big, and went with it. I'm sort of an "off-the-cuff" tinkerer/designer. My thoughts tend to be more of "will this work or not?", "can I afford this?", "Is it good enough, or not?".
I know many engineers that are good on paper, but micro-manage a project so much, that they never start it in the real world. It's death by overdesign. I am a strong proponent of just throwing yourself into something.
Learn all you can, do your reading and research, talk to everyone you can, but at some point, just start actually working on the project. Get the truck, yank the engine, and go from there. The small successes of removing the gas tank, pulling the engine, etc. are very motivating and keep a person excited and on task with the project.
Good luck on your project!
-Ben
As of right now, they really aren't in my budget. Keep in mind that you really need a good charger and battery management system to go with the batteries, but yes, Lithiums are great!
12V x 100 = 1200WH x 6 = 7200.
So, it's a 7.2KWh battery pack. However, it is all USED batteries, so I can't expect them to perform like new.
300 Wh per mile is a common number to use as an estimate of how much energy a car like this uses. If you divide the number in half (because you only want to use half the battery pack, to keep them happy and give them a nice long life) that's 3600 wh, divide that by watt-hours-per mile (estimated 300) and you get 12.
So, this car, running on only 6 used batteries, can regularly 12 miles per trip. That doesn't sound like a lot, but I live 2 miles from town, 2.5 miles from the grocery, 3 miles from the hardware store. You get the point. My typical trip of running all my errands is about 10 miles. And that's running the pack half-way down. If I want to take them down to about 80% discharge, that's a nearly 20 mile range.
6 12-volt batteries is really bare minimum for an electric car. Recently, I removed one of the used batteries and added 4 new Die-Hard Platinum batteries. The car has much more ooomf! and better hill-climbing. (There's two LARGE hills in my area)
This motor didn't have that on it. I can tell you that 1 horsepower is 746 electric watts. So....
500 amps x 144v = 72,000 / 746 = about 96.5 HP. Lets just call that 100 hp peak.
I have run this car on 144V and pegged the ammeter just to see what it will do. You CAN put that much power through this motor.
Burns rubber when you do!
The motor controller will handle up to 500 amps at up to 144V. As long as you don't melt the motor, you can put a prettty amazing amount of power through it.
This motor has only ever felt just slightly warm when running it at 144V.
A 9" diameter motor is pretty common for a full-size motor. If, by any chance, you see a motor marked as a model "4001", take it. That same motor is also sold specifically for electric cars!
Tell the junk yard guy that you want a motor big enough to drive a car.
The drive motor out of a full-size forklift is great. You only need to make sure it is small enough to fit in your car!
The power connector goes from the gas filler into the under area of the trunk where the charger is.