Paul & Sabrina's Cheap EV Conversion

[MPaulHolmes]

It was a lot of work! Actually though, I could have done it in about a week if I would have had an adapter plate made, and not had a piece of crap car.

[MPaulHolmes]

Let's say you are traveling at a constant speed 'v' on flat ground.

Let F_b be the positive force the battery is providing.
Let F_m be negative force from loss in the motor (electrical power going to the motor).
Let F_c be the negative force from loss in the controller.
Let F_t be the negative force from transmission and motor spinning (no electrical power going to the motor).
Let F_w be the negative force from the wind.
Let F_r be the negative force from the rolling resistance.


Since the acceleration is 0 (constant speed), the net force is 0. So,

F_b(v) + F_m(v) + F_c(v) + F_t(v) + F_w(v) + F_r(v) = 0.


It would be nice to have a graph with lots of points for each force function.

We can do that for F_w and F_r. F_r is approximately constant. F_w(v) can easily be found for any v. F_b(v) was found already. It's just V*I(s)/s. To find as many points as you want, you just need a volt meter and an ammeter. You can find F_c(v) by knowing the voltage drop from the mosfets in the controller. For my curtis controller, it's about a 0.5v drop at 100 amps. So, it's about 99% efficient. So, I think I'll just assume F_c(v) is approximately constant. I'll say that

F_c(v) = -0.01*F_b(v)

It's not perfect, but pretty accurate.

To find F_t(v), do the experiment where you let the car slow down, but leave it in gear. Then do the experiment again in neutral, and find the difference.

All that's left is F_m. So, you can figure out the loss from the motor for a variety of speeds (assuming the motor stays at an approximately constant temperature) by solving for F_m in the above equation!

[MPaulHolmes]

From one of the pictures, it can clearly be seen that the VW beetle is actually an automatic! See, no clutch! whow! That's amazing. Well, actually I cut off the clutch pedal and took out the clutch cable.

I also got in the PB-6 that I ordered on Tuesday and came here on Wednesday! Wow! talk about fast shipping! It was cheap to ship too. There was filth and crap in the crevices of the gas pedal, so we couldn't get enough range. The PB-6 was reading from 1 Ohm to 3500 Ohms. That made me real mad, so I took off the pedals and cleaned it. Now it goes from 1 Ohm to 4550 Ohms, which is good, because my PB-6 maxes out at 4557 Ohms. I'll save those 7 Ohms for when Forkenswift and Benjamin Nettenyahoo's pimp-mobile come around to drag race.

Oh, dang it, I forgot that the middle hole is where the LED battery monitors are going. The last picture is a few of the LED drivers and the prototype board to stick all the stuff on it.

[bennelson]

We SO need to race your e-Bug, Darin's Forkenswift, and my Electro-Metro!

Make a video of that and show it a million times on YouTube!

[MetroMPG]

No way! You guys have more volts. I get a head start.

Paul: put a button on the dashboard that gives you those 7 extra ohms. Label it DANGER! TURBO

[MPaulHolmes]

Originally Posted by MetroMPG

Paul: put a button on the dashboard that gives you those 7 extra ohms. Label it DANGER! TURBO

Oh my gosh, that is a really good idea, but to cut down on wiring, I'll have to just jump into the back seat and just pull it the rest of the way, which will temporarily cause a slight loss of control of the vehicle.

[bennelson]

Originally Posted by MetroMPG

No way! You guys have more volts.

It's not the volts....it's how you use them.

Come on guys...it's the AMPS that matter!

[MPaulHolmes]

So, evidently the force on the car due to wind is proportional to the SQUARE of the velocity! What the crap, yo. Why is that? Hmm... Maybe because the force is acting on an area. Whatever. So, it's more accurate to write

F(v) = p + q*v*v for the force on the car due to wind and rolling resistance.

Still, you can just choose speeds v1 and v2, find F(v1) and F(v2) by the deceleration experiment above, and then solve for p and q.

[MPaulHolmes]

I started attaching the lugs to the cable ends. I'm going slow and careful because my "hex crimper" is home-made. I think the crimps are very solid, however.

Also, I drilled a larger hole from the back of the car to the engine compartment, and ran 2 cables from the motor to the controller, cut them, and added the lugs. In fact, I've only crimped 4 lugs so far. I'm not sure how many more there are. Probably 12 more. Yikes. I only have 12 more. I hope that's how many.

Edit: It was how many.

[MPaulHolmes]

I just had a great idea! If I could somehow hook up a generator that is driven by a fan, I could recharge the car as I drive! hahaha. (note: the fan is actually a person in the trunk, that is a big fan of Oprah, that is forced to pedal a very small bike that turns the generator)

If I hear that idea one more time, BAM right in the eyeball, I'm going to stab myself with a fork.