Paul & Sabrina's Cheap EV Conversion

[MPaulHolmes]

I hooked up most of the wires in back, and then one random extra, and magically the headlights and blinkers work now. However the brake lights don't work. Hmm. Didn't someone tell me that that was going to be a problem, since the engine is gone? Oh dear. I might have to jerry rig it. It's all good though. I'm still waiting on the stuff from Electric Vehicles USA inc. I ordered it in the middle of July I think. I still need to glue down the extension cord.

I mounted the volt meter / ammeter up front, and ran the wires to the back. I'm running out of stuff to do. I hope the stuff comes soon, because pretty soon horror and badness will come upon me (school will start). I really love teaching, in the sense that I really love the summers, and hate the rest of the year (at least I hate every minute that I'm in a school)

[dremd]

Alright

As far as the brake lights go.

There is a switch on your master pressure switch (may be located on a "T" on later bugs)
Basically the switch should close when the pedal is pressed; if it does not the switch is bad. if it does make certain that there is 12 volts getting to one side; them make sure that when you apply 12 volts to the other the brake lights illuminate. it isn't a complicated circuit (now the turn signals are still a mystery to me) .

[MPaulHolmes]

I wired up a mini 15ft extension cord from the back of the car to the trunk up front (beetle! ha!). That is plugged into the retractable extension cord. I plug in the 6 chargers into a 6 plug power strip, and then plug the power strip and the 1 remaining charger into the 15ft extension cord. Then plug the 15 ft extension cord into the retractable cord, and then plug the retractable extension cord into the special outlet at the library while I go to check out a book! Ya!

Oh dang, I forgot to glue the retractable extension cord to the piece of wood up front. Oh dang it.

[MPaulHolmes]

We glued that retractable (it feels like my old topology class) extension cord to the piece of wood up front in the trunk with a bunch of gorilla glue. It gets all bubbly and fills in the gaps, and sticks to metal nicely. I've been using it inside the car too to attempt to have the wiring hidden. What's the real way!? It's working I guess.

Should I remove the clutch pedal? It's worthless, but I remember doing that once with a guy that fixed my clutch cable, and he had special tools, and I think the clutch pedal and brake pedal were a pair, not to be separated. Maybe I'll just leave it there. How ghetto is that.

There's a little bit of ground that can be seen under where the battery used to be. I should do something about that.

I still need to drill the hole/holes to the motor from where the controller is, so I can run the wires to it. I might change things so you have to use the key instead. Also, I might change it so that when you turn the key a little, the precharge resistor turns on, and when you turn it on the whole way, the contactor turns on. Practically nothing will be going through the precharge resistor at that point, since it would have WAY more resistance than the other path the current could take (through the 2 gauge cable).

[MPaulHolmes]

I found a useless (hopefully) wire that led to the engine compartment that became 12v once the key was turned the whole way, so I can use it for the on/off switch for the contactor. I don't know an easy way to turn on the pre-charge resistor using the middle setting of the key turning process. I guess I could use an SCR, that has a gate that can be open at around 12 volts, and the other part has to be like 72 volts. That's stupid, but it could work. I have a huge SCR, but this is stupid. I could just push the dang button how it is.

[MPaulHolmes]

I've been doing some figgerin. I guess the easiest way to find the energy usage of a car per mile at a given speed is the following:

Choose a flat stretch of road (no hill).
Choose a constant speed 's' (in miles per hour).
Measure the voltage 'V'.
Measure the current 'I'.

To find the energy usage per mile 'F' (in watt*hr/mi):

F = V*I/s


So, to find the energy usage per mile, just multiply the voltage by the current, and then divide by the speed (in miles per hour)!

By the way, what you are really measuring is how much force the batteries are pushing on the car to move it forward, because the units of watt-hours per mile can be converted to Newtons!
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Now, let's find the force fighting against the car moving forward. Let's assume we're in neutral, so the force we are about to find will be ONLY from the wind resistance and rolling resistance.

We must find the force 'F' that is resisting moving forward at a given speed.

Choose the speed 'v' (in meters per second).
Find out the mass of the car 'M' (in kilograms).

F = M*a, where 'a' is acceleration.

So, get up to a particular speed, and then put the car in neutral. Time it to see how long it takes the car to go from speed 'v' to speed v - dv, where dv is any amount you want, but the smaller the better. For example, let's say you are traveling at 30 meters/sec, and you time how long it takes to slow down to 25 meters/sec. Then dv = 5 meters in that case. Call the time measurement dt (in seconds).

Now, a = dv/dt, so

F = M*dv/dt. (the units are newtons)

To convert from newtons to watt*hr/mile, just multiply by 0.44704:

F = 0.44704*M*dv/dt (the units are now in watt*hr/mile)

The difference in this force measurement and the force from the batteries is the loss from the transmission, motor, controller, wires, etc.

You could also figure out the force from only rolling resistance by doing the above experiment while traveling very slowly, then you could figure out the drag coefficient of the car!

[MPaulHolmes]

OK, I believe it's reasonable to assume that the force from rolling resistance is constant, and the force from wind resistance is proportional to the speed of the car.

Let 'v' be the speed of the car.
Let 'F' be the force acting against the car in neutral at speed 'v'.
Let 'p' be the constant force from the rolling resistance.

F(v) = p + q*v, for some constant q.

So, choose a speed v1. Using the approach in the previous post, find F(v1).
Choose speed v2. Find F(v2). So, now you have 2 equations in 2 unknowns, where the unknowns are 'p' and 'q'. Find p and q.

Now, you can know the force acting against the car (in neutral) for any speed you want, since you now know p and q.

By the way, p is the rolling resistance. So, it would be interesting to try the experiment for various tire pressures, to see how much p changes. You could even come up with a curve for rolling resistance as a function of tire pressure. I think I'll do that.
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[MPaulHolmes]

I re-ordered some stuff to finish the car. The previous order will be here around the end of September. I MUST finish before September, so I reordered it, and will use the other stuff for a second EV that will be sold.

I saw The View today. Wow, I sure wish I had that 1 minute of my life back.

[MPaulHolmes]

So, the force that the batteries put out is:

V*I(s)/s, since current is a function of speed.

Then I can get a plot of V*I(s)/s to try to minimize it based on a certain speed range.

[Indianapolis500]

lol this sounds like alot of work for a EV... I was thinking since your gonna have front wheel?? Put the motors in the front and I wouldnt use a motor from an existing forklift sounds abit heavy?? connecting 3 moped electric motors 2 front one rear?? Then connecting them to a central circuit then wiring what else you need in them