Electric car conversion: Project ForkenSwift

[MetroMPG]

The forklift pot is interesting. With a jumper wire (short) connected between the 2 ends of the resistor, the 0-23k pot acts as a 0-6-0 k pot - meaning resistance is highest with the wiper centered between the 2 ends and drops as you turn it either way from center.

The problem with getting just any 0-5k pot is they're usually about 300 ish degrees of rotation. But the arm on the potbox only moves about 70 degrees.

I suppose this is why the strange, jumpered, 23k forklift pot setup works. When set up that way, the resistance goes from 6k-0k within about 50 degrees of rotation (which is what we want).

Anyway, finding another pot is all moot, since I figured out how to make the forklift potbox work with the Curtis.

No need to harvest the pot from something else!

Controller: we're going to go with the Curtis to start. But will probably swap in the forklift's EV-1 controller at a later date, just to compare.

The EV-1 has a higher current limit (around 400A, compared to 275A for the Curtis), but it has no filter capacitors on the input side, so it'll hammer the batteries and reduce range as a result (input capacitance wasn't a concern in the forklift application because its 3000 lbs of lead acid effectively gave it enough capacitance). This is all stuff I'm parroting from the EVDL. I don't have a thorough understanding of it.

All I know is that people who use EV-1's say their range is reduced by 20-50% compared to a modern controller (e.g. the Curtis) with input side capacitors.

Since our goal is most range (spirited performance be damned), the Curtis is the way to go.

[MetroMPG]

Tidbit: the 2 Youtube videos of the motor spin-up have been collectively viewed over 2000 times. Apparently there's a healthy interest in conversion info.

And Project ForkenSwift is inspiring other people. Check this out:

Quote:
I’m taking inspiration from http://www.forkenswift.com/ as a low-budget conversion. That’s a good model to start on for us as we will be learning much along the way – so mistakes won’t be so costly!

http://www.43things.com/people/progr...rschaq/6037794

[MetroMPG]

The guy who initially explained to me how to use a 3-wire pot on the Curtis controller tells me my hack to make the forklift potbox work ... will probably eventually wreck the controller. Sigh.

So, probably got to bite the bullet and order that $29 unit to see if it'll work I guess. No point in tempting fate. DC controllers fail "on", after all.

---

to which someone says..

Haha, YIKES!

[MetroMPG]

SW asks for clarification...

I'm still a little fuzzy about how that pot is wired. Is it off at 0 ohms and full on at 5K ohms (70 degrees)? Why did he think that "6K pot" would cause damage?

It's not the 5 vs 6k ohms that's the problem, it's that I shorted 2 tabs on the controller together so I could use the forklift pot in its *2-wire* configuration rather than in the *3-wire* config that the controller is expecting.

It's one of these things that would take me an hour to properly describe in writing and in a diagram vs a minute to show you in person. Frustrating!

I'm just going to order the expensive potentiometer rather than trying to mod this one to make it work.

[MetroMPG]

Minor update: just pursuing a few leads on potentiometers that will both work inside the potbox, and talk to the Curtis.

Taking my time. The fact that it's -20 out has removed a lot of the urgency for getting back into the garage.

[MetroMPG]

The conversation turns to temperature

Oh man, you sure do get the lake effect, don't you. I do hope you are talking about degrees C, not F. It was a balmy -17 C at my house this morning in still air, but now it's ~-21 C with the wind chill.

When I walked to class this morning it was a cool -24C and now it's up to -17C, dunno with the wind chill though,

Yep, that was in C. Just walked downtown. Got a ride back. Temperatures like this sure make you appreciate the 25% efficiency of the ICE. Gimme some wasted heat - NOW!

What's good about EVs is that you can install ceramic heaters. No need to wait for any ICE to warm up. you can get your heat as soon as you want it.

Yes, instant is nice.

Some ICE cars have instant heat too. I don't know about the US market cars, but the last generation Echo hatch that I test drove had a honking big resistor in the heating duct that you could light up as soon as you started the car. It didn't feel "hot", but warm air did come out of the vents within a few seconds.

But man, the BTUs coming out of an ICE heater once warm is pretty hard to beat with ceramic heaters.

Even the EV1 had a lousy heater, from first hand reports I've read. (Though it was a heat pump, not a ceramic resistor.) Efficiency, efficiency...

[MetroMPG]

Well crud. Just missed out on an eBay auction for a potbox that had all the right specs.

Got another price for a Curtis replacement pot: $45 CDN. That, to me, is just insane, considering you can go into radio shack and get a 5K pot for $2. But the standard seems to be 300 degrees of rotation, not 50.

It's looking like buying the replacement will be the route to take.

I just hate spending 5% of our total budget on a wee potentiometer

[MetroMPG]

The amount of time I've spent looking for a deal on the right pot, I could have just done some work and earned enough $ to buy several at list price.

But it's the principle!

(I even considered making my own wire-wound pot, but couldn't find any decent resistive wire around the workshop )

[MetroMPG]

I even took apart the Playstation analog controller to see what pots it has.

[MetroMPG]

SW lobs another good anecdote...

I don't think that's weird at all. One time my brother was in need of some kind of high wattage variable resistance for an impromptu project and used a piece of ham he had lying around. He had wires stuck in at different points.

Kids, don't try this at home.