Electric conversion: Project ForkenSwiift

[MetroMPG]

Originally Posted by brelandt

Watched the DVD, "who killed the electric car" tonight.

Me too. (Again.)

I think my Sidekick would be a good canidate for a EV project as well.

We actually started out watching for one of these as a host. Toecutter's right - only really suitable as a "town car" due to aerodynamics.

would it be wise/economical/ludicrous to use Romex

I'd never heard of Romex before you asked. I looked it up and it appears to be plastic sheathed cable. But is it structural cable or electrical? (good conductor?) Flexibility isn't necessarily a problem - you just have to plan more carefully. Some people use bent copper bus bars for battery interconnects.

[MetroMPG]

http://www.youtube.com/watch?v=2Ins29dqbac

[GasSavers_DaX]

Originally Posted by MetroMPG

http://www.youtube.com/watch?v=2Ins29dqbac

Nice! Is the 20 km/h in 1st gear? What do you estimate it will be with 48V?

I'm not sure what sizes Romex comes in, but I was wondering if it was good enough for a house (120V), will it be good enough for this (48V)? How many amps is the Forkenswift going to see? What's the max amp rating on typical romex? (general questions for anyone )

[Silveredwings]

A quick check of ohms law (and AWG sizes) tells me if you put only 15 HP into the motor on a startup (15HP x 746W/HP), you'll be cranking over 11kW through the wires. At 36 V, that'll require over 310 Amps. 12 guage wire in your house walls is great for a 15A circuit, but it has over 27 times the resistance of say 3/0 guage wire. That added resistance multiplies by the amperage and results in a voltage drop (and heat loss).

For example, 20' of 3/0 ga. copper is about 0.00124 ohms. At 310A, that drops about 0.38 V, or about 119W dissipated in the wire. With 12 ga. copper wire, the same length is 0.034 ohms and at 310A, that's 10.5V dropped and over 3kW dissipated (though this becomes a self limiting system about this point: the more resistance, the lower the current and HP output).

Resistance also goes up with temperature and that all your connections will add resistance losses as well so you want to minimize resistance wherever you can. Also, copper wire does work-temper as you bend it (not as bad as Al) and so goes up in resistance at those bends. It's small but cummulative. Solid wire is worse in this respect than stranded wire.

This is one reason why the more engineered EV designs go for higher voltage systems in order to keep peak current lower: fewer resistance losses in motors, wires and connections, lower weight conductors, etc. This is also why many people say that an EV's performance is more limited by the controller's capacity than the motor - as in what's the peak current capability of the controller?

YMMV.

[MetroMPG]

Originally Posted by Silveredwings

Also, copper wire does work-temper as you bend it (not as bad as Al) and so goes up in resistance at those bends. It's small but cummulative. Solid wire is worse in this respect than stranded wire.

Hmm - learned something new today. Thanks for the lesson.

[Silveredwings]

Originally Posted by MetroMPG

The forklift controller limit is in the neighbourhood of 400A, but it also has a bypass, which will feed full battery current to the motor under certain (logic) conditions.

That must be analogous to a tourque-converter lockup clutch. It does make a lot of sense. At those high amperages, the semiconductors are just ohmic switches dissipating a lot of loss because of their even slight resistances. If the duty cycle of the PWM gets close enough to 100%, it might as well use a relay (metal) instead of silicon.

EDIT: that should mean that the system should be more efficient at the equivalent of WOT.

BTW, silicon resistance goes down with temperature. That's why there have to be preset thermal or current limits or they will fuse together (read self-destruct). When you do overload a power transistor, you will be able to see glowing silicon a split second after it pops the lid off the device's case and a split second before it clouds the view with smoke. Don't ask me how I know this.

[Silveredwings]

Originally Posted by MetroMPG

Still, 9 HP is theoretically enough to go 55 mph in this car on level ground (assuming you don't run out of power before you eventually accelerate to that speed). What else am I missing?

That's a steady-state or straight and level cruise. I think your system's peak current limit will determine your acceleration rate and ability to climb hills. (edit: I mean that 9 hp may mean 0-50kmh in approximately 10 or 15 minutes ) - edit 2: when you hit the gas pedal, your laptop application can just show an hourglass, or better yet, one of those calendars with the individual date sheets blowing off in the wind.

[MetroMPG]

Originally Posted by Silveredwings

That must be analogous to a tourque-converter lockup clutch. EDIT: that should mean that the system should be more efficient at the equivalent of WOT.

Nice analogy!

[MetroMPG]

Thinking about EV hypermiling techniques: I wonder if the car will coast further in neutral or in gear when off the go pedal...

[brelandt]

Just showed my Landlord the "Who killed" DVD. He LOVED it.

Infact when I first walked over to his house he asked me if I wanted to sell my Sidekick. Asked why. He said to build an EV out of it!

I told him that when I get my Integra back that I had plans to do the same to it.

So he asked if I knew where he could get a Geo Metro? How weird is that was my first thought.

Anyhow ended up watching the movie again tonight with him.

That and with listening to him explain how the EV works and what parts to get I really got charged up (no pun intended) to start an EV project.

However I'm electrically retarded and will need a lot of training by a really patient teacher. Lucky for me he was a teacher at a local college in electronics and has the talent to put things into laymens terms for me.