Me too. (Again.)

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.

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.

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 :))

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.

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

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. :D

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. :D

Nice analogy!

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

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.

I just had to add something to this.

LAst year I was living in Atlanta working for a general aviation company. We were "cleaning" house and I was tasked to moving the heavier things like aircraft windshields and the like that the "girls" I was working with wouldn't move.

I remebered throwing out (recycling) two 160 pound electric motors from our massive air compressor system that ran all of the air tools in the hanger. I have no idea what the specs where on them but I'm sure they could have worked on an EV.

Just think of it. If I had been into EV's back then I would have saved myself $300 easily not to mention all of the 28V batteries I recycled as well. hell I even threw out a controller!!!!!!

Next time you see an avation company or heck even drive down to your local FOB see if they have any of these thing collecting dust? I'm sure since they have to track their spending they will be more than willing to just give them to you for free.

Also would a electric motor from a generator work? After hurricane Katrina hit my town there is bound to be a few old generators lying around?

Sounds like you've got the ideal situation with your landlord being an electronics teacher.

Schematic time...

OK, now you're talking. I have some questions.
1. Are the the coils of the contactor solenoids intended to operate at 36 - 48V?

2. Are you connecting the 12V battery ground and the 36V battery grounds together? Or is only one connected to the body (I assume atleast the 12V gnd is or you'd have to rewire the rest of the car).

3. The controller looks as if it regulates only the negative connection to the motor. If the negative side of the battery is always connected to ground (once the neg contactor is closed) and the positive is always connected to the motor (once the positive contactor is closed), then there is a risk of any short (e.g. dropping a wrench) between ground and the negative motor connections throwing the motor into full power (serious lurch).

Nope he did but it looks just like this one but baby blue......

https://www.austinev.org/evalbum/991

Yes - they're out of the forklift. It only had 1 pack (no 12

Brelandt: he's got a CitiCar/ComutaCar! Awesome. He's basically driving what I'm building. I probably would have bought one of those if there were any around here.

Yes.

Well, yes isolating the ground should greatly reduce such a risk. BTW contactors sometimes do stick.

4th question:
If so, you may be able to further mitigate accidental lurches the way Jerry does with that latching relay, though in your case, you'd may need to use a DPDT relay. Let me think about that.

If I understand Jerry's setup, his pot box latching relay prevents the pack +ve contactor from closing if the ignition is switched on while the go pedal is pressed.

His approach is sort of equivalent to forcing you to depress the clutch before starting a manual, or pressing the brake to shift out of park.

I omitted that precaution.

Right again. It does make sense to omit that interlock if you're the only one who will drive it. Some people (like my mother) have a tendency to step on the gas pedal when turning on a car - that can be bad since there's no engine that must first be started. I believe the interlock is required (in the US) of EV manufacturers but I don't think it applies here.

OK, so back to the ground issue. Your shematic shows the negative connections to the contactor coils with a "chassis ground" symbol but there is no place where that ground actually connects to the negative side of the 36V. I assume those connections go to the point just after the shunt.

I would put a small fuse (1A or less)) on the + side of both the voltmeter and the ammeter. It's just a precaution and won't affect their accuracy.

Also you should fuse the controller +36V small wire, and the clock wire (it's better than having burned wires - see I do have a serious side :) ). The Ammeter fuse may not be needed but if the shunt ever comes loose, it'll save the meter from being fried.

Maybe like this?
https://www.gassavers.org/attachment....1&d=1168401800

Awesome - thanks.

OK, so maybe I should have an interlock. I never thought it was a problem, but if there's a law...

PS - didn't realize I was mis-using the chassis ground symbol. Learned sumpin' new today! Just in time too - the day's almost over, here.

I think it's more of a dummy-proofer. A boss of mine once told me "you can't make anything foolproof because fools are so ingenious." :)

I seriously think a kill switch would more worthy of your time and more likely to be appreciated by first responders. Another place for an interlock is on any opening compartment that exposes the traction wiring - but then again good insulating covers may be better overall. Those kind of interlocks too often get defeated while the thing is in "R&D."

Pretty much. Besides being a safety valve of sorts, it's also a way to disconnect parts of the circuit w/o putting switches everywhere. The potbox probably doesn't need a fuse because it's just a 'sense' circuit. The 5k pot varies from a dead short to 5,000 ohms and is just a voltage divider for the controller input. It shouldn't have much current flowing if all connections remain correct. Besides some controller internal malfunction, the only danger would come from some higher power wire coming in contact it. This is where the quality of your physical electrical connections will pay off in overall reliability.

It would be easier to wire if everything except 'power' was 12V but it depends on the parts themselves.

A 36 volt contactor coil energized with 12V won't pull more current because of the lower voltage (prob less) and thereby heat up, but there could be another problem with the lower V. If as you said, they came out of the forklilft as 36V devices, then 12V may not be enough to get them to close firmly. If they engage weakly, or worse chatter, then the power contacts will probably arc, self destruct, and otherwise ruin your day.

Also, if the correct V is 36V, then 48V into the contactor coils would entail more power draw and more heat, but I don't know if that's destructive. If it is and you still want to go to 48V or more, there are ways you could handle that with varying amounts of scope creep:
1. Just use a wire coming from the third battery (36V worth) for the contactor circuit. This one falls into the "if it's stupid and it works then it ain't stupid" category. It means assymetrical loading of the batteries but maybe only slightly.
2. Use an electronic regulator circuit to drop the 48V down to 36V for those coils (it's not as complicated as it sounds).
3. Change the contactors to 12V ones (prob the most expensive).

BTW, I'm pretty sure the small wire to the controller still has to be at full pack V.

Sometimes a circuit will have 2 different 'grounds.' Sometimes there is a chassis ground, and an earth ground. Sometimes they're just used to simplify 2 different circuit common points to reduce clutter in the drawing. In any case they usually each use a different symbol for clarity:
https://www.gassavers.org/attachment....1&d=1168407500
In your case, the traction battery negative side isn't really a ground, especially since the negative side is the part that is regulated (chopped by the PWM). OTOH, the -12V is a true chassis ground since it's used throughout the car.

BTW, cars used to have positive ground - or in the Healey, "positive earth." The convention changed to negative ground to reduce the effects of electrolytic corrosion in the body.

You mean like a big read panic button on the dashboard

Battery news: just got off the phone with the company that sold us the forklift.

Floodie = wet cell?

Yup. Flooded lead acid batteries, that need periodic watering to replace electrolyte lost during charging.

Golf carts, industrial floor sweepers, and most EV conversions use 6v floodies.

That's my car...
 

I was just browsing along seeing how things were going with Project Forkenswift and I clicked on the link and... THAT'S MY CAR.

That's so funny. :)

I just purchased it in December and while it does run, there are problems with it--the Forward/Reverse contactor spits blue-green flame in reverse and when I try to go forward at low speed it jumps like a jerky start in a clutch--if I press down the pedal more it evens out but apparently I can't use low speed.

With the problems I haven't tried taking it further than the end of the block so far.

Len. Welcome to GasSavers. Just stay right here. Metro is the GS EV man. He may be getting tired of his own problems and welcome a new one.

Hi Len - that IS funny. Congrats on the C-Car purchase. A classic.

I don't want to chase you away, but for help with your contactor setup, have you checked in with the Yahoo C-Car group yet? Someone was describing a similar problem recently (the reverse problem, anyway) :

https://autos.groups.yahoo.com/group/C-Car/

Fairly active group, and there are some schematics and other good info available in the "files" area.

I'd try there first for getting help - that's where the expertise hangs out. I'd be really interested in hearing your car's story though. I hope you'll post more here.

Yeah, I've been lurking around on that list too, lots of good advice. I also went to my local electric vehicle association meeting and met some local EV experts who have offered to let me rummage through their spare parts to try to fix up my contactor--on the other hand I think I may just replace the contactor with a new one.

--Len

I also joined a "local" EV association - great resource for suggestions & assistance. Sounds like you've got it under control.

What's the story of your C-Car purchase? Barn find?

HA! Project Forkenswift is famous :D

AutoblogGreen discovered the YouTube videos and posted an item:

https://www.autobloggreen.com/2007/01...a-beer-budget/

Have you pointed them to this thread or will your ite be up soon?

I haven't pointed them here. Guess I should, eh? The site's pretty far down my to-do list.

Coincidentally, this week I suggested a story to ABG that got posted yesterday (EV milestones, 2006, from the EVDL).

I've been interested in electric cars for a few years now and every now and then I would check the EV Tradin' Post to see if there was anything in my area but there never was.

Then just before halloween there it was, a 1980 Comuta-Car only 30 miles away. I didn't even know what a Comuta-Car was when I first saw the ad, but I contacted the guy anyway. It took me two months to coordinate with him and by the time I was able to meet with the guy, I knew more about the cars than he did. :rolleyes: He brought the car up with him from Arizona so it has been around, but there are less than 3000 miles on the odometer.

Good story. I've only seen one C-Car in person: there used to be one parked in someone's driveway in Ottawa when I was going to school there. I walked by it regularly. I'd like to know what happened to it - nobody in the Ottawa EV association knew anything about it.

Hope you'll keep us updated with your progress.

This afternoon I picked up 8 used 6v batteries