Electro metro part II? Arkansas Version?

[ShadeTreeMech]

I have a 4 door Geo Metro collecting rust in the front yard. It has the 4 cyl auto tranny combo under the hood and the engine requires a new piston, which is suprisingly difficult to source. But the body is in decent shape, and suddenly visions of cheap transportation dance through my head.

I'm thinking the slushbox would be very inefficient even if I deleted the torque convertor, so a 5 speed is the idea to go with. I can fabricate a plate in my sleep, but the electronics are a bit above me. Mind you, I can wire basic circuits well enough, or even repair a board with a damaged component, but I've never messed with electric cars which gives me cause for hesitation. That and I'm not sure how much it will cost, especially since I lack a shop at home.

Paul and Sabrina's controller looks enticing, so here I am, on a ledge, with an assumed budget of about 2k, wondering if I can do it...

[ShadeTreeMech]

My wildest dream is to send my now defunct Geo Metro to bennelson and his buddies with 2k in cash to make it a goood runabout good for 50 or so daily miles. Why should that be wrong?

[bennelson]

Sounds like a good car, other than the automatic transmission.

If you can toss a manual one in there, it should be good. Converting from automatic to manual usually requires adding a clutch pedal, stick shifter, etc, but if you only need an in-town run-about, you could just about put it in one great and leave it there.

(I did drive my car for a few days WITHOUT THE STICK HOOKED UP. It was when I put the motor and tranny in the first time and didn't have everything lined up, so the gear selector rod just didn't reach!)

Depending on where the transmission lines up compared to the automatic gear selector, you might be lucky enough to just repurpose it. 3rd gear is straight up on the manual. At a bare minimum, you really want to at least mechanically be able to put the car into neutral. I would guess you might be able to get the D and N on the automatic selector to move the manual transmission between 3rd and neutral. That might be all you need. Use a clutchless coupler, and you don't need to add a clutch cable.

The Open Revolt is a good controller. It's more or less "paint by number" with electronics. I'm sure if you know anyone who has worked on electronics before, you could just have them put it together for you. (If you get the kit from Paul and Sabrina's, it makes it all very easy, all the parts are labeled, etc.)

Again, for a low-speed/basic vehicle, you could use a 72V controller. You could find one of those on Ebay for $300 if you look around.

The actual wiring of the controller is very easy. It's a simple circuit, you just have to use really beefy cabling (welding cable) to handle the current.

A person really needs to know very little about electronics to build an electric car. (It's fun to know electronics, and you can add some cool features, but it's not a requirement.)

You really just need to know the basics of completing electric circuits, the difference between parallel and series connections, and how to recharge batteries.

[ShadeTreeMech]

Thank you for the informative post.

Dropping in a manual sounds to be a great idea, I would likely be willing to put in the manual and skip adding the clutch; I only used a clutch when getting going anyway, once I was rolling I just adjusted my engine rpms to shift. And once I learned it, I never wore out a clutch.

Anyhoo, the mechanical bits don't worry me in the slightest, I work in a machine shop and making things for fun is sorta expected when you work with a mess of machinists. Sourcing an electric motor is what concerns me most, used electric motors are hard to come by out here....I suppose I can manage somehow. The HP rating they have listed on the decal, is that the highest they can go, or is it the HP at the listed RPM? Ie, if you over rev a DC motor rated at 1 hp @ 1500 rpm, it should make more power at higher rpms....and that brings me to another question, if you have a 5 speed manual, do you get better miles per watt in overdrive while cruising like a gasser, or is it a bit different? And can I get to 50 mph with 72 volts? 50 would be the max speed I would need to go, most of the roads out here max the limit there, except for the bit of highway closest to my road. And would the benefits of having an AC motor outweight the higher initial expense?

I apologize for what may be noob questions, but although I've read a lot of the electric car thread and understand circuits, and some of the basics of electronics, the threads tended to go well over my head quickly.

bennelson, you still selling your DVD?

[bennelson]

Yep, I'm still selling my DVD. (All proceeds go to help future projects!)
It's available at: Electric Car Instructional DVDs

Getting to 50 mph is a bit much to ask on a 72V system. I recently heard of a "rule of thumb" that you can ball-park top speed by system voltage equaling speed in kilometers per hour. Top speed in my Electro-Metro at 72 volts is 45 mph. If you convert system voltage (72V) as KPH to MPH, you get 72K = 44.739 MPH. Wow - not bad for a "rule of thumb!"

AC motors are great, but they tend to use higher system voltage ( more batteries, more weight, more expensive charger) and are more difficult to find at an appropriate size/weight affordably, compared to a DC motor.

In terms of horsepower of a motor - it's "ooomf!" times speed.
On a series-wound DC motor, the more voltage your give it, the faster it spins. The more amperage that gets draw through it (because of being at a stop, accelerating, gear selection, going uphill, etc) the more oooomf! it has. (torque)

Speed x torque = horsepower
Voltage (motor spin speed) x amperage (torque) = Watts - power required.

There's roughly 746 watts in one horsepower. So, it's pretty easy math to figure out how many horsepower a motor can produce. (And keep in mind that it's INSTANT power! None of this having to rev an engine first!)

The limitation is how much amperage a motor can draw. A small motor can't, won't, and shouldn't draw a high amount of power. A beefier motor can.
And since system voltage is part of the equation that makes horsepower - more horsepower can be created by increasing the voltage. Or, all other things being equal, you can make the same amount of power (watts) by using higher voltage, but less amps. The batteries appreciate you using less amps! That's for a number of reasons, including the Puekert Effect, C-rating, etc.

Most DC motors can spin pretty fast, just don't go around reving them with no load, because then then can spin so fast you can't imagine.

Watts per mile (electric "fuel-economy" is probably going to be at whichever gear will LOWER the amperage draw and still allow you to drive the speed you would like.

In my experience, it tended to be in one gear LOWER than you would have used with gasoline. The electric motor spins faster, but it's not working as hard, so it lowers your amperage, which improves how much power you are using to drive the car.

Higher voltages give higher top speeds and better acceleration (compared to the same amperage at a lower voltage) and generally gives the car better range and makes it more fun to drive.

Geo Metros are a bit limiting in how many batteries you can put in them. I've put up to 144V in mine. You need improved suspension at that point. (Mine has truck springs in the back.)
The Solectria Force was a factory converted Geo Metro sedan that used 13 Group 27 gel cell lead-acid batteries. Some of the batteries were up front, and the bulk of them were under a false floor in the trunk area. Those were AC motor cars with regenerative braking and even air-conditioning!

The wildest thing I have ever seen done with an electric Geo Metro is this one:
Dave Cloud's Rally Car

but if you are doing something like that, it's BEYOND what my experience can help you with!

[ShadeTreeMech]

I'm assuming you are running 6 volt golf cart batteries? Seems I read they are the best bang for the buck. Using your formula, I would need to be upwards of 100 volts to get to 62, giving me 50 with some to spare. I think if I could duplicate the performance of the metro, minus the top speed, I would be happy.

To get 50 mph would require 14 6 volters, which could reach about 700 lbs....wowzers, yeah might need beefier suspension!

[bennelson]

Your calculations sound about right.

I'm using 12V batteries though. 12V AGMs are usually expensive, but the main reason I'm using them is that I got them cheap, because there were used batteries. They are sealed batteries, which makes it a bit simpler in that there is no water to add, don't have to as easily access the tops to for watering, etc. (Technically, you could even install them sideways or vertical.)

Since the Metro is usually a hatchback, that means all cargo (including batteries) is inside the passenger compartment, so I thought sealed batteries were a good idea that way too.

[ShadeTreeMech]

so if I were to go for 12v batteries, would deep cycle batteries be better than starting batteries? For the charging, I am going with 1 trickle charger per battery that can be installed permanently to the battery, so I would just need to run a 110 volt AC wire throughout to charge each battery individually. The amp rate on them is 1.5, the cost is about $20 a piece, and they are designed for battery charge and mainaining a charge. Assuming they can charge the batteries in about 12 hours total of charging time, I should be alright....not sure if my math is accurate on that though. If I charge a battery @ 1.5 amps for 8 hours, is that 12 amp hours added to the battery? And how many miles would that be good for? What's a good rule of thumb for number of amps used per mile.......I realize you are getting 129 mpge, just not sure of the exact calculation you are using, and I think you tend to have a lower top speed than I would. My hunch is that 1.5 amps would be too low, that 10 amps may be more like it.

Mine being a 4 door sedan, it would seem to have a bit of an advantage on being able to store the batteries outside the passenger compartment. I'm thinking most in the trunk, a few under the hood.

[bennelson]

300 watt-hours per mile seems to be a common number thrown around.

If you charge at 12V times 1.5 amps, that's 18 watts. Do that for an hour and that's 18 watt-hours. Do that for 10 hours, and it's 180 watt hours. Now you have enough power to push your car for about half a mile!

You are going to want a higher amperage chargers than that. Typical is an amp rating on the charger about one tenth the capacity of the battery. For example, if you have a 100AH capacity battery, and a charger that charges at a rate of 10 amps, it will take 10 hours for a complete recharge. (You should never run the battery all the way down. No more than 80%. If you never go deeper than 50%, they are really happy and will live a long time.) Even without the battery being completely discharged, the charger slows down as the battery charges, so 1/10 the battery capacity still seems like a good ballpark for a charger.

Then that charger either needs to be of a voltage to charge the entire battery pack, or you need one charger PER battery.

For a while, I had a 48V charger on my motorcycle, which was supposed to be 5 amps. The bike had 55 amp hour capacity batteries. So, in THEORY, the most it should ever take is 10 hours to recharge. But it was a crummy little made-in-china charger that never put out as much power as advertised. Taking 20 hours to recharge a half-empty battery pack was not fun. At that point, any time I would ride the cycle, I would have to wait an entire 'nother day to ride it again.

DON'T use starter batteries. They are NOT designed for electric car use. You want batteries designed for deep cycling. Flooded 6V deep cycle will be the best for cost and durability (but not for weight and bulk) and there are various AGM and Gel 12V batteries that might cost more but get you to to higher voltage faster.

[ShadeTreeMech]

Ok, so after doing a bit of precursory reasearch, I'll have to be lucky to find electrical car components within 500 miles of here. It would seem electric forklifts are highly unpopular, and there is nearly no market around here, since there are hardly any large cities......

How much would it cost you to make a 96 volt electric car as cheaply as possible? I'm looking at close to $1400 in batteries alone!