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Old 10-03-2009, 04:43 PM   #111 (permalink)
The $500 Electric Car
 
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Originally Posted by mcmahon.craig View Post
No, it will be the LOWEST of all the batteries. In fact, it's the worst CELL.

Say you have two batteries connected in series. One can provide 20Ah to an EPV to 1.7Vpc, and the other only 15Ah to the same point.

When you discharge the batteries, the cell voltage will obviously drop. At 15Ah the voltage on the 15Ah battery will be 1.7Vpc (about 10V), but the 20Ah will be more like 11.5 volts.

At this point, if you discharge the batteries further, the lower capacity battery WILL be damaged. If you attempt to retrieve the last 5Ah out of the good battery, you will probably reverse a cell in the bad one and destroy it.

If you're going to use mismatched batteries, please at least use one of these to avoid exploding batteries. You could also perform a measured discharge (using a known load, like a headlight) to 10.5V to ensure your batteries are at least somewhat matched.
I think JasonG realized the weakest battery (or cell in that battery) is the Ah capacity of the pack; I was the one being optimistic that my weakest battery will deliver 75 Ah. Now, I was thinking about buying a load tester, but there is something wrong with that sentence: the word "buy". I've already spent a couple HUNDRED dollars on this, and I am WAY over budget, as NONE of the ICE parts have sold as I was expecting. My depression level on this project is peaking, but now I am out so much money, that I really can't afford to spend, so that I pretty much HAVE to finish. Anyway, my "load tester" is my daily commute car. I have been systematically using each battery in my pack to get to school every day since I got them. So far, so good. But I will say this: if I don't get 6 good batteries out of the eight, this project is finished....

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Old 10-03-2009, 06:29 PM   #112 (permalink)
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Quote:
Originally Posted by vpoppv View Post
I think JasonG realized the weakest battery (or cell in that battery) is the Ah capacity of the pack; I was the one being optimistic that my weakest battery will deliver 75 Ah. Now, I was thinking about buying a load tester, but there is something wrong with that sentence: the word "buy". I've already spent a couple HUNDRED dollars on this, and I am WAY over budget, as NONE of the ICE parts have sold as I was expecting. My depression level on this project is peaking, but now I am out so much money, that I really can't afford to spend, so that I pretty much HAVE to finish. Anyway, my "load tester" is my daily commute car. I have been systematically using each battery in my pack to get to school every day since I got them. So far, so good. But I will say this: if I don't get 6 good batteries out of the eight, this project is finished....
Arrgh. Sorry I missed the point. Carry on.
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Old 10-04-2009, 11:26 PM   #113 (permalink)
The $500 Electric Car
 
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I spent a bunch of time today cutting metal. No real reason. Just needed to cut metal. Broke 2 blades. The idea was to make battery racks. I sorta kinda had some thoughts here and there about how I would do it. In any case, I cut open a perfectly good gas tank. Maybe it was my conscience trying to guarantee I wouldn't reverse course and convert it back to gas again. I can't for the life of me figure out how Ben Nelson got 2 batteries in the front. When I put a battery in there, it's all slanted, leaning, and touching the adapter plate. Maybe the different body styles (mine's a 94, his is a 95) makes a difference. So the plan originally was 4 up front, 2 where the gas tank was. No way. Then I thought 4 where the gas tank was and 2 up front. Not a chance. Then I thought 4 in the spare tire well, 2 up front. Sorta, maybe kinda might work....but not really. Then I thought 2 up front, 2 where the gas tank was, and 2 in the spare tire well. Now I'm thinking I can't get 2 up front. The gas tank, it turns out, has a big indentation in the highest spot, which wont allow a 2nd battery there. The wheel well can work, but it will be a lot of work. Maybe I could run it 12v for a while, because I am only sure about 1 battery in 1 place, the other 5 are up in the air (I have been agonizing over this for like 2 weeks). I think maybe I'll just stick them all in the trunk for now and just wire it all up and see if it goes, then sort through all the other stuff later. For that, I need a contactor. I'm leaning towards a Kilovac. It's crazy expensive though: $63.99. I wish I could sell a kidney....
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Old 10-05-2009, 10:12 AM   #114 (permalink)
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On my car, I some friends and I welded in a chunk of metal that was the side of a trailer into the front of my car under where the radiator was. That gave me a nice flat place to set two batteries.
Here's a photo where you can see the "battery tray". It is the black metal surrounding and under the pink foam.

My batteries are too long to fit in there the way the one is shown. If you are using shorter batteries (group 24, etc) you can fit 4 batteries there as shown.

The way I originally started off with the batteries was to put two chunks of bedframe (free on large garbage pickup day) to span the spare tire well in back. The bedframe is sturdy and L-shaped to help hold the batteries in
place.


Notice in the second photo that there are still the caster wheels on the sections of bed frame. Bed frame is hard to weld, but it isn't that bad to drill through and bolt to the car frame.

If you remove the backseat, the metal of the car under it is still lumpy and not level. You could build a really basic wood shelf of some sort to level it out for batteries. I eventually cut out the back seat and welded in a box where the back seat and gas tank were. That keeps the batteries out of the way, with a low center of gravity, and keeps your trunk.

See, the back seat area is much better once you cut that middle chunk out.


After that, you can size it up right to weld in a battery box. Then I made a lid out of plywood with some carpet wrapped around it.
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Last edited by bennelson; 10-05-2009 at 10:28 AM..
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Old 10-05-2009, 07:43 PM   #115 (permalink)
The $500 Electric Car
 
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Ben, thanks for the pics and explanations!! I'm definitely going to weld in some form of rack in the front. All my batteries are group 27 except the WalMart one that's a 29. Well, one spare is a smaller one, but I don't plan to use it. Here's what I have to work with as far as angle iron (the crib both my kids used):



I completely demolished my gas tank, and it doesn't look like it will work anyway:



I did seem to make a perfect rack for 3 batteries by incredible luck, but have yet to find a place for it:



And the backseat on the 94 is kind of different than the 95 ( I think it has a bigger "hump" in the front, and none in the center. I have a 96 backseat in my 90, and it fits, but awkwardly):



Since I am so doubtful I can get this thing on the road, I have decided to just stick all 6 in the trunk and make sure it runs before I spend another second on battery placement. On a side note, I was quite pleased to find out that 2/0 welding cable is only $1.61/foot...
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Old 10-05-2009, 10:30 PM   #116 (permalink)
EV test pilot
 
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If you put all the batts in the trunk, you will NEED to boost the rear suspension.

I was pretty happy with chopping down some Ford Ranger front coil springs to fit in the back of the Metro.

It's cheap and works fine. The only down-side is that it's not really adjustable for if you want to play around with changing the number of batteries you have in the back.
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Old 10-05-2009, 10:58 PM   #117 (permalink)
The $500 Electric Car
 
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Quote:
Originally Posted by bennelson View Post
If you put all the batts in the trunk, you will NEED to boost the rear suspension.

I was pretty happy with chopping down some Ford Ranger front coil springs to fit in the back of the Metro.

It's cheap and works fine. The only down-side is that it's not really adjustable for if you want to play around with changing the number of batteries you have in the back.
Wellllll....You're right of course, but I wasn't planning on any permanence with that setup. Just long enough to blow up my motor, or take it down the street, whichever comes first. Actually, if it runs 2 feet on battery power I will be surprised. And I DID have all 8 batteries in the trunk (will only use 6 in my conversion) PLUS full tank of gas, 3 passengers in addition to my fat butt, stopped for a bunch of groceries at Wal-Mart, and drove home in a same year Metro when I picked the batteries up the next town over (30 miles away) without a hiccup. But then, that's nothing for me since I towed my 90 Geo Metro from Kansas to Oklahoma with another Geo (94 Metro). 3 cylinders will never cease to amaze me.....
On another note, you mentioned that you leave the power off your car when not in use, and connect it before you start. What form is that? An Anderson connector?
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Old 10-05-2009, 11:04 PM   #118 (permalink)
EV test pilot
 
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Yeah, when I have the car parked for any significant amount of time, or while charging, I have a big Anderson disconnect that I unplug.

It's right between the most positive battery and the controller, so it kills all the power. It's handy to have for working on the batteries, knowing that all the power is killed.

It's a 350 amp connector, the biggest one that I have found in common usage. I still am toying with the idea of rigging the car so that pressing the clutch pedal pops open the Anderson connector.

It would work as both an emergency disconnect AND an anti-theft device!

The last photo in post #114 shows the Anderson connectors in the bottom left corner, show disconnected. I usually work on the car with those unplugged!
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Old 10-06-2009, 06:32 PM   #119 (permalink)
The $500 Electric Car
 
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Quote:
Originally Posted by bennelson View Post
Yeah, when I have the car parked for any significant amount of time, or while charging, I have a big Anderson disconnect that I unplug.

It's right between the most positive battery and the controller, so it kills all the power. It's handy to have for working on the batteries, knowing that all the power is killed.

It's a 350 amp connector, the biggest one that I have found in common usage. I still am toying with the idea of rigging the car so that pressing the clutch pedal pops open the Anderson connector.

It would work as both an emergency disconnect AND an anti-theft device!

The last photo in post #114 shows the Anderson connectors in the bottom left corner, show disconnected. I usually work on the car with those unplugged!
Ben,

I've got a couple more questions for ya!

1) Just how hard is it, physically, to pull apart the Anderson connector? i.e. could I connect it to the hood release latch and have enough force to pull it apart?
2) On the curtis controller, pin 2 and 3 are the pot box ohm wires, and 1 is the pot box microswitch. Do you have the microswitch connected there, or simply ignition power?
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Old 10-06-2009, 10:48 PM   #120 (permalink)
EV test pilot
 
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Electro-Metro - '96 Ben Nelson's "Electro-Metro"
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The Anderson connector takes a fair amount of force to open or close. Any mechanical way of doing it may be better than by hand, as half the trick is just how you grab onto the thing.
I don't know if the hood release would have enough "throw", but it would be a cool reuse of something already in the car.

I never wired pin 1 up to the microswitch of the potentiometer. I always just used it as the power in, which was controlled by a relay to the key. Turn the key, the controller turns on.

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