I got the 60 Ah pack in parallel down to about 2.97 volts and decided it was time to connect it to the parallel pack of the 40 Ah cells. It went fine, no sparks or nothing. Well, some sparks, when the connecting plus cable hit the negative, but that doesn't really count. Anyway, it is done now and the heater based bottom balancer is happily chipping away at the rest of the remaining charge.
I think I'll let it drain the cells for a day or two after it initially hits the target 2.7 V. They'll try to bounce back for some time. Perhaps not so much that there's so many of them, but there does seem to be a about 0.02 volts of difference between the cells at the center and very ends of the packs, which may also take some time to propagate.
Just thought I'd show you what's going on. The 60 Ah batteries had arrived while I was gone and once I got back I started taking the shipment apart. Everything was there. Including the 25 pcs SE60AHA cells, a 4x20Ah 12V block, interconnects and a PowerLog 6S, which I may or may not need anymore. Thanks to my smallest offspring for helping out.
Couldn't have done with out you.
Having moved the batteries to the basement I proceeded to do a little experiment in parallel bottom balancing. Here I have the 60 Ah cells connected to each other in parallel. The 40 Ah cells are lower in charge, but once I get the sixties closer to them I may go ahead and parallel all of them and then proceed to drain them together to around 2.7 volts. Should be pretty well in balance then.
Sure looks like a lot of cells when you line them up like this.
Oh, one more thing. I thought this was pretty funny. Or sad. Can't decide which.
Personally I'd rather be on a plane with these batteries than most people.
Here's my bottom balancer - take one. The 50W 0.2ohm resistor is attached to a rather large CPU heatsink from a Dell 2U server, complete with heatpipes and thermal paste. Looked sort of nice and ready rock.
The first issues were the little clips heating up rather considerably, so I took them out. Next it seemed like the resistor was getting pretty hot too, so I added a little fan to cool the heatsink. It seemed ok. Also the voltage measured by the device was a lot off compared to a separate voltmeter. Turns out some the connections and the cell fuse were heating up and thus contributing to the error in measurement.
When I got back a bit later I found out that the resistor had given up the ghost. The device was activated, but no amps were drawn. The resistor would have needed more cooling than the little fan was able to produce. Luckily I remembered the rather large heating element from a Citroën C5 which I had purchased earlier to heat up the cabin, but which didn't give enough heat. I gave it a go and what do you know, it ended up consuming about 12 amps from a single cell. Prefect!
Also with extra fuse removed, heavier cables and unnecessary connections taken away the device also now reports correct voltages. I've set it to deactivate the relay at 2.7 volts, which means that it will drain the cell until 2.7 volts is reached and then starts to go on/off in an increasingly rapid manner as it's trying to get the cell to stay at 2.7 volts.
I'm doing this to prepare these old 40 Ah cells for marrying them to the new 60 Ah cells which should be arriving this wekk.
I thought I'd give you a little glimpse into the snake's nest which is the main wiring box next to the controller. It's not all pretty and organized inside, as you can see. I'll try to go through what I have in there now, which may of course change at any time.
In the top left we have the big orange 50 mm2 cables coming in from the batteries. They go into the controller B+ (top) and B- poles (bottom left). Cables from the controller into the motor go out to the left.
In the top right corner you can just see a fuse box with a 30 A fuse in it, coming from the B+ pole and going into the left pole of the small 80 A contactor. The contactor is there to drive the Half Speed Reverse (pin 4) of the AXE7245 controller. It also acts as a distribution point for other high voltage equipment. The contactor itself is controlled by the signal from the gearbox reverse indicator.
From the high voltage distribution pole of the contactor the blue wires go into the AXE7245 controller (pin 1 for power), into the white connector which is connected to the 400W 13.5V DC/DC Converter and the gray Linksys PSU which outputs 12 VDC.
Between the gray PSU and the contactor is a little black box, which takes that 12 VDC and converts it into 5 VDC, which drives the TPS in the carburetor housing. The 5 VDC negative is connected to the AXE controller (pin 3) and positive to the TPS (that yellow-green-pink roll of wire). The 1.2-3.5 VDC signal from the TPS goes into the controller (pin 2).
I couldn't use the +5 VDC from the car's original wiring loom, because it's ground to chassis and pin 3 of the AXE controller is connected to traction battery negative. It would create a ground leak, which is a bad idea and a big no-no if I'd like to get the car inspected.
At the bottom you can just see another black fuse box with a 50 A fuse coming in from the left from the DC/DC Converter and going out in the right to the +12 VDC vehicle positive distribution point.
That I believe is all I have in there right now. It's quite possible that I'll need to move the main contactor, shunt and service switch in to the front of the vehicle, but I think I'll have room for them in the front battery box. There certainly isn't much more room in this box.
The Linksys + 5 VDC converter combo may be replaced with a more professional solution later.
I just put some CALB SE60AHA 60 Ah LiFePO4 cells on order from ev-power.eu. I would have preferred the new CA-series, but they had none in stock. If I'm lucky, they'll arrive during next week. After I put those cells in I'll have 25 times 40 Ah plus 25 times 60 Ah for a total of 100 Ah capacity, which comes to about 8 kWh of usable juice. I'm hoping that will be enough to move the car around for about 50 kilometers (or 30 miles). It's not much, but should suffice for a city car. Also it will be easily to count amp hours from zero to 100 when driving.
In any case, it will bring the weight of the car to just about where I'd like to have it and once I've registered the car as it is, I can always swap the batteries for better ones later as they improve over time. I will probably need to construct a small battery box in the front as well. I'm thinking of placing the 40 Ah cells (35 kg of them) in the front and the 60 Ah cells (65 kg) in the back. That should give me a pretty nice weight distribution and since I've taken out around 60 kg from the back anyway with the fuel tank, spare tire and exhaust, I might even get lucky and not lose any seats. We'll see.
The two packs will be connected in parallel (25s2p, if you will) and I'm quite confident that they will balance the difference in capacity by themselves, both during charge and discharge. In any case, it will be impossible for them to be at a different voltage. I'm also sure the total voltage will immediately show if there's a problem with any of the cells in either pack, since it will start sucking juice from the other pack. It's not quite as sure shot as with a simple single series pack, but I think it will do for now. These two packs may see a new life later on in two separate motorcycles, if and when the car gets bigger cells.
In other news I solved the issue of pack negative leaking into the car chassis via Alltrax AXE7245 throttle input 2. I did this by taking the pack voltage down to 12 volts using a power supply and from there to 5 volts using a little DC to DC converter. This way I don't have to connect the 5 volts negative to the chassis at any point. For whatever reason my TPS kept on giving 1.2 volts on zero throttle instead of the 0.65V before, but that got solved with a new curve from picoamps.de. They came through again in a day or so. Very good service.
With the ground leak problem solved and a new curve in the controller I was able to take the car for a little spin in our yard. Well, not a spin really, since there's no room to spin, but some motion back and forth anyway. Looks like my reverse light wasn't working though. Probably just the reverse detector plug got loose again from the transmission. It's missing the clip to keep in place properly.
Almost forgot. The hissing sound that the car makes comes from a rather loud blower I also installed. I don't expect the motor to heat up too much, but the blower pushing filtered air into the motor should help to keep it clean inside and also blow out any carbon dust from the brushes. I don't think I'll do anything about the noise. It's not a very pleasent one, but I reckon it's not a bad idea for the vehicle to make some noise audible at low speeds to alert pedestrians, which might otherwise be taken by quite a surprise.
I've now installed a Webasto Thermo Top E-B heater under the hood. It will burn gasoline and produce 4 kW of heat. I'm still missing the fuel pump for it and there is a chance that the actual heater will be replaced as well, but the mount is done now. After taking the picture I also mounted the exhaust pipe where the original exhaust was located. Still missing are also the air intake for the heater, gasoline tank, coolant (heatant?-) pipes and a tank for that as well.
In the back I've mounted the charger on top of the rear battery box. I had to figure out how to make my charger IPXXD compliant (100mm stick test), hence the box split in two at the ends of the charger. It's not pretty, but it does the job. There's a pattern emerging here. I'm cutting corners to get the car into inspection shape and not worrying about the looks as much. I'll have all the time in the world to pretty things up later when I have the car registered.
I've bent two motor mounts so far. These electric motors sure have a lot of torque. They'll quite easily rip to pieces a less than perfect motor mount even just be going back and forth in your driveway in 3rd gear or reverse. Here's another take. It's not exactly very pretty, but I'll clean it up later if it stays in one piece.
So I ran in to the problem with the +5V input that the TPS requires. The AXE7245 controller has the throttle input 2 connected to battery negative internally, so I can't use the +5V provided by the original car wiring, since it has negative in chassis ground. I received a cheap 12V to 5V converter I bought from ebay, but as I suspected it wasn't isolated. So I put in an order for a 72V to 12V converter, which I could use to power the 5V converter. That way the isolation is not a problem, because I don't have to connect them to the chassis ground at any point. I've also gathered a number of AC to 5-12VDC converters, which I'll test for use with voltages between 48V and 84V DC. If an old Nokia charger will do the trick, maybe I'll just use one.
In other news I've decided to build a better bottom balancing system. Or actually a bottom balancing system, since before I did it by hand. Then I had 25 40Ah cells, so it wasn't too bad. Now I'll have 50 40-60Ah cells or 25 100Ah cells, and I'd like to do it as well as possible, so an automated system is in order.
The parts needed include a programmable voltmeter and a big resistor. I ordered a 0.2 ohm 50W resistor for a couple of euros and a cheap voltmeter with hopefully usable relay control for about 20 €. Both from ebay. Those two combined with a simple automotive 12V relay and a 12V power supply should be quite capable of draining LiFePO4 cells at about 15A or 50W. I'll just set the voltmeter to disengage the relay at 2.5 V and engage at 2.8 V. I should then end up with a pretty much empty cell resting about 2.75 volts.
I'll spare you the pictures this time. I took some, but it all came apart, literally, so I won't show them.
But let's start quasi-chronogically with the throttle. Remember my last report on the throttle sucess. It wasn't quite as rosy in the end. In fact, the first time I tried the throttle, with the motor installed in the car, it started up fine, but when I let go of the throttle the motor would just idle. You can imagine my amazement at this point. After some less than careful measurements I knew that the TPS gave a nice 0.49V when first plugged in, just as it should, but when I had turned the throttle it wouldn't drop back to the same voltage, but 1.09 volts instead! Oh no. I don't need to order a new cruve from picoamps do I?
Well, no. I don't. It's more interesting than that. Turns out I have a frame leak. Also turns out it is not the motor, which was my first suspect. I felt pretty lucky about that, since I had just gone through some huge trouble getting it into the car again. But it did turn out to be pin 3 on the AXE7245 controller. Pin 3 is Throttle 2, or throttle ground. It leaks pack voltage. Not cool. I've contacted AXE and we'll see what they come up with. I'm afraid it's going to turn out to be a feature. I'm guessing this causes the throttle problems too.
I know I promised no pictures. So I lied. Here's the motor going in. Again. And as you can see, it does have a clutch on it. It was quite a hassle to get it in. Notice the white stuff on the ground. It's snow. Didn't like that either. I was kind of hoping we'd be done with that stuff, but alas, no such luck.
The clutch wasn't a complete success either. It felt ok. Turns out it doesn't release. Not completely anyway. Oh, well. We'll see if I'll do something about it or just leave it like that for now. But the worst part is that I spent a considerable amount of time making a better support for the motor. It still wasn't strong enough and snapped loose. Damn those electric motors are strong.
I had filled the gearbox with new oil and was going back forth in the yard. Until there was a bang. Opening the hood revealed a motor well misplaced from it's usual location. Luckily just somewhat lower than expected. I'll have to go back to the drawing board on that one. The throttle problem and unexpected idling had gone away at this point, but the frame leak remained, so it may come back.
I was also concerned my main contactor had welded itself closed, but it seems that it just wasn't happy being on it's side. Turning it back the right way seemed to solve the issue. Or maybe it was something else in the first place. Anyway, it's working again now.
Update: AllTrax came back with a reply and suggestion to isolate the throttle input. I guess it does connect pin 3 and battery negative internally. It would have been nice of them to mention this somewhere. Anyhow, I put one of these little DC/DC converters on order and we'll see if I can use it power the TPS without causing a nasty frame leak: http://www.amazon.de/dp/B00D1GQA5O/ref=pe_386171_38075861_TE_item
