Monday, February 1, 2010

Installing Batteries Part II

In the last post I mentioned that I'd finished the mounting brackets for the A/C compressor and here is the picture I promised of the whole assembly.

You can see there are two aluminum angle pieces that are mounted to the face of the motor. The bottom one supports the compressor directly while the top one is bolted to the black bracket attached directly to the compressor. There is a slot in the top aluminum piece that allows me to adjust belt tension by pivoting the assembly back and forth. Now I need to get a belt.

The last thing will be taking the car down to an A/C shop to have some custom hoses made. Truthfully, I'm kind of worried about that. The space is so cramped that it will be hard to work in unless I dis-assemble parts of the car. That means driving it there, taking it apart at their garage, and then re-assembling it when they are done. Hmmm.... we'll see how that goes.

The big news today is that I finished the work on the back battery box. All the batteries are securely mounted in the box. There is plenty of room to allow air to move through them to cool them. And I have all the interconnects wired up.

I ended up putting 17 batteries in the back. Such a strange number, but there is that one space up front where I had intended to put a stack of 4, but can only fit 3. So, the extra one goes in the back. Notice up in the top left hand corner, there is an unconnected + terminal. That is the start of the battery pack. Below and slightly to the left, you will see an unconnected - terminal. I will be running a line from that terminal to the next positive terminal at the front of the car, continuing the series.

Truthfully, I'm not too happy with all of this. It's way too complicated. While it's strong and there's no way any of those batteries are shifting around, I approached the whole endeavor of securing the batteries as an after thought; I hadn't planned it from the onset. I don't know that it would have made much difference if I had, but I'd like to think that I could have come up with a much more elegant solution. But, at least it's done.

One thing I don't have in place yet are some "testing" lines that I'll be putting on each group of 4 batteries. I'll attach a small wire at the start, or + terminal of the first battery, and then another on the negative terminal of the fourth. I'll be doing that from start to finish, which will give me a total of 12 groups of 4, so 12 pairs of wires (a negative and a positive for each). I'll attach each to a terminal, paired up next to each other. This will allow me a handy way of checking the voltage of each group of 4. If the voltage on one battery in the group starts to get too high, or sag behind the others, I can more easily locate it and deal with it.

The real danger with these LiFePo4 batteries lies in the extremes. The closer you get to fully charged, the more likely one or more batteries is to run away, accepting too much of a charge and in the process, frying itself. The closer you get to draining the batteries, the more likely one takes a dive in voltage before the others and dies an early death. They are extremely finicky at the extremes. However, kept in the middle of the range they are stable. I'll be setting a charging scheme that will charge them to approximately 95% full, avoiding the top end where one can run away. And as I've said before, I won't be taking them below an 80% depth of discharge, meaning that they will always have at least 20% capacity left, avoiding the death spiral. It means that I'm leaving some untapped potential in the batteries, but it also means I should extend their life by not pushing them to their limits.

At some point in December, someone in my family decided to make a commentary on my progress. Well, they were probably just trying to be cute, but I took it as a comment on the progress I've made. Or rather on the slow pace of the progress I've made.

I had hoped the project would be done sooner, but with the delays I've faced waiting for components, it's pushed things back a bit. Still, when it's done, there should be few things I have to re-address. In either case, I took vengeance upon them all just to be sure I got the guilty party.

1 comment:

Anonymous said...

You'll never know ...