Knuckles said:
tron said:
Hey knucles,
What's the link where you bought the A123's from. A what the heck are you charging them with? Any BMS to protect your investment?
A few members were working on BMS's but it got pretty complicated when deciding or finalizing the PCB. It's a lot easier to do with a controller that's made by e-crazyman eh>
Just contact Robert by email but the site is http://www.purehobby.com.
As far as charging the a123's goes ... well if I tell you guys you will yell at me! I'm an engineer and I like to try to destroy stuff and do things the wrong way (think outside the box). Believe me the nickname Knuckles fits somehow. But here is a quick glimpse of my warped thinking ...
1) Don't care about balancing (F it).
2) 3.6V x 12 = 43.2V. And a 36V 2.5 amp (crazy) charger max charge is 44V and floats at 42V.
3) Plug it into a 12s pack and walk away!
easy peasy!
I'm not an engineer, but I do think you need to balance every once in a while. I use 2 Bantam balancers, to balance my 10 cell A123 sub packs. If the cells get too far out of whack, you could fry a cell or run one down too far if there is too great a variance between cells. I use a couple smart chargers that terminate the charge at 38.5 volts and each one charges 4 10s packs in parallel. I also have a mastech HY5020 that is CC/CV and I set it for 36.5 volt shut off. This power supply will bulk charge all 8 subpacks at once and I sset it at 10 amps - cause I am not in a big hurry. After about 12 cycles, I noticed, things start going south. On one pack I noticed a .5 volt difference between the best and worst cell. I did not check all of the packs. There was no need after seeing this. Time to take action.
I really thought the cells would stay pretty close, especially in the individual sub packs, but they did not. For some reason, these cells need some help to stay close enough together to suit my tastes. It only takes about an hour to balance 8 sub packs with the 2 Bantams. I got these due to a post in here from Microbatman, because I noticed these drain type balancers, would each put a 500ma load on a pack- not bad! Interestingly, each subpack took a different amount of time to balance. Some went quick, seemed like a couple 3 minutes, while others took longer- much longer!
Including the one I checked with my voltmeter. So, this tells me they were all over the board on voltage.
Yet, if you compared 1 40 cell parallel string with a voltmeter, to the other, prior to balancing, they were within 1 tenth of one volt.
I did this for the first time this weekend, because I felt the pack performace was changing- getting less range before voltage began to taper off. I watched a movie on my TV while I did it. so it was not a lot of trouble. I can bring my entire pack inside the house to do it, as it only weighs 17 pounds. An advantage of LifePo4.
"It seems" to have really re-juvenated the 10s4p pack as I rode it around quite a bit Sunday. But this is just my gut observation of a before and after using my Cycle Analyst.
I must say though, that I felt the same as you at first, that balancing was not that important. After all, the Dewalt chargers got a pretty bad rap that they didn't balance, yet came with a 3 year warranty! How important could it be? I said to myself. I am beginning to think otherwise now. The Dewalt tool made use of the built in BMS on the Dewalt pack and would shut a tool down "probably" in time. In my ebike- I have 80 cells and no BMS. I think I could pull one down too far. Time will tell. At any rate, balancing is easy and quick - if you make up your packs with balancing leads, which I fortunatly did. So, in hindsight, I guess i was a bit paranoid about it to begin with.
