I'll need either 20 or 40 x DPST relays with some simple transistor/fet/uln2003a driver devices.
If I go for 20 relays then it reduces cost quite a bit etc but you can't charge/discharge at same time.
So it takes twice as long. But as process will be unattended that doesn't really matter. With only 20 relays you could go for 10A relays allowing 1C charge/discharge. If we work on 5 x 1C discharge/charge cycles per subpack that works out at 200 hours to do the pack running 24/7 or just over 8 days. I'll probably go for that. If you ran discharge at nearer the 10A limit you could get that down to less than a week. It's good workout for the pack and if any weak subpacks are detected the system can give them a few more cycles in an effort to bring them up to spec.
I can address the indivdual relays using a Picaxe 28X1
The Picaxe 28X1 also has the various ADC/on/off inputs/outputs and allows 1000 lines of code.
I might use an sdcard writer/reader so that the card can simple be moved to a pc when finished to view data. The SD card can also store much more data.
My 20 position barrier strip has #16 wire from the sub packs to the barrier strip so I can do a complete discharge/charge on ANY one sub-pack at 10 amps if I so desire without removing the ends. But I would not go over 2 amps because of heating anyway.
But the connections from the barrier strip to the data port are #22 wire which will fuse at 7 amps but I would not try charging or discharging through #22 wire even if the table does say it will handle 2 amps easily.
__________________
Jim Isbell
2000, 5 speed, 250,000 miles
"If you are not living on the edge, well then,
you are just taking up too much space."
I've decided to use 4 pics on the board. to drive the 20 relays.
I can program the 3 relay drive pics with some fail safe software so that if the Master tries to turn on more than one relay at a time they won't allow it!!
Probably add some sort of self powered watchdog on the board as well which cuts the main power if Master locks up or there is a mains power failure during the pack cycle.
Looks like another project I need to be watching.
I did some relay based subpack monitoring back in 2001. http://www.99mpg.com/blog/batterypac...ymonitor.jpg,0
I ran the system with a notebook computer using Labview and a plug in data acquisition card.
A 4-16 line decoder chip is how I drove the relays, so only one would be on at a time.
I remember that Mike, did you do any charging via it or just monitoring voltages?
I intend access to each subpack as you see, so am using 20 relays, prob 10amp rating.
I thought about using a clever I2c mulitplexing chip but the package was a problem as was price, I can do it cheaper and easier with three £2.00 Pic's.
I simply logged the voltages,displayed them on a graph for each 12 cells, Looked for a rapid drop in voltage compared to the other subpacks, did an AH calculation.
Your plan looks sound. I was going to play with something similar as an automatic pack tester/conditioner.
One of the Guys in Texas (Eric Moore)gave me a cute adjustable constant voltage electrophoresis power supply that he picked up on e-bay, that can output 300ma at up to 300VDC
I will add a bit of circuitry and make up some long safe attachment leads, and was thinking of offering to let any Insight owner that wants to try rebalancing their pack the use of the box.
It would of course only do a rebalancing charge, and not do a discharge or AH measurement, but from my experience it could help many packs that are simply unbalanced?
I'll use a simple 16x2 serial lcd actually on the subpack balancer just to provide the most basic data about what the unit is doing at any one time during the pack cycling.
I'm going to borrow Mikes isolated voltage circuits from Mima to allow the Master to remain isolated from the battery pack during voltage readings, I'll use an isolated hall effect device for the current readings.
Sounds great.
I really like that I2C SD card driver as a data logger.
I also got one of the SV2000 serial to video chips that you used for your battery controller to try out as a MIMA Video display driver.
The only problem I have with the individual subpack conditioning is the pack removal and dis assembly.
Why not try it in a different way.
Charge the whole pack with 1-2A, which drops to 300MA once the voltage gets near the max, then let it continue until the voltage does not rise any longer and stabilizes.
This will get all subpacks to the 100% soc safely.
Next put a load on the whole pack, and watch the individual 12 cell subpacks for the tell tale signs that a cell is depleted, just as the stock system does.Several charge discharge cycles could be done in a day, with the system recording the position of the first cell dropout.
Another charge cycle, and let it sit for a week and then simply monitor the 12 cell subpack voltages to see if leakage is an issue.If a subpack pair shows leakage, disassembly and further testing will identify the leaky subpack, which can be zapped or replaced. This reduces the time required, and should still do a nice job of testing and rebalancing the pack.
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