[NSRCA-discussion] Reducing the odds...

[Chad Northeast]

>I now believe that I had a bad cell on the one that blew-up.


If you were discharging to 3 v/cell as I read it from your data then its 
not surprising that you would have bad cells....a 3v/cell resting would 
indicate that you are discharging much below that under load.

shoot for 3.7-3.8 v/cell resting (5-10 minutes) after the flight and 
your batteries will be much happier, and stay in balance all by 
themselves for the most part.

Chad


Grow Pattern wrote:

>First of all thanks for all of the suggestions and advice from the list 
>surrounding the charging of my Lipo's.
>
>
>
>I have been messing with the big Lipo's since before Jason flew his most 
>notable entry at the world's four years ago. This was my first catastrophic 
>failure of a battery pack. I have spent around $7000 on electrics in that 
>period of time and have closely monitored their technical development.
>
>
>
>Right now I am working on sport type or sport level electrics. Not the foamy 
>type or super light type of models, but the alternatives to 40 sized glow 
>motor powered models.
>
>
>
>I particularly like the HIMAX offerings where they sell a motor, a motor 
>mount, a matching speed controller and a prop all in one box. This saves a 
>lot of guessing and previous trial and error on the part of the buyer. You 
>are left with the choice of what battery pack and what plane to put it in.
>
>
>
>Which brings us back to the exploding Thunderpower 4400 pack. I had been 
>using my Astroflight 109 chargers with great success. I have 4 of them. This 
>was before the little add-on balancers were available. They charged a bunch 
>of different packs up to and including the big 4S3P packs with no problems 
>etc. I am familiar with their warning etc. In particular, it states that it 
>is not recommenced to charge a fully charged pack, (note: not forbidden). It 
>further states that the charger will shut down the charge after about 4 
>minutes if you actually try and do this.
>
>
>
>Now we get to the 3S pack in question. I was not satisfied with the 
>knowledge of what happened and the comfort of how to prevent it happening 
>again. I did not have another pack, or at least I was not going to risk an 
>old friend's second and last pack. I did a couple of things.
>
>
>
>I measured the each cell of my 3600 mAh Tanic's using the voltage taps that 
>are part of the assembled pack.
>
>
>
>CELL   UP                   CELL DOWN
>
>I           4.18                 3.01
>
>II          4.18                 3.00
>
>III         4.19                 3.01
>
>
>
>Charging the pack when at 9.2V gave-
>
>
>
>CELL   UP
>
>I           4.18
>
>II          4.19
>
>III         4.18
>
>
>
>Charging the pack when fully charged caused the charged to read it as 3 
>cells. It went through the 3 minute determination pause.  Charged for about 
>a minute and said "I'm done!" did this with two different 3600 mAh packs. 
>The charger did what it said it would do.
>
>
>
>Then just as an FYI, I flew the model with both packs wired in parallel. One 
>pack was giving me 5 minutes of flight at full throttle. I needed more 
>air-time on the sport plane. (World models Sky Raider). I now had 10 minutes 
>plus and the flight did not run out of steam.
>
>
>
>The two packs were fully charged and the plane flown for about seven 
>minutes.
>
>
>
>This created a 3S2P pack. The readings were very encouraging.
>
>
>
>PACK-A
>
>CELL   UP                   CELL PARTIALLY DOWN
>
>I           4.18                 3.68
>
>II          4.18                 3.68
>
>III         4.17                 3.67
>
>
>
>PACK-B
>
>CELL   UP                   CELL PARTIALLY DOWN
>
>I           4.18                 3.68
>
>II          4.19                 3.68
>
>III         4.18                 3.67
>
>
>
>The cells were discharging and charging nice and equally.
>
>
>
>My charging practices have been upgraded to.
>
>1. Test voltage of each cell before each charge.
>
>2. Monitor the charge initiation.
>
>3. Place pack on 1/2" metal plate on table outside of van. (Deep Cycle 
>marine 12V is in back of van).
>
>4. Check reading periodically.
>
>5. Test voltage of each cell after each charge.
>
>
>
>I now believe that I had a bad cell on the one that blew-up. I also would 
>not charge the TP pack without the after-market device. In fact I now do 
>anything to reduce the odds of another accident.
>
>
>
>Just looking at the display on the 109 charger tells you a lot. The number 
>cells, the voltage during initialization and during charge, must be correct, 
>or at least in range. Putting the pack in a fire safe place is paramount.
>
>
>
>Regards,
>
>
>
>Eric.
>
>
>
>
>
>
>
>
>
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