[NSRCA-discussion] Reducing the odds...

[Grow Pattern]

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.