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        Discussion Whats up with my old school packs??

#1 JONBOYLEMON May 26, 2007 09:59 PM

Whats up with my old school packs??
 
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I fly combat with a Unicorn almost weekly. I started with a 12 cell 1400 IB pack from Cheap Battery Packs. That pack lasted a few months. I then went to a 12 cell Elite 1500. Had a cell go bad a few weeks ago. Took it out and made 11 cell pack. Today I had one flight and then charged as normal and then put the pack in and thats when the smoke came out. See pic. The cells are all ok and show voltage of 1.39 or so. What gives. Why the short?

I am running the following
Unicorn Wing
2 HS-81 metal gear servos
1 CC 35 ESC
1 Berg Receiver
Warp 4 4 turn
Triton Charger

Always charged @ 1C at 1.5 or less.
Pulling 18-22 amps at full throttle but I never go full throttle as we do combat & 1/2 throttle is perfect.

#2 pmackenzie May 26, 2007 10:02 PM

What sort of current are you running?
What charge rate?
edit - The short was probably between the bar and the metal can of the cell. The insulation must have been compromised during solderiing.
Pat MacKenzie

#3 JONBOYLEMON May 26, 2007 10:05 PM

See edited post. I went to old school NiMH because of the combat and how tough on stuff we are but the battery really is well protected and has not been damaged.

#4 JONBOYLEMON May 26, 2007 10:06 PM

If it was a short on the cell wall wouldnt that cell be cooked. The voltage of each cell is the same as all others.

#5 JONBOYLEMON May 26, 2007 10:38 PM

So should I just solder a battery bar in place and forget about it. I am really miffed at how fragile these packs are. Also a little disappointed in CBP responce to 1st email about the original cells going bad on the IB 1400 pack. They never replied.

#6 roosevelt May 26, 2007 10:45 PM

Did the insulation on the red wire get rubbed off/ Wer'e these heat shrunk?

#7 JONBOYLEMON May 26, 2007 10:53 PM

Quote:

Originally Posted by roosevelt
Did the insulation on the red wire get rubbed off/ Wer'e these heat shrunk?


No the red wire is intact with no damage to the coating. Yes they were built by CBP and had shrink wrap originally, but I had to cut it apart to find the bad cell when the last cell went bad. I re wrapped it after that. The two cells that were connected by the arc'd tab are still glued together with the original glue from CBP so they are not moving around in flight.

#8 rampman May 27, 2007 12:47 AM

If it was not what pmackenzie said, it looks to me like the bar fatigued from movement/vibration and went open but was still touching enough to arc as you were pulling max amps.
I would get a piece of thin metal and solder it across the break. Don't just solder the gap as that would be a very weak connection.
When completed you may want to add some tape to keep the cells from moving and having a repeat of this failure.

Rick
www.commonsenserc.com

#9 JONBOYLEMON May 27, 2007 01:05 PM

I will just solder a deans battery bar in its place. I am perplexed because I was not even running the throttle when it cooked. I had just connected the deans connectors and it was 1 second after that that it smoked. Wishing I could find a good cheap battery option for my Unicorn that worked. I started out with 2, 2 cell Common Sense 2000 batteries and those lasted only a few flights as well before one of the cells in a one of the 2 cell packs went dead on me.

#10 Mark Wood May 27, 2007 01:44 PM

My bet is the shrink of the cell under the bar was compromised and the bar welded itself to it then opened up.
Make sure you insulate the bar with shrink before soldering a new one on.

mw

#11 pmackenzie May 27, 2007 02:03 PM

You can also stagger the cells slightly to increase the gap.
I usually use cardboard,masking tape or 1/64 ply as a mechanical barrier there.
Something that heat won't effect.I usually put a strip of masking tape between the rows of cells for the same reason.
Without it if the pack ever gets hot the heat shrink can split and the whole thing shorts out. :eek:
The higher tech solution is Kapton tape.

Pat MacKenzie


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