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Old Oct 12, 2002, 12:34 AM
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flytowner's Avatar
Texas,USA
Joined May 2001
617 Posts
How do I fix my Li Poly cell? :(

The positive "tab" has broken off right where it comes out of the silver battery wrap. Can I slice a little bit of this battery wrapping back or am I just screwed? I've only got TWO flights on this particular pack it's basically brand new. HELP!

Thanks,
Lewis
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Old Oct 12, 2002, 05:51 AM
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epilot's Avatar
Faroe Islands, Sandoy, Sandur
Joined Nov 2000
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Hi Lewis

It cant hurt to try - what have you got to loose?

I'm sure it is possible to cut a bit of the foil away but you might end up melting the seal when trying to solder a wire onto the small piece of tab. It *might* work if you hold the cell under water so the tab just protrudes and have a go with a reasonably hot soldering iron.

Another option might be to glue a new tab on - you can get some silver paint that is used to fix the heater wires in car windows. Might cost more then a new cell though.

Michael
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Old Oct 12, 2002, 06:51 AM
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MSC Rödinghausen, Germany
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Lewis,

be *very* careful not to open the cell! The contents might burn just by getting in touch with any humidity!

Regards, Jochen
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Old Oct 12, 2002, 07:17 AM
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What was it $8? Medium pizza. Toss it.
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Old Oct 12, 2002, 10:36 AM
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Shared learning

I hope it was a 145 pack not a 3200 pack. Sorry to hear about the potential loss.

I am about to make up some two-cell packs and I may encounter the same problem. How fragile would you say the tabs are? Do we only get one bend per tab? E.g. if we bend it over to solder then bend it over the other way to tape up/shrink wrap the pack will it break? Do we need to do an additional measure to lock the wires to the packs (hot glue to the surface before shrink wrapping/taping the pack).

There is another thread showing how to make a pack, but specifics on what breaks the tabs might be good to know.
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Old Oct 12, 2002, 11:15 AM
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Forney, TX
Joined Mar 2002
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JG- I made up 2 x 2 cell packs of 1020's. Because I wasn't sure how I wanted to orient them, I ended up bending the tabs 6 or 7 times on the 1st pack with no problems. What I did to prevent future damage to the tabs is this- I placed shrinkwrap over the wires, soldered them to the tabs (then shrunk the wrap over the tab/wire), placed 1/8" balsa strips between the cells for cooling, then bent the tabs inward (between the cells) and ran the wire/connector through the cooling space between the cells and out the other end. Bending the tabs inward like this exposed a small bit of the tab outside of the shrinkwrap, so I placed a small piece of fiber tape over the end of the pack and then put a single wrap around both cells to hold everything together. The packs are nice and solid, the tabs are completely protected and I can pull on the wires and connector without fear of bending the tabs. Let me know if you'd like to see a pic of the finished pack.
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Old Oct 12, 2002, 11:29 AM
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Whoa-- don't get the cell wet or you will have a major shortage (unless you are using very very high quality water)!

I've opened these cells under a nitrogen atmosphere-- the hot glue seal that runs around the perimeter is very robust, and you can slice away several millimeters to access the tab underneath. Then you can try to solder it with either normal or aluminium solder paste as needed.

General warning-- stop what you are doing if the cell begins to get hot. If you manage to puncture the airtight pouch and get the electrodes exposed to oxygen and water vapor in the atmosphere, the cell will warm up. Don't let anything short out your cell-- it will get very hot very fast.

As always, try at your own risk. You can buy the 140s from FMA for $6 each, so it's not worth doing anything risky unless you are curious.

-=David
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Old Oct 12, 2002, 11:38 AM
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Victoria, BC, Canada
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Graham Stabler has instructions and an animation to protect the pack without adding weight.
http://www.indoor.flyer.co.uk/terminals.htm

Rick.
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Old Oct 12, 2002, 01:31 PM
Straight up is all I ask
Fairfield Ct USA
Joined Apr 2002
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Do not despair I fixed mine 21 amp ok

You can use radio shack soldering paste Here's what i did : look at lead where thin grey coating is the only thing covering the metal tab scrape grey a 1/8 strip side to side to expose bare metal nice and shiney I used a razor blade.Make new lead extre long and strip 1/4 in off one endand flair to match batt lead. Glue lead length wise to cell body with flaired end on cleaned tab squirt the end of the wire lead with the paste work paste between lead and cleaned tab >now touch with soldering iron for about 2 sec the two will become one . On my wattmeter i pulled 21 + amps on mega 16 15 3 3cell 3200 same as before my tab came off .
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Last edited by jmolwitz; Oct 12, 2002 at 01:38 PM.
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Old Oct 13, 2002, 10:12 PM
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Texas,USA
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It's a 230mah and cost me $18. I'll attempt a small slice then try to glue the wire to it. Worth a try I guess! Thanks for all the tips guys!
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Old Oct 14, 2002, 04:32 AM
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Oxford/England
Joined May 2001
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The terminal strip goes into the cell case and is then heat sealed, you can see the heat sealed part fairly clearly. If I was going to attempt repair then I would make two short cuts (not extending past the seal) either side of the point where the terminal entered the cell and then attempt to peal back the casing either side of the terminal. Then attach a wire either by soldering (quickly) or by using solder paste if it is the + terminal. Then add a blob of epoxy for strength and insulation.

That is what I would do but I would not say that it is a good idea or that I endorse it etc etc.

Graham
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Old Oct 14, 2002, 11:19 AM
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Texas,USA
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Quote:
Originally posted by Tres Wright
JG- I made up 2 x 2 cell packs of 1020's. Because I wasn't sure how I wanted to orient them, I ended up bending the tabs 6 or 7 times on the 1st pack with no problems. What I did to prevent future damage to the tabs is this- I placed shrinkwrap over the wires, soldered them to the tabs (then shrunk the wrap over the tab/wire), placed 1/8" balsa strips between the cells for cooling, then bent the tabs inward (between the cells) and ran the wire/connector through the cooling space between the cells and out the other end. Bending the tabs inward like this exposed a small bit of the tab outside of the shrinkwrap, so I placed a small piece of fiber tape over the end of the pack and then put a single wrap around both cells to hold everything together. The packs are nice and solid, the tabs are completely protected and I can pull on the wires and connector without fear of bending the tabs. Let me know if you'd like to see a pic of the finished pack.
Tres,
I don't know if it will help my case but I would definitely like to see a picture of your Li Ploy creation.
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Old Oct 14, 2002, 11:25 AM
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Texas,USA
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Somebody needs to come up with a way to use two super small re-moveable clips to connect to these Li-Poly tabs. Then we wouldn't have to solder to the tabs, we could just clip our leads to the tabs and go.
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Old Oct 14, 2002, 08:00 PM
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Wierd thought

Could we glue the smallest rare earth magnets to the outsides of the tabs and have them attract each other and clamp the tabs together. The polarity could preclude attaching the two batteries improperly?

Six magnets glued to leads and tabs and a way to hold everything together without risk of shorting out would be required. Hmmm.

Just a wierd thought, as the prospect of soldering to these odd devices is a bit intimidating.
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Old Oct 14, 2002, 08:11 PM
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Fayetteville, GA
Joined Oct 2000
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This is off topic as far as broken tabs go....

I guess I did it wrong but here's my experience with poly cells so far.

I had a 970 mah pack swell when I was on the charger. As soon as I saw it happen I called the supplier and they told me to put a pin prick in the cells to vent them and reseal with some silicone glue. I did and the pack seems to be ok. Although, I have only put about 10 flights so far.

The dealer also told me to warm the cells before I applied the silicone to creat a vacume. He suggested I heat the cells with a hair dryer. BAD IDEA!!! As soon as air hit the holes ....sparks were shooting out. So definately don't try this!
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