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Soldering NIMH Cells Help !!!

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Soldering NIMH Cells Help !!!

Old 05-25-2005, 01:03 AM
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JettPilot
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Default Soldering NIMH Cells Help !!!

I am making some 10 cell 3000 mah NIMH packs . I want to solder them together 5 long and 2 wide. Someone told me just to pre tin the batteries, and heat two cells at once and stick them together, is this the right way to do it ??? Anything special I need to know about soldering cells (no tabs) on them [&:] If these things come apart or fail im going to lose a big plane Any advice on makeing battery packs would be greatly appreciated.
Old 05-25-2005, 04:43 AM
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Charley
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Default RE: Soldering NIMH Cells Help !!!

ORIGINAL: JettPilot

I am making some 10 cell 3000 mah NIMH packs . I want to solder them together 5 long and 2 wide. Someone told me just to pre tin the batteries, and heat two cells at once and stick them together, is this the right way to do it ???
That method sounds chancy to me. First, you'd have to apply a lot of heat to the cells in order for the solder to stay liquid long enough for you to stick them together. Second, how can you be sure that excess solder doesn't short the positive ends of the cells?

I solder straps or small pieces of stranded wire to the cells, working as rapidly as I can so as to minimize the heat buildup in the cells. I believe speed is of the essence, consistent with gettig a good solder joint. I also use insulating washers on the positive ends.

Cheers,

CR
Old 05-25-2005, 08:08 AM
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Red Scholefield
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Default RE: Soldering NIMH Cells Help !!!

Something to consider:

Soldering directly to Ni-Cds/Ni-MH or any other cells is not a good idea. Try to use the welded tabs and solder to those if at all possible. Soldering to the positive button will have a very high probability of destroying the nylon seal. You just can't get the button hot enough to get a good solder joint without compromising the integrity of the nylon seal ring. This ring is under compression and raising its temperature will allow it to relax and the sealing properties are history.

If you can hold a penny between two fingers long enough to get a good solder joint with #18 stranded wire or braid, then go ahead and solder to your cells, otherwise get cells with solder tabs. Remember, nylon is a good insulator, electrical and thermal. There is no thermal path for the soldering heat to dissipate when heat is applied to the cover button of a cell.

Nylon characteristics:
Nylon has its glass transition at 460°F - 500°F . The maximum use temperature of nylon 6-6 parts is about 300°F. (Note that this is considerably below the glass transition temperature.)

Soldering temperatures are in the 450°F to 650°F range.

I realize this flies in the face of all the electric flight “experts” that assemble their own packs but it is never the less fact.

You have never seen a pack assembled by a cell manufacturer or any other pack manufacturer (outside of the hobby market) where connections are soldered directly to a cell. There is a reason.

Sanyo Cadnica Sealed Type Nickel-Cadmium Batteries Engineering Handbook
SF-9785ND
Section 10 General Remarks and Precautions
5 Safety Insturctions (page 48)
"Never solder lead wire directly to Cadnica battery terminals. Soldering
heat may damage the safety vent in the positive cap after a terminal plate
is spot-welded on the battery terminal, solder a lead wire on it."

Sanyo Twicell Sanyo Nickel-Metal Hydride Rechargeable Batteries
Engineering Handbook SF-9787ND Section 5 Important Cautions for Handling
Batteries 5-3-3 Do Not Misuse Batteries - "Never solder a lead wire or
plate directly to Twicell batteries. The heat generated by the soldering
may melt the insulation, damage the gas release vents or protective
devices, cause leakage of battery fluid, heat generation, bursting or
fire."

General Electric Nickel Cadmium Battery Application Manual [Library of
Congress Cat Card No 86-80684 Section 6.5.3 9 (page 6-20) "Never solder
directly to the nickel-cadmium cells, only to solder tabs or wire leads.
A hot soldering iron placed directly on the cell is likely to cause seal
ring and vent seal damage as well as damage to the separator systems."


First let me say that I am not on a crusade to stop the modeling world
from soldering directly to cells in construction of packs. All that I'm
trying to do is to alert modelers that there are some caveats they should
consider in making the decision to solder or not.

In the electric propulsion application and particularly on the competitive
side, the reduction of pack resistance plays a key role in obtaining
maximum performance. Direct soldering has been found as one means to
achieve this.

Soldering directly to cells that are destined for flight control operation
is not justified and can compromise the reliability of the packs. These
packs are frequently hidden away in the plane and are not frequently
available for inspection for any leakage and corrosion that may have
resulted from damage to seals/vents from direct soldering that can
compromise the reliability of the control system.

The risk (safety-wise) of soldering directly to cells is minimal but quite
dramatic on the rare occasion that it does surface. There are probably
more "incidents" resulting from abusive charge regimes than from actually
soldering. Of course the question always comes up was the soldering
contributory to the ultimate cell burst?


Bottom line: Soldering directly to cells is not recommended. Do it
understanding the risks and possible trade offs to performance, safety and
reliability.

Old 05-25-2005, 09:37 AM
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Walt Thyng
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Default RE: Soldering NIMH Cells Help !!!

Well,
I'm not going to argue with Red's comments. If you're not a skilled solderer don't try it. That said, all my nickel/metal packs are end to end soldered and have been for at least 15 years with no known failures and only one ruined cell.

If you're concerned about soldering, you might look into the MEC solderless power tubes. It's a system of rigid plastic tubing and end caps held together with two bolts. I happen to have one and it seems to work fine.
Walt
Old 05-25-2005, 09:51 AM
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-pkh-
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Default RE: Soldering NIMH Cells Help !!!

There are "hammer-head" soldering iron tips for soldering cells end-to-end... these allow you to heat the two batt surfaces simultaneously.
Old 05-25-2005, 07:30 PM
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Walt Thyng
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Default RE: Soldering NIMH Cells Help !!!

go to the EFO (Ampeer) site. Look up articles. there are two on end to end soldering tips, particularly the hammer head iron.

URL: http://members.aol.com/kmyersefo

Walt

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