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soldering cells
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Glen
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soldering cells

well people like it or not battlepacks are gone.

so i think its time we start learning to make our own nicad/nimh packs Smile heres some info i collated in my travels:

it is ideal to use solder tags/tabs up to MW size robots. using wire is more durable and takes more current BUT they are harder to solder onto the tag and there is a possibilty you accidentally have a piece or wire short onto the case. tags however are less tollerable to shock loads and often pop of the cell as nick would know Smile

using a 100w soldering iron with a flat chisel head about the same size as the cell is the best way to go. feed the solder in at the same time your heating up the cell. the tip should only be left in contact long enough for the solder to flow.

60/40 rosin core is generally used for soldering cells but there is stuff called silver solder that is great.

mike rutt also pointed out that superglueing the cells together is a good way to keep the pack held together and stop the cells jumping around and so forth.
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Post Sat Sep 11, 2004 3:48 pm 
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3Faze



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Sounds obvious to say it, but some form of insulation between the cells is needed, and it needs to be able to withstand heat. Insulation tape isn't ideal, cardboard/plastic tubes are good, something I'm working on is a drilled, low density plastic block, possibly with intercooling.

What you need to be doing for soldering is making the joint thick and fast, then sinking the heat away. Silver solder's great, but it's a bugger to use. 100W is about fair, assuming it's a good brand iron. If it were me, I'd use my gascat iron on full (think about 150W-200W equivalent in an electric iron), then sink the heat away with a lump of ali.

Post Sun Sep 12, 2004 5:35 am 
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Nick
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Heatsinking huh? It might sound weird and it wouldn't work it you use cardboard covered cells or spacers, but a waterbath would be your best heatsink for quick cooling. Messy but effective!
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Post Sun Sep 12, 2004 8:22 am 
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3Faze



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Sorry, didn't make myself clear there. I meant use a temporary heatsink to get the heat away from the solder joint to prevent the cells being damaged.

Problem with water cooling is two fold:

1. In event of damage - Water + nicads = trouble
2. You'de need some way of cooling the water.

Post Sun Sep 12, 2004 9:02 pm 
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Nick
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Outside of cells with cardboard casing, water should do absolutely nothing to a nicad unless it somehow got past the seals - if that happened, its probably had melted a seal and is ruined anyway.

Water is minimally conductive unless it has additives, so using distilled or at least clean water will stop and electrical discharges. Drying the cells afterwards is an obvious step before heatshrinking or taping.

I was thinking of using a large waterbath, something like a glass baking dish. The thermal mass is large and if it became warm, it can be refilled.

Tilting the dish so the shallow end comes close to the top of the cells allows them to be soldered, then slide the cells to the deep end for cooling.

I would be pre-tinning all the cell tops and bars too - that way you can be sure each surface is properly covered before joining them.

Why do I think this will work? In a previous electronics job, we had a wave soldering assembly line. after seeing what the components went thru in the cleaning stage, I can't see how cold water could possibly cause a problem Smile
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Post Sun Sep 12, 2004 11:17 pm 
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3Faze



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Ah right, I thought you meant watercooling inside the bot Confused

Post Mon Sep 13, 2004 3:52 am 
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Spockie-Tech
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a reasonably good basic primer on soldering packs is here
http://members.aol.com/KMyersEFO/makepack.pdf
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Post Tue Sep 14, 2004 2:59 pm 
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Nick
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I worked out that if we used copper braid for joining cells, a 30mm strip capable of 60 amps would cost 25 cents, even at the extortionate prices of RS Components. I reckon we could halve that price at least...
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Post Tue Sep 14, 2004 3:10 pm 
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Spockie-Tech
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a further tip that is worth mentioning is that any use of bakers soldering fluid or similair acidic fluxes to assist with soldering of packs should be well cleaned afterwards with a mild residue-free solvent (isopropyl alcohol, methylated spirits etc) according the tech guy at Master Instruments, as any left over flux can attack and damge the vent seal.

I like the sound of the braid so far, although if you put too much solder onto the joint, it would probably all wick along the braid and turn it into an almost solid chunk of solder/copper which negates the flexibility advantages.
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Post Tue Sep 14, 2004 3:55 pm 
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Nick
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I use a solid paste flux that's similar to the rosin cored solder. it still needs cleaning afterwards, but it tends to stay where its placed and dries hard quickly. It can be wiped off with alcohol or chipped off.

For people using zip boxes for battery compartments, flexibility is probably good. The US forums seem to agree that shrinkwrap packs benefit from rigid links - who can really say? When I busted a Battlepack, the bar stayed put and the dodgy jolder joint broke so flexy might be better...

I was thinking that having a little solder wicked up into the middle of the braid might allow it to be formed into a bridge shape to help avoid shorting. I was also thinking about placing a plastic strip under the braid to help shorting as well. Probably paranoia but I would rather spend the time in constructing rather than cleaning up burnt batteries...
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Post Tue Sep 14, 2004 4:07 pm 
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Valen
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problem with soldering to a fibrous type material is you wind up with a knife edge where the solder ends, basically the fibers are put into tension one by one and cut themselvs off on the solder join line.

if you are soldering a multi core cable it should be soldered then mechanicly held (rigid to the solder joint) at a point after the solder so there is no stress/vibration put on the boundry between solder and free copper.
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Post Tue Sep 14, 2004 5:13 pm 
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Spockie-Tech
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Just a little tip I just discovered while practicing soldering some cells together..

Get your Dremel or Supertool and put one of those little pink grinding stones in it (I used the round ball one) and give the terminals on the cells a light scuffing with it of about the diameter you want to solder to flow to.

After you've done this, the solder just flows on as easy as, with no bakers soldering fluid (corrosive) required. Its so quick, I wouldnt even worry about overheating the cell, I can get a really good button of solder with about 2 seconds of heat.
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Post Tue Sep 28, 2004 9:26 pm 
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timmeh
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Brett

How many amps do you think that braided can wire take?
The stuff we got from franchesco.
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Post Mon Oct 04, 2004 6:49 pm 
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Spockie-Tech
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no firm idea sorry Tim. I'd *guess* it should handle 50-60 amps fairly comfortably, and quite possibly more, but I cant say for sure without measuring the diameter of a strand, and counting the strands in the braid.

It looks to be around the same size (possibly even a bit bigger) as what BattlePack are using on their new "ultra" packs though, so I would guess it should cope with whatever the cells can put out.
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Post Tue Oct 05, 2004 2:01 am 
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timmeh
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The ultra packs have silver coated copper braid wire so the current ability will be diif wont it?

And i have found some silver solder it is 98% tin and 2% silver but is ses not for electrical use why is this?
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Post Tue Oct 05, 2004 7:07 pm 
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