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Old 08-28-2008, 05:42 PM   #1
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Default Soldering up 4-cell packs...help!?!?

OK, I consider myself more than a decent hand with the soldering iron. I can usually get a "factory" look to solder joints to ESCs, Deans, motors, etc. I'm soldering up some 4-cell packs for the first time. I've never soldered to batteries before. I have Trinity copper battery bars and EP4600 cells. I've scuffed the ends of the cells with a sanding wheel on the dremel.

Here's my problem: I get perfect results on the positive ends of the batteries, but I'm having problems on the negative side. At first I thought this was coincidence, but it happens pretty much every time. I lay the bar in place, start heating it, and introduce some solder. On the (+) side it flows out beautifully, down through the 4 holes, and just peeks out the sides under the bar. Perfect. On the (-) side it just doesn't seem to get hot enough. the solder melts, but not quite enough, and won't flow down through. I've tried doing the (-) side first and second with no difference.

Is this normal? Is there a lot more material inside the battery connected to the (-) side that's acting as a heat sink? Something else going on? Am I doing something totally wrong? What gives?
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Old 08-28-2008, 06:03 PM   #2
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you need a 60W iron at least.
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Old 08-28-2008, 06:05 PM   #3
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Originally Posted by TRF415boy View Post
you need a 60W iron at least.
I've got a 60W Weller WES51. I'll crank it to 11 and see what that does.
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Old 08-28-2008, 06:29 PM   #4
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Certainly the heat capacity of the negative end is far more than that of the positive.

For this sort of work you want a very hot iron, and you want to use it for as short a time as possible, since this reduces the amount of over-heating to the cell. You can kill your precious cells with a marginal iron.

Tin the place on the negative end where the battery bar will go, before you try to solder on the battery bar. Tin the end of the battery bar too. After you've done tinning, put the parts in place with a little rosin flux in between. Get your iron hot, then use it to reflow the tinned area. If you put enough solder on when you do the tinning, you won't need to add any more solder to get a confident joint.

My favorite iron for soldering packs is the Goot TQ-77, available from bomir.com. This iron idles at 10 watts, but goes to 150 watts when you pull the trigger. It gets hot enough to solder a battery pack within a few seconds.
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Old 08-28-2008, 06:30 PM   #5
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I always wet (add solder) to the battery ends and the bars first, then re-flow them together. I'm more concerned with a good connection than a "factory look". Besides, a solid joint always looks good.
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Old 08-28-2008, 11:13 PM   #6
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Originally Posted by MarkBrown View Post
Tin the place on the negative end where the battery bar will go, before you try to solder on the battery bar. Tin the end of the battery bar too. After you've done tinning, put the parts in place with a little rosin flux in between. Get your iron hot, then use it to reflow the tinned area. If you put enough solder on when you do the tinning, you won't need to add any more solder to get a confident joint.
Quote:
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I always wet (add solder) to the battery ends and the bars first, then re-flow them together. I'm more concerned with a good connection than a "factory look". Besides, a solid joint always looks good.
That was the hookup right there. I still had to max the iron out at 850 F to get the negative side to work, but work it did. They came out great. Thanks guys!

Check out my high-tech battery workstation and jig.

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Last edited by reenmachine; 08-29-2008 at 10:17 AM. Reason: 185 to 850
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Old 08-28-2008, 11:47 PM   #7
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Your prep is ok I geuss. May change it a bit. May take less heat. Scuff the positive & Negative post of battery with sand paper. Dremel maybe over doing. Scuffing the surface other than a deep gouge. Tinning the surface where the battery + & -. Put the bar on top of tinned surface, then apply heat with iron on bar, it'll soften the tinning then apply some solder to the bar. YYou are done. Purchase a Venom Assembly jig, it make your hand free for soldering. The jig put tension on the bar and for a solid solder joint.
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Old 08-29-2008, 03:43 PM   #8
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yeah prepping the cells is the best way. I just chuck a grinding stone into my dremal and graze the tops.

I have noticed that the negative side of the cells sucks the heat faster and needs higher temps or more wattage.

When I solder I normally apply Kestors Self-Tinning flux to the bars and batteries. I will apply solder to the cell and place the bar ontop and heat. The bar normally sucks flat as the flux break the surface tension of flowing solder.
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Old 08-29-2008, 05:29 PM   #9
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Hi guys, I have posted the way that I solder up packs before, but I don't mind helping you out if possible. Here' what I do.

1) Use a decent iron and battery jig!
2) First thing is to put a dollop of flux on both ends of each cell and spread it out to where you want the joint to be.
3) Tin the cell ends (not too much solder though).
4) Put flux onto the battery bars (that are going to touch the cell ends).
5) Place the bars (one at a time) onto the cell ends and hold in place with the part from the jig.
6) Put the end of the iron onto the bar and push down on the bar with a screwdiver (the iron is used for heat, the screwdiver for pressure).
7) The flux will melt and create a really good joint between the cell end and the bar.
8) Continue until all cells and connectors are completed.
9) Thats it, job done!

The only other thing I do, is to clean up the cells once completed using petrol lighter fluid. This gets rid of any residue from the flux melting. I find this is a great way of getting a pack made up, works well and have never had a pack fall apart.

Hope that helps guys, Chris.
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