Soldering battery holders?

kuksul08 · Jan 8, 2009

I have one of these

(Moderator note: Hot linked pic removed IAW CPF image rules.)

And the wires are too small for 1A of current. I was going to modify it and use 20Ga wire instead. Is it even possible to solder them? I tried a little and it just started melting the plastic

Any better suggestions?

Mr Happy · Jan 8, 2009

If those wires are made of copper (they are), then they are not actually too small for 1 amp -- they will carry it easily. On the other hand, all those steel springs visible in the picture have a very high resistance. The wires are suitable for one amp, but the battery holder itself is not I'm afraid. In general that kind of battery holder is designed for electronics applications with a current draw of a few milliamps. For power applications you will need something altogether different (probably home made).

To solder to a battery holder, you can get similar ones to that pictured with solder tabs instead of wires. Those tabs give enough extra space from the plastic that they can be soldered (with care). Even then it is very easy to melt the plastic if you keep the iron on the tab for too long. But even the ones with solder tabs have high resistance steel springs and wires inside them.

kuksul08 · Jan 8, 2009

Mr Happy said:
If those wires are made of copper (they are), then they are not actually too small for 1 amp -- they will carry it easily. On the other hand, all those steel springs visible in the picture have a very high resistance. The wires are suitable for one amp, but the battery holder itself is not I'm afraid. In general that kind of battery holder is designed for electronics applications with a current draw of a few milliamps. For power applications you will need something altogether different (probably home made).

To solder to a battery holder, you can get similar ones to that pictured with solder tabs instead of wires. Those tabs give enough extra space from the plastic that they can be soldered (with care). Even then it is very easy to melt the plastic if you keep the iron on the tab for too long. But even the ones with solder tabs have high resistance steel springs and wires inside them.

Thanks for the response Mr.Happy, you sure are on top of it

I'm not really sure what to do in this case. Finally I got my light electronics worked out, and the power source may be lacking. All I have are rechargeable AA's so I wanted to use them until maybe I eventually get some nicer pack. I don't want to solder directly to the batteries and damage them.

Are there any other simple solutions out there for arranging the cells?

mdocod · Jan 8, 2009

I had a number of those battery adapters back in the day... and wanted to use one to charge a set of AA NIMH cells as a pack (all in same state of charge). I have a variable current pack charger and I found that anything over ~1.5A would cause the little contacts from spring to spring to get red-hot and start to melt the plastic. Point being, the resistance in these things is really high, and they don't take well to moving electrons at any decent rate.

out of curiosity.. what are you going to power with it?

kuksul08 · Jan 8, 2009

mdocod said:
I had a number of those battery adapters back in the day... and wanted to use one to charge a set of AA NIMH cells as a pack (all in same state of charge). I have a variable current pack charger and I found that anything over ~1.5A would cause the little contacts from spring to spring to get red-hot and start to melt the plastic. Point being, the resistance in these things is really high, and they don't take well to moving electrons at any decent rate.

out of curiosity.. what are you going to power with it?

Interesting, and upsetting at the same time hehe. Here's the plan... by the way this is my first ever real DIY light from scratch so I don't know much about all the details. Anyway, the light is going to be like this

(Moderator note: Oversized pic removed IAW CPF image posting rules.)

4.8V nominal input voltage to two parallel AMC 7135 chips each powering a Cree XR-E R2 (WG) at 700 or 1050mA. I haven't decided because I don't know how hot it will get.

It's a relatively simple setup. The idea was to use 4 series AA's in parallel with 4 more, so I could have 3200mAh capacity, and 4.8V. That means the current draw is going to be anywhere from 1.4-2 amps from the battery pack, correct? (depending on whether I use the 700mA or 1050mA current).

Maybe you will have some suggestions

Thanks

Fallingwater · Jan 8, 2009

Mr Happy said:
If those wires are made of copper (they are), then they are not actually too small for 1 amp -- they will carry it easily. On the other hand, all those steel springs visible in the picture have a very high resistance. The wires are suitable for one amp, but the battery holder itself is not I'm afraid. In general that kind of battery holder is designed for electronics applications with a current draw of a few milliamps. For power applications you will need something altogether different (probably home made).

What he said.
Get a box, a Dremel, a few metal tabs, and get working.

Seriously, those springs are awful. I remember trying to power a minivacuum with three NiCD AAs in a holder when I didn't know any better; after a second of operation the springs overheated so much that they got stuck in the compressed position. Pulling on them had no effect - they'd snap back as soon as I let go. The metal had actually changed colour.
In the end I shorted another NiCD pack through them while pulling them with pliers, and finally managed to get them back to working condition.

Footleg · Jan 8, 2009

Mr Happy said:
If those wires are made of copper (they are), then they are not actually too small for 1 amp -- they will carry it easily. On the other hand, all those steel springs visible in the picture have a very high resistance. The wires are suitable for one amp, but the battery holder itself is not I'm afraid. In general that kind of battery holder is designed for electronics applications with a current draw of a few milliamps. For power applications you will need something altogether different (probably home made).

To solder to a battery holder, you can get similar ones to that pictured with solder tabs instead of wires. Those tabs give enough extra space from the plastic that they can be soldered (with care). Even then it is very easy to melt the plastic if you keep the iron on the tab for too long. But even the ones with solder tabs have high resistance steel springs and wires inside them.

Interesting, as I was playing with a P7 LED using one of these packs last night. 10 x AA NiMh cells driving the LED at 2.8A, drawing 1.15A from the batteries. I did not notice any overheating from the battery pack. The LED got very hot, despite being attached to an old Intel Celeron CPU heatsink. (Well the whole heatsink got very hot to be accurate!)

Mr Happy · Jan 8, 2009

Footleg said:
Interesting, as I was playing with a P7 LED using one of these packs last night. 10 x AA NiMh cells driving the LED at 2.8A, drawing 1.15A from the batteries. I did not notice any overheating from the battery pack. The LED got very hot, despite being attached to an old Intel Celeron CPU heatsink. (Well the whole heatsink got very hot to be accurate!)

Yes, that sounds reasonable actually. At 1 amp from the batteries the springs should not overheat very much, but the voltage loss over the many springs in a ten battery pack would have been significant. If you upped the current a bit more, the current-squared law on heat dissipation would start to take effect and you would see more problems.

Footleg · Jan 8, 2009

That makes me glad I decided to go with the full 10x AA holder and 12V rather than a smaller number. The LED driver can handle upwards of 5.5V but I thought this might be rather tough for the batteries at the currents it would draw. Sounds like it would have melted the battery pack too! :sssh:

As I am using a constant current driver, I assume that using a battery holder with less resistance would ultimately just lower the current drawn from the batteries, on account of a lower voltage drop across the battery pack? So I'd gain on battery life but otherwise there would be no noticeable effect?

kuksul08 · Jan 8, 2009

Thanks for the help guys. Not sure what I'm going to do now but I guess I'll have to think of something.

I just found this

(Moderator note: Hot linked pic removed IAW CPF image rules.)

Basically no more springs and just pressure contacts.

Fallingwater · Jan 8, 2009

Footleg said:
Sounds like it would have melted the battery pack too!

Long before damaging the cells, I'll add.

Just solder to them. They are NiMH too, so you don't even have to get paranoid that they might explode in your face.

Footleg · Jan 12, 2009

Mr Happy said:
Yes, that sounds reasonable actually. At 1 amp from the batteries the springs should not overheat very much, but the voltage loss over the many springs in a ten battery pack would have been significant. If you upped the current a bit more, the current-squared law on heat dissipation would start to take effect and you would see more problems.

I gathered a bit more data on this over the weekend, running my prototype SSC P7 light at full power for 35 minutes. The current draw from the 10 x AA battery holder was a steady 1.24A and neither the contacts or the NiMh cells got noticeably warm. I measured the voltage across the batteries while the light was turned on, and got 10.6V, so then I tried putting all the batteries end to end in a cardboard tube instead of the spring contact battery holder. Still only got 11.1V (both measurements using an auto ranging digital multimeter). So while this set up appears to be dropping around 1V due to resistance in the battery holder springs, it is not a significant loss of efficiency for me.

I guess with the heat being a square relationship with current(?) then problems may occur at not much higher current with these holders. But for up to 1.25A they appear to work OK.

kuksul08 · Jan 13, 2009

I tried soldering my plastic one, and it just melted the plastic. I couldn't get solder to stick to the metal either.

I found these...a possible new option http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=192K-ND

Aluminum frame

Mr Happy · Jan 13, 2009

kuksul08 said:
I tried soldering my plastic one, and it just melted the plastic. I couldn't get solder to stick to the metal either.

Soldering to steel is much harder than soldering to copper. You need to make sure the surface is very clean and perhaps slightly roughened with fine grain sandpaper, use additional flux, use a hotter iron, and make sure you are using lead-bearing solder. (Lead-free solder is notoriously difficult to make stick to anything.) Also tin both surfaces to be joined before you make the joint. With those plastic battery holders, don't leave the iron touching the tab for more than 2-3 seconds at most. If the solder doesn't stick at first, withdraw the iron and wait for things to cool down before trying again.

Nubo · Jan 13, 2009

Couldn't you just solder wires to the contact end of each spring? Bypassing most of the resistance and just using the springs for mechanical pressure. Should be able to use a heat sink that way to keep the heat from reaching the plastic base.

kuksul08 · Jan 13, 2009

Nubo said:
Couldn't you just solder wires to the contact end of each spring? Bypassing most of the resistance and just using the springs for mechanical pressure. Should be able to use a heat sink that way to keep the heat from reaching the plastic base.

I tried that. I put the soldering iron on high (40W i believe), and touched the tinned tip to the spring and held it there. It got really hot, but never melted the solder.

The solder I am using is 96% tin and 4% silver with rosin flux core, if that helps.

Mr Happy · Jan 13, 2009

kuksul08 said:
The solder I am using is 96% tin and 4% silver with rosin flux core, if that helps.

No, that doesn't help actually. :shakehead

You will be better off using solder containing 60% tin and 40% lead. The lead-free solder you have is very difficult to work with.

I tried that. I put the soldering iron on high (40W i believe), and touched the tinned tip to the spring and held it there. It got really hot, but never melted the solder.

Did you touch the solder to the tip of the iron where it was pressed against the spring? The solder will not melt on the spring itself, it needs the heat of the iron to melt it. When you make a solder joint with an iron the heat is conducted through the molten solder from the iron to the work. You need to touch the solder wire into the gap where the iron meets the parts to be joined and the molten solder then flows from the iron into the joint.

Fallingwater · Jan 14, 2009

Get some leaded solder. Ignore the whole tree-hugging mania about lead-free solder.

roadie · Jan 14, 2009

and its so much cheaper :devil:

Fallingwater said:
Get some leaded solder. Ignore the whole tree-hugging mania about lead-free solder.

Footleg · Jan 14, 2009

kuksul08 said:
I tried soldering my plastic one, and it just melted the plastic. I couldn't get solder to stick to the metal either.

I found these...a possible new option http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=192K-ND

Aluminum frame

I soldered directly to the press stub type battery clip connectors. Yes the plastic does melt, but you can minimise this by doing it with the holder loaded with batteries, which sink some of the heat. The studs get hot enough to melt the plastic, but if you are careful they don't move about too much, and you can reposition them while the plastic is still soft so it all sets back in place. Use a big pair of pliers for this, and they such away to heat too, allowing everything to set in place quickly. Worked OK for me (I'm a quick solderer though). The advantage is I have a working 10 cell battery holder for my lamp which costs less than GBP1 (GBP = UK pound/sterling).

Soldering battery holders?

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