Solder directly to NiCds?

[CarsonReidDavis]

I'm in the process of repairing a portable Tektronix 214. I disassembled the scope and removed the batteries. Then I powered it directly with two 6 volt sources and it seems to work, although there might be some connection problems while disassembled.

So I set about getting replacement batteries for the scope. It originally took two Ax5 NiCd packs, but I settled for AA for cost reasons. I had a local shop weld the NiCds because I have been told that soldering directly to NiCds is inadvisable because of reliability problems that can be introduced if the nylon seal is over-heated.

I didn't realize until I got the new packs home, but the technician did not solder to a hanging solder tab. Instead he cut a tiny solder tab that just covers the head of the battery and soldered directly to the top. I fail to see how this is thermally distinct from soldering directly to the battery.

I have included detailed pictures of the scope, the original packs, the new packs, and some diagrams I drew at this link: https://imgur.com/a/1sSIH3a

Do I need to have these packs remade? I do not plan on opening this unit again after the repair, so I will have no way to monitor corrosion or other problems.

[bd139]

I used to solder to NiCds all the time. Apply some flux with a flux pen to the end then get some solder on the cell. Then let it completely cool. Then do the other end. Then assemble the pack. Tin everything.

NiCds I used had the shit hammered out of them in RC cars. Never had a problem.

[BrianHG]

Use Mr. Carlson's wet rag method.  Here is his battery pack upgrade for your scope.
Watch at 13min 30sec for just the battery soldering instructions.

[helius]

If the terminals are nickel-plated stainless steel, it should be possible to solder to them directly with normal alloys for electronics. If the terminals are pure stainless steel, other alloys like Sn96Ag4 may be required. Orthophosphoric acid can be used to activate stainless steel for very solid connections.

[CarsonReidDavis]

Thanks everyone for your replies, however, I don't need to know how to solder to the batteries. The soldering has already been done, against my expectations. Please refer to my original post and the pictures I submited.

I paid a decent chunk of money to have a professional weld the batteries for me, because I have read from several sources that soldering directly to a NiCd can compromise the integrity of the battery if the seal is overheated. However, when I received my packs, 4 of the 10 batteries had been soldered instead of welded.

I'm trying to find out how big of an issue this is, and whether I need to go through the effort of fighting with a technician who might be very reluctant to replace some of the batteries and redo the work.

[james_s]

I've seen it done without problems, although I personally never solder directly to batteries. I built a capacitive discharge spot welder specifically for this purpose, it's easy to weld packs together with nickel strip just the way commercial batteries are made, no need to even try to solder them.

I suppose soldering to a piece of strip does provide at least some degree of thermal isolation, only a limited amount of heat is going to conduct through the welds but it still doesn't strike me as very professional.

[BrianHG]

Thanks everyone for your replies, however, I don't need to know how to solder to the batteries. The soldering has already been done, against my expectations. Please refer to my original post and the pictures I submited.

I paid a decent chunk of money to have a professional weld the batteries for me, because I have read from several sources that soldering directly to a NiCd can compromise the integrity of the battery if the seal is overheated. However, when I received my packs, 4 of the 10 batteries had been soldered instead of welded.

I'm trying to find out how big of an issue this is, and whether I need to go through the effort of fighting with a technician who might be very reluctant to redo the work.

Redo?  Once done, and if the battery has been damaged due to heat, it's too late.  If the battery hasn't been damaged, just live with what you got.  Batteries cost more than a paying someone to solder wires to them as anyone can do this.  And if you use Mr. Carlson's wet rag trick shown in the video I posted above, using his method and tools prevents the heat from working it's way into the battery to melt the valve and insulating material.

[David Hess]

The vent is on the other side from the solder connection shown so it does not matter.

I have never had a problem with reliability and soldering to NiCd cells but I got to be very good at applying a minimum of heat.  I clean the surface with an abrasive and then use an acid type flux and it solders instantly with standard solder.

[CarsonReidDavis]

@james_s

Do you have any information on how you built your unit and what the cost was? I might be interested in building one for myself.

[CarsonReidDavis]

@Brian_HG

Yeah, I was assuming I would have to replace 4 of the 10 if the consensus on the forum was that damage was likely. Do you have an idea of how to test for the integrity of the vent?

[CarsonReidDavis]

@David Hess

Unfortunately, there are 4 batteries soldered, two on the negative terminal and two on the positive terminal. The one in the photo looks as if it has only been soldered once, but that is because I had to desolder the negative wire to remove a faulty inline fuse.

[james_s]

@james_s

Do you have any information on how you built your unit and what the cost was? I might be interested in building one for myself.

I think I spent about $100, most of which was for ~1F worth of 22,000uF capacitors. There's not much to it, a variable power supply based around an LM317, relying on the short circuit protection to limit the current, lazy but works fine. I used the biggest stud mount SCR I could find for a few dollars on ebay to dump the capacitor bank into the welding probes. For the probe assembly I used pieces of #6 solid copper wire sharpened to a point and lengths of 2AWG car stereo power cable to the box.

Since you might be tempted to try, I'll mention that prior to this design, I tried using one of those big 1F car stereo capacitors and it worked for about 10 shots then failed.

[Audioguru]

I stopped using AA size Ni-Cad batteries about 20 years ago when Ni-MH cells were introduced. I can't find anywhere today that still sells old fashioned Ni-Cads but modern Ni-MH cells are sold everywhere.
Ni-MH cells have a much higher capacity, hold a charge for 1 year instead of just a month or two and do not have the Ni-Cad "memory" problem.
Even my cheap solar garden lights use Ni-MH cells. They used Ni-Cads years ago.
Ni-Cad packs might still be used in high current RC toy cars but your 'scope does not use a high current. 

[james_s]

NiCds are still occasionally used for replacing cells in devices designed for NiCd. In many cases a charger designed for NiCd will work fine for charging NiMH but this is not always the case.

[mikerj]

Ni-MH cells have a much higher capacity, hold a charge for 1 year instead of just a month or two

This is only true for the low self-discharge types such as Eneloop.  Standard high capacity NiMH can have very high levels of self discharge.

[Audioguru]

Ni-MH cells have a much higher capacity, hold a charge for 1 year instead of just a month or two

This is only true for the low self-discharge types such as Eneloop.  Standard high capacity NiMH can have very high levels of self discharge.

Energizer and Duracell Ni-MH batteries have been sold as "pre-charged" and "holds the charge for one year" everywhere for a few years the same as Sanyo/Panasonic Eneloops.
The Energizer and Duracell Ni-MH batteries are made for them in Japan and might actually be Eneloops. They do not make or sell "standard high capacity" Ni-MH batteries anymore but the old capacity was only 9% more.

[drussell]

Yeah, more and more of the off-the-shelf NiMH cells are being made in the low self-discharge models, types and styles, many of which may or may not be actually made by Panasonic, licensing their tech or using some kind of similar methods one way or another...

They are all much, much better than older "regular" NiMH technologies which, yeah, often have (or, had) self-discharge worse than the old cheap NiCd cells.... 

[james_s]

LSD tech is what finally made rechargeable batteries really practical. Previously I used them in high drain devices that ate a lot of batteries but for stuff like flashlights they would self discharge by the time I needed them. Now I use NiMH batteries in virtually everything. I don't buy disposable batteries anymore, the only time I ever use them is when I get some for free.

[David Hess]

Low self discharge NiCd cells used to be available as well but never in the consumer market.

To my mind, NiMH cells were useless before the low self discharge types became available.