Thursday, 21 July 2016

Good use for old dead batteries - Eliminators

ok, ok, yes I will get around to the next installment of the Clansman Manpacks for Amateur Radio article, maybe tomorrow i'll cover SURFs, Audio ancillaries and batteries. The final article will cover antennas and masts.

In the meantime, ive been working on sorting and testing the large number of 12V NiCd PRC-349 battery packs ive obtained.

Theres about a third of them in this photo.  Those top left tested over 10V terminal voltage. Those top middle between 1 and 10V.  The few at the right are a dry cell cassette, and a pair of good 15V Lithiums!

Inevitably, from how I came about these, there were going to be a large number that are dead. Most of these will end up going for recycling, after any good terminals have been salvaged. However, a very sensible thing to do with a couple of dead battery packs, especially for specialist devices, is to turn them into battery eliminators! I used to do this for the Kenwood radios I serviced when I worked for NTL, an eliminator allows you to power the radio from a mains PSU and makes alignment easier, as you dont have to ensure your using a good battery!

The first thing to do when making a battery eliminator is to find a dead battery that otherwise is sound, one with a duff cell but good case and contacts. The next step is probably the hardest part and the one that takes the most skill - opening the case. Here its good to have a few that you dont mind smashing while you work out the method! In the case of the 349 batteries, I found they are lightly glued around the top, which is recessed. A few gentle strikes around the seal with a sharp chisel and I was able to pry the top off.

Actually prying the top up was hard as the inside is packed with expanded polyurethane foam. Gently easing this foam out, expanding the gaps etc took a long time but eventually I was able to pull out the cells. Incidentally, the central tube should be possible to push out to give space to dislodge the cells. I'll try that trick on the next one I build. Remember to recycle the cells!

With all the old cells removed and the foam scraped out, I was left with the collection of parts shown below. This also shows the 4mm terminals and the fuse holder.

A bit of marking next and then drilling to create the three holes needed. Tightening the nuts for the sockets and fuse holder is a nightmare as there is simply no clearance inside the pack. Those for the sockets I managed to get tight, but the fuse holder is actually held in place by hot-melt glue!

Once all the innards are installed and wired up, a task that is best done by soldering the wires with the parts outside the case, and threading them through the holes, remembering also to thread the wires through the nuts, the wires were soldered to the terminals and the case closed. The tube was then pushed back in place. Both the tube and the top I secured with a little impact adhesive. Do remember to test the thing before gluing!

The final tasks were to push the securing bolt back into the tube, and fit a fuse. This should be a 1A fast blow type (20mm glass in my case), although its currently a 5A slow-blow in mine as thats all I had!

Another option is to install a grommet and trailing wires rather than sockets, i'll do the next one that way.

One of the 1Ahr NiCd packs for the PRC-320/-351 etc would convert into a very nice eliminator, but would require a 24V PSU. Another option there is to use a metal cased 4Ahr pack, and install a small 24v SMPSU and an IEC mains socket!

1 comment:

Anonymous said...


Well you have at least one reader :-)

If you own a PRC 320 - the best thing you can ever do is to buy one of the New Old Stock plastic cased 5Ah batteries that sell on ebay for about £20-30.

Like this one which has a late date stamp (look out for lower prices from other dealers)

It's not significantly more expensive and much much less hassle than trying to refil an old one.

I got through 20 + old tatty metal cased ones that originally held some charge, before I bought one of the 5Ah NOS batteries - My only regret is that I hadn't done it a lot sooner.


Martin - G8JNJ