Repairing NiCd battery packs

[Andrew Rossmann]

I have a nice 14.4V Dustbuster where the battery pack is pretty much
unsable right now. It's a nice vac. I bought a new 18V one with a
removable battery, but it doesn't seem to work as well.

I took the 14.4V battery pack apart. It contains 12 sub-C size cells. 4
show 0V, while the rest are showing about 1V (it's not fully charged.)

Has anyone had any luck in replacing individual cells? There are no
markings on the batteries, so I have no idea what their capacity is.
These are chained together with short metal strips that are spot-welded
to the batteries. How easy/hard would it be to solder to them, and will
it damage the batteries if I try?

I have found direct replacement packs at some sites, but at $30+, I
wonder if it's worth it. It's as much as a new vac, but then the new
vacs seem to be pretty crappy.

 

[Smitty Two]

How easy/hard would it be to solder to them, and will
it damage the batteries if I try?

If you scratch the areas to be soldered with sandpaper and *use liquid
flux* then you can readily solder the batteries without damaging them.

 

[William Sommerwerck]

The problem with replacing /individual/ cells is that, even if they're
exactly the same cell used in the original battery pack, the new cells will
have higher capacity, increasing the chance of cell reversal. You really
should replace all the cells.

My experience with Black & Decker's OEM battery packs -- if you can find
them -- is that they hold up well. I wouldn't purchase a third-party battery
pack, unless the supplier offers an iron-clad guarantee.

You might consider putting together a battery pack of 2500mAh or 2700mAh AA
NiMH cells. You'll get higher capacity, though the battery will take longer
to reach full charge.

 

[Phil Allison]

"Andrew Rossmann"

Has anyone had any luck in replacing individual cells?

** Best to replace the lot.

There are no
markings on the batteries, so I have no idea what their capacity is.

** See above.

These are chained together with short metal strips that are spot-welded
to the batteries. How easy/hard would it be to solder to them, and will
it damage the batteries if I try?

** Try to get cells that have tags fitted to them.

These are very easy to solder with any decent soldering iron and flux cored
solder ( not lead free) as used for electronic work.



..... Phil

 

[shrtrnd]

The last time I wanted to do what you want to do, it became more economical to just replace the entire vacuum, and use the first one for spare parts. You have to be able to
find a really good deal on the NiCad replacement batteries to make it worth your while.
By the way, NiCad batteries were always standard 1.2VDC, ...unless somebody's improved them these days.

 

[mike]

If you scratch the areas to be soldered with sandpaper and *use liquid
flux* then you can readily solder the batteries without damaging them.

If cells with solder tabs and the bulge caused by the solder and wire
still fit in the space, that's the way to go.
Be aware that QUALITY cells will cost more than the cost of a battery pack.

Dustbusters are sold on PRICE. That means low quality batteries
and chargers with zero control that overcharge/degrade the cells.
If you don't do something about the charger, your new cells won't
last any longer than the old ones did.

People tell you that you can safely solder on cells. That ain't the case.
Yes, if you're very experienced at soldering on batteries, you may
be able to do it most of the time without serious degradation.
If this is your first attempt, expect to ruin at least some of them.
If you must solder on 'em, do it with them discharged, so when you
melt the separator and create an internal short, there's less energy
to fuel the explosion. Wear eye protection, and make sure the kids are
outa the house. They're not lithium, so making sure your fire insurance
is paid up is a secondary issue.

I can hear the villagers lighting the torches to come after me to tell
me how stupid I am...that you CAN solder on batteries.
I even did it for a number of years. I am fortunate that I got old
enough to require glasses before the first one exploded in my face.
Otherwise, you'd be reading this in braille.

There's a reason they weld the tabs. Ignore that at your peril.
People who have to ask "how hard it is" should NOT be soldering on
batteries...even if some "newsgroup expert" says THEY can.

 

[Phil Allison]

"mike"

If cells with solder tabs and the bulge caused by the solder and wire
still fit in the space, that's the way to go.

** There is a simple way to join ( un-tagged) cells very neatly, tip to
base, that uses just a few centimetres of 1.5 mm dia solid copper wire. Here
it is:

The copper wire ends are first tinned and one end soldered to the *side of
the tip* of one cell and then the other end soldered the outer edge of the
base of another. A quick twist and the two are perfectly connected in
series with no increase in overall length.

People tell you that you can safely solder on cells. That ain't the case.
Yes, if you're very experienced at soldering on batteries, you may
be able to do it most of the time without serious degradation.
If this is your first attempt, expect to ruin at least some of them.

** This is just not true.

There's a reason they weld the tabs.

** It's quick, cheap and nasty.

Most spot welded joints have so much resistance the joint gets VERY HOT
when packs are subjected to a fast discharge - ie when used on RC models
involved in racing etc.

People who have to ask "how hard it is" should NOT be soldering on
batteries...even if some "newsgroup expert" says THEY can.

** You need a good soldering iron - preferably a modern, variable temp
station and iron rated at 50 watts with a large tip size fitted and full
setting ( ie 450C) on the temp dial.

Then one works quickly and purposefully with ordinary, rosin cored 60/40
solder. The nickel plated surfaces of fresh Ni-Cd or NiMH cells usually tin
so quickly - it fair makes your head spin.


...... Phil