and again, maybe third time lucky!

reposted, original seems lost in the aether, apologies if double posted

Larry Jaques wrote:

I recently replaced one of the two dead Ryobi 14.4v batt packs which
several years of abuse before dying on me. It appears that just a few
of the dozen cells in each pack have gone bye-bye. I'd like to rebuild
one from the dregs of the other and wondered what you guys used to
spotweld the cells together. I've heard that they don't like to be
soldered _at_all_.

Who here has rebuilt packs and how did you attach the cells?

I've never _re_built packs, but I have soldered them together.

The best way I know is to use a hot hammerhead iron - that's a soldering
iron with a bit with two working ends, so you heat both cells at once.

The bit is about 1 inch long and 1/2 inch diameter, and looks like this:

| iron
| ||
| ___||___
| _/ \_
| |_ bit _|
| \________/
|

I have turned a few from copper, it's not hard - unfortunately I don't have
any now, and I can't get back to the shop before mid-Jan (long holidays!).

You really need at least a 40 watt iron, although it can be done with a
smaller one. Wait for it to get hot


People who make up a lot of packs tend to put the cells in the fridge before
soldering, use 60/40 tin/lead solder rather than the leadfree type (naughty,
but then the cells are full of cadmium ...), and make up a frame so the
cells slide easily into the right position. You heat up the ends of two
cells at once, make sure they are wet with solder, remove the iron and
quickly slide one cell to meet the other.

Then cover with heatshrink for mechanical strength.

Never had a problem once I figured out how to do it - and you could of
course practice with the hootered cells first.


It might be worth while googling "hammerhead soldering cell" , some good
links there.

Below is a post I wrote in answer to a similar question, not an immediate
answer but should have some relevant tips.


However, Tim's point about reversal during discharge sounds relevant. I've
always been a good boy and never tried mixing cells tho'. Perhaps you could
try to find the set of cells whose capacities match best.


--
Peter Fairbrother


Hawkey wrote:

Sh*T u aint kidding...30 odd pounds just for the bit!! I think I will
forget it. thanks anyway ;-)

Presuming you want to use it to end-to-end solder a few battery packs, why
not just get a lump of copper, shape it, stick it on the end of an existing
bit, preferably a worn-out one, and use that? You could use tap-and-die to
thread it, or hard solder/braze, or just drill an undersized hole and hammer
it together, whatever seems appropriate and available to attach the lump of
copper. Should be almost free.




Shape. Shape it like the bits you see in photographs, either with the ends
like the end of a flat screwdriver with the tip cut off, or with the ends
round with an extra lump in the middle between the ends. The cross section
area at the middle should be about 3x the area of the working ends.

The bulk of the metal holds the heat, and you want a good but not too good
thermal transfer to the working end - the bulk of the metal is too hot for
the joint, and the heat flowing down the constriction allows it to cool a
little. Possibly more importantly, the thermal constrictions also help
balance the heat flow between the ends, so that one end doesn't suck all the
heat out of the tip.

(the bulk has to be too hot, else when you touched it to the piece to be
soldered it would cool down below the right temperature. The element in the
iron cannot give out heat at the rate the heat flows out at the tip when
soldering, it heats the tip up between making joints. The tip looses heat
from convection and more importantly radiation when it is not making a
joint, but the equilibrium temperature of a fixed wattage iron when left in
air is usually far too hot, which is one reason why you want a Temperature
Controlled iron if you can afford one. Incidently, those spiral wire stands
you sometimes see are partly designed to stop the iron overheating while
switched on but not in immediate use)




Cladding. I usually iron-plate my bits so they will last longer, but I make
sub-millimetre bits with capillary traps [snipped myself, this is long
enough already]. Some people nickel plate, but I don't like to, the finish
is harder to wet with solder, and the chemicals nastier. Actual cladding is
probably beyond the home workshop, but I've never tried.

Anyway, you wouldn't need to bother cladding them - the reason for cladding
is that the solder dissolves the bit, but it would take ages to eat away a
large lump of copper. The tip will oxidise too, but again that will take a
long time to matter, just keep the ends covered in fresh solder. You can
redress it with a file without worrying about filing away the iron layer,
there isn't one , and as it's almost free you can just make a new one if
it ever burns away too much to be used.




You'll still have to buy the iron, I haven't bought one in years so I'm very
out-of-date here, but the Antex TCS, item XY45Y from Maplins at £40, is a 50
watt Temperature Controlled iron. It has the temperature control in the
handle. I haven't used the latest model, but the earlier versions are okay
to use, although the temperature control isn't terribly accurate.

A "proper" adjustable temperature TC iron, which can be controlled within a
few degrees, will have a seperate solder station with a transformer and
electronics, and a few extra wires for a thermocouple in the iron. Maplins
item BP53H is around £50, and seems a good buy. If you are going into
production I'd get a ~100w TC iron and station with fume extraction,
£150-ish.


"Gun" type irons are not suitable.


Fixed wattage irons in the 30-250 watt range are easily available, though
not through electronics retailers. I'd suggest 40 watts for joining cells.
The Weller SP40 is the best-known, around £20, and the only iron for which
hammerhead tips are actually available afaik. Cheaper 40W irons are
available for around £10, eg http://www.tooled-up.com/Product.asp?PID=4308
at £7, or http://www.tooled-up.com/Product.asp?PID=28096 at £8. And so on.

By the way, you do not want the "hammerhead" tips that stained glass people
use, they ends are not symmetrical and they are not designed for
simultaneous use of both ends (one way to identify them is that they are
usually bent slightly in the middle).



Another alternative is a butane gas powered iron, about £15; the cheap
versions are usully overpowered and get too hot anyway, adding a large tip
will cool them down to a sensible temperature. Plus you can do repairs in
the field. The tip will be harder to make though.



The cheapest solution? Use a 30 watt mains iron, available from around £2 in
a market, with a large mass tip which you make as above, and leave it a
while to get hot before and between uses. The tips for these are usually
solid copper rods which fit into the barrel, and a hammerhead tip would be
easy to make for this type of iron. A bit of practice and some patience is
needed, but you _can_ do quick joints on cells this way.



A bad "tip" (sorry...), but it might be useful - modern electronic solder is
lead-free, and a good thing too, but if you are only using it very
occasionally then fluxed 60-40 tin/lead solder will probably be a bit easier
to use when soldering cells directly, as it melts at a lower temperature,
wets slightly more easily, and stays liquid a little longer. And you will be
recycling your battery packs, won't you?


YMWV, no matter how good the theory is soldering is an art and needs
practice to get right!