Prev: Voltage Regulator 041M03
Next: Benq FP737S LCD monitor backlight - won't go off (longish).
From: Jeff Liebermann on 14 Dec 2009 12:58
On Sun, 13 Dec 2009 17:31:36 -0700, D Yuniskis
<not.going.to.be(a)seen.com> wrote:

>Replacing rechargeable battery packs in consumer kit
>is a bane I suspect most of us share. You can't
>"solder" to individual cells.

Yes, you can if you work fast, prepare the surface, use a very big and
hot iron, and keep the pack cool (water dunking). I've done it with
reasonable success with NiCd and NiMH packs. Total failure with LiIon
which really don't like the heat.

Plan B is a do-it-thyself spot welder:
<http://www.hobbyspotwelders.com/HSBATTERYPEN.php>
Hmmm... broken web site. Anyway, it's just a big fat capacitor and
two electrodes. The trick is to not weld the electrodes to the
battery or terminals. I use TIG welding electrodes but stainless
nails will also work. Plenty of plans on YouTube and Google videos:
<http://video.google.com/videosearch?hl=en&source=hp&q=battery+spot+welder#>
<http://www.youtube.com/results?search_query=battery spot welder>


--
Jeff Liebermann jeffl(a)cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
From: isw on 15 Dec 2009 00:24
In article <50c97a937bdave(a)davenoise.co.uk>,
"Dave Plowman (News)" <dave(a)davenoise.co.uk> wrote:

> In article <isw-09B9A0.20565613122009@[216.168.3.50]>,
> isw <isw(a)witzend.com> wrote:
> > In article <hg40gr$sba$1(a)aioe.org>,
> > D Yuniskis <not.going.to.be(a)seen.com> wrote:
>
> > > Hi,
> > >
> > > Replacing rechargeable battery packs in consumer kit
> > > is a bane I suspect most of us share. You can't
> > > "solder" to individual cells.
>
> > You can do it easily, IF you use the proper solder and flux. Look for
> > something that can solder stainless steel.
>
> Ordinary solder works just fine. It's overheating the cell that's the
> problem.

Yup. And having a better flux allows the joint to be made very rapidly.

ISaac
From: Bob Larter on 15 Dec 2009 01:20
On 14/12/2009 11:36 AM, Dave Plowman (News) wrote:
> In article<hg40gr$sba$1(a)aioe.org>,
> D Yuniskis<not.going.to.be(a)seen.com> wrote:
>> Replacing rechargeable battery packs in consumer kit
>> is a bane I suspect most of us share. You can't
>> "solder" to individual cells. And, you usually can't
>> slip a battery holder in place to make the connections
>> for you.
>
>> Sure, you can buy premade packs in a wide variety of
>> configurations. But, these often come at a premium
>> in price (to pay for the added labor of their fabrication)
>> *and* you can't just pick them up "off the shelf"
>> (well, *some* configurations are available like this
>> but not "in general").
>
>> Has anyone come up with a clever way around this problem?
>> Is there a poor man's approach to welding tabs onto
>> batteries? Or, some other conductive fastener that
>> doesn't put the cell at risk in the process?
>
> You can buy most cell sizes with tags already welded on - so you can then
> solder them together. From most decent electronics suppliers.

Exactly. And they'll probably be significantly cheaper than from a retailer.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
From: Bob Larter on 15 Dec 2009 01:23
On 14/12/2009 3:56 PM, isw wrote:
> In article<hg40gr$sba$1(a)aioe.org>,
> D Yuniskis<not.going.to.be(a)seen.com> wrote:
>
>> Hi,
>>
>> Replacing rechargeable battery packs in consumer kit
>> is a bane I suspect most of us share. You can't
>> "solder" to individual cells.
>
> You can do it easily, IF you use the proper solder and flux. Look for
> something that can solder stainless steel.

IME, standard cells take regular solder easily, if you file off the
plating. You need to use a real soldering iron (ie; a station) & work
fast though.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
From: mike on 27 Dec 2009 02:01
D Yuniskis wrote:
> Hi,
>
> Replacing rechargeable battery packs in consumer kit
> is a bane I suspect most of us share. You can't
> "solder" to individual cells. And, you usually can't
> slip a battery holder in place to make the connections
> for you.
>
> Sure, you can buy premade packs in a wide variety of
> configurations. But, these often come at a premium
> in price (to pay for the added labor of their fabrication)
> *and* you can't just pick them up "off the shelf"
> (well, *some* configurations are available like this
> but not "in general").
>
> Has anyone come up with a clever way around this problem?
> Is there a poor man's approach to welding tabs onto
> batteries? Or, some other conductive fastener that
> doesn't put the cell at risk in the process?

I fiddled with this for a decade or so and have some thoughts.

What you want is constant energy into a constant area
of a repeatable material.

Low Voltage Spot Welder

You can replace the secondary of a microwave oven
transformer with two turns of the biggest wire that will fit
the core...don't forget to take out the magnetic shunts.

Couple of issues...you have to build some logic to turn the
transformer on AND OFF at zero crossings of the mains.
You can't just leave the transformer stuck at one corner
of the B-H curve, or you'll eventually be digging bits
of your Solid-state relay out of the ceiling when the
core saturates. The residual magnetism also makes a bad
repeatability problem worse.

This is not an energy welder. The amount of current you
get is critically dependent on the total resistance in the
secondary circuit. The amount of heat depends on the current
and voltage at the weld junction. With careful control of
electrode position and pressure, I was able to get about
50% pretty-good welds. But the other 50% ranged from
no weld at all to blasting the tab completely away.

I never addressed the long-term effects of six cycles of
40-amps on a 15-amp 120VAC primary circuit.

I discovered that .005" brass that you get at the hobby
store is much easier to weld than nickel. I never
examined the electrochemical issues of brass. Resistance
is higher, so probably not viable for high-current applications.

If you're gonna experiment, a good current probe and digital
storage scope are essential. I had been messing with this thing
for months. When a digital storage scope fell into my lap,
I had significant improvement in a matter of hours. There's
no substitute for knowing what's going on.

I was experimenting with ways to stabilize the weld
when a $15 CD spot welder fell into my lap.

A CD welder is discharging the total energy stored in a cap
into the weld. Since the open-circuit voltage is higher,
the resistance of the weld junction is less critical.
Most of the energy gets dumped thru a transformer into the
weld over a wider range of contact resistance. And the leakage
inductance of the transformer softens the initial transient.
Good-weld percentage went way, way up.

Some have suggested you can discharge a cap without a transformer.
My experiments quickly dismissed that possibility. If you can
get repeatable contact resistance, you still need a switch.
Closest I came to a switch was a pair of spring-loaded nails
that blew itself up on every weld...but nails are cheap.
And you need a LOT of caps in parallel on huge copper strap
to get the peak current. My CD welder puts out 7000 AMPS.
If you could reliably get 10A from each cap, that's a lot
of caps in parallel.

A car battery will weld like gangbusters, if you could figure
how to control it accurately.

About the time I figured out how to weld tabs, reality hit.
You can replace the cells in a laptop computer pack, but you
can't make it work. Many either lose their brains completely
when discharged or remember that the cells were dead.
Symptoms range from "still dead in the computer" to
"still has the capacity of the old dead cells." Had one pack with
a pic processor inside that I could look up. Resetting the pic
reinitialized the battery, but that's rare.

Have a heavy metal can with a heavy lid
available for the times when you accidentally create an internal
short in a lithium battery. An old pressure cooker works well.

Wear safety glasses. Hot bits of nickel are not compatible with
clear vision.
I still have nightmares about the time a NiCd blew up in my face
and splattered hot electrolyte all over my glasses.

Are we having fun yet?
mike
First  |  Prev  | 
Pages: 1 2 3
Prev: Voltage Regulator 041M03
Next: Benq FP737S LCD monitor backlight - won't go off (longish).