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'[EE]: Battery Spot welding...'
2004\10\19@093853 by Gary Neal

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Guys,

Got an application where we're looking into making up a bunch of battery
packs.  Does anyone have a good source or experience with any spot welders
specifically for welding battery tabs?  I can find them for like $12k-14k,
but I can't quite justify that.  Need something ~$5k-$8k range.

Any help or knowledge would be appreciated.

Gary

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2004\10\19@162250 by Eisermann, Phil [Ridg/CO]

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piclist-bounces@mit.edu wrote:
> Guys,
>
> Got an application where we're looking into making up a bunch of
> battery packs.  Does anyone have a good source or experience with any
> spot welders specifically for welding battery tabs?  I can find them
> for like $12k-14k, but I can't quite justify that.  Need something
> ~$5k-$8k range.

a recomendation from a co-worker is http://www.hobbyspotwelders.com/

It has an attachment specifically for battery tab welding. The
power supply plus attachment is like $400
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2004\10\20@082252 by John J. McDonough

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If your run isn't too big, you might consider outsourcing it.  A lot of
folks, even DigiKey, will make up custom battery packs.

72/73 de WB8RCR    http://www.qsl.net/wb8rcr
didileydadidah     QRP-L #1446 Code Warriors #35

{Original Message removed}

2004\10\20@085327 by Lawrence Lile

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That is really interesting.

http://www.hobbyspotwelders.com/HS300A2.php

The welder controller, which apparently is a DC spot welder, is a curious object.  In a conventional spot welder, you have a big transformer, and the spot weld is controlled by time.  The longer the time, the hotter the weld, and the more metal it will go through.  In this one, apparently, you control the voltage on a capacitor instead.  Nice 24V isolated input from a cheap wall wart.

This would not be so hard to build.  It is basically a power supply with a controlled charging time, and a large, low ESR, high current capability capacitor with a high current switched output.  The $325 clams they charge for it sounds pretty steep compared to what it is.  PIC?

It is AMAZING what you can do with a spot welder, a notcher, and a press brake.  Boxes, standoffs, mounting brackets, all this stuff becomes a piece of cake.  

-- Lawrence Lile, P.E.
Electrical and Electronic Solutions
Project Solutions Companies
http://www.projsolco.com
573-443-7100 ext 221

> {Original Message removed}

2004\10\20@092350 by hael Rigby-Jones

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>-----Original Message-----
>From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu]
>On Behalf Of Lawrence Lile
>Sent: 20 October 2004 13:49
>To: Microcontroller discussion list - Public.
>Subject: RE: [EE]: Battery Spot welding...
>
>
>That is really interesting.
>
>http://www.hobbyspotwelders.com/HS300A2.php
>

I'd be dissapointed to have made something that badly for my own use, let
alone to sell on a comercial basis!.  Just look at the grid of holes drilled
for ventilation!

680,000uF is a fair bit though, I guess they are using an SCR to fire the
capacitor bank.

Mike

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2004\10\20@092736 by Mike Hord

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So am I then to understand that spot welding, in its simplest form,
simply involves two electrodes on a metal object?  Say, a ground
clamp in one corner of the sheet metal and a "wand" with which
the desired spot weld points are tapped and PING! the metal is
miraculously* joined?

That sounds like it would be ridiculously easy to fabricate at home,
but I suppose Lawrence already said that below...

Mike H.

*for those who don't understand electricity, anyway...

> That is really interesting.
>
> http://www.hobbyspotwelders.com/HS300A2.php
>
> The welder controller, which apparently is a DC spot welder, is a curious object.  In a conventional spot welder, you have a big transformer, and the spot weld is controlled by time.  The longer the time, the hotter the weld, and the more metal it will go through.  In this one, apparently, you control the voltage on a capacitor instead.  Nice 24V isolated input from a cheap wall wart.
>
> This would not be so hard to build.  It is basically a power supply with a controlled charging time, and a large, low ESR, high current capability capacitor with a high current switched output.  The $325 clams they charge for it sounds pretty steep compared to what it is.  PIC?
>
> It is AMAZING what you can do with a spot welder, a notcher, and a press brake.  Boxes, standoffs, mounting brackets, all this stuff becomes a piece of cake.
____________________________________________

2004\10\20@100841 by hael Rigby-Jones

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>-----Original Message-----
>From: piclist-bouncesspamKILLspammit.edu [.....piclist-bouncesKILLspamspam.....mit.edu]
>On Behalf Of Mike Hord
>Sent: 20 October 2004 14:28
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE]: Battery Spot welding...
>
>
>So am I then to understand that spot welding, in its simplest
>form, simply involves two electrodes on a metal object?  Say,
>a ground clamp in one corner of the sheet metal and a "wand"
>with which the desired spot weld points are tapped and PING!
>the metal is
>miraculously* joined?
>
>That sounds like it would be ridiculously easy to fabricate at
>home, but I suppose Lawrence already said that below...
>
>Mike H.

Not quite. The two metal sheets to be joined are tightly clamped between two
electrodes and a high current passed through.  The junction between the two
steel sheets exhibits the highest resistance, and hence generates the most
heat, melting the metal and the pressure applied via the electrodes ensures
the two sheets fuse together.  The electrodes typical have a very small
surface area on the clamping faces, giving the high current density required
to melt the metal.

Regards

Mike

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____________________________________________

2004\10\20@102929 by Bob Axtell

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Keep in mind that nickel tabs have a high resistance, so the whole
process is somewhat "tuned". This product might not work well with
other tab thicknesses, for example.

They charge $320 to get back the awesome amount of time they spent
tinkering with it to make it work right.

--Bob

Michael Rigby-Jones wrote:

>>{Original Message removed}

2004\10\20@104124 by Martin McCormick

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       How do you know besides the obvious fact that the spot weld
didn't come apart after a tug that you've got a good weld?

       I remember as a teen-ager, being in the orthodontist's office
one day in 1967 or so when the doctor was using the spot welder to
affix a bracket to a brace band.  Normally, one heard the hum of the
transformer briefly when he turned it on to make the weld.  This time,
I heard a loud snap and asked why did it do that?  He said, "oh,
probably a dirty band."  I understood enough about electricity at that
time to appreciate what he meant, but I wondered if that momentary
break in the circuit or at least that increase in resistance didn't
effect the quality of the weld.

       I seemed to remember he would give it several brief bursts of
current.  The bands went around a tooth and the brackets were little
tracks for the wire so they weren't very large but I don't remember
any of them failing so the process must have been fairly reliable in
skilled hands.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Information Technology Division Network Operations Group
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2004\10\20@120717 by John Ferrell

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In a Lab environment, nearly 50 years ago... we used a similar contraption
to weld thermocouples to test specimens. We charged a fat capacitor charged
to whatever the line voltage was and used a knife switch to fire the weld.
Everything came out of the junk box & it worked for our experiments.

John Ferrell
http://DixieNC.US

{Original Message removed}

2004\10\20@155001 by Lawrence Lile

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We made homemade thermocouple welders in another similar way:

60 watt light bulb in series with the AC line
Clamp the end of an unwelded thermocouple pair in an alligator clip

Twist the other end together, and stick it into a grounded steel cup full of powdered graphite.  BXZZZT!  

We had a welding glass clamped onto the affair so you could watch the weld without burning out your eyeballs.  

When I showed up in the lab I insisted that isolation transformers be put in front of these killers.  I also replaced the welding glass for the first time in 25 years, and insisted people look through it and not just squint at the weld.....


-- Lawrence Lile, P.E.
Electrical and Electronic Solutions
Project Solutions Companies
http://www.projsolco.com

> {Original Message removed}

2004\10\21@101620 by Peter L. Peres

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On Wed, 20 Oct 2004, Mike Hord wrote:

> So am I then to understand that spot welding, in its simplest form,
> simply involves two electrodes on a metal object?  Say, a ground
> clamp in one corner of the sheet metal and a "wand" with which
> the desired spot weld points are tapped and PING! the metal is
> miraculously* joined?
>
> That sounds like it would be ridiculously easy to fabricate at home,
> but I suppose Lawrence already said that below...

Actually it's fairly hard. The point is to get a resistance that is *just*
right between the pieces to be joined so that your power supply dissipates
its power there and not somewhere else at least until the facing work
pieces are red hot (by which time the heat increases their resistance and
they start being willing to dissipate most of the power sent into the
circuit as more heat). Actually achieving this is hard. For battery
welding it is even harder because the battery contacts offer very little
contact surface to make a low R contact on with the counter-electrode.
Circuit resistances of 1-10 milliohms are usual, with up to 5V voltage for
spot welding (means 500A - 5000A or more). Capacitor impulse welding
requires that this current be switched nearly instantly, in addition to
the above. 160,000 uF is a bit large imho, I had success using ~40J for
capacitive impulse welding of tabs 0.4mm thick, which requires about
100,000 uF and 25V. Additionally, using the right amount of force on the
contacts is essential.

Peter
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2004\10\21@131450 by John Ferrell

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I think you have to make enough of them to determine the failure rate and
assess the cost of failures.

John Ferrell
http://DixieNC.US

{Original Message removed}

2004\10\21@161337 by M. Adam Davis

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A simple spot welder using a car battery charger/starter is detailed here:
http://www.nmia.com/~vrbass/models/solderer.pdf

They call it a resistance solderer.

-Adam

Mike Hord wrote:

{Quote hidden}

>_____________________________________________

2004\10\22@042043 by Alan B. Pearce

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>A simple spot welder using ...
>
>They call it a resistance solderer.

Resistance soldering is different to spot welding. With spot welding the
current melts the original metal to make the joint. With resistance
soldering you still apply external solder, and it does not (intentionally)
melt the original metal. Resistance soldering is used a lot in model making
using etched brass as the items to be joined.

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