I was on the verge of building a capacitive-discharge spot welder to join a
mess of NiCad batteries for cordless tools.

Then I got to wondering. And wondering. Whether a 90-amp MIG welder would
substitute? Seems like 0.030" wire is pretty close to a spot weld...

Anyone ever try this or something similar?

I guess I could experiment, but preliminary cautions and advice would be
appreciated.

Thanks.

On 3/20/2013 6:35 AM, HeyBub wrote:
I was on the verge of building a capacitive-discharge spot welder to join a
mess of NiCad batteries for cordless tools.

Then I got to wondering. And wondering. Whether a 90-amp MIG welder would
substitute? Seems like 0.030" wire is pretty close to a spot weld...

Anyone ever try this or something similar?

I guess I could experiment, but preliminary cautions and advice would be
appreciated.

Thanks.


Capacitive-discharge gives you a limited and controlled energy to the
weld. How are you going to do that with MIG? Maybe put a 5A fuse in the
welding lead to control the time?

My understanding is that the reason why battery rebuilding shops use spot welders is that a spot weld spark will deliver an intense amount of energy to a small area for an extremely short period of time. The amount of steel that gets melted together to make the connection is tiny, and so the total amount of heat the battery cells are exposed to is small, and not enough to harm them.

Were it not for that unique way in which spot welders can connect steel strapping to the battery cells, then anyone and everyone could rebuild cordless tool battery packs by soldering copper wires to the ends of the battery cells. But, that's not done because of the much greater amount of time involved. As a result of that slower process, the battery cells get exposed to very much more heat, and by the time you get the metal ends of the battery cell hot enough for the solder to melt onto them, you've already wrecked the cell.

Or, at least, that's my understanding. Why not phone any place that rebuilds cordless tool battery packs and get their opinion on whether or not a MIG welder would work?

bud-- wrote:
On 3/20/2013 6:35 AM, HeyBub wrote:
I was on the verge of building a capacitive-discharge spot welder to
join a mess of NiCad batteries for cordless tools.

Then I got to wondering. And wondering. Whether a 90-amp MIG welder
would substitute? Seems like 0.030" wire is pretty close to a spot
weld... Anyone ever try this or something similar?

I guess I could experiment, but preliminary cautions and advice
would be appreciated.

Thanks.


Capacitive-discharge gives you a limited and controlled energy to the
weld. How are you going to do that with MIG? Maybe put a 5A fuse in
the welding lead to control the time?

I guess I'll stop the weld when it seems done.

I don't think a 5A fuse would hold up long against a 90A current...

On Wed, 20 Mar 2013 11:38:06 -0500, "HeyBub"
wrote:


I guess I'll stop the weld when it seems done.

I dunno. With to much heat there is risk of damaging the battery cell?

The spot welder is a better choice -- I think. I have a link to build
one from a (free) 1500W Microwave. I can post them.

Oren wrote:
On Wed, 20 Mar 2013 11:38:06 -0500, "HeyBub"
wrote:


I guess I'll stop the weld when it seems done.

I dunno. With to much heat there is risk of damaging the battery cell?

The spot welder is a better choice -- I think. I have a link to build
one from a (free) 1500W Microwave. I can post them.

No need. There must be 100 plans on the net.

The simplest seems to be the capacitive-discharge model. You charge up one
or more capacitors whose combined capacity is in the neighborhood of 1 Farad
(with a 12-24V battery charger) and discharge the pack through the substance
to be welded.

There's more to it, of course. The switch is a Thyistron that can handle
2400Amps, and it, in turn is driven by a 12v wall-wart and a doorbell
switch. The electrodes are copper rods, and so on. Parts, however, should be
less than $100.

On Mar 20, 6:33*pm, "HeyBub" wrote:
Oren wrote:
On Wed, 20 Mar 2013 11:38:06 -0500, "HeyBub"
wrote:

I guess I'll stop the weld when it seems done.

I dunno. With to much heat there is risk of damaging the battery cell?

The spot welder is a better choice -- I think. I have a link to build
one from a (free) 1500W Microwave. I can post them.

No need. There must be 100 plans on the net.

The simplest seems to be the capacitive-discharge model. You charge up one
or more capacitors whose combined capacity is in the neighborhood of 1 Farad
(with a 12-24V battery charger) and discharge the pack through the substance
to be welded.

There's more to it, of course. The switch is a Thyistron that can handle
2400Amps, and it, in turn is driven by a 12v wall-wart and a doorbell
switch. The electrodes are copper rods, and so on. Parts, however, should be
less than $100.

I have a friend who welds with 2 car batteries in series. Affordable,
works great, and requires no real equiptement other than 2 or 3 car
batteries, some connecting wires and clamps and welding rods

bob haller wrote:
On Mar 20, 6:33 pm, "HeyBub" wrote:
Oren wrote:
On Wed, 20 Mar 2013 11:38:06 -0500, "HeyBub"
wrote:

I guess I'll stop the weld when it seems done.

I dunno. With to much heat there is risk of damaging the battery
cell?

The spot welder is a better choice -- I think. I have a link to
build one from a (free) 1500W Microwave. I can post them.

No need. There must be 100 plans on the net.

The simplest seems to be the capacitive-discharge model. You charge
up one or more capacitors whose combined capacity is in the
neighborhood of 1 Farad (with a 12-24V battery charger) and
discharge the pack through the substance to be welded.

There's more to it, of course. The switch is a Thyistron that can
handle 2400Amps, and it, in turn is driven by a 12v wall-wart and a
doorbell switch. The electrodes are copper rods, and so on. Parts,
however, should be less than $100.

I have a friend who welds with 2 car batteries in series. Affordable,
works great, and requires no real equiptement other than 2 or 3 car
batteries, some connecting wires and clamps and welding rods

When a teen, I welded using 3 old car batteries, and it worked pretty well. It
would not work well with 2.

On 3/20/2013 10:38 AM, HeyBub wrote:
bud-- wrote:
On 3/20/2013 6:35 AM, HeyBub wrote:
I was on the verge of building a capacitive-discharge spot welder to
join a mess of NiCad batteries for cordless tools.

Then I got to wondering. And wondering. Whether a 90-amp MIG welder
would substitute? Seems like 0.030" wire is pretty close to a spot
weld... Anyone ever try this or something similar?

I guess I could experiment, but preliminary cautions and advice
would be appreciated.

Thanks.


Capacitive-discharge gives you a limited and controlled energy to the
weld. How are you going to do that with MIG? Maybe put a 5A fuse in
the welding lead to control the time?

I guess I'll stop the weld when it seems done.

Lots of luck doing that welding on a NiCd.


I don't think a 5A fuse would hold up long against a 90A current...


That is the point. The 5A fuse can pass a much larger current but will
open fast to limit the energy at the weld. It is a kludge to make a spot
welder.

bud-- wrote:

Capacitive-discharge gives you a limited and controlled energy to
the weld. How are you going to do that with MIG? Maybe put a 5A
fuse in the welding lead to control the time?

I guess I'll stop the weld when it seems done.

Lots of luck doing that welding on a NiCd.

??? What's the problem. The terminal on the battery is, I think, nickle. Why
would there be any unusual difficulty?



I don't think a 5A fuse would hold up long against a 90A current...


That is the point. The 5A fuse can pass a much larger current but will
open fast to limit the energy at the weld. It is a kludge to make a
spot welder.

Ah! I see. How about a 5A circuit breaker? Surely something dramatic would
happen when it sees 2,000A.

On 3/21/2013 1:09 PM, HeyBub wrote:
bud-- wrote:

Capacitive-discharge gives you a limited and controlled energy to
the weld. How are you going to do that with MIG? Maybe put a 5A
fuse in the welding lead to control the time?

I guess I'll stop the weld when it seems done.

Lots of luck doing that welding on a NiCd.

??? What's the problem. The terminal on the battery is, I think, nickle. Why
would there be any unusual difficulty?

Send a picture of your weld with a 90A MIG welder on a NiCd. Or better,
a video.




I don't think a 5A fuse would hold up long against a 90A current...


That is the point. The 5A fuse can pass a much larger current but will
open fast to limit the energy at the weld. It is a kludge to make a
spot welder.

Ah! I see. How about a 5A circuit breaker? Surely something dramatic would
happen when it sees 2,000A.


2,000A from a 90A welder?
And when using fuses (and circuit breakers) their "fault current" rating
should be appropriate to the circuit they are used on.

bud-- wrote:
On 3/21/2013 1:09 PM, HeyBub wrote:
bud-- wrote:

Capacitive-discharge gives you a limited and controlled energy to
the weld. How are you going to do that with MIG? Maybe put a 5A
fuse in the welding lead to control the time?

I guess I'll stop the weld when it seems done.

Lots of luck doing that welding on a NiCd.

??? What's the problem. The terminal on the battery is, I think,
nickle. Why would there be any unusual difficulty?

Send a picture of your weld with a 90A MIG welder on a NiCd. Or
better, a video.


Good idea. I will.


Ah! I see. How about a 5A circuit breaker? Surely something dramatic
would happen when it sees 2,000A.


2,000A from a 90A welder?

90A x 120V = 10,800 (momentary) Watts

10,800W / 5V = 2,160 (momentary) Amps

It could happen.

On 3/22/2013 4:21 PM, HeyBub wrote:
bud-- wrote:
On 3/21/2013 1:09 PM, HeyBub wrote:
bud-- wrote:

Capacitive-discharge gives you a limited and controlled energy to
the weld. How are you going to do that with MIG? Maybe put a 5A
fuse in the welding lead to control the time?

I guess I'll stop the weld when it seems done.

Lots of luck doing that welding on a NiCd.

??? What's the problem. The terminal on the battery is, I think,
nickle. Why would there be any unusual difficulty?

Send a picture of your weld with a 90A MIG welder on a NiCd. Or
better, a video.


Good idea. I will.


Ah! I see. How about a 5A circuit breaker? Surely something dramatic
would happen when it sees 2,000A.


2,000A from a 90A welder?

90A x 120V = 10,800 (momentary) Watts

10,800W / 5V = 2,160 (momentary) Amps

It could happen.


90A is the secondary side amps.