Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Andy Dingley
 
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Default Using a welder for electroplating

On Wed, 16 Nov 2005 01:44:26 GMT, Ignoramus15120
wrote:

Is it possible to use a constant current DC welding machine for
electroplating or derusting?


It's not a sensible thing to do. The voltage is too high and the
overall output is enormous for any reasonable "rec.crafts" process.

Electronics is cheap these days. Do it right,
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Pete C.
 
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Default Using a welder for electroplating

Andy Dingley wrote:

On Wed, 16 Nov 2005 01:44:26 GMT, Ignoramus15120
wrote:

Is it possible to use a constant current DC welding machine for
electroplating or derusting?


It's not a sensible thing to do. The voltage is too high and the
overall output is enormous for any reasonable "rec.crafts" process.

Electronics is cheap these days. Do it right,


Good TIG welders will happily run down to 5A output. The open circuit
voltage may be ~30V, but it will be lower when under load.

Pete C.
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Andy Dingley
 
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Default Using a welder for electroplating

On Wed, 16 Nov 2005 14:56:39 GMT, Ignoramus7434
wrote:

Andy, I will check my welder for what the minimum amperage of its
output could be.


The _voltage_ will be too high. You don't have any way of reducing this
(for any welder I've seen) down to the low voltages required.

Besides which, electroplating is a foul process. If you're into the
region where you need kW of power, then it's a serious chemical waste
handling problem. For "backyard" scale work you can just lash something
up from the junk pile.

Here's a piece of electroformed copper (the underlying skeleton is
plastic) about 12" across - work by a friend of mine. Nothing more
obscure electrically than scrap-box transformers.
http://www.jarkman.co.uk/catalog/random/butterfly.htm

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Andy Dingley
 
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Default Using a welder for electroplating

On Wed, 16 Nov 2005 17:41:50 GMT, Ignoramus7434
wrote:

The constant current welder adjusts the voltage, up to a certain
amount, and down to almost zero, to produce desired current.


Plating wants a voltage of around 6-7V, with good control of current.
This isn't a "constant current" source, because if it does vary (owing
to workpiece conditions changing) then it's better if the source behaves
as a constant voltage source, once set. Current needs good manual
control though and is a crucial adjustment for plating.

Some processes want higher voltages: 12V for hard chrome, 16V+ for
anodising and some quite high voltages for anodising titanium.

I've also not seen a welder that went down to this 6V level.

If I short the leads of the welding machine, the voltage drops to
almost zero.


I'm pretty certain that it _is_ zero. The welder will detect this as a
specific case and go into a "shutdown" condition.

We live in a world full of cheap scrap electronics. I just wouldn't use
a welder for this, when I have any number of small compact 5V and 12V
high-current PSUs just looking for new homes.


Right. Right now I am mainly interested in derusting, using steel
electrodes, which is environmentally safe.


Car battery charger (old non-auto one). You only need maybe 5A tops at
12V for anything that fits in a dustbin. I've done boat hulls where I
used an old computer PSU and about 60A.
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Andy Dingley
 
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Default Using a welder for electroplating

On Thu, 17 Nov 2005 14:07:19 GMT, Ignoramus24428
wrote:

I'm pretty certain that it _is_ zero. The welder will detect this as a
specific case and go into a "shutdown" condition.


Nope. It continues to happily produce current, as evidenced by the
DC ammeter on the welder. I tried this, a dead short as well as a
short with a copper bar that had about 2 volts or so of voltage across
it.


You can't have "a copper bar" with "about 2V across it". The power
required to maintain such a voltage would be enormous.

There are no true "constant current" sources, outside of Norton and
Thevenin - when you get to the limits, something has to give.


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Pete C.
 
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Default Using a welder for electroplating

Andy Dingley wrote:

On Thu, 17 Nov 2005 14:07:19 GMT, Ignoramus24428
wrote:

I'm pretty certain that it _is_ zero. The welder will detect this as a
specific case and go into a "shutdown" condition.


Nope. It continues to happily produce current, as evidenced by the
DC ammeter on the welder. I tried this, a dead short as well as a
short with a copper bar that had about 2 volts or so of voltage across
it.


You can't have "a copper bar" with "about 2V across it". The power
required to maintain such a voltage would be enormous.

There are no true "constant current" sources, outside of Norton and
Thevenin - when you get to the limits, something has to give.


You most certainly can, it's essentially a current shunt. With a welder
happily pumping 200A+ through the bar, you will develop a voltage across
it based on it's resistance.

You've clearly never had any experience with a quality TIG welder
before.

Pete C.
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Grant Erwin
 
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Default Using a welder for electroplating

Andy Dingley wrote:

You can't have "a copper bar" with "about 2V across it". The power
required to maintain such a voltage would be enormous.


If he shorts his welder, the voltage AT THE SHORT is zero. You are correct,
Andy. However, the connections and the welding lead have nonzero resistances,
and so some current is still flowing through those resistances and generating a
small voltage back at the welder. So he is also correct.

It's easy to think of a piece of welding lead as having zero resistance, because
in many ways that's an excellent approximation. However, *nothing* has zero
resistance except maybe a piece of superconductor.

His welder is a fancy one, too, one of those TIG stick machines.

GWE
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Andy Dingley
 
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Default Using a welder for electroplating

On Thu, 17 Nov 2005 15:46:39 GMT, Ignoramus24428
wrote:

I tried this, a dead short as well as a
short with a copper bar that had about 2 volts or so of voltage across
it.


You can't have "a copper bar" with "about 2V across it". The power
required to maintain such a voltage would be enormous.


that was a 6mm by 1.6 mm by 180 cm copper bar, more properly called
copper strip.


That's more like "two yards of thin cable" rather than "a copper bar".

2m of 10mm^2 cable, and copper has a resistivity of 2e-8/m is a
resistance of about 4m ohms With 2V across it is a power of 1kW, which
is certainly practical for a welder.

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Andy Dingley
 
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Default Using a welder for electroplating

On Thu, 17 Nov 2005 16:20:37 GMT, "Pete C." wrote:

You most certainly can, it's essentially a current shunt. With a welder
happily pumping 200A+ through the bar, you will develop a voltage across
it based on it's resistance.


Of course you will. And for 200A current, that's about 8kW of power and
a voltage of 40mV (for a nominal "copper bar" shorting link of
0.0002ohms). To develop 2V across this sort of resistance needs 10kA,
not 200A - just how powerful a welder are we talking about here?.

You just can't get 2V across a "copper bar" - it would melt almost
instantly.

You've clearly never had any experience with a quality TIG welder
before.


Nope, my experience is all with Ohm's law.
Good on electrons, bad on bogons.

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Pete C.
 
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Default Using a welder for electroplating

Andy Dingley wrote:

On Thu, 17 Nov 2005 16:20:37 GMT, "Pete C." wrote:

You most certainly can, it's essentially a current shunt. With a welder
happily pumping 200A+ through the bar, you will develop a voltage across
it based on it's resistance.


Of course you will. And for 200A current, that's about 8kW of power and
a voltage of 40mV (for a nominal "copper bar" shorting link of
0.0002ohms). To develop 2V across this sort of resistance needs 10kA,
not 200A - just how powerful a welder are we talking about here?.

You just can't get 2V across a "copper bar" - it would melt almost
instantly.

You've clearly never had any experience with a quality TIG welder
before.


Nope, my experience is all with Ohm's law.
Good on electrons, bad on bogons.


If he's going by the volt meter on the welder it most likely represents
the voltage across not only the copper bar, but also the welding leads.

Pete C.


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Andy Dingley
 
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Default Using a welder for electroplating

On Thu, 17 Nov 2005 21:22:55 +0000, Andy Dingley
wrote:

You just can't get 2V across a "copper bar" - it would melt almost
instantly.


Sorry, this is annoying me.

You just can't get 2V across any short length of copper, of any
thickness - it would melt almost instantly.


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S G S G is offline
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Default Using a welder for electroplating

replying to Andy Dingley, S G wrote:
for a car body like a mustang use 6v 1000amp for 2 hours , start the solution
off hot, ue carbon/graphite blocks to avoid making sludge

--
for full context, visit https://www.polytechforum.com/metalw...ng-453044-.htm


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external usenet poster
 
Posts: 5,888
Default Using a welder for electroplating

"S G" wrote in
message
oupdirect.com...
replying to Andy Dingley, S G wrote:
for a car body like a mustang use 6v 1000amp for 2 hours , start the
solution
off hot, ue carbon/graphite blocks to avoid making sludge

--
for full context, visit
https://www.polytechforum.com/metalw...ng-453044-.htm


Load vs temperature rise testing of the variable power supply I built
from a 50A, 20% duty cycle arc welder transformer and a variac showed
that the output current should be limited to around 20A continuous or
25A for 1/2 hour. This corresponds to a derating to 20% of the squares
of the currents, ideally 22.36A.

P = I^2 * R, where R is the copper winding resistance.



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Default Using a welder for electroplating

"Jim Wilkins" wrote in message
...
...
....variable power supply I built from a 50A, 20% duty cycle arc
welder transformer and a variac ...


Arc welding transformers have a fairly high internal impedance to
cheaply provide high no-load voltage to start the arc and current
limiting when welding, especially when the electrode sticks. The
tradeoff is low efficiency. This means that the voltage drops
significantly as load current increases, and conversely the voltage
rises if the load's current demand decreases, as when a battery nears
full charge.

This voltage and current regulator is a good match to the 50A
transformer:
https://lygte-info.dk/review/Power%2...-USB%20UK.html

The rectified transformer output is almost useless and high enough to
be considered dangerous without either the variac or DPS5020 to
control the voltage.
https://www.osha.gov/laws-regs/stand...ons/2015-09-04
"OSHA considers all voltages of 50 volts or above to be hazardous."



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