Transformer for arc welding

B

Bob Masta

Guest
I've been thinking of buying one of those cheap
(~$100) 120 VAC "stick" arc welders for a
particular project: Welding an angle-iron frame
to hold a larger version of my experimental
electric kiln.

(No, I don't need or want a big 240V model, and
the low duty cycle of a cheapie is no problem at
all for my purposes.)

But then I had a "duh!" moment: The monster 120
VAC transformer (easily over 100 lbs) for the kiln
is far more capable than that of any cheap welder,
or anything I could rig from microwave oven
transformers (MOTs). It has massive switches for
coarse and fine output voltage control from 33 to
over 100 V and can put out a solid 25A
continuously for hours. (Originally, this was an
industrial furnace for melting test specimens,
etc. Uses silicon carbide heating elements.)

The secondary windings (at least the leads coming
from it) are better than 8 gage... maybe 7 or even
6. (The overall leads are 0.250 with insulation,
and I'm only peeking at the stranded conductors
where they connect to the switches.)

So I'm quite sure this could handle the larger
currents needed for welding, with some duty cycle
constraints. The problem is, it doesn't have the
current-limiting due to puny primary windings that
a commerical cheapie welder (or MOT homebrew)
would have. I imagine that I'd pop the mains
breaker a lot, meaning a trip to the basement each
time.

Anyone have any suggestions for a simple current
regulator / limiter? I found one MOT design that
used a choke in series with the primary to
"soften" things. I have a MOT, and plenty of old
junk box chokes and transformers, that I could use
for the choke. Any selection advice?

Is that the best way to go? I don't think I need
anything fancy, since this is pretty much a
one-off job, with maybe further "improvements" to
the kiln design at a later date.

Thanks, and best regards,


Bob Masta

DAQARTA v5.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
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"Bob Masta" <N0Spam@daqarta.com> wrote in message
news:4b473038.501975@news.eternal-september.org...
I've been thinking of buying one of those cheap
(~$100) 120 VAC "stick" arc welders for a
particular project: Welding an angle-iron frame
to hold a larger version of my experimental
electric kiln.

(No, I don't need or want a big 240V model, and
the low duty cycle of a cheapie is no problem at
all for my purposes.)

But then I had a "duh!" moment: The monster 120
VAC transformer (easily over 100 lbs) for the kiln
is far more capable than that of any cheap welder,
or anything I could rig from microwave oven
transformers (MOTs). It has massive switches for
coarse and fine output voltage control from 33 to
over 100 V and can put out a solid 25A
continuously for hours. (Originally, this was an
industrial furnace for melting test specimens,
etc. Uses silicon carbide heating elements.)

The secondary windings (at least the leads coming
from it) are better than 8 gage... maybe 7 or even
6. (The overall leads are 0.250 with insulation,
and I'm only peeking at the stranded conductors
where they connect to the switches.)

So I'm quite sure this could handle the larger
currents needed for welding, with some duty cycle
constraints. The problem is, it doesn't have the
current-limiting due to puny primary windings that
a commerical cheapie welder (or MOT homebrew)
would have. I imagine that I'd pop the mains
breaker a lot, meaning a trip to the basement each
time.

Anyone have any suggestions for a simple current
regulator / limiter? I found one MOT design that
used a choke in series with the primary to
"soften" things. I have a MOT, and plenty of old
junk box chokes and transformers, that I could use
for the choke. Any selection advice?

Is that the best way to go? I don't think I need
anything fancy, since this is pretty much a
one-off job, with maybe further "improvements" to
the kiln design at a later date.

Thanks, and best regards,


Bob Masta

DAQARTA v5.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!
Click to expand...
Twentyfive Amps is insufficient for welding. You need from about 50 amps to
200 amps or so depending on the heat requirements for the gauge you are
welding.

Six or eight ga. wire on the secondary? That's not consistent with 25 amps
which would only require 10 ga.

If the transformer is designed to drive silicon carbide elements, it should
have some form of current control or be a constant current trasformer.

2500 Watt, 100lb transformer for operation on 120VAC? Something doesn't add
up. We need actual specs to answer your question.
 
On Fri, 8 Jan 2010 07:35:15 -0800, "Bob Eld"
<nsmontassoc@yahoo.com> wrote:

Twentyfive Amps is insufficient for welding. You need from about 50 amps to
200 amps or so depending on the heat requirements for the gauge you are
welding.

Six or eight ga. wire on the secondary? That's not consistent with 25 amps
which would only require 10 ga.
Click to expand...
I think the OP was saying that 25A "continuous" works well.
But I think the OP also wrote that this was an "industrial
furnace for melting test specimens," which may have supported
discontinuous currents that were higher. At least, I can
tentatively accept the idea.

If the transformer is designed to drive silicon carbide elements, it should
have some form of current control or be a constant current trasformer.

2500 Watt, 100lb transformer for operation on 120VAC? Something doesn't add
up. We need actual specs to answer your question.
Click to expand...
If the peak current it supports is more than 25A, the
transformer rating might be higher. I don't know, so it's
good to ask.

But here's a 10kW transformer that weighs 130 lbs:

http://www.voltageconverters.com/itemdesc.asp?ic=MS10G8

To provide some kind of very rough weight vs watt benchmark.

Jon
 
"Jon Kirwan" <jonk@infinitefactors.org> wrote in message
news:c4lek5lo97unsndl47n9q4te62aeuecfl3@4ax.com...
On Fri, 8 Jan 2010 07:35:15 -0800, "Bob Eld"
nsmontassoc@yahoo.com> wrote:

Twentyfive Amps is insufficient for welding. You need from about 50 amps
to
200 amps or so depending on the heat requirements for the gauge you are
welding.

Six or eight ga. wire on the secondary? That's not consistent with 25
amps
which would only require 10 ga.

I think the OP was saying that 25A "continuous" works well.
But I think the OP also wrote that this was an "industrial
furnace for melting test specimens," which may have supported
discontinuous currents that were higher. At least, I can
tentatively accept the idea.
Click to expand...
Agreed, but how much of a current overload is reasonable, 4 times? for 100
Amps out or something similar? Secondly where does the power come from? 120
VAC input is already over taxed. I can't imagine that one would expect to
get 80 Amps out of a 120 Volt wall socket on a 20 Amp breaker. In other
words this transformer sounds like a missmatch for welding. Too much
voltage, not enough current.

If the transformer is designed to drive silicon carbide elements, it
should
have some form of current control or be a constant current trasformer.

2500 Watt, 100lb transformer for operation on 120VAC? Something doesn't
add
up. We need actual specs to answer your question.

If the peak current it supports is more than 25A, the
transformer rating might be higher. I don't know, so it's
good to ask.

But here's a 10kW transformer that weighs 130 lbs:
Click to expand...
10 kW, 130lbs sounds about right. Then shouldn't this 2500 Watt unit be
about 33lbs?

http://www.voltageconverters.com/itemdesc.asp?ic=MS10G8

To provide some kind of very rough weight vs watt benchmark.

Jon
Click to expand...
 
On Fri, 8 Jan 2010 09:41:04 -0800, "Bob Eld"
<nsmontassoc@yahoo.com> wrote:

"Jon Kirwan" <jonk@infinitefactors.org> wrote in message
news:c4lek5lo97unsndl47n9q4te62aeuecfl3@4ax.com...
On Fri, 8 Jan 2010 07:35:15 -0800, "Bob Eld"
nsmontassoc@yahoo.com> wrote:

Twentyfive Amps is insufficient for welding. You need from about 50 amps
to
200 amps or so depending on the heat requirements for the gauge you are
welding.

Six or eight ga. wire on the secondary? That's not consistent with 25
amps
which would only require 10 ga.

I think the OP was saying that 25A "continuous" works well.
But I think the OP also wrote that this was an "industrial
furnace for melting test specimens," which may have supported
discontinuous currents that were higher. At least, I can
tentatively accept the idea.

Agreed, but how much of a current overload is reasonable, 4 times? for 100
Amps out or something similar? Secondly where does the power come from? 120
VAC input is already over taxed. I can't imagine that one would expect to
get 80 Amps out of a 120 Volt wall socket on a 20 Amp breaker. In other
words this transformer sounds like a missmatch for welding. Too much
voltage, not enough current.

If the transformer is designed to drive silicon carbide elements, it
should
have some form of current control or be a constant current trasformer.

2500 Watt, 100lb transformer for operation on 120VAC? Something doesn't
add
up. We need actual specs to answer your question.

If the peak current it supports is more than 25A, the
transformer rating might be higher. I don't know, so it's
good to ask.

But here's a 10kW transformer that weighs 130 lbs:

10 kW, 130lbs sounds about right. Then shouldn't this 2500 Watt unit be
about 33lbs?
snip
Click to expand...
Did the OP say it was a 2500 watt unit? I may have missed
it.

Jon
 
"Jon Kirwan" <jonk@infinitefactors.org> wrote in message
news:eek:nsek5lsq6n8kk58n2np4oog3bh7l9klsg@4ax.com...
On Fri, 8 Jan 2010 09:41:04 -0800, "Bob Eld"
nsmontassoc@yahoo.com> wrote:

"Jon Kirwan" <jonk@infinitefactors.org> wrote in message
news:c4lek5lo97unsndl47n9q4te62aeuecfl3@4ax.com...
On Fri, 8 Jan 2010 07:35:15 -0800, "Bob Eld"
nsmontassoc@yahoo.com> wrote:

Twentyfive Amps is insufficient for welding. You need from about 50
amps
to
200 amps or so depending on the heat requirements for the gauge you
are
welding.

Six or eight ga. wire on the secondary? That's not consistent with
25
amps
which would only require 10 ga.

I think the OP was saying that 25A "continuous" works well.
But I think the OP also wrote that this was an "industrial
furnace for melting test specimens," which may have supported
discontinuous currents that were higher. At least, I can
tentatively accept the idea.

Agreed, but how much of a current overload is reasonable, 4 times? for
100
Amps out or something similar? Secondly where does the power come from?
120
VAC input is already over taxed. I can't imagine that one would expect to
get 80 Amps out of a 120 Volt wall socket on a 20 Amp breaker. In other
words this transformer sounds like a missmatch for welding. Too much
voltage, not enough current.

If the transformer is designed to drive silicon carbide elements, it
should
have some form of current control or be a constant current trasformer.

2500 Watt, 100lb transformer for operation on 120VAC? Something
doesn't
add
up. We need actual specs to answer your question.

If the peak current it supports is more than 25A, the
transformer rating might be higher. I don't know, so it's
good to ask.

But here's a 10kW transformer that weighs 130 lbs:

10 kW, 130lbs sounds about right. Then shouldn't this 2500 Watt unit be
about 33lbs?
snip

Did the OP say it was a 2500 watt unit? I may have missed
it.

Jon
Click to expand...
He said 25 Amps and up to 100 Volts. Admittedly it's an arm waving kind of a
discussion that why I asked for name plate specs. But, 120 VAC input is a
dead giveaway that we are not talking about much power. Most single phase
small kilns and furnaces run on 240VAC on 50 or 70 Amp circuits.

BTW, for welding it would be better if the current and voltage were
reversed; i.e., 100 Amps @ 25 Volts.
 
On Fri, 8 Jan 2010 12:22:24 -0800, "Bob Eld"
<nsmontassoc@yahoo.com> wrote:

"Jon Kirwan" <jonk@infinitefactors.org> wrote in message
news:eek:nsek5lsq6n8kk58n2np4oog3bh7l9klsg@4ax.com...
On Fri, 8 Jan 2010 09:41:04 -0800, "Bob Eld"
nsmontassoc@yahoo.com> wrote:

"Jon Kirwan" <jonk@infinitefactors.org> wrote in message
news:c4lek5lo97unsndl47n9q4te62aeuecfl3@4ax.com...
On Fri, 8 Jan 2010 07:35:15 -0800, "Bob Eld"
nsmontassoc@yahoo.com> wrote:

Twentyfive Amps is insufficient for welding. You need from about 50
amps
to
200 amps or so depending on the heat requirements for the gauge you
are
welding.

Six or eight ga. wire on the secondary? That's not consistent with
25
amps
which would only require 10 ga.

I think the OP was saying that 25A "continuous" works well.
But I think the OP also wrote that this was an "industrial
furnace for melting test specimens," which may have supported
discontinuous currents that were higher. At least, I can
tentatively accept the idea.

Agreed, but how much of a current overload is reasonable, 4 times? for
100
Amps out or something similar? Secondly where does the power come from?
120
VAC input is already over taxed. I can't imagine that one would expect to
get 80 Amps out of a 120 Volt wall socket on a 20 Amp breaker. In other
words this transformer sounds like a missmatch for welding. Too much
voltage, not enough current.

If the transformer is designed to drive silicon carbide elements, it
should
have some form of current control or be a constant current trasformer.

2500 Watt, 100lb transformer for operation on 120VAC? Something
doesn't
add
up. We need actual specs to answer your question.

If the peak current it supports is more than 25A, the
transformer rating might be higher. I don't know, so it's
good to ask.

But here's a 10kW transformer that weighs 130 lbs:

10 kW, 130lbs sounds about right. Then shouldn't this 2500 Watt unit be
about 33lbs?
snip

Did the OP say it was a 2500 watt unit? I may have missed
it.

Jon

He said 25 Amps and up to 100 Volts. Admittedly it's an arm waving kind of a
discussion that why I asked for name plate specs. But, 120 VAC input is a
dead giveaway that we are not talking about much power. Most single phase
small kilns and furnaces run on 240VAC on 50 or 70 Amp circuits.
Click to expand...
The way I read the OP was that this was a repurposed unit,
now being used as a kiln -- but not designed at the outset as
one. Maybe I am the one who misunderstood, though.

BTW, for welding it would be better if the current and voltage were
reversed; i.e., 100 Amps @ 25 Volts.
Click to expand...
Yes, I think you made that point abundantly clear. I have no
experience and no reason to doubt it, either.

Jon
 
Bob Eld wrote:
"Jon Kirwan" <jonk@infinitefactors.org> wrote in message
news:c4lek5lo97unsndl47n9q4te62aeuecfl3@4ax.com...
On Fri, 8 Jan 2010 07:35:15 -0800, "Bob Eld"
nsmontassoc@yahoo.com> wrote:

Twentyfive Amps is insufficient for welding. You need from about 50 amps
to
200 amps or so depending on the heat requirements for the gauge you are
welding.

Six or eight ga. wire on the secondary? That's not consistent with 25
amps
which would only require 10 ga.

I think the OP was saying that 25A "continuous" works well.
But I think the OP also wrote that this was an "industrial
furnace for melting test specimens," which may have supported
discontinuous currents that were higher. At least, I can
tentatively accept the idea.

Agreed, but how much of a current overload is reasonable, 4 times? for 100
Amps out or something similar? Secondly where does the power come from? 120
VAC input is already over taxed. I can't imagine that one would expect to
get 80 Amps out of a 120 Volt wall socket on a 20 Amp breaker. In other
words this transformer sounds like a missmatch for welding. Too much
voltage, not enough current.
Click to expand...

What are the duty cycles?


--
Greed is the root of all eBay.
 
I bet you can use your transformer, at least for the job you're
talking about. I've used a variety of transformers for welding, and
many were not at all ideal..

What Might Work:

- Use small (say 1/16 or 5/64 ) CONTACT type rods only (Type 7014 I
think) . You can start/keep an arc much easier than with other types.
They work OK at 50 amps.

- You need approximately constant current, with a higher arc-starting
voltage. So, use as much secondary as has both large wire and puts out
40 to 80 volts no load.

- Control the arc current with 'stuff' in series with the primary. I
have used toaster elements, and those Edison screw base heating
elements used in old 'reflector' space heaters. Back before I HEARD
of binary I somehow figured out to use 3 switches with sets of toaster
elements: 1, 2, 4 elements gave me, Hey! Anything from 1 to 7! I
was a lot smarter in 1956 than I am now :) This was on a bigger
rewound pole transformer, you probably only need something like the
resistance of a 1000 or 2000 watt 120V heater (total elements).

The voltage under load will be 25 or 30 volts, I think.

If this is REALLY a one-shot deal, use your jumper cables as welding
cables.

REALLY, REALLY use a REAL welding helmet! Don't ask me why I know...

And, tell us how it went, so someone else can find your info!

Regards, Terry King ..On the Red Sea at KAUST
terry@terryking.us
 
On Sat, 9 Jan 2010 02:18:02 -0800 (PST), TerryKing
<terry@terryking.us> wrote:

I bet you can use your transformer, at least for the job you're
talking about. I've used a variety of transformers for welding, and
many were not at all ideal..

What Might Work:

- Use small (say 1/16 or 5/64 ) CONTACT type rods only (Type 7014 I
think) . You can start/keep an arc much easier than with other types.
They work OK at 50 amps.

- You need approximately constant current, with a higher arc-starting
voltage. So, use as much secondary as has both large wire and puts out
40 to 80 volts no load.

- Control the arc current with 'stuff' in series with the primary. I
have used toaster elements, and those Edison screw base heating
elements used in old 'reflector' space heaters. Back before I HEARD
of binary I somehow figured out to use 3 switches with sets of toaster
elements: 1, 2, 4 elements gave me, Hey! Anything from 1 to 7! I
was a lot smarter in 1956 than I am now :) This was on a bigger
rewound pole transformer, you probably only need something like the
resistance of a 1000 or 2000 watt 120V heater (total elements).

The voltage under load will be 25 or 30 volts, I think.

If this is REALLY a one-shot deal, use your jumper cables as welding
cables.

REALLY, REALLY use a REAL welding helmet! Don't ask me why I know...

And, tell us how it went, so someone else can find your info!

Regards, Terry King ..On the Red Sea at KAUST
terry@terryking.us
Click to expand...
Thanks, Terry. Yep, I definitely plan to use a
REAL welding helmet, cables, clamp, and gloves.
I was hoping to use some simple series inductance
instead of resistance, but I do have some space
heaters around that could do in a pinch.

For the other respondents who wondered about
transformer kVA and current: The nameplate on the
transformer only has volts and cycles (it's from
the '40s or 50s), but the exterior furnace
nameplate says that the input at 2500 degrees F is
1.55 kVA.

I may have been off on the weight, but my point is
that cheapie stick welders have dinky transformers
by comparison. They run them at *much* more
current than what a conventional transformer would
be rated at for continuous use, because they
always have a "duty cycle" listed, typically in
the 15% range. So you would be able to weld only
1.5 minutes out of every 10.

I'm sure I could get a much higher duty cycle out
of this beast, but I have no need for that. My
main concern is to not keep popping breakers.

Best regards,


Bob Masta

DAQARTA v5.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!
 
   What are the duty cycles?
Click to expand...
For reference: Typical welding duty cycle is about 30% for most shop
work.. Time between welds to move things, reclamp, get another welding
rod, etc.

Production welding like building a ship may be up to 80%.

My Lincoln Welder ($250 Home Depot class) is rated only (about 20% or
so: not here) duty cycle at full output (225 Amps). But I rarely use
that high a current for more than a minute or two..
 
TerryKing wrote:
What are the duty cycles?

For reference: Typical welding duty cycle is about 30% for most shop
work.. Time between welds to move things, reclamp, get another welding
rod, etc.

Production welding like building a ship may be up to 80%.

My Lincoln Welder ($250 Home Depot class) is rated only (about 20% or
so: not here) duty cycle at full output (225 Amps). But I rarely use
that high a current for more than a minute or two..
Click to expand...

That's why I asked. You can add some forced air cooling and even
bolt large, finned heat sinks to the core to keep the transformer cooler
as long as you aren't pulling moisture or corrosive material through the
welder's cabinet.


--
Greed is the root of all eBay.
 
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