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From: Bob Masta on 8 Jan 2010 08:51
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

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From: Bob Eld on 8 Jan 2010 10:35

"Bob Masta" <N0Spam(a)daqarta.com> wrote in message
news:4b473038.501975(a)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!

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.


From: Jon Kirwan on 8 Jan 2010 10:55
On Fri, 8 Jan 2010 07:35:15 -0800, "Bob Eld"
<nsmontassoc(a)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.

>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:

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

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

Jon
From: Bob Eld on 8 Jan 2010 12:41

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

> http://www.voltageconverters.com/itemdesc.asp?ic=MS10G8
>
> To provide some kind of very rough weight vs watt benchmark.
>
> Jon


From: Jon Kirwan on 8 Jan 2010 13:02
On Fri, 8 Jan 2010 09:41:04 -0800, "Bob Eld"
<nsmontassoc(a)yahoo.com> wrote:

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