Fitting a 14 pin remote control to an engine drive welder

[User Bp]

I've recently acquired a newish (early '90's) Miller Legend AEAD-200LE welder and subsequently
an HF251D1 arc starter with a TIG torch. The welder does not have remote control, and by all
accounts a footpedal (or equivalent) current control is nice to have.

Miller apparently offered a 14 pin remote as an option on the welder, but it was never common
and hasn't been available for some years now. Much Google searching reveals considerable interest
in adding a remote control to Miller Legends, but no indication of how to do it (nor any hint
why it can't/shouldn't/won'twork) be done emerges. The welder manual shows a schematic complete
with component values, but without knowledge of how both the welder and the remote control are
intended to work it's not trivial to duplicate the functions of the board.

I've been unable to find aftermarket remotes for the Miller Legend, though units do exist for
larger Miller and Lincolnmachines. I inquired of one vendor and was rebuffed with surprising
speed, saying simply they don't have the part. It's hard to believe the Legend is all that
different.

Does anybody know what the impediment is?

bob prohaska

[John B.]

On Thu, 10 Mar 2016 03:09:17 +0000 (UTC), User Bp <b...@www.zefox.net>
wrote:

I've fitted a remote control (pedal) to several Chinese made welders.
In every case the hand amperage control has been a simple rheostat and
what I did was add a switch and external socket so that either the
welder circuits or the foot pedal could be selected.

I don't remember the ratings but it turned out that the welders had
the same capacity internal rheostat as a Miller foot control that
someone had given me.
--
cheers,

John B.

[Ignoramus26799]

I have a engine driven welder, and this welder has a generator. It is
a similar miller welder. "250"

There is no way to stop the generator from producing welding
electricity, while the welder is running.

If yours is the same way, I cannot see how a remote control could
work.

[User Bp]

John B. <slocom...@gmail.xyz> wrote:
>
> I've fitted a remote control (pedal) to several Chinese made welders.
> In every case the hand amperage control has been a simple rheostat and
> what I did was add a switch and external socket so that either the
> welder circuits or the foot pedal could be selected.
>

That seems like an eminently reasonable thing to try. What I can't figure out
is why nobody says so, or says no. They behave as if they're afraid to speak.

> I don't remember the ratings but it turned out that the welders had
> the same capacity internal rheostat as a Miller foot control that
> someone had given me.
> --

The rheostat on my welder is 30 ohm, rated 100 watt. An old fashioned
sewing machine rheostat might do the trick..... I wonder if they can
still be found. Might be worth a try.

You don't happen to have a model number for that Miller foot control,
do you?

Thanks for your help!

bob prohaska


Thanks for reading,

bob prohaska

[User Bp]

My welder uses a tapped inductor for coarse current control and varies
the field current (effectively adjusting the open-circuit output voltage)
to set the fine current. I think this is fairly standard. In principle
one can adjust the output current all the way to zero by opening the
field current circuit. In practice the range is more limited, so a contactor
is used to terminate the arc. Completely opening the field circuit should
do much the same thing, but far as I can tell that method isn't used.
One fairly basic puzzle is why not. Possibly other components in the welder
react badly to a loss of field current, but nobody has offered an explanation.
That is the error I'm trying to avoid.

Thanks for reading!

bob prohaska

[Ignoramus26799]

You have a good welder, do not make it into a bad welder by messing
with its most basic principles of operation.

i

[Ecnerwal]

It's a simple enough remote setup.

A not connected to B, contactor open, no weld voltage.
A connected to B, contactor closed, weld current enabled.
Just possible (description vague) that this is inverted, but unlikely.

C provides 4.5V to one end of the remote (current control) pot.
D is the control circuit common on the other end of the pot.
E is the wiper of the pot (value of the pot will typically be 5 or 10K,
and is not critical, as the voltage, at little current, is the control
signal. The remote pot is NOT a high-power unit.

K is chassis ground.

Order a connector and go. It's not rocket science. Or are you saying the
welder does not have the remote socket/internal board? In either case,
the above is how the remote works, and Lincoln remotes are quite similar.

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

[Bob Engelhardt]

On 3/10/2016 9:49 PM, User Bp wrote:
...

> In practice the range is more limited, so a contactor
> is used to terminate the arc. Completely opening the field circuit should
> do much the same thing, but far as I can tell that method isn't used.

> One fairly basic puzzle is why not. ...

Probably because there is residual magnetism in the stator that would
give some output voltage.

Bob

[John B.]

On Fri, 11 Mar 2016 02:38:11 +0000 (UTC), User Bp <b...@www.zefox.net>
wrote:

>John B. <slocom...@gmail.xyz> wrote:
>>
>> I've fitted a remote control (pedal) to several Chinese made welders.
>> In every case the hand amperage control has been a simple rheostat and
>> what I did was add a switch and external socket so that either the
>> welder circuits or the foot pedal could be selected.
>>
>That seems like an eminently reasonable thing to try. What I can't figure out
>is why nobody says so, or says no. They behave as if they're afraid to speak.
>
>> I don't remember the ratings but it turned out that the welders had
>> the same capacity internal rheostat as a Miller foot control that
>> someone had given me.
>> --
>
>The rheostat on my welder is 30 ohm, rated 100 watt. An old fashioned
>sewing machine rheostat might do the trick..... I wonder if they can
>still be found. Might be worth a try.
>

I tried that and it didn't work although my "trial" was simply to
connect the Singer pedal and step on it,

I'm not sure what value rheostat I used and I'm a long way from where
the welder is but 30 ohms sounds sort of like what I remember although
I'm really not positive.

>You don't happen to have a model number for that Miller foot control,
>do you?

No I don't have any idea. I asked at a welding machine vendor if he
had any "foot controls" and he fished this used one out of the back
room and gave it to me. It turned out to be the same value rheostat as
the welder so I used it. And it worked :-)

>Thanks for your help!
>
>bob prohaska
>
>
>Thanks for reading,
>
>bob prohaska
>

--
cheers,

John B.

[BobH]

I went to the Miller web site, and pulled up the users manual and
schematic, and it looks like they show how the fine current control
adjustment works. You could put a double pole, double throw switch that
would substitute your foot pedal variable resistor for the fine current
control. Or you could use the switch to put your foot pedal resistor in
series with the existing fine current control resistor which is how my
old Dialarc 250HF did it. The parts list shows a 30Ohm 100W resistor for
the fine current control.

The last version of the users manual showed the schematic for the remote
control version of that machine. It used a board to control the field
instead of the 30 Ohm power resistor for the remote. The 14 pin foot
pedals have a small 5 or 10 KOhm pot in them (1/2 watt or so) so you
would need the control board to use that style foot pedal.

The old Dialarc 250HF used a 24 or 30 Ohm 100Watt variable resistor to
control the current. They used a 3 pin connector for current control and
a 2 pin twist locking connector to control the contactor. A pedal like
that would work without a control board.

I think that the foot pedal that you want is the Miller RFC-23A

Good Luck,
BobH

[User Bp]

Ignoramus26799 <ignoram...@nospam.26799.invalid> wrote:
>
> You have a good welder, do not make it into a bad welder by messing
> with its most basic principles of operation.
>

Agreed entirely! That's why I'm seeking knowledgeable counsel. What
really surprised me is that nobody on the Miller Electric welding
forum has been willing to comment. A simple "won't work, here's why...."
or " can be done, here are the pitfalls/limitations...." would suffice.
Thus far the silence is deafening.

bob

[User Bp]

Bob Engelhardt <BobEng...@comcast.net> wrote:
>
> Probably because there is residual magnetism in the stator that would
> give some output voltage.
>

Possibly you meant residual magnetism in the field? The idea makes sense,
but I'd think it too feeble to maintain an arc. It's one of the many things
I don't yet know.

bob p

[User Bp]

Ecnerwal <MyName...@replacewithmyvices.com.invalid> wrote:
>
> Order a connector and go. It's not rocket science. Or are you saying the
> welder does not have the remote socket/internal board? In either case,
> the above is how the remote works, and Lincoln remotes are quite similar.
>

Aye, there's the rub. No contactor and no remote board. No OEM remote boards
available, nobody willing to tell me how to adapt a generic board or why
it can't be done.

bob prohaska

[Jim Wilkins]

"BobH" <wanderingmetalhe...@yahoo.com> wrote in message
news:nbvpl...@news4.nntpjunkie.com...

http://www.amazon.com/Ceramic-Disk-Variable-Resistor-Rheostat/dp/B008DFUQAI
It's the diameter of a coffee cup. The reviews of some similar ones
call out the brush as a weak spot.

--jsw

[User Bp]

BobH <wanderingmetalhe...@yahoo.com> wrote:
>
> I went to the Miller web site, and pulled up the users manual and
> schematic, and it looks like they show how the fine current control
> adjustment works. You could put a double pole, double throw switch that
> would substitute your foot pedal variable resistor for the fine current
> control. Or you could use the switch to put your foot pedal resistor in
> series with the existing fine current control resistor which is how my
> old Dialarc 250HF did it. The parts list shows a 30Ohm 100W resistor for
> the fine current control.
>

That's what I found also.

> The last version of the users manual showed the schematic for the remote
> control version of that machine. It used a board to control the field
> instead of the 30 Ohm power resistor for the remote. The 14 pin foot
> pedals have a small 5 or 10 KOhm pot in them (1/2 watt or so) so you
> would need the control board to use that style foot pedal.
>

The control board is what I don't have, can't find and can't learn how
to adapt. Their scarcity makes me wonder if maybe they didn't work all
that well and Miller simply wants to banish the bad memory....

> The old Dialarc 250HF used a 24 or 30 Ohm 100Watt variable resistor to
> control the current. They used a 3 pin connector for current control and
> a 2 pin twist locking connector to control the contactor. A pedal like
> that would work without a control board.
>
> I think that the foot pedal that you want is the Miller RFC-23A
>

That's a good clue, at least I have something to look for now. I'll poke around
a little.

> Good Luck,
> BobH
>
>
Thank you!

bob p

[Bob Engelhardt]

Well, I meant "residual magnetic field in the stator".

The voltage across a tight arc is much less than the OCV, maybe 10 -
20v. Whether the residual field could produce that - I dunno, but maybe.

Bob

[BobH]

You're welcome.

If you look at the schematic for the unit without a remote board, it
just shows the variable resistor for the fine current control (R1 on the
schematic I looked at). A Double Pole Double Throw switch would let you
swap the remote resistor (foot pedal) in for R1. A contactor would give
you the make/break for the on/off. My Dialarc used a big 3 phase
contactor, but it was the highest maintenance part of the machine.

You may need to figure out how to trigger the "Idle Up" from the
contactor control, or it will be awkward starting. I didn't see any link
from the remote board to the idle control, but there may still be one
that I didn't notice.

Looking at the HF-251D-1 manual, it looks like all that it cares about
from the foot pedal is the contactor control. That contactor option they
offer would be really nice if it were installed, it would take care of
the on/off part with the HF control.

If you are planning to TIG weld outside, you need really good wind
breaks, or you lose the shielding gas around your weld. My luck with TIG
welding outside has not been great.

Good Luck,
BobH

[User Bp]

BobH <wanderingmetalhe...@yahoo.com> wrote:
>
> If you look at the schematic for the unit without a remote board, it
> just shows the variable resistor for the fine current control (R1 on the
> schematic I looked at). A Double Pole Double Throw switch would let you
> swap the remote resistor (foot pedal) in for R1.

I'm starting to think that's the only viable approach. Absolutely nobody
offers the OEM remote control board, nor will anybody offer guidance on
how to improvise one.. I've been studying the schematic for several days
and still don't understand how the voltage regulation scheme works. The
schematics aren't the clearest, but even if they were it's a real brain
teaser. Some things just don't make sense yet, and one poster observed
that the schematics "aren't always right" 8-( At some point I'm going
to break out the meter and start measuring voltages while running.

> A contactor would give
> you the make/break for the on/off. My Dialarc used a big 3 phase
> contactor, but it was the highest maintenance part of the machine.
>

I'm hopeful that a big enough resistance in place of R1 will reduce the
output voltage to the point of extinguishment. It turns out one can still
buy carbon pile rheostats rated 4 amps on Amazon, sold for controlling
univeral-motor tools. For $20 it seems worth a try, but I want to be fairly
sure of not doing damage with the experiment. It seems no harder on the
machine than having a brush go open, but still I'm cautious.

> You may need to figure out how to trigger the "Idle Up" from the
> contactor control, or it will be awkward starting. I didn't see any link
> from the remote board to the idle control, but there may still be one
> that I didn't notice.
>

Oddly enough that problem seems to be solved. The welder revs up when it
detects a load on either the weld terminals or the 100Hz accessory outlet.
Pressing the trigger switch for the HF251 makes it draw enough current to
rev the welder.

> Looking at the HF-251D-1 manual, it looks like all that it cares about
> from the foot pedal is the contactor control. That contactor option they
> offer would be really nice if it were installed, it would take care of
> the on/off part with the HF control.
>

I did manage to find a contactor listed for sale, but at more than $400 it
seems worth trying to live without, at least to begin with. I can't help
but wonder if a few starter relays in series with varistors across them
might be a usable substitute.

> If you are planning to TIG weld outside, you need really good wind
> breaks, or you lose the shielding gas around your weld. My luck with TIG
> welding outside has not been great.
>

I have the luxury of waiting till the weather is nice 8-)

> Good Luck,
> BobH
>
With my thanks!

bob prohaska

[BobH]

snip

> I'm hopeful that a big enough resistance in place of R1 will reduce the
> output voltage to the point of extinguishment. It turns out one can still
> buy carbon pile rheostats rated 4 amps on Amazon, sold for controlling
> univeral-motor tools. For $20 it seems worth a try, but I want to be fairly
> sure of not doing damage with the experiment. It seems no harder on the
> machine than having a brush go open, but still I'm cautious.

snip

> With my thanks!
>
> bob prohaska
>

Digikey lists a 25 Ohm, 100W watt rotary variable resistor from Ohmite
for about $92. This is what I used when I built a foot pedal for my
Dialarc. They don't stock them, but at least they still exist. Surplus
might be a better choice if you could find one.

You might try open circuit for a big enough resistance for
extinguishment. Increasing the value of the variable resistor value a
lot will compress the useful range of adjustment to a very narrow range
of motion.

The contactor on my Dialarc was just a big 3 phase unit, I think it was
an 80 amp unit with all 3 circuits in parallel.

I will take another look at the schematic on the circuit board. When I
looked at it, I was more curious what the output looked like than the
control aspects.

If you want to take this conversation to email, my address needs a
little editing.

Regards,

BobH

[User Bp]

BobH <wanderingmetalhe...@yahoo.com> wrote:
> Digikey lists a 25 Ohm, 100W watt rotary variable resistor from Ohmite
> for about $92. This is what I used when I built a foot pedal for my
> Dialarc. They don't stock them, but at least they still exist. Surplus
> might be a better choice if you could find one.
>

I've ordered the carbon pile rheostat foot control, just to try it.
For $25 it seems a reasonable gamble.

> You might try open circuit for a big enough resistance for
> extinguishment. Increasing the value of the variable resistor value a
> lot will compress the useful range of adjustment to a very narrow range
> of motion.

One of the nice features of carbon piles is that they go open, or nearly so,
when pressure is released. Whether the non-linearity will happen in a useful
range remains to be seen. They're prone to flakiness, but at this stage I
don't think it matters much, and they distribute dissipated power more
evenly over the volume of resistive material.

>
> The contactor on my Dialarc was just a big 3 phase unit, I think it was
> an 80 amp unit with all 3 circuits in parallel.
>

Sounds like it must have been on the mains side....

> I will take another look at the schematic on the circuit board. When I
> looked at it, I was more curious what the output looked like than the
> control aspects.
>

There are two big puzzles for me: The first is that the voltage regulator
gets signal from two places. One is a center tapped transformer that samples
the 60 Hz AC when in generator mode. That signal appears to supply both a
voltage sense and power to a 15 volt regulator that powers the op amps and
biases the transistors. It goes away in weld mode, because the relay upstream
disconnects the power windings while welding. Meanwhile a second signal comes
from a dedicated "regulator power winding" that's always active, whether
generating or welding. It seems intended to merely turn the field circuit
full on, though just how it does so isn't obvious. I guess that competition
between the two inputs provides regulation when generating, lack of signal
from the center-tapped input lets the regulator run wide open.

The other puzzle is the importance of the CR3 contacts paralleling R1. It
seems logical to suppose that CR3 would close while generating, giving
field control to the regulator to produce output voltage. However the
instructions explicitly state that the fine amperage control must be at
100% while in generator mode. The purpose of CR3 is thus unclear. The
"Idle Lock" mode is intended for exclusive generator operation, but the
fine amperage control must still be set to 100% per the operator manual
and according to the schematic "Idle Lock" disconnects CR3 entirely.

> If you want to take this conversation to email, my address needs a
> little editing.
>

We can take it off the record if you like, but I'd have been very happy
to find a thread like this one.

bob prohaska

[BobH]

On 03/13/2016 07:51 PM, User Bp wrote:
> BobH <wanderingmetalhe...@yahoo.com> wrote:

>> The contactor on my Dialarc was just a big 3 phase unit, I think it was
>> an 80 amp unit with all 3 circuits in parallel.
>>
> Sounds like it must have been on the mains side....

The contactor was definitely on the secondary side. With all 3 circuits
paralleled, it had about 240A rated capacity. I think it had problems
with extinguishing the arc because I had to dress the contacts 3 or 4
times over the 15 years that I had the machine. I never had the AC feed
capable of running it at full capacity, and most of my welding is
smaller stuff anyway. It probably would have been a lot worse if I was
running it close to capacity all the time.

BobH

[BobH]

I have been looking at the remote Control Board PC3 schematic. I think
it is just a simple PWM generator. Q1 and the nearby R's and C5 look
like a sawtooth generator. A1A is operating as a comparator with the
sawtooth in the + input and the wiper voltage from the adjustment pot
driving the - input. The remote contactor input (J) gets grounded when
the pedal is not in the off position, pulling the anode of D4 close to
ground. This reverse biases D4 and allows the comparator output pulses
to go to the - input on A1B. The + input voltage is set by the
optocoupler that is driven from the panel/remote switch. In the remote
position, the + input will sit about 2.7V and the PWM will pass through
A1B and drive the IGBT module gate to pulse the field. It doesn't look
like there is any feed back on the current flow or voltages.

I suspect that the caution about putting the fine current control at
100% is a leftover from before they added CR3. With CR3 there, it makes
no sense from what I understand (which may be wrong still).

It looks like the power while welding and current to excite the welding
generator field come from the coils on the left side of center and the
welding current and aux power come from the coils to the right of
center. I think that the voltage regulator board is just operational
when running as a standby generator and not as a welder. When CR4 opens
up, it looks like it turns off most of the regulator board. I haven't
figured out the SCR/UJT and NPN stuff on the right side of the print yet.

I am getting close to all I can skull out of the prints without a
machine in front of me to poke at and test on.

BobH

[User Bp]

BobH <wanderingmetalhe...@yahoo.com> wrote:
> I have been looking at the remote Control Board PC3 schematic. I think
> it is just a simple PWM generator. Q1 and the nearby R's and C5 look
> like a sawtooth generator. A1A is operating as a comparator with the
> sawtooth in the + input and the wiper voltage from the adjustment pot
> driving the - input. The remote contactor input (J) gets grounded when
> the pedal is not in the off position, pulling the anode of D4 close to
> ground. This reverse biases D4 and allows the comparator output pulses
> to go to the - input on A1B. The + input voltage is set by the
> optocoupler that is driven from the panel/remote switch. In the remote
> position, the + input will sit about 2.7V and the PWM will pass through
> A1B and drive the IGBT module gate to pulse the field. It doesn't look
> like there is any feed back on the current flow or voltages.
>

That seems reasonable. I wondered the same thing but couldn't see through
most of the details. A DC motor speed control module could probably be
adapted to do the same job. Possibly it could be made to do both the
regulator's job and the welder control's job by selecting either current
set pot or output voltage error amplifier as signal source.
That's for another day...

> I suspect that the caution about putting the fine current control at
> 100% is a leftover from before they added CR3. With CR3 there, it makes
> no sense from what I understand (which may be wrong still).
>

I took a look at S1B today and it makes even less sense 8-) The panel
labels agree with the schematic markings, which make no sense. Even
better, the switch is open! The contact slider for S1B appears
to be missing. Everything else is there, S1A is fine.

> It looks like the power while welding and current to excite the welding
> generator field come from the coils on the left side of center and the
> welding current and aux power come from the coils to the right of
> center. I think that the voltage regulator board is just operational
> when running as a standby generator and not as a welder. When CR4 opens
> up, it looks like it turns off most of the regulator board.

That's my impression also. The welder is open loop, mostly just a fixed
voltage on the current setting choke. Any feedback would be too slow.

> I haven't figured out the SCR/UJT and NPN stuff on the right side of the print yet.

That has me stumped as well. I have been told it's possible to build a
PWM circuit using SCRs, either by gate-turn-off or current diversion,
but either approach seems to require more parts than are shown.

> I am getting close to all I can skull out of the prints without a
> machine in front of me to poke at and test on.

For the moment I'm tempted to leave well enough alone. As Iggy pointed
out, the last think I want to do is mess up a working welder. In the
meantime you've given me some good things to think about.

I'm probably better off practicing than tinkering. Google found a few
examples of folks hooking up remote rheostats, so when the carbon pile
arrives it makes a low risk experiment. At this stage just keeping the
tungsten out of the puddle takes most of my attention; another control
to think about could easily make matters worse.
>
> BobH
>
Thanks for all your help!

bob prohaska

[User Bp]

I'm rather surprised: Seems like there's be less inductance to fight on
the primary side. The secondary side is _designed_ to maintain an arc.
Leakage between primary and secondary would give the primary a little
isolation.

bob p

[BobH]

On 03/14/2016 10:31 PM, User Bp wrote:
> I'm probably better off practicing than tinkering. Google found a few
> examples of folks hooking up remote rheostats, so when the carbon pile
> arrives it makes a low risk experiment. At this stage just keeping the
> tungsten out of the puddle takes most of my attention; another control
> to think about could easily make matters worse.
>>
>> BobH
>>
> Thanks for all your help!
>
> bob prohaska

You're welcome. Welding machines interest me a lot. A slightly different
tack on this might be to try building your own current control/HF system
to run off the weld outputs of your Legend, something like:
http://www3.telus.net/public/a5a26316/TIG_Welder.html

That way, your machine would stay unmodified and retain what value it
has now.

I have wanted to build my own design inverter TIG machine for a long
time, but I wanted to have one that would always work and not be a
perpetual project in the way of just going out and welding. As a result,
I bought a Miller machine. Maybe after I retire...

Good Luck,
Bob

[User Bp]

BobH <wanderingmetalhe...@yahoo.com> wrote:
> You're welcome. Welding machines interest me a lot. A slightly different
> tack on this might be to try building your own current control/HF system
> to run off the weld outputs of your Legend, something like:
> http://www3.telus.net/public/a5a26316/TIG_Welder.html
>

That's an astoundingly ambitious project! Given what could be bought
in 2011, it might have made economic sense. Given what can be bought
today it's not so obviously worthwhile. The challenge might be satisfying
but I'm not sure there's any functional gain to be had.

> That way, your machine would stay unmodified and retain what value it
> has now.

The machine I have is no collector's item. There are a few photos here:
http://www.zefox.net/~bob/welder/ (The reddish stuff in the photos is
paint overspray; what got inside didn't stick and cleaned up with a
soft brush but the outside has pink highlights.) The un-grooved slip
rings are what persuaded me to buy it, suggesting relatively low run
time. The exterior is very beaten up. The HF-251D-1 is less bad but
also somewhat beaten up.

Mostly I like to play with old machinery. If it can be made easier to
use on the cheap I'm not afraid to make changes. What the AEAD-200LE's
taught me so far is that the faults are in the bum on the seat....

>
> I have wanted to build my own design inverter TIG machine for a long
> time, but I wanted to have one that would always work and not be a
> perpetual project in the way of just going out and welding. As a result,
> I bought a Miller machine. Maybe after I retire...
>

There are times when it's possible to build better than one can buy.
It was true of hi-fi speakers in the '70s for a short time, maybe ten
years. Probably true of welders when IGBTs first appeared, but now?

> Good Luck,
> Bob
>
Thank you!

bob p

[BobH]

On 03/15/2016 08:36 PM, User Bp wrote:
> BobH <wanderingmetalhe...@yahoo.com> wrote:
>> You're welcome. Welding machines interest me a lot. A slightly different
>> tack on this might be to try building your own current control/HF system
>> to run off the weld outputs of your Legend, something like:
>> http://www3.telus.net/public/a5a26316/TIG_Welder.html
>>
> That's an astoundingly ambitious project! Given what could be bought
> in 2011, it might have made economic sense. Given what can be bought
> today it's not so obviously worthwhile. The challenge might be satisfying
> but I'm not sure there's any functional gain to be had.

snip

>> I have wanted to build my own design inverter TIG machine for a long
>> time, but I wanted to have one that would always work and not be a
>> perpetual project in the way of just going out and welding. As a result,
>> I bought a Miller machine. Maybe after I retire...
>>
> There are times when it's possible to build better than one can buy.
> It was true of hi-fi speakers in the '70s for a short time, maybe ten
> years. Probably true of welders when IGBTs first appeared, but now?

I don't have any illusions about being able to build a better machine
than I could buy. Mostly, it would be a very cool technical challenge.
Building ambitious projects has been one of my favorite ways to learn
new stuff and increase or keep current with stuff that I can use in my
day job or maybe my next day job.

BobH

[User Bp]

BobH <wanderingmetalhe...@yahoo.com> wrote:
>
> I don't have any illusions about being able to build a better machine
> than I could buy. Mostly, it would be a very cool technical challenge.
> Building ambitious projects has been one of my favorite ways to learn
> new stuff and increase or keep current with stuff that I can use in my
> day job or maybe my next day job.
>

Ok, understood. Might it make sense to try much higher than normal working
frequency, tens of kHz or even higher? I wonder what effect it would have...

bob prohaska

[BobH]

The Dynasty box that I got will run 250Hz on AC and you get
significantly better penetration on aluminum at 250Hz. It also sounds
like a hive of really angry bees. I don't know how far upward that
extends in frequency though.

BobH

[User Bp]

BobH <wanderingmetalhe...@yahoo.com> wrote:
>
> The Dynasty box that I got will run 250Hz on AC and you get
> significantly better penetration on aluminum at 250Hz. It also sounds
> like a hive of really angry bees. I don't know how far upward that
> extends in frequency though.
>

There's a remark in one of the welding forums that Lincoln built a
400Hz welder at some point. The writer praised it considerably, though
he offered no details.

I was thinking in terms of considerably higher frequency, high enough
so that electrode capacitance, rather than electron emission, contributes
to the discharge. I'd think that would be in the hundreds of kHz if not
higher. Admittedly, I do not know if it's worth the trouble. But, inverters
weren't worth the trouble twenty years ago, now the trouble is much less
and the virtues seem considerable.

Once the frequency goes over 20kHz at least you won't hear the bees....
8-)

bob p

[Pete Keillor]

On Fri, 18 Mar 2016 03:24:27 -0000 (UTC), User Bp <b...@www.zefox.net>
wrote:

Sounds like a dandy radio frequency jamming device...

[David Billington]

My Hitachi GP2 TIG goes to 500Hz IIRC it was made around 1998.

[Jim Wilkins]

"Pete Keillor" <Pete.K...@gmail.com> wrote in message
news:jh0oebpcd255ur2cg...@4ax.com...

The FCC regulates emissions down to 10 KHz.

[BobH]

What would be the advantage of capacitive coupling? I suspect that the
plasma in a normal TIG arc is so conductive, that the difference would
be lost. But then I don't understand why the higher frequency AC
penetrates better. I'm not criticizing here, I am just trying to piece
it together.

It just occurred to me that the voltage drop between the electrode and
the work times the current flow is dissipating a LOT of power, that may
be the primary source of the welding heat. This is pure speculation on
my part though, I am just an engineer, not a plasma physicist.

Curious,
BobH

[BobH]

On 03/18/2016 06:54 AM, David Billington wrote:
> My Hitachi GP2 TIG goes to 500Hz IIRC it was made around 1998.

Do you notice much difference between 250 and 500Hz on aluminum welding?

BobH

[User Bp]

Pete Keillor <Pete.K...@gmail.com> wrote:
> Sounds like a dandy radio frequency jamming device...

Shielding would likely be a significant problem. However,
if the advantages justify it the work could be done in a
Faraday cage. They can be made of screen or metal covered
wood and aren't really very exotic, apart from being low
production items. Think of a carefully costructed screened
porch. Or, a sandblasting cabinet.

There are some FCC allocations for industrial heating applications.
One at 13.56 MHz is used quite widely, though that frequency may
be impractically high. Induction heating is lower frequency, but
I'm not sure how or if it's regulated. Microwave ovens have a slot
at 2.4 GHz, but I'm pretty sure that's too high for convenience,
if not for effectiveness.

bob prohaska

[User Bp]

BobH <wanderingmetalhe...@yahoo.com> wrote:
>
> What would be the advantage of capacitive coupling? I suspect that the
> plasma in a normal TIG arc is so conductive, that the difference would
> be lost. But then I don't understand why the higher frequency AC
> penetrates better. I'm not criticizing here, I am just trying to piece
> it together.
>
> It just occurred to me that the voltage drop between the electrode and
> the work times the current flow is dissipating a LOT of power, that may
> be the primary source of the welding heat. This is pure speculation on
> my part though, I am just an engineer, not a plasma physicist.
>

The power dissipated is distributed between the electrode, the workpiece
and the arc itself. I think the major effect of raising the AC frequency
would be to change the distribution of power dissipation among those
components. If you could build a 13.6 MHz welder I'm pretty sure it would
behave very differently than a conventional one. Better or worse, and
for what purpose, I'll admit to being unsure.

In a DC arc electrons have to be emitted by the cathode and collected
at the anode. Most of the current is carried by the electrons and most
of the power is delivered to the surface they land on. To make the cathode
emit electrons either ions must strike it with enough energy to dislodge
sufficient electrons or the cathode must be hot enough to emit thermionically.

This remains true in an AC arc up to the frequency where electrons don't have time
to transit the arc before the voltage reverses. Then, they're trapped, sloshing
back and forth in the arc, collisionally ionizing the gas and ensuring an adequate
supply of charge carriers to keep the discharge going. The result is that the
electrodes don't _have_ to supply the electrons. This allows the cathode to
run colder than required for thermionic emission and avoids the erosion caused
by ions hitting the cathode. More power goes into the arc, less into the electrode
and workpiece. That opens an opportunity to manipulate where the heat goes.
At the same time, ion cleaning of the workpiece would decrease, perhaps to
the detriment of the welding process.

The frequency at which electrons don't have time to transit the arc isn't known
to me and is probably rather hard to estimate accurately. Ordinary fluorescent
lamps have an efficiency peak in the tens of kHz, electrodeless lamps have been
commercially available in that frequeny range. Microwave frequencies have been
tried but far as I know they were a technical success and a commercial failure.

I'm not sure plasma physics is much help in a puzzle like this; it's a very
messy problem. Direct experimentation is apt to be easier and more persuasive.
Quite possibly experiments have already done, probably for somebody's Defense
Department during the 1950's. They'd have been stuck using vacuum tubes, which
would have made the project much harder than it would be today.

Apologies for the length, thanks if you read this far!

bob prohaska

[Jim Wilkins]

"User Bp" <b...@www.zefox.net> wrote in message
news:ncidc0$l6t$1...@dont-email.me...

The speed of electrons in a solid wire was one of my college physics
homework problems.

https://www.uu.edu/dept/physics/scienceguys/2001Nov.cfm
"In the case of a 12 gauge copper wire carrying 10 amperes of current
(typical of home wiring), the individual electrons only move about
0.02 cm per sec or 1.2 inches per minute"

You'd have to know the free electron density in the plasma channel to
figure it for an arc.
--jsw

[Jim Wilkins]

"Jim Wilkins" <murat...@gmail.com> wrote in message
news:ncif7b$q8k$1...@dont-email.me...

This gives around 200 m/s as the plasma velocity in a 10mm long arc,
which corresponds to one wavelength at 20 KHz.
http://www.jmst.org/fileup/PDF/02043.pdf

[User Bp]

Jim Wilkins <murat...@gmail.com> wrote:
> The speed of electrons in a solid wire was one of my college physics
> homework problems.
>
> https://www.uu.edu/dept/physics/scienceguys/2001Nov.cfm
> "In the case of a 12 gauge copper wire carrying 10 amperes of current
> (typical of home wiring), the individual electrons only move about
> 0.02 cm per sec or 1.2 inches per minute"
>
> You'd have to know the free electron density in the plasma channel to
> figure it for an arc.
> --jsw

Yes, and the various electron collision frequencies (or equivalently,
the mean free path between those collisions). I think one of the assumptions
of the copper wire case is that there is one conduction electron per
atom and negligible scattering. In an arc there are many more neutral
atoms than electrons and electron-neutral collisions dominate transport.

An estimate could be made, but an accurate estimate would likely cost
more than a simple experiment.

It occurs to me that selecting a driving frequency which maximized the
electron-neutral collision frequency would effectively raise the resistance
of the arc, allowing more power to be delivered with less current and a
lighter, smaller torch and electrode. That might be of some value.

thanks for reading,

bob prohaska

[User Bp]

Jim Wilkins <murat...@gmail.com> wrote:
>
> This gives around 200 m/s as the plasma velocity in a 10mm long arc,
> which corresponds to one wavelength at 20 KHz.
> http://www.jmst.org/fileup/PDF/02043.pdf
>
>
>

That's an interesting paper, I wish I could understand the
math better. It seems to treat only the DC case, however.
I wonder if there's an AC treatment around somewhere. It'll
surely be much messier! One of the guiding assumptions is
that the arc is a resistive fluid obeying Ohm's law. Arcs
generally don't obey Ohm's law.

As the authors note, the paper is a "useful intermediate step".

Thanks for writing!

bob prohaska

[Jim Wilkins]

"User Bp" <b...@www.zefox.net> wrote in message

news:ncl374$c02$1...@news.albasani.net...

http://www.physics.csbsju.edu/370/jcalvert/dischg.htm.html

[Gunner Asch]

[Gunner Asch]

On Wed, 16 Mar 2016 21:42:18 -0700, BobH
<wanderingmetalhe...@yahoo.com> wrote:

Mine will do up to 1.8kh...anything over 250hz as Bob
indicates...doesnt seem to do much. Or Im not good enough to puzzle
it out in practice

[BobH]

On 03/20/2016 11:33 AM, Gunner Asch wrote:
> Mine will do up to 1.8kh...anything over 250hz as Bob
> indicates...doesnt seem to do much. Or Im not good enough to puzzle
> it out in practice
>

What machine are you using?

Thanks,
BobH

[User Bp]

Jim Wilkins <murat...@gmail.com> wrote:
>
> http://www.physics.csbsju.edu/370/jcalvert/dischg.htm.html
>
>
A very helpful description of electrical discharges. It
doesn't get much into AC effects, however.

Welding is probably somewhat unique, in that practically
all of the work on gaseous electronics was motivated by
rectifier and amplifier applications, where the current
is varying DC. Nobody was much interested in in the regime
corresponding to welding conditions. When things start
to melt the tube designers usually used a bigger tube.....

8-)

bob p

[Gunner Asch]

Airco 300 Squarewave. No idea who made it. It was new in the
early/mid 90s. Big..big bastard..bigger than a Syncrowave 300.

https://picasaweb.google.com/104042282269066802602/ShopDec282012#5827202975647183106

I actually have 2 of them....

https://picasaweb.google.com/104042282269066802602/ShopDec282012#5827203342162815218


Some of my Stuff...a bit dated..but..you get the idea...

https://picasaweb.google.com/104042282269066802602/ShopDec282012#