# MIG Welding, CC Inductor, and bypass thereof

I

#### Ignoramus20083

Jan 1, 1970
0
This is in regards to an old Hobart CyberTIG welder that I modified by
putting in a new microcontroller that I programmed in BASIC.

http://igor.chudov.com/projects/Welding/11-New-Rectifier/

Basically because I have a separate SCR controller, and separate
module for controlling it, I can program it to do anything I want, to
supply any voltage and any current, within my power limits, of course.

So it is basicallly an arbitrary DC power supply, with a few extra
relays that control high frequency arc starting and gas valve.

This thing works just fine in constant current mode, letting me stick
weld as well as TIG weld.

Note that it has a big inductor that helps with constant current
welding.

Now that I am done with CC mode welding, I started exploring MIG
welding, which requires constant voltage. Found a LN-25 wirefeed unit
on Craigslist.

The issue at hand is that the output of my welder goes through a large
inductor that is helpful in CC mode, but counterproductive for wire
feed welding. This inductor weighs perhaps 50 lbs. (?)

So, for nice wire feed welding, I would need to bypass it. I see two
ways of doing it:

1) Make a simple bypass circuit using a big contactor and big cable
(to be turned on when MIG welding is being done).

2) Instead of bypassing the inductor, install a capacitor that would
"cancel out" the effect of the inductor.

Can that be done at all, is this an insane idea or not? My hope is
that it would be done with a smaller "work envelope", utilizing
smaller wires and a smallish capacitor, instead of a bulky contactor
and big wire, etc.

Any thoughts on bypassing the inductor?

thanks

i

D

#### [email protected]

Jan 1, 1970
0
2) Instead of bypassing the inductor, install a capacitor that would
"cancel out" the effect of the inductor.

Can that be done at all, is this an insane idea or not? My hope is
that it would be done with a smaller "work envelope", utilizing
smaller wires and a smallish capacitor, instead of a bulky contactor
and big wire, etc.

Any thoughts on bypassing the inductor?

thanks
In order for the capacitor to cancel the current going through the
inductor, the current through the capacitor would have to be as large
as the current going through the inductor. So a lot of capacitance and
large wire.

Dan

J

#### John Popelish

Jan 1, 1970
0
Ignoramus20083 said:
This is in regards to an old Hobart CyberTIG welder that I modified by
putting in a new microcontroller that I programmed in BASIC.

http://igor.chudov.com/projects/Welding/11-New-Rectifier/

Basically because I have a separate SCR controller, and separate
module for controlling it, I can program it to do anything I want, to
supply any voltage and any current, within my power limits, of course.

So it is basicallly an arbitrary DC power supply, with a few extra
relays that control high frequency arc starting and gas valve.

This thing works just fine in constant current mode, letting me stick
weld as well as TIG weld.

Note that it has a big inductor that helps with constant current
welding.

Now that I am done with CC mode welding, I started exploring MIG
welding, which requires constant voltage. Found a LN-25 wirefeed unit
on Craigslist.

The issue at hand is that the output of my welder goes through a large
inductor that is helpful in CC mode, but counterproductive for wire
feed welding. This inductor weighs perhaps 50 lbs. (?)

So, for nice wire feed welding, I would need to bypass it. I see two
ways of doing it:

1) Make a simple bypass circuit using a big contactor and big cable
(to be turned on when MIG welding is being done).

2) Instead of bypassing the inductor, install a capacitor that would
"cancel out" the effect of the inductor.

Can that be done at all, is this an insane idea or not? My hope is
that it would be done with a smaller "work envelope", utilizing
smaller wires and a smallish capacitor, instead of a bulky contactor
and big wire, etc.

Any thoughts on bypassing the inductor?

The capacitor cancels the inductor impedance, only at one
frequency. I don't think this approach is feasible for this
application. I would be thinking in terms of splitting the
inductor winding and connecting the halves in series for
stick or tig welding and in parallel (1/4 the inductance)
for mig welding.

But you might just be able to short the inductor with a low
voltage contactor, similar to what is used for cranking
motors. As long as you don't open it during welding, you
don't have to worry much about its voltage rating, and the
current rating will be pretty conservative.
http://www.mouser.com/catalog/630/1640.pdf

I

#### Ignoramus20083

Jan 1, 1970
0
In order for the capacitor to cancel the current going through the
inductor, the current through the capacitor would have to be as large
as the current going through the inductor. So a lot of capacitance and
large wire.

Not true actually, the inductor is there to smooth current
fluctuations due to change in arc length, etc, and keep the arc going,
so the capacitor would only see action when welding parameters change
-- hopefully only a fraction of the time. I may very easily be
mistaken, though.

i

I

#### Ignoramus20083

Jan 1, 1970
0
The capacitor cancels the inductor impedance, only at one
frequency. I don't think this approach is feasible for this
application. I would be thinking in terms of splitting the
inductor winding and connecting the halves in series for
stick or tig welding and in parallel (1/4 the inductance)
for mig welding.

Yep, you are 100% right, a cap won't work. I realized it too. :-(
But you might just be able to short the inductor with a low
voltage contactor, similar to what is used for cranking
motors. As long as you don't open it during welding, you
don't have to worry much about its voltage rating, and the
current rating will be pretty conservative.
http://www.mouser.com/catalog/630/1640.pdf

Yes, I have a few suitable contactors, one three pole motor control
type contactor with 65 amp rating on each pole and 110v coil. I would
parallel all poles. I also have 24v coil, 400A rated DC contactors.

I collect contactors and motor controls.

Thanks. I will just do that bypass -- shoould not be a problem, it is
simple work.

i

N

#### Nick Mueller

Jan 1, 1970
0
Ignoramus20083 said:
The issue at hand is that the output of my welder goes through a large
inductor that is helpful in CC mode, but counterproductive for wire
feed welding.

Did you *ever* look at the parts list of a MIG/MAG welder before making that
clueless claim?
I bet not!

This inductor weighs perhaps 50 lbs. (?)

Oh yes, and voltage is measured in gallons, amperage in miles...

Nick

D

#### Don Young

Jan 1, 1970
0
Ignoramus20083 said:
This is in regards to an old Hobart CyberTIG welder that I modified by
putting in a new microcontroller that I programmed in BASIC.

http://igor.chudov.com/projects/Welding/11-New-Rectifier/

Basically because I have a separate SCR controller, and separate
module for controlling it, I can program it to do anything I want, to
supply any voltage and any current, within my power limits, of course.

So it is basicallly an arbitrary DC power supply, with a few extra
relays that control high frequency arc starting and gas valve.

This thing works just fine in constant current mode, letting me stick
weld as well as TIG weld.

Note that it has a big inductor that helps with constant current
welding.

Now that I am done with CC mode welding, I started exploring MIG
welding, which requires constant voltage. Found a LN-25 wirefeed unit
on Craigslist.

The issue at hand is that the output of my welder goes through a large
inductor that is helpful in CC mode, but counterproductive for wire
feed welding. This inductor weighs perhaps 50 lbs. (?)

So, for nice wire feed welding, I would need to bypass it. I see two
ways of doing it:

1) Make a simple bypass circuit using a big contactor and big cable
(to be turned on when MIG welding is being done).

2) Instead of bypassing the inductor, install a capacitor that would
"cancel out" the effect of the inductor.

Can that be done at all, is this an insane idea or not? My hope is
that it would be done with a smaller "work envelope", utilizing
smaller wires and a smallish capacitor, instead of a bulky contactor
and big wire, etc.

Any thoughts on bypassing the inductor?

thanks

i
Why not just install a separate output terminal not including the inductor
for the MIG?

Don Young

I

#### Ignoramus20083

Jan 1, 1970
0
Why not just install a separate output terminal not including the inductor
for the MIG?

Don, that's another great idea, the simplest so far. The minor
disadvantage is that it would not go along well with the polarity
commutator that I have, but it is surely no big deal.

i

M

#### Mark Rand

Jan 1, 1970
0
Any thoughts on bypassing the inductor?

thanks

i

Note that MIG/MAG welders still have inductance in the output, they just have
less than stick welders. Decent ones also have variable inductance.

Can you rebuild the inductor to make part of the core movable?

Mark Rand
RTFM

J

#### John Husvar

Jan 1, 1970
0
Mark Rand said:
Note that MIG/MAG welders still have inductance in the output, they just have
less than stick welders. Decent ones also have variable inductance.

Can you rebuild the inductor to make part of the core movable?

Mark Rand
RTFM

Just peeking at the parts lists on lincolnelectric.com indicates the
difference between CC and CV welders seems to be capacitance in the
output circuit at a casual look.

I'd imagine the inductance would be smaller than that in a CC welder
too, but adding in switchable capacitance should smooth output voltage
variations to some degree.

The question, of course, would be: how much capacitance and how to wire
it so you can switch between modes easily.

I

#### Ignoramus10518

Jan 1, 1970
0
Just peeking at the parts lists on lincolnelectric.com indicates the
difference between CC and CV welders seems to be capacitance in the
output circuit at a casual look.

I'd imagine the inductance would be smaller than that in a CC welder
too, but adding in switchable capacitance should smooth output voltage
variations to some degree.

The question, of course, would be: how much capacitance and how to wire
it so you can switch between modes easily.

Yes. A point was well made that the capacitance value would depend on
"frequency", but since this is not something where there is a fixed
frequency, we do not know the needed capacitance.

Practically speaking, I should simply bypass the inductor by adding
one more output that bypasses the inductor. It is a $10 solution and is totally bulletproof. All I need it bolt a welding cable connector to a piece of thick insulation board and mount it into a hole on the welder, and connect it properly to the output of the SCR rectifier. i I #### Ignoramus10518 Jan 1, 1970 0 Note that MIG/MAG welders still have inductance in the output, they just have less than stick welders. Decent ones also have variable inductance. Can you rebuild the inductor to make part of the core movable? Not easily, no, it is all well bolted down to the case of the welding machine. I thought that I did not need the inductor at all? Esp. considering that I am rectifying three phase (smoother voltage)? i G #### Glen Walpert Jan 1, 1970 0 Yes. A point was well made that the capacitance value would depend on "frequency", but since this is not something where there is a fixed frequency, we do not know the needed capacitance. The frequency issue was WRT "cancelling" the effect of the inductor, not really pertinent to your DC application. The function of stabilizing the output voltage against fast arc impedance fluctuations suggested by John is not the same and I recommend you give it serious consideration. Practically speaking, I should simply bypass the inductor by adding one more output that bypasses the inductor. It is a$10 solution and
is totally bulletproof. All I need it bolt a welding cable connector
to a piece of thick insulation board and mount it into a hole on the
welder, and connect it properly to the output of the SCR rectifier.

The suggestion of looking at how other machines do the CC/CV switch
was also a good one IMO.

And don't forget the adjustable droop .

G

I

#### Ignoramus10518

Jan 1, 1970
0
The frequency issue was WRT "cancelling" the effect of the inductor,
not really pertinent to your DC application. The function of
stabilizing the output voltage against fast arc impedance fluctuations
suggested by John is not the same and I recommend you give it serious
consideration.

Glen, I am a little lost, John talked about using only a part of the
inductance?
The suggestion of looking at how other machines do the CC/CV switch
was also a good one IMO.

Good idea. I looked at the Miller Deltaweld 451 manual:

http://www.millerwelds.com/om/o232s_mil.pdf

Its schematic is really very simple.

It has a three phase transformer, three phase SCR rectifier and a
control board -- all like I have in my current welder. If you recall,
I threw away the six phase rectifier and put in a regular SCR
rectifier with a modern SCR controller.

Now look at the top right corner of the picture. The first thing you
see is a fuse-protected capacitor bank C6. (part number 29,
6*16000uF). Then to the right, you see a transformer Z1, with its
"CR1". That "Z1" is called a "stabilizer" and is part number 22.

CR1 is a 24 VAC, definite purpose contactor (!)

I am not sure WTH this contactor is doing here.
And don't forget the adjustable droop .

G, I will definitely work on the droop and constant power welding in
general. I need to make some changes that I am afraid to make. That
is, make the voltage and current adjustment pots be inputs to the
BASIC controller, as opposed to being inputs to the SCR firing
controller (as it is now). I am afraid that a bug in BASIC may make
the welder fry something or someone by outputing a lot more than it
was asked for. Now, at least, I know that output will be no more than
what I dialed.

i

D

#### David R Brooks

Jan 1, 1970
0
In order for the capacitor to cancel the current going through the
inductor, the current through the capacitor would have to be as large
as the current going through the inductor. So a lot of capacitance and
large wire.
Putting an L-C circuit with an arc, you might end up building a power
oscillator. Look up "Poulsen arc transmitter" in the usual places.
An arc can exhibit a negative AC resistance: this was used in the very
early days of radio, to build CW transmitters before tubes were
available (at that power level, anyway).

J

#### Joseph Gwinn

Jan 1, 1970
0
Ignoramus10518 said:
Glen, I am a little lost, John talked about using only a part of the
inductance?

Good idea. I looked at the Miller Deltaweld 451 manual:

http://www.millerwelds.com/om/o232s_mil.pdf

Its schematic is really very simple.

It has a three phase transformer, three phase SCR rectifier and a
control board -- all like I have in my current welder. If you recall,
I threw away the six phase rectifier and put in a regular SCR
rectifier with a modern SCR controller.

Now look at the top right corner of the picture. The first thing you
see is a fuse-protected capacitor bank C6. (part number 29,
6*16000uF). Then to the right, you see a transformer Z1, with its
"CR1". That "Z1" is called a "stabilizer" and is part number 22.

CR1 is a 24 VAC, definite purpose contactor (!)

I am not sure WTH this contactor is doing here.

When the contactor activates, the second winding on the inductor is
shorted, which will cause the inductance to become very low. Shorting a
winding rather than the main winding allows one to use a relatively
small contactor.

Joe Gwinn

M

#### Martin H. Eastburn

Jan 1, 1970
0
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/

Putting an L-C circuit with an arc, you might end up building a power
oscillator. Look up "Poulsen arc transmitter" in the usual places.
An arc can exhibit a negative AC resistance: this was used in the very
early days of radio, to build CW transmitters before tubes were
available (at that power level, anyway).

Before tubes was hardly radio. That was massive RF noise bursts hoping
that someone got the interference. Tubes refined to bands and channels.
Transistors to sub channels while tube and transistors had sidebands.

When high power is needed, tubes are still used. Solid state is catching
up but RF power is still complex for solid state for big stuff.

Martin

J

#### Jasen

Jan 1, 1970
0
Now that I am done with CC mode welding, I started exploring MIG
welding, which requires constant voltage. Found a LN-25 wirefeed unit
on Craigslist.

does it really need to be constant?
The issue at hand is that the output of my welder goes through a large
inductor that is helpful in CC mode, but counterproductive for wire
feed welding. This inductor weighs perhaps 50 lbs. (?)

So, for nice wire feed welding, I would need to bypass it. I see two
ways of doing it:

1) Make a simple bypass circuit using a big contactor and big cable
(to be turned on when MIG welding is being done).

that sounds simplest.
2) Instead of bypassing the inductor, install a capacitor that would
"cancel out" the effect of the inductor.

this will only work at a single frequency.
Can that be done at all, is this an insane idea or not? My hope is
that it would be done with a smaller "work envelope", utilizing
smaller wires and a smallish capacitor, instead of a bulky contactor
and big wire, etc.

Any thoughts on bypassing the inductor?

The bypass current has to flow somewhere, thin wires won't cut it.

Putting the capacitor to ground may be more productive, you'd get the
basic buck regulator topology.

how much voltage regulation is needed for wirefed welding anyway?

Bye.
Jasen

G

#### Glen Walpert

Jan 1, 1970
0
Glen, I am a little lost, John talked about using only a part of the
inductance?

Pardon the slow response, I have been in an internet free zone

Consider what is going on in the arc in GMAW welding: There are
variations in arc impedance which occur on a fast time scale due to
the motion of metal droplets within the arc, and there are variations
on a slower time scale due to changes in average arc length due to the
difference in wire feed rate and burnback rate.

As the wire gets closer to the puddle you want the current to increase
and cause the wire to burn back faster; as it burns back you want the
current to drop so that the arc does not get too long. Thus the wire
feed rate determines the average current and the power supply voltage
determines the average arc length in the CV mode used for GMAW -
nominally.

On a faster time scale however a true constant voltage characteristic
would cause problems due to excessive current fluctuation. Consider
the 3 "modes" of GMAW: short circuiting mode at low power for thin
materials where the liquid metal droplets form repetitive short
circuits, droplet transfer modes at medium powers where fairly large
droplets periodically break off and transfer without shorting, and
spray mode at high powers where there is a continuous spray of fine
droplets in the arc. (Not that there is a sudden transition between
modes as power is increased, it is actually a gradual and continuous
decrease in drop size as power is increased.) The variations in arc
impedance due to droplet position in the arc are obviously worst in
short circuiting mode and reduce in severity as power is increased.
But in all cases you do not want to allow droplet position to have a
big effect on arc current, which should change more slowly with
average arc length - at a speed which cam be handled by your SCR
controller.

The variations due to droplet movement are way to fast for your SCR
controller to respond to, and you don't want the arc current to
fluctuate that fast anyhow, so on the fast time scale you want the arc
characteristics to approximate constant current. Hence an inductor.
Good idea. I looked at the Miller Deltaweld 451 manual:

http://www.millerwelds.com/om/o232s_mil.pdf

Its schematic is really very simple.

It has a three phase transformer, three phase SCR rectifier and a
control board -- all like I have in my current welder. If you recall,
I threw away the six phase rectifier and put in a regular SCR
rectifier with a modern SCR controller.

Now look at the top right corner of the picture. The first thing you
see is a fuse-protected capacitor bank C6. (part number 29,
6*16000uF). Then to the right, you see a transformer Z1, with its
"CR1". That "Z1" is called a "stabilizer" and is part number 22.

CR1 is a 24 VAC, definite purpose contactor (!)

I am not sure WTH this contactor is doing here.

It is there to vary the inductance of Z1, as Joe Gwinn already
mentioned. When the contactor is closed the current induced in the
second winding tends to cancel the flux produced by the main winding,
hence reducing the inductance. Presumably CR1 is closed only in CV
mode.

G

#### Grant Erwin

Jan 1, 1970
0
2) Instead of bypassing the inductor, install a capacitor that would
"cancel out" the effect of the inductor.

Can that be done at all, is this an insane idea or not? My hope is
that it would be done with a smaller "work envelope", utilizing
smaller wires and a smallish capacitor, instead of a bulky contactor
and big wire, etc.

If you add a capacitor, you are making an LC filter which may strongly affect
your waveform. When you want a nice rising edge of current, you might get a
sinusoidal pulse followed by ringing. I think the capacitor idea might be doable
but it would require a ton of electrical engineering.

Grant

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