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Would this work for a simple 0.1 - 2.0 A micro tig welder circuit?

microtig welders typically run from 0.1A or less to 2.0A, constant
current. Unfortunately machines that can do this are very expensive.

These use (I think) squarewave DC to acheive a tight arc.

If I were to make a simple constant current circuit and drive it with a
benchtop function generator through a power mosfet or some other
switching device, would you foresee any problems?

Now also, apparently any sort of current surges during arc-start is bad
as it can blow a hole in the material being welded. I haven't the
foggiest idea what to do to prevent that, maybe some sort of capacitor
or something to buffer surges?

I know only a tiny bit about electronics, so forgive me if I am asking
something obvious or stupid.
 
F

Fred Bloggs

Jan 1, 1970
0
microtig welders typically run from 0.1A or less to 2.0A, constant
current. Unfortunately machines that can do this are very expensive.

These use (I think) squarewave DC to acheive a tight arc.

If I were to make a simple constant current circuit and drive it with a
benchtop function generator through a power mosfet or some other
switching device, would you foresee any problems?

Now also, apparently any sort of current surges during arc-start is bad
as it can blow a hole in the material being welded. I haven't the
foggiest idea what to do to prevent that, maybe some sort of capacitor
or something to buffer surges?

I know only a tiny bit about electronics, so forgive me if I am asking
something obvious or stupid.

Without going into a lot of detail, you want something like shown below.
This is an adjustable current source that flows constantly and is
shunted around the work piece or not to pulse current into it. Diodes in
series with load ensure the shunting action.

View in a fixed-width font such as Courier.

..
..
.. V+
..
.. | Rc
.. +------------/\/\--+--------------.
.. | | |
.. +--------. | PFET|
.. | | | | S
.. | | | (-) ||-+
.. _|_/ / POT +----|\ ||>-
.. // \ \ | >----||-+
.. --- / <------------|/ G | D
.. |zener \ (+) |
.. | | ADJ OA |
.. | | CURRENT +-----|>|-|>|---.
.. +--------' | |
.. | OFF | |
.. / --- | D |
.. Rbz | | ||-+ |
.. / ON | | ON >-----||<- NFET WORKPIECE
.. \ --- -- G ||-+ |
.. | | S |
.. +---------------------------------+---------------+
.. | |
.. --- ---
.. /// ///
..
..
 
F

Fred Bloggs

Jan 1, 1970
0
microtig welders typically run from 0.1A or less to 2.0A, constant
current. Unfortunately machines that can do this are very expensive.

These use (I think) squarewave DC to acheive a tight arc.

If I were to make a simple constant current circuit and drive it with a
benchtop function generator through a power mosfet or some other
switching device, would you foresee any problems?

Now also, apparently any sort of current surges during arc-start is bad
as it can blow a hole in the material being welded. I haven't the
foggiest idea what to do to prevent that, maybe some sort of capacitor
or something to buffer surges?

I know only a tiny bit about electronics, so forgive me if I am asking
something obvious or stupid.

View in a fixed-width font such as Courier.

..
..
..
.. V+
.. | Rc
.. +------------/\/\--+--------------.
.. | | |
.. +--------. | PFET|
.. | | | | S
.. | | | (-) ||-+
.. _|_/ / POT +----|\ ||>-
.. // \ \ | >----||-+
.. --- / <------------|/ G | D
.. |zener \ (+) |
.. | | ADJ OA -----
.. | | CURRENT |'''''|
.. +--------' AMP | / |
.. | METER -----
.. / |
.. Rbz +-----|>|-|>|---.
.. / | |
.. \ OFF | |
.. | --- | D |
.. | | | ||-+ |
.. | ON | | ON >-----||<- NFET WORKPIECE
.. | --- -- G ||-+ |
.. | | S |
.. +---------------------------------+---------------+
.. | |
.. --- ---
.. /// ///
..
..
 
F

Fred Bloggs

Jan 1, 1970
0
One last time- this one makes more sense if you're pulsing with an
external generator- CMOS voltage levels will work:

View in a fixed-width font such as Courier.

..
..
..
.. V+
.. | Rc
.. .------+------------/\/\--+--------------.
.. | | | |
.. | +--------. | PFET|
.. | | | | | S
.. | | | | (-) ||-+
.. / _|_/ / POT +----|\ ||>-
.. Rpu1 // \ \ | >----||-+
.. / --- / <------------|/ G | D
.. \ |zener \ (+) |
.. | | | ADJ OA -----
.. | | | CURRENT |'''''|
.. | +--------' AMP | / |
.. | | METER -----
.. | | |
.. +------|-----------------+---------. +-----|>|-|>|---.
.. | | | | | |
.. | | | D | | |
.. / / ||-+ | | D |
.. Rpu2 Rbz +---||<- 2N7000 | ||-+ |
.. / / | G ||-+ +--||<- NFET WORKPIECE
.. \ \ | | S G ||-+ |
.. | | | | | S |
.. +------+-----------------+---------------+---------------+
.. | | | |
.. --- | / ---
.. /// | 1K ///
.. | /
.. ON | \
.. --- | |
.. | | | |
.. OFF| | OFF | |
.. --- --- >----+------+
 
J

James Meyer

Jan 1, 1970
0
microtig welders typically run from 0.1A or less to 2.0A, constant
current. Unfortunately machines that can do this are very expensive.

These use (I think) squarewave DC to acheive a tight arc.

If I were to make a simple constant current circuit and drive it with a
benchtop function generator through a power mosfet or some other
switching device, would you foresee any problems?

Now also, apparently any sort of current surges during arc-start is bad
as it can blow a hole in the material being welded. I haven't the
foggiest idea what to do to prevent that, maybe some sort of capacitor
or something to buffer surges?

I know only a tiny bit about electronics, so forgive me if I am asking
something obvious or stupid.

You can buy 60 volt, 17 amp power supplies for around $200 from surplus
dealers on eBay. Those supplies have adjustable voltage and current outputs.
Then all you would have to build is the high frequency, low power, arc starting
circuit.

Here's a link:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=58286&item=7523999616&rd=1

Jim
 
F

Fred Bloggs

Jan 1, 1970
0
Hmmm- if you have jittery hands then it would be a good idea to add a
compliance clamp- this ensures that the current source remains in
regulation at all times:
View in a fixed-width font such as Courier.

..
..
..
.. V+
.. | Rc
.. .------+------------/\/\--+--------------.
.. | | | |
.. | +--------. | PFET|
.. | | | | | S
.. | | | | (-) ||-+
.. / _|_/ / POT +----|\ ||>-
.. Rpu1 // \ \ | >----||-+
.. / --- / <------------|/ G | D
.. \ |zener \ (+) |
.. | | | ADJ OA -----
.. | | | CURRENT |'''''|
.. | +--------' AMP | / |
.. | | METER -----
.. | | |
.. +------|-----------------+---------. +------+---|>|-|>|--.
.. | | | | | | |
.. | | | D | NFET| +---+ |
.. / / ||-+ | | zener|_/ | |
.. Rpu2 Rbz +---||<- 2N7000 | ||-+ D // \ | WORK
.. / / | G ||-+ +--||<- --- | PIECE
.. \ \ | | S G ||-+ | | |
.. | | | | | S | | |
.. +------+-----------------+---------------+-------------------+
.. | | | | | | |
.. --- | / | | | ---
.. /// | 1K | | c ///
.. | / | 1K | |/
.. ON | \ +-/\/\-+-|
.. --- | | | |\
.. | | | | | e
.. OFF| | OFF | | | |
.. --- --- >----+------+ +----------+
.. compliance clamp
..
..
..
 
F

Fred Bloggs

Jan 1, 1970
0
You can buy 60 volt, 17 amp power supplies for around $200 from surplus
dealers on eBay.

For *micro* TIG? You can't be serious.
Those supplies have adjustable voltage and current outputs.

You would think.
Then all you would have to build is the high frequency, low power, arc starting
circuit.

DC touchstart is suitable for microTIG.
 
S

Spehro Pefhany

Jan 1, 1970
0
You can buy 60 volt, 17 amp power supplies for around $200 from surplus
dealers on eBay. Those supplies have adjustable voltage and current outputs.
Then all you would have to build is the high frequency, low power, arc starting
circuit.

Here's a link:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=58286&item=7523999616&rd=1

Jim

Plus $95 for shipping to the CONUS. Ouch.

I'm not too sure what to make of 'Unable to test no Power Cord'
either. If I was selling a $300 delivered-price doodad, I'd sure as
heck find a way to plug it in and check for functionality.

http://toolhaus.org/cgi-bin/negs?User=surplus-supply-com&Dirn=Received+by



Best regards,
Spehro Pefhany
 
M

mike

Jan 1, 1970
0
Fred said:
For *micro* TIG? You can't be serious.



You would think.


DC touchstart is suitable for microTIG.

More details on arc starting please.

I have a 0-16V 0-40A regulated supply that I've been wanting to convert into
a *mini*tig welder. Something for welding thin aluminum boxes together.

My experience with macrotig has been horrible. I can't do ANYTHING
without turning on the "buzz-box" RF generator.

It's not obvious how you get big RF volts to start the arc without
blowing up the regulated supply.

Then there's handpiece design and the plumbing to get the argon flowing.
thanks, mike

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F

Fred Bloggs

Jan 1, 1970
0
mike said:
More details on arc starting please.

I have a 0-16V 0-40A regulated supply that I've been wanting to convert
into
a *mini*tig welder. Something for welding thin aluminum boxes together.

My experience with macrotig has been horrible. I can't do ANYTHING
without turning on the "buzz-box" RF generator.

It's not obvious how you get big RF volts to start the arc without
blowing up the regulated supply.

Then there's handpiece design and the plumbing to get the argon flowing.
thanks, mike

This microTIG stuff requires only a few volts to keep the arc going once
started , I am guessing something less than 5V, but this pulsating stuff
is not an on/off action, it is an alternation between the set current
and a "background" current ( needed to keep the arc going?). Lincoln has
some patents on what they claim to be a low voltage current limited high
frequency starter, Micro-Start. It would be worth taking a look if you
can find it. I don't know why an inductor in series with drain of
current regulator PFET shouldn't work as a touchstart arc.

View in a fixed-width font such as Courier.

..
..
.. .-----------------------------------.
.. V+ | |
.. | | Rc |
.. .------+--------+---/\/\--+--------------. |
.. | | | | |
.. | +--------. | PFET| |
.. | | | | | S /
.. | | | | (-) ||-+ Rback
.. / _|_/ / POT +----|\ ||>- /
.. Rpu1 // \ \ | >----||-+ \
.. / --- / <------------|/ G | D |
.. \ |zener \ (+) | |
.. | | | ADJ OA ----- |
.. | | | CURRENT |'''''| |
.. | +--------' AMP | / | |
.. | | METER ----- |
.. | | | |
.. +------|-----------------+---------. +-|>|-|>|--+----.
.. | | | | | |
.. | | | D | | |
.. / / ||-+ | | D |
.. Rpu2 Rbz +---||<- 2N7000 | ||-+ |
.. / / | G ||-+ +--||<- NFET WORKPIECE
.. \ \ | | S G ||-+ |
.. | | | | | S |
.. +------+-----------------+---------------+---------------+
.. | | | |
.. --- | / ---
.. /// | 1K ///
.. | /
.. ON | \
.. --- | |
.. | | | |
.. OFF| | OFF | |
.. --- --- >----+------+
 
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