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Electronic circuit design discusions
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MIG Welding, CC Inductor, and bypass thereof
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
On May 14, 9:46 am, Ignoramus20083 <ignoramus20...@NOSPAM. 20083.invalid> wrote: > 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
-----------------------------------------------Reply-----------------------------------------------
Ignoramus20083 wrote: > 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
-----------------------------------------------Reply-----------------------------------------------
On 14 May 2007 15:00:34 -0700, dcas @krl.org <dcas @krl.org> wrote:
> On May 14, 9:46 am, Ignoramus20083 <ignoramus20...@NOSPAM. > 20083.invalid> wrote: >> 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.
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
-----------------------------------------------Reply-----------------------------------------------
On Mon, 14 May 2007 19:17:38 -0400, John Popelish <jpopel @rica.net> wrote: > Ignoramus20083 wrote: >> 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.
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
-----------------------------------------------Reply-----------------------------------------------
Ignoramus20083 wrote:
> 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
-----------------------------------------------Reply-----------------------------------------------
"Ignoramus20083" <ignoramus20 @NOSPAM.20083.invalid> wrote in message ...
> 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
-----------------------------------------------Reply-----------------------------------------------
On Mon, 14 May 2007 21:30:21 -0500, Don Young <n @nonesuch.com> wrote: > "Ignoramus20083" <ignoramus20@NOSPAM.20083.invalid> wrote in message
> news:zLadnSV-WPHOD9XbnZ2dnUVZ_ragnZ2d@giganews.com...
>> 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, 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
-----------------------------------------------Reply-----------------------------------------------
On Mon, 14 May 2007 11:46:11 -0500, Ignoramus20083 <ignoramus20 @NOSPAM.20083.invalid> wrote: >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
-----------------------------------------------Reply-----------------------------------------------
In article <afui43dl2te2vdj5inl9ah5e6h38a4b @4ax.com>, Mark Rand <r @internettie.co.uk> wrote:
> On Mon, 14 May 2007 11:46:11 -0500, Ignoramus20083 > <ignoramus20 @NOSPAM.20083.invalid> wrote: > >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
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.
-----------------------------------------------Reply-----------------------------------------------
On Tue, 15 May 2007 12:54:13 GMT, John Husvar <jhus @sbcglobal.net> wrote: > In article <afui43dl2te2vdj5inl9ah5e6h38a4b @4ax.com>, > Mark Rand <r @internettie.co.uk> wrote: >> On Mon, 14 May 2007 11:46:11 -0500, Ignoramus20083
>> <ignoramus20@NOSPAM.20083.invalid> wrote:
>> >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
> 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
-----------------------------------------------Reply-----------------------------------------------
On Tue, 15 May 2007 10:18:45 +0100, Mark Rand <r @internettie.co.uk> wrote: > On Mon, 14 May 2007 11:46:11 -0500, Ignoramus20083 ><ignoramus20 @NOSPAM.20083.invalid> wrote: >>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?
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
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