Are MOSFETS best for this?

Greetings All,
I have a small Lincoln wirefeed welder. Depending on the wire and the
process the welding wire will be either + or - polarity. To switch
polarity two thumb nuts must be removed and swapped. This sounds
easier than it is. Partly because of the way the welder is made. I
swap polarity on a pretty regular basis so I would like to do this
with just a switch. The max voltage is 30 volts and the max amperage
is 140 amps. That 140 amps is very brief, maybe just a few seconds.
Continuous current is 100 amps and 30 volts. I thought an H bridge
would work but I can't find and MOSFETS that are rated this high for
positive current. Can the MOSFETS be paralleled easily? Is there a
better choice? The polarity would never be changed with power applied.
I thought about using a relay with contacts rated at 150 amps or a
double pole contactor or even a big toggle switch. All these options
are too expensive. I'm cheap. I don't wanna spend more than $75 US on
this project. Anybody here have some guidance?
Thanks,
Eric

 

[Phil Allison]

et...@whidbey.com wrote:

I have a small Lincoln wirefeed welder. Depending on the wire and the
process the welding wire will be either + or - polarity. To switch
polarity two thumb nuts must be removed and swapped. This sounds
easier than it is. Partly because of the way the welder is made. I
swap polarity on a pretty regular basis so I would like to do this
with just a switch. The max voltage is 30 volts and the max amperage
is 140 amps. That 140 amps is very brief, maybe just a few seconds.
Continuous current is 100 amps and 30 volts. I thought an H bridge
would work but I can't find and MOSFETS that are rated this high for
positive current. Can the MOSFETS be paralleled easily? Is there a
better choice? The polarity would never be changed with power applied.
I thought about using a relay with contacts rated at 150 amps or a
double pole contactor or even a big toggle switch. All these options
are too expensive. I'm cheap. I don't wanna spend more than $75 US on
this project. Anybody here have some guidance?

** This ought to do he job nicely, a 100amp rated knife switch.

http://www.ebay.com.au/itm/100-Amp-Disconnect-Knife-Switch-100A-Two-Pole-Circuit-Breaker-Backup-Generator-2-/170881623181

Within your puny budget too.



..... Phil

 

>"a 100amp rated knife switch..."

Good goin mate. You just threw that guy out of electronics into electricity, makinbg most of us useless.

But you are right, IIRC DC welding is not filtered so the inductance is still there. In faxct the pulsating DC is almost desirable from what I have gleaned and the few time I have done it. Long time ago.

But really, anyone who knows should be calling for a knife switch or a super uper duper relay to switch this. this is simply not a job for semicondutors. Period.

OK you fuck are going to prove me "wrong" pointing out some super six million amp welder in bumfuct Israel somewhere that uses the FETs. Yeah well you know them people got technology about twenty years ahead of the rest of the world when it cones to weapons. But they can weld steel to glass I am sure.

At any rate, nopne of this shit is filtered. Even the rectifiers in a welder have to be over rated because of that. It actually welds better than pure, filtered DC.

Because of the inductance factor and all that, using semoconductor devices in that aplication is contraindicated IMO. I think my opinion is valid.

However there might be something out there better than a knife switch. But then do we care ? A knife switch wil do the job, what more do you want ? Pancakes ?

 

Oh fuck, now I know I am nuts. ...

How about a motorized knife switch that can be controlled by a pedal. Like a guitarist changing channels...


???

 

[amdx]

On 2/27/2015 9:05 PM, Phil Allison wrote:

et...@whidbey.com wrote:


I have a small Lincoln wirefeed welder. Depending on the wire and the
process the welding wire will be either + or - polarity. To switch
polarity two thumb nuts must be removed and swapped. This sounds
easier than it is. Partly because of the way the welder is made. I
swap polarity on a pretty regular basis so I would like to do this
with just a switch. The max voltage is 30 volts and the max amperage
is 140 amps. That 140 amps is very brief, maybe just a few seconds.
Continuous current is 100 amps and 30 volts. I thought an H bridge
would work but I can't find and MOSFETS that are rated this high for
positive current. Can the MOSFETS be paralleled easily? Is there a
better choice? The polarity would never be changed with power applied.
I thought about using a relay with contacts rated at 150 amps or a
double pole contactor or even a big toggle switch. All these options
are too expensive. I'm cheap. I don't wanna spend more than $75 US on
this project. Anybody here have some guidance?


** This ought to do he job nicely, a 100amp rated knife switch.

http://www.ebay.com.au/itm/100-Amp-Disconnect-Knife-Switch-100A-Two-Pole-Circuit-Breaker-Backup-Generator-2-/170881623181

Within your puny budget too.



.... Phil

I wish I had seen that when I had my electric gokart, I always wanted
reverse, that would have been great and also work as an emergency
disconnect. The cost of solenoids made it unreasonable.
Hey, it's a great idea for the welder too!

Mikek

 

[Ecnerwal]

In article <6162fa1uvaemdgsiqbas914mi3h2sqv40o@4ax.com>,
etpm@whidbey.com wrote:

I have a small Lincoln wirefeed welder. Depending on the wire and the
process the welding wire will be either + or - polarity. To switch
polarity two thumb nuts must be removed and swapped. This sounds
easier than it is. Partly because of the way the welder is made. I
swap polarity on a pretty regular basis
....
All these options
are too expensive. I'm cheap. I don't wanna spend more than $75 US on
this project. Anybody here have some guidance?

Just put a pair of Tweco MPC cam-type quick disconnects either on the
output terminals, or in-line in the leads. Or add a loop of leads that
comes out where you can get to them if the thing gives you no room for
that inside (small wirefeed, probably true.)

Might cost you $28-60 altogether, or more if you are supporting a local
supplier who's not in competition with the internet/does not give you a
nice fat discount.

I color code the ground clamp green, the stinger yellow, so it's easy to
see at a glance how it's connected to the normally-coded terminals
(Red+/Black-)

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

 

[default]

On Fri, 27 Feb 2015 17:35:32 -0800, etpm@whidbey.com wrote:

Greetings All,
I have a small Lincoln wirefeed welder. Depending on the wire and the
process the welding wire will be either + or - polarity. To switch
polarity two thumb nuts must be removed and swapped. This sounds
easier than it is. Partly because of the way the welder is made. I
swap polarity on a pretty regular basis so I would like to do this
with just a switch. The max voltage is 30 volts and the max amperage
is 140 amps. That 140 amps is very brief, maybe just a few seconds.
Continuous current is 100 amps and 30 volts. I thought an H bridge
would work but I can't find and MOSFETS that are rated this high for
positive current. Can the MOSFETS be paralleled easily? Is there a
better choice? The polarity would never be changed with power applied.
I thought about using a relay with contacts rated at 150 amps or a
double pole contactor or even a big toggle switch. All these options
are too expensive. I'm cheap. I don't wanna spend more than $75 US on
this project. Anybody here have some guidance?
Thanks,
Eric

Check out some winch reversing switches, they handle the current you
want, reasonably priced, compact. Only downside is that you need 12
for some of the solenoid coils.

 

[Phil Allison]

et...@whidbey.com wrote:

Phil Allison wrote:

** This ought to do he job nicely, a 100amp rated knife switch.

http://www.ebay.com.au/itm/100-Amp-Disconnect-Knife-Switch-100A-Two-Pole-Circuit-Breaker-Backup-Generator-2-/170881623181

Within your puny budget too.


That knife switch would work if I can find room inside the welder.

** FFS - it cannot go *inside* anything.

Mount it on top or one of the sides if you must.


> Simple too.

** No fooling.......

I'll have to see. I looked on ebay for knife switches and
didn't see any that would work. I'll need to look again.

** What for ?

The switch can go in-line with the welding leads.

Mount it on a heavy base and run short leads to it from the welder.

You may even be able to operate it with your spare foot.



..... Phil

 

On Fri, 27 Feb 2015 22:02:15 -0600, amdx <nojunk@knology.net> wrote:

On 2/27/2015 9:05 PM, Phil Allison wrote:
et...@whidbey.com wrote:


I have a small Lincoln wirefeed welder. Depending on the wire and the
process the welding wire will be either + or - polarity. To switch
polarity two thumb nuts must be removed and swapped. This sounds
easier than it is. Partly because of the way the welder is made. I
swap polarity on a pretty regular basis so I would like to do this
with just a switch. The max voltage is 30 volts and the max amperage
is 140 amps. That 140 amps is very brief, maybe just a few seconds.
Continuous current is 100 amps and 30 volts. I thought an H bridge
would work but I can't find and MOSFETS that are rated this high for
positive current. Can the MOSFETS be paralleled easily? Is there a
better choice? The polarity would never be changed with power applied.
I thought about using a relay with contacts rated at 150 amps or a
double pole contactor or even a big toggle switch. All these options
are too expensive. I'm cheap. I don't wanna spend more than $75 US on
this project. Anybody here have some guidance?


** This ought to do he job nicely, a 100amp rated knife switch.

http://www.ebay.com.au/itm/100-Amp-Disconnect-Knife-Switch-100A-Two-Pole-Circuit-Breaker-Backup-Generator-2-/170881623181

Within your puny budget too.



.... Phil




I wish I had seen that when I had my electric gokart, I always wanted
reverse, that would have been great and also work as an emergency
disconnect. The cost of solenoids made it unreasonable.
Hey, it's a great idea for the welder too!

Mikek

That knife switch would work if I can find room inside the welder.
Simple too. I'll have to see. I looked on ebay for knife switches and
didn't see any that would work. I'll need to look again.
Thanks,
Eric

 

On Sat, 28 Feb 2015 09:45:59 -0500, Ecnerwal
<MyNameForward@ReplaceWithMyVices.Com.invalid> wrote:

In article <6162fa1uvaemdgsiqbas914mi3h2sqv40o@4ax.com>,
etpm@whidbey.com wrote:

I have a small Lincoln wirefeed welder. Depending on the wire and the
process the welding wire will be either + or - polarity. To switch
polarity two thumb nuts must be removed and swapped. This sounds
easier than it is. Partly because of the way the welder is made. I
swap polarity on a pretty regular basis
...
All these options
are too expensive. I'm cheap. I don't wanna spend more than $75 US on
this project. Anybody here have some guidance?


Just put a pair of Tweco MPC cam-type quick disconnects either on the
output terminals, or in-line in the leads. Or add a loop of leads that
comes out where you can get to them if the thing gives you no room for
that inside (small wirefeed, probably true.)

Might cost you $28-60 altogether, or more if you are supporting a local
supplier who's not in competition with the internet/does not give you a
nice fat discount.

I color code the ground clamp green, the stinger yellow, so it's easy to
see at a glance how it's connected to the normally-coded terminals
(Red+/Black-)

Greetings Lawrence,
I looked at those some time ago and there is really no room for them
inside the wire spool enclosure. But thanks for the suggestion. It's
important to me to have the switching inside the enclosure, one reason
being that I have already added some knobs and switches to the welder
that take up the available space. I added a purge button and a pulse
timer to the welder. So now I can purge the welding lead of air before
I start welding without feeding the wire out and I can do stitch
welding.
Cheers,
Eric

 

On Sat, 28 Feb 2015 10:12:08 -0500, default <default@defaulter.net>
wrote:

On Fri, 27 Feb 2015 17:35:32 -0800, etpm@whidbey.com wrote:

Greetings All,
I have a small Lincoln wirefeed welder. Depending on the wire and the
process the welding wire will be either + or - polarity. To switch
polarity two thumb nuts must be removed and swapped. This sounds
easier than it is. Partly because of the way the welder is made. I
swap polarity on a pretty regular basis so I would like to do this
with just a switch. The max voltage is 30 volts and the max amperage
is 140 amps. That 140 amps is very brief, maybe just a few seconds.
Continuous current is 100 amps and 30 volts. I thought an H bridge
would work but I can't find and MOSFETS that are rated this high for
positive current. Can the MOSFETS be paralleled easily? Is there a
better choice? The polarity would never be changed with power applied.
I thought about using a relay with contacts rated at 150 amps or a
double pole contactor or even a big toggle switch. All these options
are too expensive. I'm cheap. I don't wanna spend more than $75 US on
this project. Anybody here have some guidance?
Thanks,
Eric

Check out some winch reversing switches, they handle the current you
want, reasonably priced, compact. Only downside is that you need 12
for some of the solenoid coils.

I didn't even think about winch reversing switches and I have a winch
on my Jeep. Thanks, I'll look at them.
Eric

 

[Phil Allison]

Jeff Layman wrote:

The switch can go in-line with the welding leads.

Mount it on a heavy base and run short leads to it from the welder.


That switch is just exposed metal,

** GIANT Huh ???????

You blind - the fucking thing is PLASTIC !!

and Sod's Law will arrange for
something heavy and metallic (such as a screwdriver) to fall onto it
someday and short it.

** You drunk or on illegal dugs ???

The OP will also need a couple of heavy-duty
connector blocks for the crossover wiring,

** Wot is YOUR fucking problem ???

Have you actually LOOKED at the pic of the thing ?

Jesus fucking Christ Almighty we have some -

LOPEY dickheads posting here.



..... Phil



..... Phil

 

[Jeff Layman]

On 01/03/15 02:27, Phil Allison wrote:

The switch can go in-line with the welding leads.

Mount it on a heavy base and run short leads to it from the welder.

Makes sense. I would also suggest a cover which closes over the switch.
That switch is just exposed metal, and Sod's Law will arrange for
something heavy and metallic (such as a screwdriver) to fall onto it
someday and short it. The OP will also need a couple of heavy-duty
connector blocks for the crossover wiring, which could go on the heavy
base as well. Doesn't look like there's room on the switch connectors
for two wires.

--

Jeff

 

[Ron M.]

Very nice response Phil. You could have just said look at it again. What possible reason have you to be in such a foul mood all the time?

 

[Jeff Layman]

On 01/03/15 10:51, Phil Allison wrote:

Jeff Layman wrote:

The switch can go in-line with the welding leads.

Mount it on a heavy base and run short leads to it from the welder.


That switch is just exposed metal,


** GIANT Huh ???????

You blind - the fucking thing is PLASTIC !!

I see what you mean. For some reason the first time I looked at it the
touchpad went into touch-to-click mode and all I got was the large
picture of the uncovered switch.

--

Jeff

 

[Phil Allison]

Ron M. wrote:


> Very nice response Phil.

** Yep.

You could have just said look at it again.

** That would be a completely idiotic thing to say.

What possible reason have you to be in such a foul mood all the time?

** I'm in a fine mood.


.... Phil