120 amp max welder needs only a 20amp breaker

[mikeinfodoc]

I have a 90amp flux core welder which works on standard US 115V mains.

It says it uses 120amps max/peak, yet the manual says it only needs a 20amp breaker (as a min)

Can someone explain to me how a 120peak amp welder needs only a 20amp breaker?

I assume it may be cap's inside which handle the shorter amp pulses...

I am probably wrong. I welcome feedback

[rstofer]

Well, 20A times 120V is pretty much the same as 100A times 24V.  So, they do it by reducing the voltage at the arc.
There are limits to how low the arc voltage can get and still be a viable welder but it must work because these MIG machines are all over the place.

My old 240A stick welder needs a 50A 240V circuit (IIRC).

[Zero999]

Put another way: Power = Volts × Amps.

A 20A breaker on 115V. Power = 20 × 115 = 2300W.

As stated above, the output of the welder is a much lower voltage, so the current can be much greater for the same power level.

The reverse will be true inside your car's ignition system: a few Amps at 12V in, milliamps at 12kV out.

[CaptainNomihodai]

I assume it may be cap's inside which handle the shorter amp pulses...

I'm fairly certain pulsed mode is exclusive to high-end TIG machines... Anyway, I'm curious as to how well a 115V powered wire-feed welder actually works. I had a 115V cheap Chinese inverter-based stick machine and it was crap. It worked, but it was very difficult to use (I am not a skilled welder) compared to an American 240V machine.
I would be skeptical of that 120A figure, since the power factor of the machine is probably quite low (assuming it's a transformer machine).

My old 240A stick welder needs a 50A 240V circuit (IIRC).

That's what the manual says it needs, or that's what it actually uses? My ~30 year old Dialarc 250 says it needs something ridiculous like a 150A breaker (for the non-PFC version, which I have)... I have yet to trip the 60A breaker that I run it off of.

[james_s]

There is also the matter of peak power. My air compressor has a LRA of something like 60A, but it will plug into a 15A circuit. It draws a very brief surge when the motor first starts up, but it is short enough that it does not trip the breaker. Circuit breakers can carry surge currents substantially higher than their steady state holding current.

[SeanB]

My 120A welder has a rating plate of needing 26A at full 120A welding current, but you only use that kind of current with a 6mm welding rod ( quarter inch in the USA) to weld a pair of 30mm steel plates together, and if you are doing that at all regular then you need a bigger welder in any case. Open circuit voltage is around 70VAC, but drops to around 10VAC when you have an arc struck, so running it off a standard 16A socket is fine. Typically I use it around 60A or so, with 2.5mm rods, and there it is fine.

Of course, now I have an inverter welder I use it instead most of the time, much better weld, much better starting and I can actually weld thin plate with it, instead of having an impromptu plasma cutter that uses a welding rod. But yes, the welder transformer puts the power from the wall output into a very small spot, so can do some serious heating on metal.

[johansen]

20 amp breakers need 30 amps to trip at 50% duty cycle.

[Paul Moir]

It's unlikely you'll find a capacitor in there.  Usually it's transformer, rectifier and choke.  The transformer does the 20A->120A transformation, hence the name.  The rectifer gets you DC and the choke is used for smoothing.  If it was just a capacitor, as soon as the wire made contact all the energy stored in the capacitor would get dumped into the stickout and blow the wire to bits. 

[langwadt]

It's unlikely you'll find a capacitor in there.  Usually it's transformer, rectifier and choke.  The transformer does the 20A->120A transformation, hence the name.  The rectifer gets you DC and the choke is used for smoothing.  If it was just a capacitor, as soon as the wire made contact all the energy stored in the capacitor would get dumped into the stickout and blow the wire to bits.

MIG usually have capacitors as well they use ~constant voltage, stick and TIG is constant current

[Paul Moir]

Ah yes, my cheapy 90/130 doesn't but I see people "upgrade" them by adding some.  Better ones appear to have some capacitance as part of their design.

[cs.dk]

My 120A welder has a rating plate of needing 26A at full 120A welding current, but you only use that kind of current with a 6mm welding rod ( quarter inch in the USA) to weld a pair of 30mm steel plates together

A 6 mm rod won't even light at such low amperes. Typical figures (depends on rod though), 2,5 mm 60-110A, 3,2 mm 70-150, 4 mm 150-240A.

(Sorry for OT)

[tautech]

It's unlikely you'll find a capacitor in there.  Usually it's transformer, rectifier and choke.  The transformer does the 20A->120A transformation, hence the name.  The rectifer gets you DC and the choke is used for smoothing.  If it was just a capacitor, as soon as the wire made contact all the energy stored in the capacitor would get dumped into the stickout and blow the wire to bits.

Every proper Mig I've had anything to do with has had capacitance on the secondary and plenty of it, my single phase 180 A has 80,000 uF. 
Without capacitance you need additional inductance to smooth mains frequency otherwise Migs create too much splatter. The only exception I've seen is a 3 phase Mig, the frequency of the rectified secondary being 3x that of single phase.
Inverter type welders is where the future is, so much grunt for their size and weight not to mention better efficiency.

[Paul Moir]

Oh I agree completely about the inverters. 
Note that this is a flux core welder we're talking about here so it's likely a low end one.  In fact, I'll stand by what I said about it being likely there's no capacitor.    But that's obscuring the point that capacitance after the rectifier does make sense, and I certainly was wrong in spirit as I was thinking that MIGs generally don't have them.

[tautech]

Oh I agree completely about the inverters. 
Note that this is a flux core welder we're talking about here so it's likely a low end one. 

Not necessarily.
A Fitter/Boilermaker I know only uses gasless flux cored Mig wire in his 3 phase Mig, along with CO² for the nicest finished Mig welds you ever did see.
Sure this sort of defeats the main advantage of using Mig, that is no post weld cleanup but they sure did look classy.

A buddy has a fairly new Strata inverter Mig, a single phase unit and the welds that thing makes are pretty nice too but not as good as the old fella that uses gasless wire and CO².

[gnif]

I have a lovely old adjustable AC CigWeld arc welder I inherited from my dad, its just a huge transformer on wheels. I would like to have a play with DC welding, would a heavy enough (200A) bridge rectifier stand up to this kind of abuse/use? Obviously would need to be sufficiently cooled. The welder's maximum output is 160A, but I have never measured it's voltage (and wont until the rain outside stops)

[langwadt]

Oh I agree completely about the inverters. 
Note that this is a flux core welder we're talking about here so it's likely a low end one. 

Not necessarily.
A Fitter/Boilermaker I know only uses gasless flux cored Mig wire in his 3 phase Mig, along with CO² for the nicest finished Mig welds you ever did see.
Sure this sort of defeats the main advantage of using Mig, that is no post weld cleanup but they sure did look classy.

I think the main advantage of MIG in that case is productivity and quality, long continues welds are faster and doesn't risk inclusions from starts with a new stick every so often

[tautech]

I have a lovely old adjustable AC CigWeld arc welder I inherited from my dad, its just a huge transformer on wheels. I would like to have a play with DC welding, would a heavy enough (200A) bridge rectifier stand up to this kind of abuse/use? Obviously would need to be sufficiently cooled. The welder's maximum output is 160A, but I have never measured it's voltage (and wont until the rain outside stops)

If you mean using it as a Mig supply, no.
Mig uses variable voltage while stick arc welding uses variable current.

[langwadt]

I have a lovely old adjustable AC CigWeld arc welder I inherited from my dad, its just a huge transformer on wheels. I would like to have a play with DC welding, would a heavy enough (200A) bridge rectifier stand up to this kind of abuse/use? Obviously would need to be sufficiently cooled. The welder's maximum output is 160A, but I have never measured it's voltage (and wont until the rain outside stops)

a number of big rectifiers in parallel with enough wire resistance to sorta balance current between them could work

[gnif]

I have a lovely old adjustable AC CigWeld arc welder I inherited from my dad, its just a huge transformer on wheels. I would like to have a play with DC welding, would a heavy enough (200A) bridge rectifier stand up to this kind of abuse/use? Obviously would need to be sufficiently cooled. The welder's maximum output is 160A, but I have never measured it's voltage (and wont until the rain outside stops)

If you mean using it as a Mig supply, no.
Mig uses variable voltage while stick arc welding uses variable current.

No, not MIG, just stick arc welding, it is variable current.

[tautech]

Oh I agree completely about the inverters. 
Note that this is a flux core welder we're talking about here so it's likely a low end one. 

Not necessarily.
A Fitter/Boilermaker I know only uses gasless flux cored Mig wire in his 3 phase Mig, along with CO² for the nicest finished Mig welds you ever did see.
Sure this sort of defeats the main advantage of using Mig, that is no post weld cleanup but they sure did look classy.

I think the main advantage of MIG in that case is productivity and quality, long continues welds are faster and doesn't risk inclusions from starts with a new stick every so often

Quite true for the inexperienced welder.

One other advantage of Mig (for steel) is the welds are high tensile....try a fillet weld with stick and Mig, then try to break them and you'll see which is the stronger. 

[tautech]

I have a lovely old adjustable AC CigWeld arc welder I inherited from my dad, its just a huge transformer on wheels. I would like to have a play with DC welding, would a heavy enough (200A) bridge rectifier stand up to this kind of abuse/use? Obviously would need to be sufficiently cooled. The welder's maximum output is 160A, but I have never measured it's voltage (and wont until the rain outside stops)

If you mean using it as a Mig supply, no.
Mig uses variable voltage while stick arc welding uses variable current.

No, not MIG, just stick arc welding, it is variable current.

Not so successful for an old style single phase welder, the rectified secondary frequency is a little too low for smooth DC welding. In 3 phase machines they form a bridge with hory big stud diodes.
Inverter type welder outputs are high frequency by nature and only a rectifying stage is then required.

[Paul Moir]

I think the major advantage with MIG vs fluxcore* is that you don't have crap shooting everywhere and fumes shooting up your nose! 
Fortunately I now live in TIG land almost exclusively, where I don't have to be fast nor do I have all that junk flying about.  It's the classical music of welding. 
While I'm sure your pressure welder is doing it right for what he's doing, on thin metal fluxcore* is a real pain.
* fluxcore without gas.

[tautech]

I think the major advantage with MIG vs fluxcore* is that you don't have crap shooting everywhere and fumes shooting up your nose! 
Fortunately I now live in TIG land almost exclusively, where I don't have to be fast nor do I have all that junk flying about.  It's the classical music of welding. 
While I'm sure your pressure welder is doing it right for what he's doing, on thin metal fluxcore* is a real pain.
* fluxcore without gas.

There's another:
Try using ordinary Mig outside on other than the calmest of days.

Yep, you need a suite of tools to meet your needs, just like in electronics.
400 A arc, 180 A Mig, 150 A Tig/stick and an Oxy set do most anything I need. 

[Vtile]

There is more than just "higher frequency" the 3-phases do interlap. Because of this the six-pulse DC (fully rectified three phase AC)  looks roughly with the scope like a 1-phase pulsed DC that is smoothed out with bad capacitors.

Put these three functions in your preferred graphing calculator or even Excel. First phase does not come with rectification, it is broken.

1: SIN(x)
2: SQRT((SIN(x+(PI/3)))^2)
2: SQRT((SIN(x+(2PI/3)))^2)

It's unlikely you'll find a capacitor in there.  Usually it's transformer, rectifier and choke.  The transformer does the 20A->120A transformation, hence the name.  The rectifer gets you DC and the choke is used for smoothing.  If it was just a capacitor, as soon as the wire made contact all the energy stored in the capacitor would get dumped into the stickout and blow the wire to bits.

Every proper Mig I've had anything to do with has had capacitance on the secondary and plenty of it, my single phase 180 A has 80,000 uF. 
Without capacitance you need additional inductance to smooth mains frequency otherwise Migs create too much splatter. The only exception I've seen is a 3 phase Mig, the frequency of the rectified secondary being 3x that of single phase.
Inverter type welders is where the future is, so much grunt for their size and weight not to mention better efficiency.

[mjrandle]

The welder will have a limited duty cycle at maximum welding current of 120 A, e.g. 20-30% every 10 min, to ensure average input current does not exceed 20 A.  The thermal overload control shuts down the welder and effectively sets the duty cycle.  The allowable weld current will be greatly reduced at 100% duty cycle, could be 80 A or less. This information should be specified on the welders name plate for each applicable weld modes.


Regards,

Mike