120 amp max welder needs only a 20amp breaker - Page 1
Forum section: electronics / beginners

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: April 04, 2017, 04:15:54 pm
content: 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

author: rstofer
author_rank: Super Contributor
timestamp: April 04, 2017, 04:22:07 pm
content: 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).

author: Zero999
author_rank: Super Contributor
timestamp: April 04, 2017, 05:59:07 pm
content: 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.

author: CaptainNomihodai
author_rank: Contributor
timestamp: April 04, 2017, 06:33:00 pm
content: Quote from: mikeinfodoc on April 04, 2017, 04:15:54 pmI'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).Quote from: rstofer on April 04, 2017, 04:22:07 pmThat'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.

author: james_s
author_rank: Super Contributor
timestamp: April 04, 2017, 06:33:26 pm
content: 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.

author: SeanB
author_rank: Super Contributor
timestamp: April 04, 2017, 07:16:42 pm
content: 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.

author: johansen
author_rank: Super Contributor
timestamp: April 04, 2017, 08:25:31 pm
content: 20 amp breakers need 30 amps to trip at 50% duty cycle.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: April 04, 2017, 08:47:23 pm
content: 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.

author: langwadt
author_rank: Super Contributor
timestamp: April 04, 2017, 09:18:19 pm
content: Quote from: Paul Moir on April 04, 2017, 08:47:23 pmMIG usually have capacitors as well they use ~constant voltage, stick and TIG is constant current

author: Paul Moir
author_rank: Frequent Contributor
timestamp: April 05, 2017, 12:38:41 am
content: 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.

author: cs.dk
author_rank: Unknown
timestamp: April 05, 2017, 03:32:12 am
content: Quote from: SeanB on April 04, 2017, 07:16:42 pmA 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)

author: tautech
author_rank: Super Contributor
timestamp: April 05, 2017, 04:35:21 am
content: Quote from: Paul Moir on April 04, 2017, 08:47:23 pmEveryproperMig 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.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: April 05, 2017, 06:12:44 am
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: April 05, 2017, 07:28:08 am
content: Quote from: Paul Moir on April 05, 2017, 06:12:44 amNot necessarily.A Fitter/Boilermaker I knowonlyuses gasless flux cored Mig wire in his 3 phase Mig, along with CO2for 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.

author: gnif
author_rank: Unknown
timestamp: April 05, 2017, 07:37:04 am
content: 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)

author: langwadt
author_rank: Super Contributor
timestamp: April 05, 2017, 07:45:38 am
content: Quote from: tautech on April 05, 2017, 07:28:08 amI 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

author: tautech
author_rank: Super Contributor
timestamp: April 05, 2017, 07:46:49 am
content: Quote from: gnif on April 05, 2017, 07:37:04 amIf you mean using it as a Mig supply, no.Mig uses variable voltage while stick arc welding uses variable current.

author: langwadt
author_rank: Super Contributor
timestamp: April 05, 2017, 07:46:57 am
content: Quote from: gnif on April 05, 2017, 07:37:04 ama number of big rectifiers in parallel with enough wire resistance to sorta balance current between them could work

author: gnif
author_rank: Unknown
timestamp: April 05, 2017, 07:49:56 am
content: Quote from: tautech on April 05, 2017, 07:46:49 amNo, not MIG, just stick arc welding, it is variable current.

author: tautech
author_rank: Super Contributor
timestamp: April 05, 2017, 07:50:45 am
content: Quote from: langwadt on April 05, 2017, 07:45:38 amQuite 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.

author: tautech
author_rank: Super Contributor
timestamp: April 05, 2017, 07:56:46 am
content: Quote from: gnif on April 05, 2017, 07:49:56 amNot 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.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: April 05, 2017, 08:08:56 am
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: April 05, 2017, 08:17:19 am
content: Quote from: Paul Moir on April 05, 2017, 08:08:56 amThere'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.

author: Vtile
author_rank: Super Contributor
timestamp: April 05, 2017, 08:28:49 am
content: 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)Quote from: tautech on April 05, 2017, 04:35:21 am

author: mjrandle
author_rank: Contributor
timestamp: April 05, 2017, 08:57:07 am
content: 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

author: tautech
author_rank: Super Contributor
timestamp: April 05, 2017, 09:15:06 am
content: True things are built to a price but with a Mig there is thefeatureof being able to weld until the wire spool runs out, theoretically. Stick welders on the other hand get a forced break each time you have to replace the electrode.I run my big 400 A 3 phase stick welder on a 20 A breaker, an ordinary one will trip in seconds @ 400 A but if you use a D curve motor rated breaker that permits a significant current overload for a fixed duration I can weld @ 300 A long enough to consume a full 5mm rod. By the time you've chipped and brushed the weld and replaced the rod the duty cycle starts over.BTW, in case you wonder why I have a 400 A welder....it was only $200 on a trolley and with longer than normal leads so couldn't resist buying it.Transarc 400 IIRC.

author: CaptainNomihodai
author_rank: Contributor
timestamp: April 05, 2017, 08:51:02 pm
content: QuoteWhile this is true, and oh how I would love to have a nice inverter TIG setup, there's something to be said for the simplicity and durability of a good transformer. About a year ago I noticed that my open circuit voltage was too high. It took me about 30 seconds to figure out that the "suppressor" (just a resistor across the output terminals) had failed open. If I've got a Dynasty or Synchrowave (sorry, I speak Miller, not sure what the rest of the world has) that fails, fixing it would probably take a lot of help from people on this board. My current welder was built before I was born and, barring intentional damage or something catastrophic, will be working after I die. That being said, it also weighs significantly more than I do and would probably win in a fight, and uses enough electricity to power a small country, so ... tradeoffs.QuoteIn addition to what people have mentioned about MIG machines having caps on the secondary, some machines will also have capacitors for power factor correction. Unlikely here, though, this one sounds like a big box store model.QuoteYes. I open up my Miller and there are just 4 gargantuan diodes. I don't see why a sufficiently large bridge rectifier would be any different.Quote from: tautech on April 05, 2017, 09:15:06 am3 Phase, so that's 20A per phase on that breaker right? I've tripped 20A single phase breakers with a big angle grinder before...I'm not sure what I'm more jealous of, that you got that monster welder for such a steal (though, I can't think of a situation where I would actually need 400A), or your apparent access to 3 phase.

author: james_s
author_rank: Super Contributor
timestamp: April 05, 2017, 08:54:11 pm
content: Quote from: CaptainNomihodai on April 05, 2017, 08:51:02 pmThat is a valid point. I saw a guy once who had an arc welder that looked like it had been dredged up from the bottom of a lake after being run over by a truck. The thing still worked somehow.

author: tautech
author_rank: Super Contributor
timestamp: April 05, 2017, 10:15:59 pm
content: Quote from: CaptainNomihodai on April 05, 2017, 08:51:02 pmYep.QuoteD curve motor rated breakers and available in single phase versions too.Breakers to weaken with age, particularly if they've been tripped a good few times. A sparkie mate replaces a few that give trouble and then troubles are gone.QuoteTBH I rarely use it over 200 A but it's sure nice to know the extra grunt is there when and if you need it.3 pase is something that I would be reluctant to be without as so much older 3 ph gear is available at low pricing as the market for them is smaller. If you have 3 ph there are bargains to be had.

author: moz
author_rank: Regular Contributor
timestamp: April 05, 2017, 10:28:59 pm
content: Quote from: tautech on April 05, 2017, 10:15:59 pmHeysoos! I had a 180A TIG that I think I only ran at 180A once (welding 25mm reinforcing rod). Albeit I mostly build bicycles, the only real jobs I do bigger than that are the usual "I have a workshop so I can build things for my workshop" stuff. Then I sold it to MakerSpace because I barely use it, and if it's in there I can go and have access to a much better workshop than I can fit in my shed (or afford/justify).I have a 15A breaker that I plug in when I want to run the welder, the rest of the time I leave the 25A breaker in. Purely because the wiring in this house is a joke but I'm still saving up to fix it. 25A at random spots about the house, sure. 25A continuous to the far end of the property I am not so sure about. The loopback resistance on the garage circuit makes me doubt it's a single length of 2.5mm^2 cable the whole way (or it's running 100m of cable to cover 50m).

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2017, 10:32:50 pm
content: Quote from: james_s on April 05, 2017, 08:54:11 pmDid it look like any of these transformers?http://halbot.haluze.sk/?id=3555https://expatinaddis.wordpress.com/

author: james_s
author_rank: Super Contributor
timestamp: April 06, 2017, 12:21:47 am
content: Yeah I think that's the one I was thinking of, that's nuts!