amps and voltage

[BrokenBiker]

i dunno what section to place this one

can someone explain what amps, and volts do in a welder, i know the difference electrically, i.e. voltage is pressure and ampage is the current flow,

but what will changing the amps or voltage settings do to a welder, cos on my mightymig, changing the settings around doesnt have much of an effect

 

[shenion]

Current is the product of several factors, the wire size, the voltage and the wire speed.

Once the voltage is set, there is a usable range of wire speed. On most small welders with voltage switches, one voltage setting with a higher wire speed will be near the next higher voltage on a lower wire speed.

On my Clarke and 0.8mm wire, voltage setting 1 could use 2-3.5 on the wire speed, setting 2 could use 3-4, setting 3 could use 4-5.5 and setting 4 could use about 5 to 6.

Increasing the wire speed increases the number of times the wire touches the weld pool, so with more high-current pulses per second, the average current goes up.

Using 0.6mm wire it would use about 1.5x the wire speed but the current was a bit less as the wire carries half the current. So the resulting current was about 70% as with 0.8mm.

Edit: torch to work length makes a difference too. The longer the gap, the more the wire resistance drops the current. This is much more pronounced on thinner wire.

 

[Wozzaaah]

Very basically speaking, the 'power' switches on the front panel control the voltage, not the current/amperage. You set the switch to the required output voltage then adjust the wire feed speed, wire diameter, arc length (wire stickout) etc to suit that voltage which gives you the output (welding) current.
If you turn the volts up but have a low wire speed or small diameter wire then you won't get the current/amperage that power setting should deliver.

 

[BrokenBiker]

so could it be said, that higher voltage = deeper penetration, and faster wire = fatter weld?

and visa versa obviously

 

[Wozzaaah]

Sort of.
A higher voltage for better penetration but you have to trim the wire speed to suit that voltage or you won't get the current you're supposed to.
If the wire speed is too fast for the voltage you'll get popping and farting rather than a fatter bead as the chosen voltage will be insufficient to properly melt the wire.

 

[BrokenBiker]

ok then, so higher voltage is better penetration, and higher wire speed means fatter welds as long as the wire speed doesnt exceed the voltage setting?

cheers for the replies, i though that was what they were for, but my dad thinks different, but using what you have said, and ohms law, it all makes sense

 

[Wozzaaah]

Yes, higher voltage for thicker material and more penetration.
If the wire speed exceeds that for a given voltage you'll get crappy welds, often with 'unmelted' wire just sat on the surface.

Try this, choose the lowest voltage setting and whack the wire speed to max and it will most likely spit and fart and lay pieces of wire on the plate without actually putting down any proper weld.

Similarly, choose the highest voltage setting but turn the wire speed right down and all that will happen is that the wire will ball up at the contact tip until it's too big then the ball will fall off.

Then try this;
Mid power setting, mid wire speed, start welding then increase the wire speed control until you just feel the torch start to push away then back the wire speed knob off slowly until it just stops pushing. This should result in a nice, stable arc and (as long as your arc length is correct) should be pretty much the optimal settings for that voltage step.
That will work for all the power settings so not a bad idea to experiment with it and write down the wire speed settings for each power setting for use as a quick reference guide.

If you want fatter welds then you need to travel slower but by travelling slower you increase the risk of burning through.
Fat welds aren't necessarily good welds.

 

[BrokenBiker]

thanks. i only really wanted to know a bit of the theory, and with what you have said, and using v=IxR it stands to reason that, the higher the voltage, the higher the current needs to be to overcome the resistance of the wire.

this all cam about cos my dad thought that turning the amps down on his arc welder would allow him to weld thin sheets (1mm or lower) and i tried explaining thet it is very hard or impossible to get it good with arc for this reason, and being an apprentice spark i tried using ohms law to prove it, but he wouldnt have it and changed the subject. but with ohms law and the theory you have told me, it all makes perfect sense to me

 

[Wozzaaah]

Ahh, different kettle of fish altogether. The issue with turning an arc welder down is that you may end up having not enough current to weld properly.
Rods have a specified current range, too low and they tend not to strike at all or they may stick, too high and you'll get allsorts of other weld defects, wide bead, undercut etc.
The main reason it's so difficult to weld thin steel with an arc welder is that the minimum current required to melt the rod is too much for the thin steel, resulting in blow-through.

 

[BrokenBiker]

yeah, the way i looked at it is, you need a thin rod to weld thin steel, so thin rod = higher resistance of the rod. you need a lower current for the smaller diameter rod, and if you have high resistance, and low current, you will end up with a higher voltage ( ohms law, V = IxR ), and a high voltage, on thin steel, in my experience, never goes well, even with lower currents.

and as his arc welder has no voltage control, it is never going to work on very thin steel.

and joining that together with the theory you have given me, it all links in that thinner material requires less voltage and current

obviously with a variable current and voltage settings, and you can control the resistance to a degree with the rod size, or wire size, ohms law doesnt apply as everything is variable

 

[shenion]

In arc welding the voltage is not really set as they are constant current.

The resistance of the wire is not an issue, it is the size of the arc. Thicker rod, wider arc and more current.

As you lower the current, the voltage drops until there is not enough current to maintain the arc.

As Woz said, rods have a range they work well. When you get down to where you don't blow holes, there is not enough heat to keep the flux fluid and you get slag inclusions, the flux does not burn well so not enough protective gas.

This is where I find cheap rods are worst. Good rods will work over a wider current range. Cheap rods seem to only work well at the higher range.

On thinner metal, you want a welder with a high open-circuit voltage to help maintain the arc. Some welders have a higher voltage setting for thin metal.

 

[BrokenBiker]

thanks for all the replies. i have also been looking into it on wikipedia, and it all comes back to the same answers.

just because i am that type of person that has to know everything about the stuff im using, i may put a multi meter in various configurations tomorrow and see what happens witht the voltage using various currents and rods

 

[shenion]

i may put a multi meter in various configurations tomorrow and see what happens with the voltage using various currents and rods

Probably blow the meter

The arc voltage can jump to hundreds of volts; especially when the arc is broken.

 

[BrokenBiker]

i have a fluke worth 800 quid, capable of 1000Vdc and 750V ac and can handle enough current to test a 120amp induction hardener in work so i should be ok

 

[shenion]

I know mine has done spikes as high as 1500 volts.

When I break the arc, it will extand as far as 2-3 inches before going out. I doubt your meter maintains anywhere that kind of gap.

Good luck

 

[BrokenBiker]

im sure my meter has overload protection but incase it hasnt i will use my not so important one that runs the same values lol