Duty cycle / Amps confusion...

[Red2000SS]

First post here - been reading the site for a while and have learned a lot. I have bought my first MIG welder - a Hobart Handler 140 mostly due to inspiration I got from this site seeing other complete novices learning to weld.

This site is really fantastic for newbies just starting out - I have learned a lot just from reading the tutorials and forums. I have managed to make several welds on scrap material - some pretty good and some not so good - I am still learning.

The manual for my welder shows the following performance data:

My specific questions are:

1. How do I know what amperage I am welding at?
2. Is amperage related to wire speed at all, or more wire size - thicker wire conducts more current (for a given voltage)?

This is more an academic question since I probably spend a lot more time setting up a weld than actually welding. I also realize that my machine running on 120V is more a hobbyist machine rather than an industrial production machine.


Any input would be appreciated.

 

[shenion]

1. You don't know. The only way would be to hook of a volt meter while welding and measure voltage then look up in the chart or use an amp meter.

3. There are several factors that effect current: Wire size, wire speed and the wire stickout length of the torch (closer to work increases current).

Usually the min/max current is 0.030" wire.

Just practice and get a feel for the settings. On my Clarke 130 I know power setting 1 is about 2.5 on speed, 2 is 3.5, 3 is about 4, 4 is 5.5 for 0.030 wire. Speed is 0.5 less for CO2 and can go higher for pure argon.

I started writing down what worked. I have done 0.030 wire so far. I tried some 0.035 and did not seem to get any more current/heat. Would like to try 0.025 wire and see how it works on thin metal.

Posts some picts of your test welds.

Not many Hobart users here. Let us know what you think of the machine. My only experience has been using Hobart wire, works great.

 

[Alex]

I think the resistance of the welding circuit is roughly around 0.2 ohms. This is very rough due to all the variables.

So if your running 25 Volts under load, then

25/0.2 = 125 amps

30/0.2 = 150 amps

It could be however 0.15 ohm resistance which makes a big difference

25/0.15 = 167 amps

30/0.15 = 200 amps


Its all about the resistance in the circuit along with the voltage that will determine the current thats going to flow.

The resistance is most highly altered by the wire speed and the guage of the wire.

Best way to know for sure is using an amp meter, but it would fluctuate quite a lot when in use.

 

[irondarren]

My mig is a constant voltage unit, 26.5volts relates to 250amps at normal wire speed

 

[Red2000SS]

Thanks for the inputs. Your responses have cleared things up a bit.

My original curiostiy came after looking at the duty cycle chart in my manual - the natural question that came up was how many amps I am using so I know how much I can weld in a given time. My welder goes anywhere from 100% duty cycle at 40 amps to 10% at 140 amps. Short of hooking up an amp meter I won't really know.

Is it safe to assume that welding 1/8 inch steel on my highest voltage I am probably using at between 90 amps (20% duty cycle) and 140 amps (10% duty cycle)?

This gives me a ballpark to know how long to let the machine cool down.

I will try to post some pics of some of my test welds soon. I was reasonably impressed with the appearance of some of my test welds after a few practice sessions - I have ZERO welding experience before reading this site and buying my welder. My problem is not so much appearance of the weld, but getting proper penetration - some of my welds look good from the top, but flip them over and the metal is just discolored, not melted all the way through.

My welds look way better than these:

http://www.mig-welding.co.uk/forum/showthread.php?t=1040

LOL

Not trying to pick on the guy, I sort of expected that some of my first welds would look like that.

The advice on this forum is very helpful to people just learning.

I am trying to get good enough to weld a frame for a sliding gate across my driveway made of 3" square tubing 1/8" thickness.

It is an ambitious project (for me) - the gate will be about 30 ft long and 8 ft high - steel frame will only be about 6 ft high.

 

[malcolm]

A rough method for figuring out what amps you are using is calculating using the manufacturers specs. If the welder has 4 power settings with min 30 amps and max 90amps then the settings could be guessed as 30, 50, 70, 90.

Not altogether accurate as amps are influenced by all sorts of other things other than the voltage setting as has been suggested, but a fair punt.

If your penetration is poor then knock up the power another notch. You'll probably need to knock the wire speed up a little to compensate for the increased power and get the nice fizzy noise.