Unstable Arc help

[FelisCatis]

Hi!
Being a student, and therefore almost broke, I was offered a multi-mig MIG 160 machine ex-university for nothing, so naturally I accepted. Problem is, according to the technician there, it has never worked properly since it was new, having had less than 4 hours use from new because of this.
The Symptoms:
It feels like the arc is unstable in some way, like it loses power and almost pulses. I can see the light in the on/off switch pulsing a bit too. Sometimes, especially just after the machine is started, it works perfectly. Does anyone have any ideas? I'm not electrically minded really, but can't really afford to take it to anyone to look at.
Cheers,
Gareth

 

[bronze]

I had a similar problem once, whereas the problem was an unstable wire feed. All the symptoms except for the pulsing light on the machine. I looked at the amps though, and they were jumping 0-300 (naturally). The solution was to just change the entire wire, because the old one was of poor quality.

 

[lexi]

Is this where all our money is going to? Brand new machines being given away? Poor student....how many times have I heard that! You prolly spent more on drink and condoms this year than I`ve made!! Obviously joking mate!! Now.. is the feed nice and steady if you keep a bit of pressure on it?

Alex

 

[FelisCatis]

Bronze, I don't think the quality of the wire is the problem, although as a last resort I will change it for another reel, thanks.

Alex, the feed has always been steady, it's the arc that seems to be unstable in some way I'm sure. When you say "keep some pressure on it" do you mean on the rollers or the wire reel or the trigger? BTW it's more likely that I'd spend all my money on cars and parts!

Gareth

 

[FelisCatis]

Also, I meant to add that when it misbehaves there's no penetration, it just seems to lay the weld on top of the workpiece!
Cheers

 

[peterd51]

Hi,

is it losing current?

It could be some problem with the electronics, dry joint, dodgy capacitor, etc.

Does it do it from cold or after the set's warmed up for a few minutes?

Regards
Peter

 

[malcolm]

Could be a bad joint in the power or earth leads or one of the leads frayed. Well worth undoing all the connections and giving them a good clean up. Had a similar thing happen to mine when the screws holding the earth lead to the clamp came loose (through angle grinding with the clamp still attached).

 

[lexi]

Yeah check all earth connections. Get someone to check the roll of wire on their machine for results. As for spending the money Gareth.....If it`s got wheels or a skirt .........It`s gonna cost..lol

Alex

 

[weldequip]

Also, I meant to add that when it misbehaves there's no penetration, it just seems to lay the weld on top of the workpiece!
Cheers

Does it happen on all voltage settings or just the one?
weldequip

 

[FelisCatis]

It seems to happen on all power settings, it seems ok when it's cold but not long into the job it starts misbehaving.
Cheers,
Gareth

 

[peterd51]

Hi,

sounds like a dry joint, or a loose connection breaking down when it gets warm.

It could also be a component such as a capacitor breaking down.

If all connections look OK and you want to be adventurous then you can by a tin of freezer spray...

get the kit warm and the fault present...

spray individual components to cool them down and test after spraying each one.

When it suddenly starts working OK the last thing you cooled down is what's causing the problem.

I'd switch off the power before I sprayed though!

Also for safety reasons and to keep the unit warm you should replace the lid before testing it!

Regards
Peter

 

[irondarren]

My old thermal arc has been getting worse for a while now, could no longer get the wire speed near what was suggested for the given voltage. I noticed one of the leads getting a little warm yesterday, so today have replaced the earth connector and the polarity connector, what i did notice was on the polarity connector the last 2 inches of the powercable was breakinging up. To the extent that the copper would powder up when twisted, so i cut the 2 inches out put a new connector on and now i can set the wire speed up as per instructions, end result being the machine has much more power, possibly to the fact there is less resistance on the welding cables. the machine still has other minor issues, but is much more stable with the arc. Havent go the machine warm yet, you used to have to touch the wire speed down a little as it got warmer, but will see what its like tommorrow

 

[zardoz]

Thats a nice wee gift you have there. I hope you can fix it up and get it working. Good for you, and good on the college and the guy who gave it to you.