Mig Power Setting Problems...

[diesel..weasel]

Evening Folks,

Been on here for a while and picked up alot of tips and techniques to get started...great stuff.

All is well with my aquired mig welder and am just getting to grips with the settings wire speed etc. getting some decentish welds on bits of scrap after finding the best settings on 0.6mm/0.8mm wire. But it seems to have a problem with power settings which has become apparent after doing some research on here.

The welder is a sureweld monomig 151
40-145 amp,
4 power settings,
min1: 40
min2: 75
max1: 100
max2: 145

Seems an oldish one but all is in good working order bar this problem. Testing on some 1mm steel, which I would expect would be easily dealt with on low min1 setting, i can only get a decent weld on the top 2 settings which should be way to high for the thin 1mm steel? All the settings work , min1: the weld does not penetrate, almost at all, and min2: not much better.

Any ideas, suggestions would be greatly recieved.

 

[tlovatt]

A few questions to get things started

Is the metal clean before you try to weld it
Is the area of the earth clamp clean
Are you changing the contact tips to suit the wire size (and are they worn)
Do you blow holes in the metal welding at the higher settings
What wire speed are you using

Look at the thread Tried again http://www.mig-welding.co.uk/forum/threads/tried-again.46656/

 

[diesel..weasel]

A few questions to get things started

Is the metal clean before you try to weld it
Is the area of the earth clamp clean
Are you changing the contact tips to suit the wire size (and are they worn)
Do you blow holes in the metal welding at the higher settings
What wire speed are you using

Look at the thread Tried again http://www.mig-welding.co.uk/forum/threads/tried-again.46656/

yea all ground down,
i have ordered a new earth clamp to see if this improves things,
you could have a point on the tips, i havent checked the size relevant to wire, i have just stuck with the one it came with.
it does blow through if you move too slowly, but moving quickly it seems to penetrate evenly.

Will a dodgy tip, earth etc throw the power settings out considerably?

Thanks for the fast reply..

 

[mike 109444]

As above but would add check security screws/crimp on the earth clamp and it's jaws for cleanness. The internal connections could also be checked (UNPLUG BEFORE PUTTING YOUR HANS INSIDE).
If above does not improve then meter between the tip (with wire feed backed off) and the earth clamp. Meter set on DC volts. See what readings you get on the 4 power settings.

 

[diesel..weasel]

thanks for the reply, i'll try these investigate further

 

[tlovatt]

Will a dodgy tip, earth etc throw the power settings out considerably?

Yes any poor connection in the circuit will cause a voltage drop and hence will lower the power delivered by the welder into the workpiece. Also not that checking continuity or resistance with an ohm meter may not always show a problem, visual inspection is normally needed as well.

 

[diesel..weasel]

If above does not improve then meter between the tip (with wire feed backed off) and the earth clamp. Meter set on DC volts. See what readings you get on the 4 power settings.

I've ordered a new earth clamp and a new tip so hopefully will get some better results. All seems ok inside, no loose wires dirty spades etc. I have used the multimeter to check the voltage on each setting if this points to anything, but they seem a little out from the spec chart on the front (in brackets)... which might explain why i'm using the higher settings. 22V only comes in at setting 3.

min1: 16.6V (22V)
min2: 19.2V (24V)
min3: 22.3V (26V)
min4: 27.1V (30V)

Any ideas??

 

[mike 109444]

Does the welder have a large capacitor size of a can of peas! (or bank of caps linked by a buzz bars) ?

 

[tlovatt]

The lower voltages do point towards a problem, How old is the welder?

 

[diesel..weasel]

i

Does the welder have a large capacitor size of a can of peas! (or bank of caps linked by a buzz bars) ?

I can remeber seein a large cap? It has 3? plates towards the rear with various wires connecting them, Are these the bars you refer too?

It. looks maybe 10 years old or more.

 

[mike 109444]

i


I can remeber seein a large cap? It has 3? plates towards the rear with various wires connecting them, Are these the bars you refer too?

It. looks maybe 10 years old or more.

No what you are describing is the diode pack/bridge It takes the AC voltage from the BIG transformer and changes (rectifies) it into DC voltage which is what we need for MIG welding.
A capacitor (s) should look like one of theses pics One big blue can or several smaller ones linked with strips Does yours have that?

 

[diesel..weasel]

No. Defo no cap. Had the diode pack apart tonite, to check for anything broken, legs atc. All seems fine, however using the diode tester on the multimeter, im only getting a reading on the secondary side. Would this be normal? I think there 6 diodes on each.

 

[tlovatt]

Can you post some photos of the machines internals

 

[shenion]

What do you mean by "seconday side" of the rectifier bridge? (diode pack.)

You should test each diode individually. Normally you should get 0.5 or so on the meter one way and an open the other.

 

[diesel..weasel]

I'll put some pics on later.

Secondary is probably the wrong term. I had the diode pack apart, it's 2 sided. I tested each diode on one side all got a reading on the diode tester. On the other side there were no readings at all. This was the one closest to the transformer.

 

[shenion]

Sounds like one set of diodes is open.

If any of the diodes are bad, you should replace them all as the rest are soon to go.

 

[diesel..weasel]

Yea seems one plate has no diodes working. However welder still operates ok just at the reduced voltage.

Any tips on replacing those button diodes? Where can I get some? Would like to improve it if I can too.

 

[shenion]

The diodes are pressed or spotwelded in.

Really, you need to replace the whole assembly. You could get some stud diodes and bolt them on. First, the polarity of the plates would need to be determines. Often one plate has normal diodes and the other has reversed-polarity ones.

If you cant get the rectifier assembly from the OEM, one from a similar welder can probably be used. Pits might help identify others that would fit or work.

 

[diesel..weasel]

Me and a friend are going to attempt to make a new rectifier from scratch as a new replacement assembly is abit pricey, about 45 quid. Should be ok to make one for between 10-15 quid. Should have a decent little welder after to cope with most diy garage jobs.

 

[shenion]

Don't know how you can make a rectifier assembly for 10-15 quid as the diodes cost about £20 each and you will need several of them.