Possible potentiometer failure?

[Memmeddu]

Hi everyone
Yesterday I was welding something with my cheapo inverter
Was repairing a clam fishing rake to be short we'll call this thing CFD if we need to repeat
So essentially I had my welder set at around 85/90A I was welding a new thoot on the CFD
Material thickness was 8mm (rebar thoot) to 4mm
Instead of welding I've practically cut through using 2.5mm 6013 ,the rebar became water (C34)
I thought that might be just because the thoot was small so it will heat quickly so dial down to around 70A still to hot,50A to hot ,40A was good enough and the welder was working very well .
Two things to consider
the CFD being used in salt water is very very rusted out ,but the rebar wasn't.
With 40A I being able to open root

I thought various causes to that expecially a potentiometer failure but before to open up the welder I would like get advice about.
-I've recently cleaned up my ground clamp an electrode holder (shiny brass seems gold)
May this affect welding ?
-being the CFD heavily corroded might be part of the causes of blowing through 4mm thick flat bar?
(Ps rusty but not corn flakes looking rust)
-maybe my fault ?
Wrong rod angles?

what I thought is a potentiometer failure but before to open desolder and check would like to know what you think about
Thanks in advance

 

[gaz1]

try on another few more pieces to see if same fault apears may not be the machine

could be poor metal

 

[Memmeddu]

try on another few more pieces to see if same fault apears may not be the machine

could be poor metal

Later I will try on some new 4mm flat stock
How much amperage you would like to use in my situation?
I'm thinking to start with 40A and see if run as same as yesterday
Than 60 ,80 ,90 , 100
Quenching the workpiece between the various beads to not overheat the it

 

[Dcal]

I had (still have it in bits somewhere) an inverter and it faulted so that it would only weld.at full power.
Might be a common fault


A problem

 

[Memmeddu]

Ok I've just tried to lay down some beads
The welder is working weird
It's doing things it being never capable to do before
No matter what amperage I set , it's kind of hot starting and welds perfectly but is kind of hot
It's not full power because is capable of 250A but seems to give more current than what it usually gives at same amperage setting.
Used at 40A welds perfectly with 2.5mm 6013 , just little bit cold on 4mm
60A seems to be the perfect amperage for 2.5mm 6013
90A is very hot and at this amperage the welder can run 3.2mm E6010 with crispy start but the flux on the rod doesn't catch on fire
It usually needs 130 150A to do that without sticking to much and it still stick and break the arc , but now it's practically eating E6010 like my engine driven ,also got little bit of slag peeling and that's not normal
I'm thinking that my welder is going to death
It's too weird I will check the ocv give me a second

 

[Memmeddu]

It's giving 70.4V ocv instead of the usual 60.0V and the declared 56V
Now I want to try 7018 and see what happens at 40A

 

[Memmeddu]

Left to right
E6013 2.5mm at 40A
E7018 2.5mm at 60A
E6010 3.2mm at 90A

 

[Memmeddu]

I'm starting believing my welder was broken before and now is fixed by itself.
Made research , it's probably because a series of things about input side
Starting remember that my welder always needed little bit of current adjustments .
In these days I will take it a part to clean it from dust because I've shot grinding dust an sparks on it before it was starting to give me problems.
Today I've used a Fimer 250A three phase transformer based welder of a friend of mine (this welder will be mine once he decides to stop welding ) , my inverter works better than it