Inverter Welder Strangeness

[CapLeaker]

Re: Inverter Welder Strangeness

I haven’t seen anything like this. Looks almost they use this full bridge rectifier in a half bridge mode. Connecting one side of AC to the AC pin on the rectifier and then connecting the other side of the AC to the negative terminal on the bridge rectifier? So your measurements are a bit wrong.

[Crystaleyes]

Re: Inverter Welder Strangeness

As it says in the thread title... strangeness!

But yeah, you were correct, my measurements were wrong. I should have measured the voltage across the caps and not the bridge. Across one of the caps measured 160v, whilst the other was 1.7v which is what you would expect looking at the original drawing I made in the opening post. Sometimes I forget to take a step back and remember what has already been noted.

So.. Anyway... progress report;

With the IGBT's back in, and running through a dimbulb, the main output voltage is 47v and both gate signal frequencies run at around 45KHz. The duty cycle fluctuates between 49 and 52%, however I only have a crappy 'Chingy Lingy' Habotest to measure Hz and %, so maybe it is actually running at 50%?
Maybe a 50% duty cycle is not even so important? I am just 'assuming' that the IGBT's should be triggered in balance, as that makes sense to me.
Another thing to note is that the dimbulb is lightly glowing whilst flickering somewhat. I've seen this before with dodgy filter caps, so maybe I'll delay judgement until there a different caps in place? Then again, maybe this is just a quirk of the machine and is fine?

I suppose I should really try welding some steel tomorrow morning and then I'll know for sure whether I'm just looking for problems which no longer exist, or if the caps have indeed failed?

Regardless, after changing those main caps, there will only be one more component of note to be changed and that is an LNK626PG, which is sold as an,
'Energy-Efficient, Off-line Switcher with Accurate Primary-side Constant-VoltageControl'
...if anyone was wondering?

[CapLeaker]

Re: Inverter Welder Strangeness

All I can tell you is that IF you want to test these big higher voltage caps properly, skip the ESR tester and find someone that can these capacitors under rated voltage and measure leakage. So far my ESR tester always said the high voltage cap is good, while in reality they were leaking. Or shotgun it and replace with proper branded capacitors and call it good.

I wouldn't weld any heavy things until this thing is fixed properly.

[petehall347]

Re: Inverter Welder Strangeness

out of interest where does the other mains wire connect to as in i guess the neutral wire .

[Crystaleyes]

Re: Inverter Welder Strangeness

out of interest where does the other mains wire connect to as in i guess the neutral wire .

It goes to one side of both of the large caps.

Below is a rough sketch I made at the start of this adventure

[Crystaleyes]

Re: Inverter Welder Strangeness

I wouldn't weld any heavy things until this thing is fixed properly.

Agreed. I was just looking at the dimbulb again and it is clear that there is so much current being drained that there is no way it will ever arc properly, so I'll order the new caps tomorrow.
There's not the greatest selection here however there are some Rubycon ones or Nippon Chemicon easily available.


EDIT:

Here is a picture or two of the unit in question...

[Crystaleyes]

Re: Inverter Welder Strangeness

So...

The new Rubycon caps arrived and were duly installed.

Now the fuckin thing no longer turns on!


Considering the caps are new, I didn't test them before putting them in, however testing them now reveals both to be well below the rated 2200uF. One is holding steady-ish at around 2050uF whilst the other keeps dropping and I stopped measuring when it hit 1980uF.

I'm just wondering if these caps could be preventing the unit form switching on? I suppose one way to confirm is to reinstall the old caps, for at least with them the welder fired up with the fan and LED display both working fine.


I think the expression in French is, FUCKING BOLLOCKS!!!

[Per Hansson]

Re: Inverter Welder Strangeness

No, the capacitors have a 20% tolerance, they are fine measuring like that.

[Crystaleyes]

Re: Inverter Welder Strangeness

Mmmm?

Thanks for the info. Would be proper headache to have to send them back.

I'll have a proper look at the power input section later.

It was a bit strange, because even though I discharged the original caps with a resistor before unsoldering them, there was a distinct kind of 'clicking' which came from the board. Hopefully it is the bridge rectifier or something else as simple?

I can't complain, as I bought this thing learn.. It has definitely forced me to think deeper than I've been used to.

[CapLeaker]

Re: Inverter Welder Strangeness

Hopefully it is something stupid like a plug not properly seated blown fuse or something. I cannot see the new capacitors preventing the unit to turn on. If the bridge rectifier is bad, there would be a short on the main filter caps.

[Crystaleyes]

Re: Inverter Welder Strangeness

Seems to have been a bad connection on one of the two 4mm cables between the main on/off switch and the circuit board.

Removed it. Resoldered it. And now the unit has fired up again. Has been running steadily for the last twenty minutes or so.


I have a major doubt though...

The dimbulb is glowing brightly and flickering still. Probably flickering less than before but surely it shouldn't be glowing at all?
There is also now a distinct smell of slight burning. Whoever had electric train sets, or Scalelectrix, will remember the smell of the brushes as they arced. Well THAT smell is there. Faintly... but there...

Another note, is that the AC current flowing through the welder measures around a steady 0.50A. Due to the dimbulb drawing so much current, the AC actually reaching the PCB is down from 127v to around 94v AC. The ouput voltage to the main welding cables is still around 40v and the frequency is still around 40KHz across both IGBT's, with 'around' 50% duty cycle.



My concern is whether to connect it directly to the mains, as I can't really afford to be buying more IGBT's, at least, not just to toast them. Maybe I'll just try some welding whilst here on the bench and fuck the fire risk!?!


Any other ideas?

[Per Hansson]

Re: Inverter Welder Strangeness

Something must be getting quite hot with such a load, try to see what it is.
If you can't find it just leave it running longer and then disconnect it and check for the hottest components?

[CapLeaker]

Re: Inverter Welder Strangeness

What size dim bulb? A wrong size can make you chase rabbit holes. Take the igbt’s out and fire up that welder. Given, you can’t weld like that, but you can turn it on and play around and maybe figure out where that current draw comes from.

New capacitors can increase the current draw. It was like that on that plasma cutter. After the caps and adjustments, that thing was cutting really good. There is just more power available to the mosfets / igbt’s in the inverter.

Just don’t get the idea to start welding with the dim bulb tester in circuit.

[Crystaleyes]

Re: Inverter Welder Strangeness

Thanks for the suggestions chaps.

I'm out all day today, but I do have an hour now to leave the unit running and see what gets hot.
If that doesn't reveal anything then I'll remove the IGBT's...



The dimbulb is 60W 127v

[Crystaleyes]

Re: Inverter Welder Strangeness

So, it ran for an hour and nothing (that I could sense) got anywhere near hot.

I'm off to work, I'll get back on it later

[petehall347]

Re: Inverter Welder Strangeness

60w is pretty low .. maybe 150w and up will be a better choice .

[Crystaleyes]

Re: Inverter Welder Strangeness

Don't have any bulb here above 60W. Has anyone ever tried putting in a 150Ω resistor as temp solution? (100W lamp @ 120v is 144Ω)

Anyway, just had it running for over an hour again, and spraying it with IPA didn't reveal any excessively hot spots.

[CapLeaker]

Re: Inverter Welder Strangeness

Run it without the dim bulb tester and measure the current draw?

[Crystaleyes]

Re: Inverter Welder Strangeness

Run it without the dim bulb tester and measure the current draw?

Bad idea.

It went crack/pop.. and now no longer switches on


Hang on. REWIND...

Now it IS switching on and running again!

There has to be some really poor connection that I am missing somewhere or else the Gremlins are playing around?

Anyway, the AC input voltage is 130v, the AC current is fluctuating anywhere betwwen 0.5A up to 1.2A, and the main output voltage is steady around 64v DC.

Gotta go out again, but the next step is to take it to the garage and try to actually weld something.

Perhaps this thing is fixed and I'm just looking for problems which don't exist?

[CapLeaker]

Re: Inverter Welder Strangeness

What went up in smoke?