Cemont CEMIG160T - Also known as?

[Hopefuldave]

Hi all, Newby posting warning...

Borrowed one of these from a mate for a few weeks, as I have some Thin Stuff to weld (oil-drum to make a furnace, I think the Oxford oil-cooled would murder it), I've sussed that it has wire speed and "power" settings without much trouble and I can see how to tension the wire feed, but wondered if I could find a manual online - the Cemont website denies all knowledge of it when I search for manuals! I wonder if it's also known as someone else's MIG (which I suppose this is, being borrowed...), and they might have a manual to download.... It would be handy to know which spares etc. are compatible, too. Any points to check before I start using it (or at least, learning it!)?

The hose from the gas reg to the welder looks a bit iffy, taped up in a couple of places, and I like to return stuff better than when it left, can I buy cheap replacement hose easily? It looks like the fittings are 3/8" BSP, so they're readily available and cheap (e.g. Screwfix) - if it's anything like TIG, air leaks in the hose will knacker the weld quality even before I start, not good when I've not used it before! I also noticed the wire armour? on the torch lead was a bit raggedy with a few strands poking out, I assume it terminates like a SWA cable in the bushing through the front panel - is this fixable by re-terminating it, or am I looking at a new cable...? While I have it, I'm going to straighten a few bent panels, put a replacement caster on the front and use a bit of my nice 20mm stainless tube to replace the missing handle - should look nice when I eventually hand it back!

Also: the regulator on the bottle (Y size Argoshield light, at least half full, thanks Gaz!) has the output gauge calibrated in psi / bar (up to 20 psi, 1.4 bar), how do I convert to litres/min, if that's possible, or do I need to add a flow meter downstream of it? I think I have one lurking in the Shed of Danger, ex medical oxygen, which goes up to 10 or 15 litres/min... I think it has the right threads, too

I've used TIGs before, although my efforts on ally weren't pretty, and have a basic clue of flow rates, but they had flow gauges (the floating ball type), and that was TIG, not MIG... Should I just guess / trial and error?

Any hints and tips welcome,

Cheers all,
Dave H. (the other one)

 

[the snooper]

post a picture of it someone may recognise it as something rebadged

 

[Hopefuldave]

Good idea Snooper... just took some!

Front, top (in the lid), feed rollers and the state of the torch cable, can it be fixed?

Cheers,
Dave H. (the other one)

 

[the snooper]

the wire feed looks very similar to a sip topmig which also mounts the mig wire in the top exactly the same

although not the topmig here is a sip which shows the same wire feed

 

[Hopefuldave]

CeMIG 160T - also modding / improvements

Thanks, Snooper,

I guess then that it's probably a DIY type MIG - figures, knowing where it came from.

Now I've looked through TopMig posts, it looks like as a breed they aren't that well designed (cost cutting...) - maybe I'll do a few mods once it's opened up!

The separate supply for the wire feed looks easy enough, I have a few spare mains transformers etc. kicking about (any info on the current requirement for the motor?),

I was wondering whether it's worth adding pre/post gas like a TIG (could use a relay to deliver AC from the wire feed transformer to the gas solenoid, delay before operating the welding transformer contactor, then delay closing the gas solenoid after coming off the torch switch).

*IF* I have a couple of big capacitors (probable, knowing my junk box) the weld current smoothing mod looks good too - is the capacitor value critical, seems that going too high would delay arc start / stop a bit, too little wouldn't smooth it much?

The wire feed brace makes good sense, pretty easy to do as well! I've already found the free roller was a bit iffy, but a soak in perpetrating oil and some grease sorted it out pretty quickly.

Once I peeled off a mile of tape from where the torch cable attaches to the wire feed / gas feed block it looked OK, so some self-amalgamating tape and a bit of hefty heatshrink can cover it back up, neaten it up.

So... that covers the *free* mods, I'll spend some money on a curtain wire liner ( ) as some wire was left in the original plastic one and appears to have rusted in there, anywhere else I should be looking?

Thanks again,
Dave H. (the other one)

 

[Hopefuldave]

Less to do than I thought...

Well, today I took the side off (which meant taking the wire feed tray off, which meant...) and discovered it came with a separate 24V control transformer from the factory - powering the gas solenoid, main transformer contactor and the wire speed board, so most of that seems to be under control I guess it's not as cheapo as I thought it was!

Left to do is the wire feed roller brace - piece of plate at the ready - and possibly the capacitor smoothing the arc voltage, on which a couple of questions:

1) does adding a pair of big electrolytic caps make a worthwhile difference to weld quality? Enough difference for a newby to MIG to do it before getting on the learning curve?

2) I guess the caps go between the torch lead at the rectifier and choke (inductor, reactor, whatever it's called today) centre-tap side? I've dug into the forum, and it looks like too high a value will raise the minimum current setting, this may be a Bad Thing, I suspect, as I have thin stuff to weld as well as thick (1mm up to 5 or 6mm)...

3) What's a good value for the caps, presumably 63 or 100 volt rating will do on the low voltage side of the transformer, but how many uF would be good?

Back to my original question, does it look familiar to anyone?

Cheers, all feedback gratefully etc.
Dave H. (the other one)

 

[mike 109444]

Cap goes between the output of the inductor/coil and the output to the tourch. Note this is after the diode pack so is DC and cap will need to be correct way round. 30,000 to 50,000 micrfared at 50 or more voltes (££'s) maybe a bank of lesser ones to total same value. Does smooth welding I have found.

 

[mike 109444]

Lesser Mf's not voltage!

 

[Hopefuldave]

Thanks Mike,
I understand about the voltage, I was planning on either 63 or 100 volt rated electrolytics, lowest esr I can find as there's likely to be significant ripple current in 'em. Definitely after the choke? I remember seeing a post suggesting the caps should go between the rectifier dc out and the transformer centre tap, would having the cap after the choke not affect current stability but give better voltage stability? On a TIG current regulation is the desired effect, is MIG more voltage dependent?

Thanks again,
Dave H. (the other one)

 

[Wallace]

Is the fan noisy? Looks like it has a blade missing.

 

[shenion]

You want the caps after the rectifiers and before the choke.

The choke does not add "voltage stability"; in fact it does just the opposite. It helps maintain a constant current. In dip transfer, the wire shorts to the weld pool, current builds up in a controlled fashion then when the droplet is pinched off, the energy stored in the choke ups the output voltage to maintain the arc current. The voltage will spike to several times its normal voltage. This added current during the arc, adds heat and "wets" out the weld pool.

If you were to put the caps after the choke, the wire would literally explode as they would dump a huge current when the wire touches the weld pool (calculated at 1200 amps for a 200A MIG), then the current would drop to near 0 when the arc is formed and you would have a mess with lots of spatter and little penetration.

 

[Hopefuldave]

Thanks Scott, that makes more sense to me than having caps after the choke, and ties in with TIG welder construction, where the choke is immediately 'upstream' of the torch.

So, up to about 100,000 uF of 63 or 100v electrolytics where I originally thought, between the rectifier dc terminal and the transformer centre-tap, with a hefty wirewound resistor to bleed the cap voltage when off the trigger?

As I have spare 24vac contactors, is it worth putting in a pair of normally-closed contacts (off trigger) to switch in a lower resistance to bleed the caps down faster and take the voltage off the tip? If so, it would be good practice to put in a hefty diode across the caps in anti-parallel to help snub the choke's induced emf, or would that be OTT? Just thinking that coming off the trigger would see the electrolytics reverse-polarised due to the current in the choke and could pop 'em in pretty short order! A low resistance would lower the Q of the choke/cap circuit (as would the diode) so less ringing, giving everything an easier time... I'm being sloppy though, not considering the transformer mutual inductance

Taking a WAG, the choke's about 200 uH, assuming 100A and the current falling to zero in 5ms (1/4 of a 50Hz cycle), the induced voltage on the caps would be about -8v, not a lot but enough to eventually pop electrolytics and a diode would limit that to 0.6v... I may have to put my 'scope on it for a look-see! Is it safe to do this with the torch/earth shorted for a second or so?

Thanks again,
Dave H. (the other one)

 

[Hopefuldave]

Is the fan noisy? Looks like it has a blade missing.

Tricky of the light or bad photography, managed to catch it edge on and lined up with the corner of the case.... I was surprised the fan doesn't have a shroud though, will add one to improve it a bit! Ha'porth of tar and all that....

Dave H. (the other one)

 

[Wallace]

Tricky of the light or bad photography, managed to catch it edge on and lined up with the corner of the case.... I was surprised the fan doesn't have a shroud though, will add one to improve it a bit! Ha'porth of tar and all that....

Dave H. (the other one)

What are the chances of that? Looking closer I can just see it! Without a shroud it's more or a stirrer than a fan, should improve the cfm for a little effort.

Mike

 

[shenion]

No need to worry about reverse polarity protection, the bridge will provide that. Besides, the choke energy will be drained by the end of the last AC cycle..

My take on cap size is 1,000 to 4,700 is good for a more stable arc. Above that, it will raise the minimum current and you will find it becomes more sensitive to torch/work length due to the average voltage varying with load.

I have 60,000uf on my Miller and it seems to work fine. I do see the volt meter go up to 28V then drop down to 19 when welding. Just the caps charging to peak then dropping toward the RMS voltage. I think I calculated they would raise the voltage on anything below 50 amps.

I have a 250ohm resistor (100watt) to dissipate the voltage. Still takes a few seconds. I'll drop it to 250.

I'm still trying to figure the best choke value (my Miller did not have one.)

 

[Hopefuldave]

Thanks Scott
I think I have a couple of suitable caps lurking somewhere, probably 'audio grade' low esr, so half way there already I borrowed the MIG to do some thin sheet work my Oxford would blow holes in (modding an oil drum or two into a casting furnace) so I'll put a lower value cap/s in as it's low current I want.
For the resistor, could I get away with a 500w or 1kw 240v heater element? That would give a dc resistance around 120 or 60R, plenty of power handling if I put it in the breeze from the fan... And I have one handy! I'll probably still add a contactor to put another in parallel to get the voltage down faster, as I have a few spare. Thinking about this, the ocv across the resistor is the worst that can happen if the contactors get knickers in a twist, so shouldn't put faults on as long as the 24vac transformer has enough urge for an extra coil hung off it.
I'm not intending to spend a fortune on it, it 's borrowed after all, but raiding the scrap box is fair exchange for the loan and gas I use?

Dave H. (the other one)