SIP / Cosmo Mods

[Jake SS]

Ok so I am going to be gentle here with this post, after all its only common sense really

If this was my welder for home use I.......

I would have an actual circuit drawing of my machine then draw another one according to the mod that I want to make, double or triple check it

I would take current and voltage measurements on all original components, i.e. all inputs and outputs open circuit and under load, to compare after I had done the Mod

I would mount all components in the live side of the welder as it is not easily accessible, I would never mount any electrical components in such a manner that someone or something can touch any live wire or terminal. Transformers are available either "open" or "closed" meaning that one can buy a purpose built enclosure for a transformer. Make sure that the case is earthed using the correct colour earth.

I would fuse the transformer on both the primary side and secondary sides. I would measure the actual current open circuit and under load to ascertain what size fuses you would need, yes it can be done mathematically but there are variables such as motor current draw which can change depending on the load. Usually a PCB will be taken out by an overloaded motor, too much tension etc.

The wires used must be the same diameter as the originals if you are joining them to continue a circuit. I would never put wires through a drilled out hole
where there is a chance to wear through the insulation

I would use a small amount of heat sink grease on the back of the bridge then mount it to an actual heatsink, I have seen bridges blow up. I would not solder wires to the bridge terminals as I have seen heat melt them, they also corrode easily. I would use purpose made terminals, crimped with a proper crimper, With crimp terminals or spade connectors there are two diameters of the plastic part, the bared wire should be pushed in and there should be enough insulated part of the conductor pushed into the first section (larger) and crimped securely, I would place a small capacitor across the bridge to help smooth the DC and it also helps to share the load.

Some people may say that you dont have to worry about polarity in AC circuits. This is simply not true in most circumstances, always be aware of polarity whether it is AC or DC.

I would then go over everything with an ohmeter and megger before powering up, but I would be sure that PCB is not meggered or any"delicate" components.

I would then recheck all my connections making sure that I have made all connections as per my mod drawing

Check all insulation

OK I think I have done everything that I want to do before powering up.

I would then switch on and check all voltages with a good meter.

Then I would bang test it and take all voltage and current measurements and compare with original, I may be drawing a little extra current from the input, so I would have to check that my wiring and breaker are OK

I would weld for a while then pull the plug from wall and check everything for excessive heat, if OK I would continue on welding but keeping an eye on the machine.

I think that about covers it, I may have missed some detail, would be easier if I had a machine here to do the mod on though.

Sounds a bit hard?
I wouldnt want to hurt anyone now would I

Have a good close look at the pics in the posts on this thread

I would do this mod having safety as my main priority, If I was unsure about any aspect of what I was doing I would not attempt to do it in the first place!
Cheers

"Let common sense prevail"

 

[tankarmour]

Hi all,

I just new member in this forum, my own Cosmo 170, I carefully read on all forum about Cosmo / SIP Mod - Transformer. i bit confused of which of transformer type will fit in my cosmo 170.

Transformer Primary :240v and Secondary : 2 x 24v or 2 x 12v ?

Please let me know then i will be order at JMS online ( Transformer Supplier ) by tomorrow.

Thanks

 

[ethos]

Just finished modding my SIP 105 and for the first time in its life, it can now lay down a smooth, clean bead on every power setting. What a transformation!

I added a fuse to the transformer mod and put the rectifier on a finned heatsink under the fan.

Terry

 

[Jake SS]

Just finished modding my SIP 105 and for the first time in its life, it can now lay down a smooth, clean bead on every power setting. What a transformation!

I added a fuse to the transformer mod and put the rectifier on a finned heatsink under the fan.

Terry

Pleased that you added the fuse and put the rectifier on a heat sink.
Should post a pic.

Cheers

 

[malcolm]

From an email sent to me about this thread by KB. Might be of use:
-----------------------------------------------------------------

Greetings,
I'd like to pass on a small bit of electronics knowledge that I've picked up over the decades. I have to admit up front that I haven't had time to read the eleven pages of replies that come after the bit I'm commenting on, so forgive me if someone else has mentioned this to you. I noticed that on the pics of the full-wave-bridge diode rectifier you added for stability, that the solder joints appear to all be "cold". Cold solder joints are very common with people who don't do much soldering. Fortunately they can easily be made sound.
On joints like this I find that the best solution is to add a drop of (electronic) solder flux (paste or liquid) to each joint and then reheat the joint sufficiently to make the solder flow like water. As soon as it flows remove heat as overheating can cause chalky joints. Perhaps the iron you used wasn't large enough, or maybe you didn't apply heat long enough. The actual time required depends on several factors, but just look for the solder to suddenly flow like a thick liquid around the wires/posts and you'll soon see what I mean. BTW, best to hold the soldering iron so that the tip heats the wire and the other half of the connection at the same time! Using a typical hobby iron of around 40 watts one would expect a connection like you're doing there to take around 5-10 seconds for the solder to flow properly and coat both pieces. That could vary with iron size (watts and tip size). Also, rectifiers of that type often have a heat-sink built in which makes it a bit trickier to get a good joint.
Leaving joints "cold" can cause intermittent problems to occur as the joint ages, and in some cases there isn't even a good electrical connection from the beginning (as in high resistance or intermittent). It might sound trivial to the uninitiated, but I assure you that it does matter, and is easy to rectify. Cold joints could even nullify the addition of the extra transformer.
I also see another improvement that's possible if the welder in questions doesn't use Pulse Width Modulation (PWM) for wire speed control. PWM is commonly used in many applications these days where speed control is needed. Modern model railroad speed controls are one example. Most wiper speed controls for vehicles also use it.
In fact, there are a few inexpensive kits around that would make it easy to add PWM control for the small wire feed motor (details on request).
Sorry if later posts have already pointed these items out, but I felt it best to pass them on rather than waiting until I get time to read all the threads (might forget). I'm sure I'll learn a lot about welding from your site, so I hope you don't mind these well intentioned pointers about soldering and speed control technology.
I know you're busy, so no reply is necessary.
Cheers,
KB.

PS- rosin core flux for plumbing can be used in a pinch, but there are electronic solder pastes/liquids made for such situations (where there isn't enough flux in the solder). Just avoid any acidic fluxes as they are deadly to electronics.

 

[rtbcomp]

KB is dead right. Cold or Dry Joints can cause no end of problems; whilst re-melting or making a soldered joint make sure the wire doesn't move.

Also the correct flux is vital, as he says avoid acidic fluxes (Fry's and such) that you get from DIY shops. Places like RS components stock proper electronic solder fluxes.

The composition of the solder is important too, use 60% tin, 40% lead.

 

[Jake SS]

Personally I would never soft solder wires to a bridge rectifier, this type is made to suit spade connectors.

Good advice on the soldering though

Cheers

 

[Eggy]

I'm going the whole 9 yards on this at the weekend (motor bracing, cooling fan and seperate supply for the motor). I've got a 25w SM PSU kicking around that I was thinking of using for the motor and fan. But I'm having a "moment" with the wiring. Am I right in thinking that the -ve of the psu will now got direct to the motor while the +ve needs to connect to the black wire on the small green connector. The +ve feed is then switched by the pcb and to the motor using the existing white wire? (I hope my rambling makes sense).

 

[martinez]

wish I'd found this site a year ago when I was struggling with the Cosmo I bought off ebay.
Yesterday I decided enough is enough and bought a better Mig.
I've got 2 other old Migs too with similar problems, ones a Clarke and the other is a Sealey, so I'll look at modding them and see if I can get any kind of a decent weld.
I bought the Cosmo after giving up on the others, and an initial brief weld seemed fine, a year later all I could get (after numerous strip-downs and adjustments) was a sort of alternating weld every second or so.
I just got used to joining up the dots.
You really don't expect a welder to perform so badly from new.

 

[BChild]

wish I'd found this site a year ago when I was struggling with the Cosmo I bought off ebay. Yesterday I decided enough is enough and bought a better Mig.

I'm so glad I did before I got utterly frustrated and did exactly the same thing put the purchase down as a bad experience and threw it in the bin and bought a better one

I bought the Cosmo after giving up on the others, and an initial brief weld seemed fine, a year later all I could get (after numerous strip-downs and adjustments) was a sort of alternating weld every second or so. I just got used to joining up the dots.
You really don't expect a welder to perform so badly from new.

Joining up the dots is pretty much all they are good for out of the box

 

[peter1]

Wire feed upgrade on topmig 170

have just finished the upgrade folowing the details word for word from page 1 of this thread . Came to turn welder on and when i do so the feed roller runs as soon as you turn the power on pressing the button on the torch makes no diffrence.
was wondering if anyone could help me ?

 

[rtbcomp]

Do the main contactor and gas valve operate as well?

If so sounds like a short in the trigger wiring.

Does the speed control knob alter the speed of the motor?

 

[peter1]

yes the gas valve opens and the speed knob alters the roller speed but the trigger does not work.

 

[WindWalker]

Hi Peter

I had exactly the same with mine when I did it. Mine was an older model than most of them on here but connecting the wire to the relay/selector/middle switch instead of the right hand side of the board cured mine.

I followed post #63, 64, 65 and post 66 on this very thread to correct the problem.

 

[rtbcomp]

Can you disconnect the trigger from inside the box and check continuity between trigger wires?

If disconnecting the trigger stops the motor running then the fault lies within the trigger wiring.

 

[WindWalker]

You're right rtbcomp, it could well be a fault with the torch, best to check if changing the wires doesn't work. Mine puzzled me for a while but it was only the connections.

I'm assuming it worked ok before fitting transformer?

Peter, you may want to check the trim pot impedance as well, 100 ohm is good, 1k ohm is a bit all or nothing and can be replaced with the 100 ohm one. I will do this on mine when I get time, got the pot just need to do it and report back on another thread about it.

 

[peter1]

Think i have it, all back together and it is welding like a dream lets hope it stays like it.

Many Thanks to everyone for there help

 

[katana]

Hi,
excellent thread and have now taken the 'plunge' ...but have a problem..........could someone please help....after doing the mod, my wire feed is permanently running when the welder is switched on. I have checked all wiring getting 24V from the transformer. Conected 'black VE-' to the black motor connection. The VE+ connection to the black lower wire also.....but have the wire feed problem (on all the time).

Trigger is fine (in fact reverting the two 'DC' wires back to original and leaving the transformer connected, the wire feed is fine)

Tracing the wires from the 'block' connector...I have (from top to bottom) Blue (trigger) Red ( rear transformer) White ( + motor) Black ( to earth).

I assumed that the red wire (power supply from transformer) would be the one to cut and connect to (with the VE+ wire) ....but once done the relay clicks when trigger pressed ... has little voltage ....but not enough to 'pull' the wire. Again putting the DC wires back to original 'feed' works fine

The welder is a SIP 105 .....please has anyone any ideas, thanks

Regards David

 

[BChild]

Hi,
excellent thread and have now taken the 'plunge' ...but have a problem..........could someone please help....after doing the mod, my wire feed is permanently running when the welder is switched on. I have checked all wiring getting 24V from the transformer. Conected 'black VE-' to the black motor connection. The VE+ connection to the black lower wire also.....but have the wire feed problem (on all the time).

Trigger is fine (in fact reverting the two 'DC' wires back to original and leaving the transformer connected, the wire feed is fine)

Tracing the wires from the 'block' connector...I have (from top to bottom) Blue (trigger) Red ( rear transformer) White ( + motor) Black ( to earth).

I assumed that the red wire (power supply from transformer) would be the one to cut and connect to (with the VE+ wire) ....but once done the relay clicks when trigger pressed ... has little voltage ....but not enough to 'pull' the wire. Again putting the DC wires back to original 'feed' works fine

The welder is a SIP 105 .....please has anyone any ideas, thanks

Regards David

I'm useless with electrics but from memory the feed to the transformer needs to be from the switched voltage.

On the board in my SIP I had switched and permenant live - I had the same problem but quickly realised I'd connected to permenant rather than switched so the wire feed was constantly on

It would probably help a bit if you could post pictures of the mods and maybe label up the wires to help us guide you

 

[katana]

I'm useless with electrics but from memory the feed to the transformer needs to be from the switched voltage.

On the board in my SIP I had switched and permenant live - I had the same problem but quickly realised I'd connected to permenant rather than switched so the wire feed was constantly on

It would probably help a bit if you could post pictures of the mods and maybe label up the wires to help us guide you

Hi,
thank you for taking the time to post......and apologies for the late reply (I've just had a minor 'op' and wasn't feeling too good )
I did try both terminals ....and had constant 'feed' from both, when I get chance I'll re-check everything....and if I cannot find the 'fault', I'll post some wiring pics ....perhaps the circuit boards are slightly different on some welders.
All the best
David