Cosmo where to now ?

Hi all

Before I kick my new/unused/cr*p Cosmo 150 welder again should I try this ?

Reading the other mods [ I have done the strap and new transformer mod ] it seems the 24volt transformer mod on it's own does not give enough fine control over the wire speed and 24 volts instead of 18volts max ?

The person doing the Maplin PWM speed mod is only using 12volts to drive the Maplin unit ?

So why not wire up the 24volt transformer to give only 12volt ? that would increase the sensitivity at the lower end on the speed scale at the expense of losing maybe 1/3 of the maximum speed [ 12volt instead of a reported 18volt in unmodified form ? ]

If this may work how do I wire up a 0 - 12 0-12 transformer to give me max current at 12volts ?

I only want to weld 1mm - 2mm m/s so can afford to lose some wire speed ?

regards Paul

Originally Posted by Paul-n So why not wire up the 24volt transformer to give only 12volt ? that would increase the sensitivity at the lower end on the speed scale at the expense of losing maybe 1/3 of the maximum speed [ 12volt instead of a reported 18volt in unmodified form ? ] If this may work how do I wire up a 0 - 12 0-12 transformer to give me max current at 12volts ? I only want to weld 1mm - 2mm m/s so can afford to lose some wire speed ? regards Paul

I don't know but would be interested if it was do-able welding 5mm steel I still only need 35% max of the avaliable wire speed with a 24V transformer mod - I could happily lose 12v and I reckon still have enough range to weld 5mm steel

I have no skill in Mig welding and have not proved mine welds yet !

Is your speed control very coarse ?

However this would be easy to try , you originally wired up the transformer as:-

0 Volt ----------- 24 Volt out


12 Volt

Link

0 Volt


12 Volt ---------- 24 Volt out [ Move this wire for 12 Volt ]

just move one wire to

0 Volt ----------- 12 Volt out


12 Volt

Link ---------------12 Volt out [ to here ]

0 Volt

12 Volt

The current will remain the same but the voltage will halve.

As we are only moving one wire this could be done with a switch to allow selection of 12 Volt or 24 Volt.


If we need more current we can :-

Wire both 0 Volts together and both 12 Volts together and wire our 12 Volt across the pairs , this will halve the voltage but double the current available.

Hopefully someone will come along and confirm this , I am sure I am right regards the wiring , but a little rusty in theory.

regards Paul

Originally Posted by Paul-n I have no skill in Mig welding and have not proved mine welds yet ! Is your speed control very coarse ?

Nope not any more a 10 turn pot solved the coarse adjustment issue as well as fixing the non linear nature of the original single turn pot

Originally Posted by Paul-n However this would be easy to try , you originally wired up the transformer as:- 0 Volt ----------- 24 Volt out 12 Volt Link 0 Volt 12 Volt ---------- 24 Volt out [ Move this wire for 12 Volt ] just move one wire to 0 Volt ----------- 12 Volt out 12 Volt Link ---------------12 Volt out [ to here ] 0 Volt 12 Volt The current will remain the same but the voltage will halve. As we are only moving one wire this could be done with a switch to allow selection of 12 Volt or 24 Volt. If we need more current we can :- Wire both 0 Volts together and both 12 Volts together and wire our 12 Volt across the pairs , this will halve the voltage but double the current available. Hopefully someone will come along and confirm this , I am sure I am right regards the wiring , but a little rusty in theory. regards Paul

I haven't got a clue what you mean - don't take offence it's just I don't understand it cos electrickery is not my best subject - now it has oil in it I can understand it!!!

I just know I have this

Attachment 8972

I can't see any reason to change your voltage if you already have the 10 turn pot and don't consider your speed control to be coarse.

This idea was to save me buying either the 10 turn pot OR the PWM speed controller mentioned in another thread.

I have already spent enough of this cr*p welder and don't want to spend anymore on it !

regards Paul

Originally Posted by Paul-n I can't see any reason to change your voltage if you already have the 10 turn pot and don't consider your speed control to be coarse.

I'm only using the first 30% of the range so 3 x less coarse compared to the original but could be 10 x better

Ok

How did you wire up the transformer you show in the picture ?

I cannot identify it from the web site but it looks to me like it is 240 Volt in and 24 Volt out ?

if you look at this one :-

http://uk.rs-online.com/web/search/s...19&y=17#header

It has more terminals.

Top 2 are 240 Volt in

Bottom 4 will be labeled 0 - 12 0 - 12 and so it can be either 12 Volt or 24 Volt depending on which wires you connect together.

Don't apologise for lack of knowledge , we can't all know everything,

That's why we use these forums , someone out there knows the answer !

I can't weld yet but hopefully soon.

Life keeps getting in the way of getting this welder fixed and practicing with it , this winter hopefully !

regards Paul

Originally Posted by Paul-n Ok How did you wire up the transformer you show in the picture ? I cannot identify it from the web site but it looks to me like it is 240 Volt in and 24 Volt out ? if you look at this one :- http://uk.rs-online.com/web/search/s...19&y=17#header It has more terminals. Top 2 are 240 Volt in Bottom 4 will be labeled 0 - 12 0 - 12 and so it can be either 12 Volt or 24 Volt depending on which wires you connect together. Don't apologise for lack of knowledge , we can't all know everything, That's why we use these forums , someone out there knows the answer

Ahh Now I understand - I only have 240 240 and 24 24 on mine

I should get chance to continue my investigation tonight I should be able to establish what the heck is going on!!!

It would only take 3-4 components to make a voltage regulator for the motor circuit.
A TIP transistor a zener or two and a resistor, you could rig it to put out 12,18 or 24v with just a tap or two.
Robert

Does this look like what you need ?
It's what I put on my welder.
Just mount Q1 on a heatsink.
http://www.mig-welding.co.uk/forum/a...pictureid=3062
Robert