New user with Cosmo 170 (SIP) and a headache

[BChild]

The control board's job is to reduce the voltage by an amount controlled by the knob on the front. If, say, it were to reduce the voltage by a lot initially but then over time (a component warming up?) reduce it by less and less, that would give the symptoms you describe.

This could also depend on the load presented by the motor, though. If the motor (or the mechanism it is driving) were stiff initially and then freed up gradually, again you could have the symptom described. Thick grease warming up in the gearbox or something like that?

All speculation but...

OK

I've looked back thro my post and there are lots of occasions where I seem to get changing results based on the same settings - lack of repeatability

I know I have a cold start problem on low settings and thin metals but that can be fixed with a gas change to argoshield light

I'll have another go at it tonight and see if I can isolate the problem

I'll check the wire feed speed after 30 mins of being powered up no welding too just in case like!!

 

[BChild]

You've tuned into Cosmo TV presented by BC in tonights thrilling installment we are going to cover relays that should stop the wire feed dead (and don't)and voltages at the wire feed motor...........

OK on a serious note the relay I fitted to stop the run on had a serious problem on the training day - it killed the wire feed as soon as you went over 30% so was disconnected and hadn't been reconnected since. (I'd never been above 25% on the wire feed so it was a bit of shock!!!)

It worked wrong anyway as I had to swap 87 and 87a round to make it work despite being pretty sure that the oracle that guided me probably was right and I'd got summut wrong

So tonight while I waited for the welder to warm up I got my head round it and tried to rewire it in my head and I realised I'd made an error when I fitted it I was trying to use the wire feed voltage to operate the coil so when it was a low speed the relay couldn't cut in so it just buzzed untill you wound the pot up to 50% when bing enough voltage to bring it in and it braked fine

Swaping 87 and 87a made it work but it was working the opposite way (I think - using coil off to make the contact and coil on to break it so with low voltages it wouldn't brake the motor)

I really should read posts carefully and ask more annoying questions because now I understand it I've been back and I can see that this was clearly pointed out to me earlier in the thread so I have to face it electrickery and me don't make good bedfellows but everyday is a schoolday - More later

Anyway Motor voltages (no steel wire or CO2 was harmed during this process)

Cold 10.2 volts at 30%
5 mins later 11.8 volts
10 mins later 13.4 volts
15 mins later 14.4 volts

During this whole time the output from the relay bridge remained constant at 21.3 v

So then it seems the PCB has something that is warming up or breaking down and I need to look closer at that

Then I thought it's a 24V transformer surely I should get 24V?

What volts do I get at the motor when it's at 100% - 27.8 volts

So I do have an electricty generator - how cool

Hear me out here but what the chances of the PCB adding to the voltage sent to the motor? I mean I have a separate transformer but the feed goes to the board and then from board to motor doesn't it? Could this be the reason for the cold starts too? I wish I understood some of this stuff better!!!

Time for that later thing

So filled with enthusiasm I turned the power off and I rewired the relay using power direct from the bridge to control the coil and just had the outputs from the PCB to the motor to the other terminals and bingo relay works fine any setting wire feed stops dead from 0% to 100%

So I did a bit of - same old rubish having to change the wire feed speeds down from 30% to 10% over the course of 10 mins but hey no trimming required at the end of each welding run so that really is major progress

So I cleaned the floor up of the previous weeks trimmings - enough to weigh in and get some pennies back I reckon

End of scheduled programming

 

[BChild]

PS must take some pictures of the welding on 5mm angle iron - much much better than my attempts on thin stuff

 

[R Kraft]

Glad you got another thing fixed, as long as you don't hurt yourself or costs money,education is good.

40% is a lot of voltage change.
Did you check to see if the drive transistor is heating ?
Robert

 

[BChild]

Glad you got another thing fixed, as long as you don't hurt yourself or costs money,education is good.

40% is a lot of voltage change.
Did you check to see if the drive transistor is heating ?
Robert

What would one of them look like?

 

[BChild]

Then I thought it's a 24V transformer surely I should get 24V?

What volts do I get at the motor when it's at 100% - 27.8 volts

So I do have an electricty generator - how cool

This is kinda explained by Shenions post elsewhere

34VDC is what you should get from a 24VAC output. The rectifter and caps will charge to the peak voltage: 24 x 1.414 = 33.93V. Will drop some under load.

However it doesn't explain why apparently the output from the relay bridge is 21.3 volts

 

[BillJ]

You've probably mentioned this somewhere but I can't remember - is the trim pot on your control PCB 1K Ohm or 100 Ohm?

 

[BChild]

You've probably mentioned this somewhere but I can't remember - is the trim pot on your control PCB 1K Ohm or 100 Ohm?

Still the original 1K Ohm one - on my list of things to change but I had perceived it to be a fringe benefit - just being a fine tuning on the start point

I maybe very wrong in this respect

 

[BChild]

I was getting very depressed with this POS welder late last week and early this week but getting the relay brake to work properly accross the full range of wire speeds was a victory (well for me anyway)

If I can fix the variable (increasing) wire speed so my settings are repeatable it will only leave me with the cold start (slow start on the motor) issue and I'll then be asking lots of questions about capacitors!!!

You can groan - I won't mind honest

 

[BillJ]

Still the original 1K Ohm one

I found that this had to be right at one end of its adjustment to allow the speed to go down low enough. At this extremity it was prone to speed variation due to vibration. Perhaps it's sensitive to heat too?

I changed mine for a 100R one from Maplin.

Well done on getting the brake working!
Figuring out things like that unaided is teaching you more about electrics than you'll want to admit to

 

[R Kraft]

The transistor is the 3 legged plastic and metal thing, hooked to the heatsink , with a screw through the metal tab.
Robert

 

[BChild]

The transistor is the 3 legged plastic and metal thing, hooked to the heatsink , with a screw through the metal tab.
Robert

With the machine on can I feel for heat with a finger or do I need some sort of safer non contact method?

 

[malcolm]

The transistor will get hot - that's why they are often mounted on a heat sink. I suspect it's unlikely to be the issue - the 1k resistor thing seems more worth a shot for travel speed issues that make themselves more of a pain when the wire speed is low.

Fancy trying a PWM controller? - I have a spare which could be yours for £15 (which I think is what I paid). It made absolutely no difference to my SIP but would help rule out PCB issues.

I was very impressed by Bill's conversion with the regulated power supply. Transformed the welder and made it perform like the Clarke ones do. The game with that one was no longer setting the wire speed accurately so the welder would work, more allowing use of a fair range of the original knob to adjust the weld to how you want it You ought to arrange to visit to try it out - you aren't too far away.

 

[BChild]

The transistor will get hot - that's why they are often mounted on a heat sink. I suspect it's unlikely to be the issue - the 1k resistor thing seems more worth a shot for travel speed issues that make themselves more of a pain when the wire speed is low.

OK I'll get one on order

Fancy trying a PWM controller? - I have a spare which could be yours for £15 (which I think is what I paid). It made absolutely no difference to my SIP but would help rule out PCB issues.

I'd be up for that - not like I've filled the case up completely yet!!! does that include post and packaging (and a three page idiots guide on how to wire the damn thing up!!)

Pay pal?

I was very impressed by Bill's conversion with the regulated power supply. Transformed the welder and made it perform like the Clarke ones do. The game with that one was no longer setting the wire speed accurately so the welder would work, more allowing use of a fair range of the original knob to adjust the weld to how you want it You ought to arrange to visit to try it out - you aren't too far away.

Nice idea - only thing stopping me ripping all the wire fed mods out and copying Bill's modification is I have this nagging doubt in my mind that my Cosmo has always had this problem from new - sure all the mods have helped to make it better but it's always been there and probably caused a lot more problem with a less than sensitive wire feed pot etc etc - if I find the problem/fix it and it works well I think it would be nice to do a back to back evaluation of the two

Cosmo Welder shoot out comparison

 

[malcolm]

Nice idea - only thing stopping me ripping all the wire fed mods out and copying Bill's modification is I have this nagging doubt in my mind that my Cosmo has always had this problem from new

I'm sure it has had the problem from new - that's why we tend not to recommend them on the forum.

I'll have a search around for the spare PWM controller - I bought two as the PCB on my own welder was playing up at the time and I wanted to have a backup plan. But It's not where it should be - I have a little filing cabinet for this sort of thing and it's not there.

 

[R Kraft]

Have you looked at this page, if yours is the same it may help.:http://eddiem.com/projects/mig/speedfix.html
Robert

 

[BChild]

Have you looked at this page, if yours is the same it may help.:http://eddiem.com/projects/mig/speedfix.html
Robert

Wow - I found that page on the interweb before I found this forum - I'm sure it's really helpfull but without serious help even now I get lost after the word slack

 

[BillJ]

Have you looked at this page, if yours is the same it may help.:http://eddiem.com/projects/mig/speedfix.html

That's where I got the 100R mod from. It seems later SIP/Cosmo units come with a 100R trim-pot on the PCB.

 

[BChild]

The transistor is the 3 legged plastic and metal thing, hooked to the heatsink , with a screw through the metal tab.
Robert

I have an infra red thermometer (I use it for evaluating tyre temperature across the profile during track days) so I used that to measure component temperatures

Temp from first switch on - no wire feeding

Start 16.4 Deg C
after 5mins 16.4 Deg C
after 10 mins 16.6 Deg C

Conclusion is it's not getting hot on it's own just powered up

So I stripped down the motor and gearbox - SIP were a bit mean with the grease some dry cogs - rebuilt not excessively greased but at least every cog shaft now has some applied

Found that the connection (negative to the motor) was breaking up a bit so cut off, trimmed wire and removed sleeving before resoldered that to the motor (probably due to the number fo times I've disconnected wires)

The motor spun freely but the gearbox definately has a tight spot somewhere on the cog assembly as on the slowest speed there is definately some noticable sound change briefly as it turns the wire feed rollers but it's no better or worse than it's ever been - so in summary no issues found there

Tweaked the 1K pot to try and get the wire feed min speed down (this has affected settings previously used)

Temp during wire feed - no welding 50% wire feed (no wire in the rollers)

Start 16.4 Deg C
after 5mins 17.2 Deg C
after 10 mins 18.8 Deg C

Temp during welding (power 5 initial wire speed 45%)

Start 17.2 Deg C
after 5mins 24.5 Deg C
after 10 mins 32.4 Deg C

Wire feed started at 45% but by the end of welding it had been reduced to 25-30% so similar reduction to that seen previously

So is 32.4 Deg C to hot for one of these components - to my untrained mind it's not but I'm not an electrical expert

The main transformer outer windings was at 155 Deg C and the smaller transformer was far behind it - just for interest

Oh and for reference the make of wire feed motor is Johnson but there wasn't a part number - just the manufacturer stamped into the nose of the motor casing

Thats it for tonight - not much more I can do

 

[BChild]

Oh and for reference the make of wire feed motor is Johnson but there wasn't a part number - just the manufacturer stamped into the nose of the motor casing

There was also a logo and this matches the company I found with google

http://www.johnsonelectric.com/

Seems to be some good product info on the site but again I wouldn't know what I was looking for to find details on the motor