SIP / Cosmo Mods

[Mattycoops43]

Thank you, great info. I'll sit down and work through it all to make sure I'm doing it right, but that's all logical to me.

don't know what happened to the links you posted but they definitely go to two relays, although one has a pic of a base as its main image, I guess its a blip on their site.

 

[skotl]

Ah - no worries - sorry for the confusion.

That writeup took me three attempts as I kept forgetting bits - it's been 18 months since I did the mod

Still... think it's correct now! Best of luck

 

[Mattycoops43]

Waiting for components now, I'll let you know how it goes and the difference in the welding.

Really appreciate the help.

Matt

 

[Mattycoops43]

I have noticed the power supply you linked to needs a £7 mains cable (dell s pin in line) I guess I can just hardwire mains cable to the psu direct. Don't want to pay that much for a lead that would be chopped and hard wired in anyway.

 

[skotl]

Ah... slight problem there, in that these PSUs take a variety of mains input plugs; some are 2 pin "figure of eight", some are 3 pin cloverleaf and some are 3 pin straight. Unfortunalely, the picture on that ad don't show what lead it takes, and I'm not sure I'd wager £7 on the one they link to - probably best to wait for the PSU to arrive and then check what it takes (my welder is at my friend's house as I'm off on holiday tomorrow, otherwise I'd go and check what connector it has).

You should be able to get a lead for less than £7, once you know what it takes.

The other benefit to waiting until you see the PSU is that I think these units are sealed. If it's screwed together then yes, you should be able to join any old (240V 1A) cable to it. If it's sealed then I'm afraid that you'll need to buy a lead.

 

[Mattycoops43]

Its very specific in the ad it needs the Dell s pin in line cable, unfortunately, I dont seem to be able to find one. tbh, if it's sealed I can probably get spades on it or something and fix them so they can't come undone. or even solder direct to the pins. There's normally lots of room around the pins in those type of cables.

 

[Mattycoops43]

So whos ordered from Maplins then? bit surprised nothing has turned up yet and its still showing as 'processing' despite it all being in stock.

 

[skotl]

Hi Matty, bienvenue from France (we're on holiday!). Did the bits turn up yet? Any progress on the mod?

edit: Oops - scratch that! I see you posted on the other thread - will pop over and have a read of that

 

[Mattycoops43]

Hi Matty, bienvenue from France (we're on holiday!). Did the bits turn up yet? Any progress on the mod?

edit: Oops - scratch that! I see you posted on the other thread - will pop over and have a read of that

Thanks for your help skotl! I got a bit confused as to what post was where!

 

[jiv_4321]

Hi all,

I’m new to the forum. I came across this thread last night after looking for some information on my old SIP Migmate Super dual purpose, which I’ve not used for more than 10 years. I got it used in the early 90’s and used it for fixing up my car and making metal furniture. I was never really satisfied with the welds I made, and assumed that it was me. This was pre-internet, now reading through the forums this welder seems to be regarded as having wire feed problems; however, I don’t think I’m having as bad problems as others on the forum. The feed rollers on mine seem to be fine with no slipping or flexing, but the noise of the drive motor does vary while welding. So, I was thinking about doing the power supply mod mentioned here. However, when I measured the voltages and currents at the motor, it is supplied with 35V at max power with wire feed on 9/10 and draws about 200mA when running, with a surge of about 1.4A at startup. This would suggest that the mods for my model would not be the same as for the other migmate models that I’ve seen on this forum. I’m wondering if I would be better off using a 36V transformer (more expensive). The motor looks identical to those in the pictures of the other migmate models in this thread.

Does anybody have any experience modifying this particular model? The motor control PCB is the MIG 3F PCB. I have posted a picture of a practice bead I ran this morning on 1.5mm tube at the 2nd highest power setting. I don’t know if improving the wire feed would make much difference to this or not. The power was probably too high and it was outside and a bit draughty.

I’m planning to use the welder for modifying some old bikes, so the quality of the welds I get from it are quite important - I don’t want one failing as I’m barreling down a hill with my daughter on a bike.

Many thanks in advance for any advice, it’s much appreciated. These sort of forums are the internet at its best.

Ron

 

[skotl]

Hi Ron, and welcome!

Another common problem with the Topmig (I know this isn't the model you have) is that the wire speed control is not fine-grained enough, so it's very difficult to adjust the speed in tiny increments.
So to answer your question, I wonder whether a 36V PSU would be too fast for the motor. You say that your motor looks identical to ours, and we tend to peak at 30V (pre-mod) so, to be honest, I suspect that you should be looking at a 20-24V transformer for the motor.

Could you post a few pics of the innards of your welder, please? Transformer, PCB and motor would be handy.

Cheers
Scott

 

[jiv_4321]

Hi Scott,

Thanks for the swift reply. I don’t remember having problems with the wire speed pot being too coarse, but as I said it’s been a while since I used it in earnest. I found some time this evening to do some tests. I measured the supply to the motor control PCB at the different power settings. At the minimum setting, the input is 21V with the wire speed pot at min and 27V at max speed. The voltages across the motor are 13V at min wire speed and 26V at max speed. So it seems the wire speed pot reduces the max voltage supplied to the PCB. At max power setting, input to the PCB is 36V and 30.6V at max and min on the speed pot, respectively, with 36V and 22V across the motor at these settings.

I rigged up a makeshift 24V supply with a motorbike battery and battery charger in series and the motor speed was definitely lower than normal, and I suspect too low for 0.6mm wire, which needs quite a fast feed (I was at 9/10 on the dial on the second highest power setting the other day). However, I’ve not tried welding, so I can’t be sure. Since the power will go to the PCB and not directly to the motor, somewhere between 21 and 36V would be ideal. I’m thinking a 36V transformer might be too fast on the lowest speeds, but I haven’t tried fiddling with the pot on the PCB yet. That leaves me in the range around 30V, but I don’t think I’ve ever seen a PSU at that voltage. The local junk market has loads of used switching PSUs, so I’ll have a look this weekend. If I find something suitable, I’ll install it with a relay.

I’ve uploaded a couple of pictures of the insides of the welder. I also plan to install a fan, as it cuts out too often in hot weather.

Cheers,
Ron

 

[Charles Hepburn]

I have just completed this modification but the wire speed is far too fast. I have used a 24 v transformer and tried to adjust the trim pot but I cannot get it slow enough. Any suggestions, I am not an electronics wizard.

 

[skotl]

I have just completed this modification but the wire speed is far too fast. I have used a 24 v transformer and tried to adjust the trim pot but I cannot get it slow enough. Any suggestions, I am not an electronics wizard.

Welcome to the forum

When you say you've adjusted the trim pot do you mean the item circled in Ron's photo;

If you've tried that at either extreme then you may need to become slightly more of an electronics wizard (or find someone to help)
How are you with a soldering iron?

If the feed is too fast (mine was) then you'll need to replace that pot with a 100 ohm one. See here for more info, and here for a run-down on all the mods I made to my SIP.

Edit: I'm doubting myself. Surely going from a 1K inline resistor to a 100 ohm one will speed up the wirefeed? Anyways - have a look at the writing on your trim pot (a photo would be good) and whatever it is (1k or 100R) swap it for the other one

 

[Charles Hepburn]

Welcome to the forum

When you say you've adjusted the trim pot do you mean the item circled in Ron's photo;
View attachment 71984

If you've tried that at either extreme then you may need to become slightly more of an electronics wizard (or find someone to help)
How are you with a soldering iron?

If the feed is too fast (mine was) then you'll need to replace that pot with a 100 ohm one. See here for more info, and here for a run-down on all the mods I made to my SIP.

Edit: I'm doubting myself. Surely going from a 1K inline resistor to a 100 ohm one will speed up the wirefeed? Anyways - have a look at the writing on your trim pot (a photo would be good) and whatever it is (1k or 100R) swap it for the other one

Thank you I will have another look.

 

[Marty J]

[QUOTE="

This is the relay, mounted on the floor.

[/QUOTE]

Am I correct with the pin base numbers on a 8 pin round-base relay?

 

[Marty J]

Have I numbered the relay base correctly in the diagram ? I don't want to spend the weekend in casualty . . . . . .

 

[skotl]

Have I numbered the relay base correctly in the diagram ? I don't want to spend the weekend in casualty . . . . . .

Do you have the pinout for the relay? Or a part number?
Without either of these I'm afraid we'd just be guessing...

 

[Marty J]

I'm using the same relay as you skotl. Looking at your photo of the relay, bottom left, blue pin 1, red pin 2. Bottom right blue pin 3, yellow with green stripe pin 4. Top left, brown pin 7. To me the base numbers printed on the base are laid out a bit weird, but I have never used eight pin relays before. If I start from the brown wire and work down the numbers are 7, 8, 2, 1. From top right, 6, 5, 4, 3.

 

[Marty J]

I'm using the same relay as you skotl. Looking at your photo of the relay, bottom left, blue pin 2, red pin 1
. Bottom right blue pin 3, yellow with green stripe pin 4. Top left, brown pin 7. To me the base numbers printed on the base are laid out a bit weird, but I have never used eight pin relays before. If I start from the brown wire and work down the numbers are 7, 8, 1, 2. From top right, 6, 5, 4, 3.