SIP wire feed power mod question.

[Reman]

Hi everyone, You've all been so warm and welcoming since I joined yesterday that you've only got yourselves to blame for me asking stupid questions now. LOL !

Anyway, I just want to check I'm not being thick here.

I understand that the point of adding a 24V PSU to cheap MIG welders is because the voltage on the transformer's wire feed tap drops off and becomes unstable when the welders striking an arc.

But does the wire feed board on my SIP Migmate 100 see any power until the welders trigger is pulled and the transformer energises? After looking at the circuit diagrams I've found for other SIP machines of the era it looks like there's no actual "trigger" signal to start the feed. All the feed control board does is sit there waiting to be powered up so it can start spooling out wire at it's pre selected speed?

OK, If that's right, Doesn't that mean I could just cut the 24v connections to the wire speed board, use those to energise a 24V "Truck" relay, run the positive side of a 24V (2 or 3A) laptop style power brick through the relays switch, and run the PSU's negative directly to the original negative on the wire feed board? Unless I'm missing something this would mean a constantly powered PSU having it's output "Connected" (And subsequently having the wire feed running) only when the transformer is energised, and the bare minimum of intrusive rewiring of the welder? I know doing it this way wouldn't bridge the feed motors terminals and stop it dead, But just to get a more stable wire feed speed, Would it work?

I'm only asking because I HATE playing with high amperage equipment. Whenever I have to do this sort of stuff it literally make's me feel like I'm going to vomit ! So I'm thinking that if I can just pre assemble a stupidly simple collection of 2 bit's, Then just crimp/solder 4 wire's when the covers are off the welder I'd feel a lot better about doing this mod.

........ Or am I missing something?

Reman,

 

[skotl]

Ask away - that's why we're here!

I understand that the point of adding a 24V PSU to cheap MIG welders is because the voltage on the transformer's wire feed tap drops off and becomes unstable when the welders striking an arc.

Correct. The key is "dropping off" and "unstable" - what actually happens is that the transformer can only give out so much Volt/Amps (power) and is not particularly sophisticated so, when the arc starts, the power output (simplistically: amps) jumps up so the voltage drops.
The wirefeed motor's speed is directly proportional to the voltage it is fed with so a 10% drop in volts will lead to a 10% drop in speed.

What makes this worse is the "unstable" nature of the high-voltage side, which you refer to - there's a huge gulp of power when the arc starts but then the power demand varies based on what's happening at the torch. Ironically, the stuttering wire feed speed means an erratic arc gap which leads to a fluctuation in power supply through the mig wire, which in turn means an erratic drain on the main power supply, leading to erratic voltage going to the wirefeed motor. And so on...

But does the wire feed board on my SIP Migmate 100 see any power until the welders trigger is pulled and the transformer energises? After looking at the circuit diagrams I've found for other SIP machines of the era it looks like there's no actual "trigger" signal to start the feed. All the feed control board does is sit there waiting to be powered up so it can start spooling out wire at it's pre selected speed?

That's pretty much correct. I'll go dig up one of the circuit diagrams in a sec, but the wirefeed board is driven by a relay which is triggered by the torch switch.

OK, If that's right, Doesn't that mean I could just cut the 24v connections to the wire speed board, use those to energise a 24V "Truck" relay, run the positive side of a 24V (2 or 3A) laptop style power brick through the relays switch, and run the PSU's negative directly to the original negative on the wire feed board? Unless I'm missing something this would mean a constantly powered PSU having it's output "Connected" (And subsequently having the wire feed running) only when the transformer is energised, and the bare minimum of intrusive rewiring of the welder? I know doing it this way wouldn't bridge the feed motors terminals and stop it dead, But just to get a more stable wire feed speed, Would it work?

And that's exactly what the wirefeed mods suggested on here do. A discrete and stable power supply, which is always on when the main power supply is on, and is relayed in to the wirefeed board when the trigger is pulled.
I used a Dell laptop 20V "brick" power supply when I did mine.

I'm only asking because I HATE playing with high amperage equipment. Whenever I have to do this sort of stuff it literally make's me feel like I'm going to vomit ! So I'm thinking that if I can just pre assemble a stupidly simple collection of 2 bit's, Then just crimp/solder 4 wire's when the covers are off the welder I'd feel a lot better about doing this mod.

I feel your pain, or certainly did when I did the same to my SIP Topmig 150 eight or nine years back.
It's mostly "mains wiring" level electrical work, compared to either minuscule electronics or big heavy-duty high power work.
Just make sure the unit has been powered off for ten minutes to let any capacitors discharge, make sure you've drawn it out on paper and understand where the connections will be made, and why they will be made, and double check your wiring before powering it up!

Easy

 

[a111r]

The best outcome in doing SIP mods is that you learn quite a bit about how MIG welders work, which is worthwhile. As then you can repair better ones!
The easiest route is to sell it and buy a Clarke, as the s/h market doesn't recognise the SIP issue at all.

 

[skotl]

For reference, this is the post you want to follow: https://www.mig-welding.co.uk/forum...feed-power-supply-alternative-approach.11532/

The second image shows the changes you're shooting for. Before we start, though, here's the first image which is the "before" state:

What's happening is:

1. Torch button comes in to cn1.1 (where cn1 has 4 pins 1...2...3...4)
2. The wirefeed motor (right hand side "(M)") has its DC negative coming straight from the transformer
3. The wirefeed motor takes its DC positive from cn1.3
4. cn1.3 is fed its switched DC positive voltage from cn1.4 which, in turn, is jumpered to the +ve rail fed by the power supply
5. In summary, when the torch button is pressed it triggers a signal to cn.1, which bridges the input voltage from cn1.4 to cn1.3, which powers up the wirefeed motor

So what we want to do is:

1. Introduce a new power supply and power it from a switched, semi-permanent 240v source (so it's always powered up and ready to go)
2. Cut the wirefeed input to cn1.4 and replace it with the output of the new PSU
3. Tie the ground/0v line of the new PSU to the ground of the rest of the low-voltage side (aka original transformer)
4. Introduce a relay that is energised when the torch trigger is pulled

Now on the latter, the big change in the thread I linked to compared to earlier mods is that the relay is actually energised on the high voltage* (240v) side rather than the low voltage side. One of the reasons for this is that the 240V side isn't as affected by power surges when the torch fires as the low voltage side. Remember that the main thing we're trying to address is erratic voltage levels on the low voltage side.

So that means getting a relay with a 240VAC coil rather than a 24VDC one - well worth the change.

Where we get the switched 240V is the high-voltage side of the main board. Here, there is a connector "cn2" marked "T S R":

• T is the switched 240V output, which is energised when the torch trigger is pressed
• S is live in
• R is neutral in (technically, as it's AC, there is no actual difference between S and R)

So the relay coil is energised from the T connector.

The updated circuit diagram looks like this:

Where:

1. The new power supply is wired across S and R so it is always live, while the welder power switch is on
2. A new relay, 240VAC coil and 24VDC switched, is introduced across R & T (T being the switched 240V feed)
   • In reality, you'd probably tie the "negative" coil and "negative" power supply to the incoming neutral connection
3. The motor's negative (0VDC) line is untouched - it's going to the shared 0VDC between the old and new transformers
4. 0VDC of the new power supply is introduced to the motor's negative connection (and the 0VDC from the main transformer)
5. Snip the link to cn1.4, and connect the new transformer's +VDC to cn1.4 - this allows the the new PSU to feed the motor
6. The motor's +ve connection is tied to the common output of the new relay. This common output rests at NC (Normally Closed) when the relay coil is not energised.
7. The relay's Normally Closed (NC) and Normally Open (NO) pins are connected to:
   • NC is tied to 0VDC - this cause the motor to stop suddenly when the trigger is released (a good thing!)
   • NO is tied to cn1.3

When the relay coil is energised (240VAC arrives at #T), the relay contacts on the right hand side flip from NC to NO.This connects the motor's positive wire to cn1.3, which is fed its power from cn1.4 (the new power supply).

Spoiler: * High/Low Voltage

I'm referring to "High Voltage" as the 240VAC that most amateurs (like me) would recognise, and "Low Voltage" being the ~24VDC side of the transformers.
This isn't semantically correct in the electricians' world, as they tend to operate in a world where "Low Voltage" is 240v, Extra Low Voltage is anything below that, and "High Voltage" is anything in the 1,000V and up side!
But I'm using the terms here as most of us would recognise them

 

[skotl]

The best outcome in doing SIP mods is that you learn quite a bit about how MIG welders work, which is worthwhile. As then you can repair better ones!
The easiest route is to sell it and buy a Clarke, as the s/h market doesn't recognise the SIP issue at all.

Couldn't agree more!

I learned so much about welding (including not being terrified about what I perceived to be some kind of arcane nuclear reactor in the middle of the unit) by getting stuck into mine.
This is my thread on all the mods I did (before, admittedly, selling it and buying an RTech!): https://www.mig-welding.co.uk/forum...ade-my-topmig-150-actually-rather-good.48253/

 

[skotl]

Final hints'n'tips

Link to a couple of pics of my mods: https://www.mig-welding.co.uk/forum/threads/sip-cosmo-mods.4061/page-8#post-539241

And then a discussion on the pinouts of the relay: https://www.mig-welding.co.uk/forum/threads/sip-cosmo-mods.4061/page-10
Note that there are a number of pinouts available, depending on the relay spec - read pages 10 and 11 and compare to what you end up buying.

 

[Reman]

The more I see on the internet the more I realise I'm going to HAVE to dig my actual welder out and look at it to work out exactly what I'm going to do.
I've seen several different pages on sites about the Migmate 100, and even found a copy of the original manual online (https://www.qsl.net/g4usp/SIP MIGMATE 100/Migmate 100 120.pdf), But a couple of things look a little odd straight away. For a start, I've found a few different versions of the welder where the feed control knobs on the bottom left OR on the bottom right of the front. The manual says my welders got a solenoid gas valve in the back, But I'm 99% sure mines got a mechanical valve in the gun. There's also at least 2 different PCB's mine might have, maybe even 3 ........ I'm really going to NEED to dig the old thing out from the stacks in the back of the garage. Once I'm sure exactly what I've got I can start working out what I need to do to it.

Reman.

(I wouldn't mind having to dig through all the junk in my garage, But it's not even MY junk ! A nephew downsized his family home 5 or 6 years ago and asked if they could store some stuff in there while they got themselves sorted out. They did it while I was at work, So they made space for their quite expansive collection of junk by STACKING LOADS OF MY TOOLBOXES AGAINST THE BACK WALL AND ENCAPSULATING THEM BEHIND A 6 FOOT THICK MOUNTAIN OF THEIR SH*T !!!!! Annoyingly, a couple of years later, a friend who was using my propper compressor in his workshop (A ruddy great Clark Air on a 150 liter tank) geared up to move abroad and needed to give my compressor back....... So that ended up having to be stored in my sisters garage, And that's also now behind a wall made up of one of HER friends sh*t. If it wasn't for the cost involved, I'd hire a couple of skips and dump ALL the stuff that's been abandoned in both our garages! I'd Ebay the lot, But the stuff they've dumped is worthless junk like old boxes of toys, file boxes of paperwork, well used kids bikes, and garden furniture. All tied in together with what I assume is a large disassembled garden trampoline frame and a rusty barbecue that's still half full of ash. Unfortunately I'm a nice guy and the last several years have been tough for them, so I can't really hit them an ultimatum......... But does it show that I REALLY want my fr**gin' "Toy room" back?!?!? LOL)

 

[skotl]

Not sure what to suggest - open up your welder and compare the circuit board to the diagrams. If it has a circuit board with cn1 and cn2 (TSR) then you're good to go, as above.
If not then we're starting from scratch.

 

[wacky7791]

did this mod a few years ago before giving up on the machine altogether, it was this mod that led me to find and join this fantastic forum

did this mod, added the motor brace, replaced the trim pot with a multiturn unit for finer WFS adjustmnt, all made it better but still couldn't get a steady weld from it. did learn a lot about how MIGS work tho!

 

[a111r]

Beware, SIPs can be found incognito...here's one that's not a Cosmo:
https://www.ebay.co.uk/itm/Mig-weld...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649

 

[a111r]

And here's one that is! Dream on...
Maybe if it was a '200 Arc MMA welder'..?

https://www.ebay.co.uk/itm/COSMO-200-Arc-MMA-Welder-Welding-Garage-DIY-Metalwork-Workshop/114196255870?hash=item1a96a0947e:g:ElwAAOSwGAVeliko&LH_ItemCondition=4

 

[Reman]

So what's the deal with Cosmo and SIP? Parts of the same parent company (like the Volkswagen audi group)? Or just companies who licence/rebrand some of each others products to fill gaps within their respective ranges ?