Aliexpress universal PCB

[a111r]

A couple of weeks ago there was a helpful post, linking to a AE universal PCB. On the site there were a fair few, so I had to buy the simplest one:

9.4US $ 6% OFF|NBC tapped gas shielded welding machine control board universal board improved type two shielded welding circuit board|Air Purifier Parts| - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

It arrived in 10 days. The quality seems good, better than in many MIGs.
I'm not an electronics engineer but the design is unusual: 27 VAC in, three relays, two 220V outputs but no transformer unless it's part of the blue relay?

 

[awemawson]

I'd guess that your 'two 220 volt" outputs are actually relay contacts RATED at 220 volt but the 220 volts is sourced elsewhere.

 

[a111r]

Thanks. Yes, I guess that has to be it.
If I can find a 22K pot and a transformer I can see if it works.

 

[eddie49]

From the left, terminals 5 & 6 are 27v AC in ( from a suitable off-board transformer ), 7 & 8 are the torch trigger switch, 9 & 10 are the relay contacts to power-up the main welding transformer, and 11 & 12 are the relay contacts for the gas valve.

I haven't traced all of the circuit from the screw terminals and PCB tracks to the corresponding components on the other side of the PCB ( it's not easy when you can't actually hold the board in your hand and turn it repeatedly back & forth ! ).
I think the two black relays on the top right are for the gas valve and the main welding transformer.
The blue relay connects power to the wirefeed motor, or shorts it with the large 1 Ohm resistor to brake it to a stop.
Four of the five large diodes rectify the 27v AC for the wirefeed motor, but there are also two more bridge rectifiers ( KBP310 ) ?

Since there are no terminals to connect the main welding DC voltage to this board and drive the wirefeed motor, the off-board 27v AC transformer has to be large enough to be a real auxiliary power supply. That means it has to be rated at 30 VA or more, not just a tiny 3 VA relay-driver.

 

[a111r]

Thanks Eddie. I would order one of those Toltec transformers to try but recall they're only 22 volts.

 

[eddie49]

The eBay Seller "hellzbellz_inc" still has them:

Laminated Core 22VAC Transformer Approx 75VA 240V - 24V Isolating TOLTEC 50Hz | eBay

Find many great new & used options and get the best deals for Laminated Core 22VAC Transformer Approx 75VA 240V - 24V Isolating TOLTEC 50Hz at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

and some smaller ones too:

PCB Mounted Transformer Mains 230v - 28v Basler Electric BE25774 | eBay

Find many great new & used options and get the best deals for PCB Mounted Transformer Mains 230v - 28v Basler Electric BE25774 at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

When I tested the larger 75VA ones, I found that with a 3.5 Amp load the 22.5v AC secondary drops to 19.1v AC.
Connecting a bridge rectifier gives 22.0v DC, and then adding a large 10,000uF 63v capacitor results in 30.5v DC.
So they are probably close enough to do the job.

 

[a111r]

Thanks, I hadn't seen his smaller ones.
The VA estimate seems good and the voltage is closer, would they be a better bet than the Toltec, do you think?

 

[eddie49]

I would prefer the larger transformers. For the small ones, I think he is a bit optimistic with the "30 - 50 VA" rating, and after rectifying and smoothing the 31.5v AC will be too high.
The power requirement depends on the motor. For early "toy motor" wirefeeds and the modern black plastic ones ( 15W ? ), 30 VA would be enough. The better all-metal feeds need 20 - 30 Watts, and old windscreen-wiper-motor types probably pull 2 to 3 Amps.

 

[a111r]

I'll go for another Toltec, thanks Eddie.

Or maybe I'll buy yet another big Sealey Supermig (170, 180, 195) but with a known or claimed failed board.
They sell for about the same price, the last two of these models cost me £15 and £20.

 

[Wedg1e]

I'll go for another Toltec, thanks Eddie.

Or maybe I'll buy yet another big Sealey Supermig (170, 180, 195) but with a known or claimed failed board.
They sell for about the same price, the last two of these models cost me £15 and £20.

Why not just repair the faulty boards, MIGs are not exactly complicated...?

 

[a111r]

I do repair them, if possible.
Some machines I get have badly damaged boards or they're missing, hence looking at this economical PCB option.

 

[Wedg1e]

I do repair them, if possible.
Some machines I get have badly damaged boards or they're missing, hence looking at this economical PCB option.

Fair enough then

 

[Monkeypeas]

Ello there, sorry to bump an old thread, but i just wondered if any of you fellas had messed with one of these yet or fitted one to a machine, i've been playing with one today, they do seem to work at least, speed control seems reasonably smooth, only quirk that may (not sure) be abit of an oddity is the fact in my case the gas and contactor relays are a little slow when you let off the trigger, so with the contactor for example the torch would stay live for a second or so after letting off the trigger.

i'm using a 24v coil contactor here obviously

Other than that its hard to say without having a machine to fit one too, lemme know if you guys know any more, might be helpful to someone down the line, these things sure are cheap.

 

[Hutcho]

Have you tried without that link wire and put the contactor where that is

 

[Monkeypeas]

Have you tried without that link wire and put the contactor where that is

Havent but dont see what it matters, doing that would put the contactor before the relay on the board but the power to it would still be being switched the same surely, its just going to the other side of the transformer regardless of how i wire it (as it is its twisted together with one of the ac inputs to the board, thats just where i'm taking one side of the ac from), i can hear the delay in the relays even with no contactor wired up.

I can try it mind, will report back

 

[Hutcho]

Havent but dont see what it matters, doing that would put the contactor before the relay on the board but the power to it would still be being switched the same surely, its just going to the other side of the transformer regardless of how i wire it (as it is its twisted together with one of the ac inputs to the board, thats just where i'm taking one side of the ac from), i can hear the delay in the relays even with no contactor wired up.

I can try it mind, will report back

View attachment 387670

Ok I see now - yeah won’t work

 

[HughF]

The contactor should always stay on for a fraction of a second to give you burnback of the wire. The gas should stay on for a bit of postflow.

 

[Monkeypeas]

The contactor should always stay on for a fraction of a second to give you burnback of the wire. The gas should stay on for a bit of postflow.

yeah, i'd considered that, this just seems somewhat excessive, more than a fraction of a second, far longer than every other machine i have in here anyway, enough to immediately strike me as odd, like i say though, i dunno what difference this would make in a machine as i havent gotten there yet, need to find a machine broken enough to need this putting in, or an old sip topmig or something that i can try and make less crap with this + an aux transformer

Vid of the esab for comparison sake

 

[Relic]

I am picking 24 to 28v actually will do.
Just got my hands on same board.
Looking forward to having feeder braked and some burn back.