NBC Auto Weld 2 - inside a 50 year old MIG

[a111r]

Progress at last!
The field coil was being fed 115 vdc in both states, as expected.
The armature - nothing, idling or when triggered.

Looking at the pot, yep it has worn on the track and the wiper had to be forced past 90 degrees, whereby it felt awful. I removed it and it has overheated, the damage was clear.
Joined the wires together and the motor now works, slowly, when triggered.

A new 10 Ohm pot, then and it should be sorted, sounds a very low value?

Thanks to all who have helped.

 

[eddie49]

With the two wires at the pot shorted, the motor should be running flat out. What is the voltage across the armature?

This pot may do the job:

Colvern Ltd Wire Wound Potentiometer Terminal Panel Switch | eBay

Part Number : Colvern Ltd Wire Wound. To Fit : ---.

www.ebay.co.uk

No indication of the resistance value, but the wire thickness looks about right.

 

[DSR]

Not so sure that's a pot - it looks like an Ammonite fosil though I suspect it's too old for that

10 Ohm sounds about right, I think the F25 says its rated at 25 Watt. They are still available but you will need to do some shopping round - RS are asking £72.00 for one. !!!

 

[DSR]

Amazon for the pot...

@eddie49 is right, the motor should be running flat out with the wires shorted. How fast is the actual wire roller going round - does it look about right ? and does the wire size switch make a difference.

 

[a111r]

Amazon for the pot...

@eddie49 is right, the motor should be running flat out with the wires shorted. How fast is the actual wire roller going round - does it look about right ? and does the wire size switch make a difference.

I also thought it would behave that way. It seemed a speed too slow for normal use. Pondering over lunch, I thought to try flicking the wire size switch and also using the other voltages, higher than 1, in case it has the 'faux-synergy' - but probably not, as it's not welding voltage here.

I'll also measure the armature voltage as Eddie suggested. Thanks for the links.

 

[a111r]

A bit of poking reveals the break:

 

[a111r]

The wire size switch does affect the motor speed, as does the welding voltage.

With the removed pot shorted out, the voltage over the armature ranged from 25 vdc to 75 vdc, from voltage 1 to 5.

 

[eddie49]

That sounds like a realistic voltage range for the armature, and the variation with welding voltage means the machine is semi-synergic. At 75 volts, was the motor and feed roller running at a usable speed?

 

[a111r]

Yes the speed range seemed OK. I suppose when the pot is replaced it will slow it down.

Should be able to try welding with it soon!

 

[DSR]

@eddie49
the machine is semi-synergic.

So the machine really was ahead of its time

 

[a111r]

Still awaiting the new pot.

This AW-2 just popped up on Marketplace for a good price:

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[a111r]

The replacement has arrived.

 

[Seadog]

That's amazing. An original part?

 

[a111r]

No, it's the PRC Amazon one that DSR found in #84
It's a close copy, just metered it and it works fine.

 

[a111r]

I temp. fitted the replacement pot a few days ago.
The 'original' Japanese 10 Ohm pot was found to be incorrectly fitted; max and min speeds were transposed.

The motor speed range does not seem right, though. Just too small a range (by a large factor) on both of the wire size settings.
I'll put some wire in and weld, but not holding up much hope...

On a positive note, the 'thing' I need to weld is right next to the Leviathan.

 

[a111r]

Today the AW-2 did its thing, using 0.6 wire and the age appropriate gas.
Yes, it did welds. After a probable 25 year hiatus.

As I suggested above, the wire speed is all to cock, though.
Min to max on the pot. gives only a 6 m/min. to 7 m/min. variance, which is no good.

Stuck with this issue, I had to use the voltage selection to get the best burn.
It did the job, which was one of extrication - welding an Allen key into a mullered head on a bike JIS screw.

What next ..?

 

[Bobbes]

You have the wrong pot meter.10 Ohm is to low. 100 to 160 is normall in tnis case.

 

[a111r]

Thanks. I did wonder if the 'original' that I replaced was incorrectly rated.
Wouldn't a higher value pot. widen the WS range but lower the motor speed?

 

[Bobbes]

A higher value gives a better range of the wire speed.

 

[a111r]

Thanks, I will try your suggestion.