Oxford Mig 170

[BiTurbo228]

Hi folks,

Hoping someone might be able to help! I've recently bought myself an old Oxford Mig 170 (from the 80s I think!). Got everything hooked up but it's tripping the breaker when I pull the trigger. Initial testing suggested it might be the wire feed as with that set to zero you could pull the trigger and it didn't trip, but doing so 5 or 6 times in a row ended up tripping it so I figured that wouldn't be it (or at least not the sole cause). Here's the welder in question:

I've done a bit of electrical work before but it's not my native habitat! Bit of reading suggests it could be a diode on the rectifier bridge, but I'm not sure I'd recognise a rectifier bridge or a diode if it punched me in the face maybe a diode, although I'm used to the little glass things you see on circuit boards.

Popped the side off the welder and this is what it looks like:

I figure it might be the red and blue things between the big fat wires on the bottom right, but who knows! Anyone know how to go about testing it?

The other thing to mention is that it's on a 32A b-type breaker and I read that with older machines a c-type breaker can be more resistant to tripping on initial startup (or is that specific to the old Oxford oil-filled stick welders?).

Simon

 

[MetalMonkey]

Looks like it needs a good clean before you go any further....

 

[eddie49]

What settings of the rotary voltage selector switch have you tested? Normally the power-on surge when pressing the torch trigger will be moderate at the lower settings, and may only trip the breaker at the top one or two steps. If this is happening, the machine may not be faulty. Changing to a C-type breaker may solve this.

If the breaker trips even on the lowest settings of the rotary selector, that may be due to one or more failed ( shorted ) diode(s) in the rectifier. These are normally large press-fit components ( like car alternator diodes ) mounted on those aluminium cooling fins. The red & blue components are capacitors and varistors ( voltage-dependent resistors ) that protect the rectifier from voltage spikes.

The medium-sized transformer at top right is the separate power supply for the wirefeed motor. It is very unlikely that a fault in that section is causing the trip.

Have you been able to strike an arc at the tip of the MIG wire before the breaker trips?

With the gas shut off and the wirefeed pressure slackened, set the welding voltage to the lowest position and measure the DC voltage from the tip of the MIG torch to the work return clamp ( "Earth" clamp ), with the trigger pressed. This should be about 15 volts. Increase to the next voltage step, and repeat. At the highest position, you should be seeing about 30 volts, but you may not get that high before it trips.

 

[Nick DV]

The Euro connector on that torch looks a bit iffy

 

[BiTurbo228]

You're not wrong on either the clean or the eurotorch front! I've got a new one on order, and will attack it with the air gun when I get back from work.

I've been testing it on the lower settings and it's been tripping, although there have been times it'll spool out a little before tripping. I can have a play around and see if it'll spool more frequently at the lower settings than the higher ones. Haven't got to the point of trying to strike an arc as it trips just pulling the trigger.

Will test the voltage on the MIG wire and report back!

 

[Nick DV]

Not wishing to teach you to suck eggs but have you tried taking the Euro plug off and shorting the contacts on the euro socket?

 

[BiTurbo228]

No teach me by all means! I haven't tried that so will give that a go as well.

 

[BiTurbo228]

Interesting developments of the 'Simon isn't as smart as he thinks he is' variety

Turns out that this little dial here doesn't work how I thought it did:

I thought it was the longer side that pointed to the number, but upon close inspection there's a line on the shorter side which points to the setting. I thought I'd been testing it on the minimum setting, but it was actually on 4. Turned the dial down a little and it'll now engage and spool fine, although not yet tried striking an arc. Is that pointing towards needing a C-type breaker?

Tested the voltage on each of the settings and I'm getting 17, 20, 23, 27, 29 and 33 on 1-6 respectively. Interestingly it didn't trip when I was trying the higher voltages like I'd expect it to. There was a little wiggle of the torch connector that happened before this test so that might be confounding things a little.

 

[BiTurbo228]

Just tried a quick little bead on setting 1 and it seems to work! Will grab a c-type breaker and see if that sorts it out!

 

[Nick DV]

Just tried a quick little bead on setting 1 and it seems to work! Will grab a c-type breaker and see if that sorts it out!

And sort out that connector

 

[hotponyshoes]

The breaker would only need changing to cope with items that have a higher inrush current (start-up draw), something like an air compressor.
If you remember to turn the welder down before turning the power on you should be ok with the existing breaker.

It might still trip when you actually try welding, especially at higher settings, but that's a different issue.

 

[BiTurbo228]

Will have a look at the connector too, don't worry!

Interesting. If it makes any difference I've just tried turning it on at setting 1, welding a little, then turning it up to setting 6 and trying again (so continues to be on the whole time). Tripped the second I pulled the trigger. Would it have an inrush of current when the trigger is pulled?

 

[hotponyshoes]

Yes it will but on number 6 the continuous current might be more anyway.
Have you a photo of the electrical rating plate on the back of the machine,?

 

[BiTurbo228]

Ah gotcha. There wasn't a plate on the back I'm afraid, and the information on the front is a little worse for wear!

If it's helpful, I think the chappy in this thread is talking about the same welder as I have and he mentions it's 100% duty cycle @ 125 amps.

I can confirm though that it's function enough on setting 3 to pop a couple of tacks on some 1" box. Will be picking up the c-type breaker today so hopefully can test it out on the higher settings this evening.

 

[johnrev]

Just FYI I have that machine too and it's a great welder. I altered the wire feed system by fitting a PWM speed controler because the feed was 'stuttery' at low speeds and I was told this was a 'feature' of these old machines because of the way the feed speed circuit worked. It was working fine but I decided it was worth 'improving' it.

The thread about mine is 'very old migmaster help' because I had a brain f''t and changed it to a BOC for some reason.

My machine has been painted at some time and there is no visible ratings on it any more.

I find I have no problems welding at the lower settings from my domestic 13amp plug circuit but have found it will often trip at the highest two settings. (my oxford oil filled 110amp stick welder does the same thing).

The rectifier on these consists of two bl...y great bolt-on diodes mounted on the heatsink next to the fan. One of mine was blown when I got the machine and @eddie49 tracked down replacements at a good price for me.

The set of inductor sockets for the return lead really do make a big difference to the weld depending on which one you plug into. The advice seems to be that the higher the welding current you are running the higher the inductance you should use.

I have been very tempted to try adding some capactance to the machine to see how well it would smooth out the weld but I have had no luck doing it on other machines and I think it tends to raise the power generally so the lower settings become more fierce. I'll experiment one day when I have spare time.

As with most old school machines and especially the better brands such as Oxford, the quality is good and they can be expected to last pretty much forever. That's not to say they never break down but when they do there's a good chance we can expect to be able to repair them. If you don't mind the sheer bulk of the thing I suspect it will always be there and ready to work when you need it. As MetalMonkey said a good dust would be a worthwhile exercise and the welders droop of the torch lead could also be worth a check over.
All the best

John

 

[Wedg1e]

I had a 300A Oxford from that series and it was a monster - rated for 225A at 100%.
Came with faults from a forum user down in Cheshire; I repaired it, used it a handful of times (it needed the entire National Grid to power it) and sold it on.
Bizarrely, the guy who bought it came from... Cheshire. And then moaned about the price, despite it having been his winning bid on Ebay.
My guess would be that yours will run fine from a C- or D- curve breaker.

 

[BiTurbo228]

Very late reply, but thanks for the advice folks! I've been using this on a C-Type breaker for a while now and it's been working well. I think there might have been something up with setting number 4 in addition to the current inrush as that's now totally non-functional, but 5 and 6 work well. I've yet to trace the fault with setting number 4. If anyone has any initial ideas I'm all ears!

I'd like to offer @Nick DV an award as the Eurotorch was in fact dodgy, but not in the way I expected. It started burning the wire back into the tip when the torch run wasn't straight enough, getting worse to the point of it needing to be dead straight out of the machine. I tried a brand new Eurotorch (proper Binzel one, not a knockoff)) as I thought it might be drag in the liner/torch causing the wire to stick. That didn't help at all, but in having a poke around I found that the electrical connectors in the eurotorch connector on the machine itself were looking a little worse for wear. Had a poke around and one of the connectors for the trigger just disintegrated, which would explain why the wire feed was iffy. I replaced it with one of these Sherman universal euro connectors, although I had to scavenge parts off the old connector to get it to work. The Oxford connector has a big clamp for the main current wire attached to the wire-feed tube on the back which doesn't fit the new connector. However, the threads were the same for the wire feed tube on both the Oxford and Sherman connectors so I swapped them over and it now works beautifully!

@johnrev I like the idea of a smoother wire feed. I've noticed on 1 and 2 it's not the smoothest. Will have a wander through your thread!

Thanks for the tips on the inductance. I spotted the different plugs, but had popped it in the middle one and decided not to touch it just yet! I do most of my welding on setting 3 though, so figured that would be about right. Will definitely have a play around with it on the higher and lower settings though. I think I get the concept of higher inductance resulting in more puddle wetting (and vice versa). I wonder if low inductance might help with car body repair work where you want to build up a joint of lots of little tacks and minimise warping...

@Wedg1e 100% duty at 225A! You could weld warships with that!

 

[arther dailey]

Wow, I had the exact same as this mig a few years back and regret the day I sold it , it would arc up on rusty tin in an instant , super smooth arc even though I didnt clean rust of 1mm tin and was just the best to use for bodywork , stupidly sold due to its massive size. When I sold it showed the guy who was doing up his rusty vw camper , rusty tin, arced up, let him have a go and he snatched my hand off, couldnt pay me quick enough !

 

[Wedg1e]

le wetting (and vice versa). I wonder if low inductance might help with car body repair work where you want to build up a joint of lots of little tacks and minimise warping...

@Wedg1e 100% duty at 225A! You could weld warships with that!

Well, I never actually tried it... I don't own a power station
That's just what it said on the data plate. Of course it dated from the 1980s when Amstrad, Murphy and others claimed their 'hifi' equipment put out 100MegaWatts... so who knows. The size of the transformer in it, it probably could have welded warships together (modern ones are wafer-thin anyway).