Large single phase stick welder tripping breaker

I have inherited a large Oxford 250 amp welder. On connecting it up to what I thought was a suitable supply, it trips a 32 amp breaker, when I input between the 0 and 240 volt terminals, there are also connection for 400 and 415 volts ac.

I have conected the 240 vac to the 0 and 415 connections, to see what happens and the set does not blow the breaker, so I do not think there is much wrong with it. The voltages across all the taps and the secondary seem to be about the right levels given that the 240 volts is a lot less than the primary connection that I am connecting to.

This is a really heavy machine and has lots of adjustments and is oil filled. However I am a bit worried by going up to an even heavier breaker, without a bit of advice. What would be the allowable size for a transformer of 7.5 KVA which is only 32 amps on full load and I am starting it off load, of course. How can I calculate the starting surge?

Any comments would be welcome.

Thanks George.

Reply to
George
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Magnetising current of the transformer will give a very big switch on surge, even when not welding. You need a breaker with a suitable curve. Type C or maybe type D

AWEM

Reply to
Andrew Mawson

the starting surge is of course massive.

It cannot be predicted because it depends at what part of the waveform you actually close the trip. Going to a higher trip should be OK as the surge doesn't last long enough to over heat cables. Or fit a slower acting trip.

Reply to
The Natural Philosopher

Thanks very much, I shall have a look into what is available, I take it - that as it is a device with very low DC resistance the inductance, off load will be such that there is watt-less current of some magnitude, will this be significant if I leave it switched on? I also have another 110 volt transformer which is extremely powerful, (like 20 KVA) I should like to use this and it would be nice to leave this on too, and have a 110 vac ring main round the workshop. Are big transformers really 100% efficient?

Thanks George.

Reply to
George

Just go for a Type C breaker. We have a comms site thats got a load of transformers in it and every time there're switched on more often than not the 32 amp breaker would trip.

A type C one was fitted and no further problems:)...

Reply to
tony sayer

Don't mess with the "oil". It may well be PCB and be strongly carcinogenic. Ok so long as it's not leaking.

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Reply to
harry

no surprise there

As harry mentioned, the oil is likely to be nasty transformer oil. Unless you know otherwise, treat any leak with paranoia, it does kill people.

The nearest you'll get is to measure the primary dc resistance

Use a slower 32A breaker or a wire fuse. If fusewire pops you can tie a few knots along it to slow it down.

NT

Reply to
meow2222

you know otherwise, treat any leak with paranoia, it does kill people.

ew knots along it to slow it down.

I found another breaker of 40 amps, the same sort, but it worked after tripping twice, I can live with that. There are no leaks and I shall leave well alone, I did check the level on the dipstick and it looked OK.

I am waiting for the manuual which might be here tomorrow, but the voltage does not change when I change the adjustment knobs, it may well be a mechanical core adjustment and not taps, however the voltage between the "work" and the two "live" terminals does not seem to be high enough, We will see what the manual says.

Thanks George.

Reply to
George

I have inherited a large Oxford 250 amp welder. On connecting it up to what I thought was a suitable supply, it trips a 32 amp breaker, when I input between the 0 and 240 volt terminals, there are also connection for 400 and 415 volts ac.

I have conected the 240 vac to the 0 and 415 connections, to see what happens and the set does not blow the breaker, so I do not think there is much wrong with it. The voltages across all the taps and the secondary seem to be about the right levels given that the 240 volts is a lot less than the primary connection that I am connecting to.

This is a really heavy machine and has lots of adjustments and is oil filled. However I am a bit worried by going up to an even heavier breaker, without a bit of advice. What would be the allowable size for a transformer of 7.5 KVA which is only 32 amps on full load and I am starting it off load, of course. How can I calculate the starting surge?

In all honesty I'd eBay it. It's far more suited to a more industrial application really than the occasional home use.

A smaller welder that's more portable and without oil can be sourced which will give less issues with supply and of course allow you to take it anyplace.

Reply to
Nthkentman

I have used an Oxford many times on a standard 13A outlet ... but these were on wireable fuses not mcb. Not on highest current setting, just connecting it should not.

Put a meter across the 0 - 240V terminals to make sure you don't have a short to earth

Reply to
Rick Hughes

Bollocks. The oil-filled industrial sets are a delight to use and great for learning on. Much better than the shitty Machine Mart or other toolshed shitboxes.

Reply to
Grimly Curmudgeon

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