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welder
Apr 13, 2009 21:17:29 GMT
Post by 02jcole on Apr 13, 2009 21:17:29 GMT
Does anyone know if you can run a 3 phase welder off of a rotary convert?
James.
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SteveW
Elder Statesman
Posts: 1,399
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welder
Apr 13, 2009 21:32:23 GMT
Post by SteveW on Apr 13, 2009 21:32:23 GMT
James,
These things take a shed load of current and I doubt if any converter would be able to do much more than hold the lights on.
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welder
Apr 14, 2009 11:00:09 GMT
Post by kneedeepinswarf on Apr 14, 2009 11:00:09 GMT
Hello James, You certainly can run welders from a rotary converter. As long as the converter is rated to the input current of the welder, and you have a suitable single phase supply. Remember that the output current at the welding electrode will be much higher than at the mains input. For example, my single phase welder will supply over 140 amps but the input current rating is only 16 amps and I run it from a 13 amp supply without any problems. This is because the welding voltage is usually about 50 volts open circuit, dropping to 25 volts once the arc is struck. As the voltage is reduced, the current can increase in proportion, without increasing the input current over the welder's rating. More info here: www.motorun.co.uk/htm/rotary_phase.htmLionel
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steam4ian
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One good turn deserves another
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welder
Apr 14, 2009 13:38:31 GMT
Post by steam4ian on Apr 14, 2009 13:38:31 GMT
Gg'day Lionel
Take a bit of care. Your 140 amp welder with an open circuit voltage of say 48 volts will draw 28 amps from a 240 volt supply.
I guess the 16 amp figure is the thermal rating of the primary of the transformer at the nominated duty cycle. This means you can't drag 140 amps from it continuously.
The welder will work off a 13 amp circuit on account of the duty cycle. If you had a long run of weld you would pop the fuse.
I recall a nasty incident where somebody was using a welder plugged into a 10 amp socket (10A is standard in Oz) when an outlet on the same circuit overheated and caught fire; a child died in the resulting blaze.
Regards Ian
Regards Ian
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russell
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welder
Apr 14, 2009 14:50:01 GMT
Post by russell on Apr 14, 2009 14:50:01 GMT
I can see your reasoning Ian and you would be correct if there were no losses in the transformer. However these welding transformers are designed to have a high leakage inductance so, when it is feeding 140 A into an arc the voltage produced drops from the 48 V and the input current is nowhere near as high as you would think. A 13 A fuse would blow in a few seconds if the current was 28 A.
Regards, Russell.
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welder
Apr 14, 2009 14:53:07 GMT
Post by drjohn on Apr 14, 2009 14:53:07 GMT
Got a bit of a stammer today Ian with the Gg'day and the regards Ian regards Ian - what sauce are you on? And should you be advising about welding in your current (no pun) state?
DJ ;D
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welder
Apr 14, 2009 16:00:54 GMT
Post by kneedeepinswarf on Apr 14, 2009 16:00:54 GMT
Gg'day Lionel Take a bit of care. Your 140 amp welder with an open circuit voltage of say 48 volts will draw 28 amps from a 240 volt supply Hello Ian, This is not so! Welding transformers have a drooping voltage characteristic, this means that as soon as the arc is struck or the output is shorted, the open circuit voltage is reduced by about half. So the current drawn at the mains, in the case of a 140 amp unit will be about 14 amps. In the UK we use ring circuits, rated and fused at 32 amps, with a 13 amp fuse in each plug. This fuse would blow first, thus protecting the rest of the circuit. It sounds like you are using radial circuits in Oz where any overload could go right back to the distribution board. This could be dangerous under the conditions you describe. You are right about duty cycle, but this depends on the quality of the welding set, Some diy type sets are not capable of running at full power for very long. Mine is a proper industrial set, made in Oz incidentally, which can run for longer periods at full current. Lionel
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welder
Apr 14, 2009 16:40:16 GMT
Post by weldsol on Apr 14, 2009 16:40:16 GMT
Hi James several questions/answers 1. is it a MMA (stick welder ) you want to use on a converter or MIG or even TIG ? 2. Why do you need to use a 3 phase set ? as the cost of a suitable converter would cost more than an adequate inverter welding set 3. Normal duty cycles on quality inverters for MMA run out at 35% and have soft start circuits to stop the high in rush currents if it is an old type transformer / rectifier then it will have a very high in rush current. if you want to talk further on welding send me a PM
Paul
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jackrae
Elder Statesman
Posts: 1,333
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welder
Apr 14, 2009 20:31:24 GMT
Post by jackrae on Apr 14, 2009 20:31:24 GMT
In the UK we use ring circuits, rated and fused at 32 amps, with a 13 amp fuse in each plug. This fuse would blow first, thus protecting the rest of the circuit. Lionel Without wishing to go off topic I feel there is need to clarify a possible misunderstanding regarding plug fuses. The fuse in the plug, be it 13A, 5A OR 3A is soley to protect the section of cable running between the plug and the appliance. This is the reason why 13A fuses should never be used in the plugs for the likes of table lamps, TVs etc (where the cable in clearly incapable of handling up to 13A.) The fuse, circuit breaker, rcd or whatever in the distribution board of the ring circuit feeding the socket is the protection device for the circuit. Jack
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welder
Apr 14, 2009 20:58:59 GMT
Post by 02jcole on Apr 14, 2009 20:58:59 GMT
Hi James several questions/answers 1. is it a MMA (stick welder ) you want to use on a converter or MIG or even TIG ? 2. Why do you need to use a 3 phase set ? as the cost of a suitable converter would cost more than an adequate inverter welding set 3. Normal duty cycles on quality inverters for MMA run out at 35% and have soft start circuits to stop the high in rush currents if it is an old type transformer / rectifier then it will have a very high in rush current. if you want to talk further on welding send me a PM Paul Arc, MIG and TIG welders really, I already possess a rotary phase converter that I run my lathe from, I have recently been offered a few 3 phase welders from a workshop closure and just wondered if I could run them off of my phase converter. Also 3 phase equipment is generally* cheaper to purchase. James.
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welder
Apr 14, 2009 20:59:09 GMT
Post by kneedeepinswarf on Apr 14, 2009 20:59:09 GMT
You are absolutely correct Jack. I was trying to emphasize that using a welder drawing 14 or 15 amps on a 13 amp supply, although not entirely correct practice, would not normally result in the unfortunate event described by Ian. The 13 amp fuse would probably blow first if the main protection device was also a fuse, but not necessarily if it was circuit breaker. I think that in the event described by Ian, there must have been some fault present to cause the fire, as the fuse should have limited the maximum current to a safe level.
Lionel
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steam4ian
Elder Statesman
One good turn deserves another
Posts: 2,069
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welder
Apr 14, 2009 21:11:06 GMT
Post by steam4ian on Apr 14, 2009 21:11:06 GMT
G'day Lionel (Sobered up now DrJ ) I agree regarding the droop due to the leakage reactance of the transformer which limits the current and stabilises the arc. BUT, the open circuit voltage ratio is also the loaded current ratio, hence my calculation of the current. A fuse following a typical curve would take 10 seconds to blow with 3 times its rated current and about 30 seconds at twice the current. Hence you can run a weld for 30 seconds without blowing the fuse. I guess your welder is made by WIA, their works was about 15 minutes from my home? I am sure the quality is much better than my Chinese import. You UK ring systems allow more current from an outlet. Our systems have 10 amp sockets daisy chained along a radial with any rating from 16 to 25 amps. One thing to watch is long circuits and long 240V extension leads. These have a comparatively high resistance which causes more voltage droop (not of the inductive variety which stabilises the arc) resulting in difficult welding. Regards Ian And for Dr J Regards Ian
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welder
Apr 15, 2009 8:31:31 GMT
Post by Staffordshirechina on Apr 15, 2009 8:31:31 GMT
A lot of 3 phase welders are not actually 3 phase. They only connect across two of the phases and ignore the third. These tend to be the MMA type but not exclusively. I suspect that a converter would not like that configuration.
Les
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welder
Apr 16, 2009 18:59:34 GMT
Post by weldsol on Apr 16, 2009 18:59:34 GMT
A lot of 3 phase welders are not actually 3 phase. They only connect across two of the phases and ignore the third. These tend to be the MMA type but not exclusively. I suspect that a converter would not like that configuration. Les I agree a non inverted AC /DC 300amp TIG power source would use two phases and would require fusing at 63 amps per phase, even the electricity board used to hate to many of these in one company as it upsets their phase balance Paul
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