Generator & Welder

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  1. #1
    Senior Member turnstiles's Avatar
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    Default Generator & Welder

    Could anyone advise me on which amp stick welder I ought to buy. I will be mostly working on steel no thicker than 6mm and a chart I found recently gave me "Electrode Dia: 3.2mm / Amps: 105 - 130 / Metal Thickness: 4 - 6mm.

    My question is: I have a 7kVA Inverter generator so what would be the optimum amp welder I could run from it (if nothing else was being run off it at the same time)?

    Would 170 amp run comfortably? 140amp seems sufficient for my needs but would it be worthwhile getting the higher one for any unforeseen thicker metal jobs in the future?

    Is a 170 amp unit running at say 130amps likely to have a better duty cycle than a 140amp running at 130amp???

    And does anyone have recommendations for a machine with a high performance duty cycle?


    Cheers.

  2. #2
    Owner Builder Belair_Boy's Avatar
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    Quote Originally Posted by turnstiles View Post
    I have a 7kVA Inverter generator so what would be the optimum amp welder I could run from it
    G'day turnstiles

    I have a little stick welder (not inverter) which I was not able to run off my 3.3kVA Dunlite / Honda Generator.
    I hired a 6KVA generator when I needed to weld up my gantry prior to having mains power. It was barely sufficient to do the job (2.5mm electrodes on 3mm thick steel). 7KVA is probably on the small side for running a welder but maybe an inverter type would be more successful but I have not had any experience with them.
    Tools are good, more tools are better!

  3. #3
    Senior Member turnstiles's Avatar
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    Thanks Belair_Boy,

    I've been doing a bit more research and found a 200amp welder on *Bay which states in its ad that it is suited to a 5.5kVA generator with duty cycle: 60% @ 160A / 100% @ 120A which sounds pretty good to me!

    I might have to take the ad at its word and try it out.

    (And it's been inspiring following your build - looking forward to more posts.)

    Turnstiles

  4. #4
    4K Club Member Marc's Avatar
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    200 amp on a stick welder at 50 V, is 10 kw. So your generator will struggle to drive your welder at 100amp may be 120. You will be able to weld 3mm that way. Penetration will be an issue. An inverter will draw less power and are easier to use yet they are notoriously unreliable and blow up the board with alarming consistency.
    Ebay claims on chinese products are not worth the paper they are written on...or the pixel ... anyway you get the idea.
    Real knowledge is to know the extent of one's ignorance
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  5. #5
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    Default Generator & Welder

    I'm not sure of those figures, I think Marc is spot on.

    I've got a razor weld stick, think it goes up to around 200amps and at around 160a doing 2 sticks in a row will trip a 10a overload on a power board.

    Oh that's a dc inverter model. I can have a look tomorrow for you and see if it has how many kW it draws.

  6. #6
    4K Club Member Marc's Avatar
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    Remember that the KW claimed by the generator are also embellished so, think 25% less at best.

    Whitey180, the inverter works on lower volts not 50 like the small transformers, still you are probably welding at 160a x say 25V (guess) = 4KW
    A 10 amp circuit breaker carries 10a x 240 v = 2.4 kw You need a 20 amp circuit breaker and of course the corresponding heavier wiring if you want to weld with any consistency.
    If you welder is starved of juice, your weld will be poor and you never understand why. I had a MIG 250 transformer that was giving me poor results and for some time I put it down to being a novice with MIG even when I have 40 years of stick welding. Eventually I worked out that the factory had supplied the machine with 2mm lead and a 10 amp plug just to appeal to the home market. In the back of the instructions manual in small print it said that if you want to get the most of your machine you must change the lead to 6mm and a 32 amp plug. I did so and it is a different machine. It welds like a 3 phase machine.
    I remember doing a job for a friend out in the sticks. They had home power but the tension was way low almost 200V. I tried to weld with a small transformer but the result was very poor and my machine overheated and I had to stop all the time. You can weld with a generator but limited to how much juice you can get out of it. Most people who weld that way use diesel or petrol generators that produce DC straight from the gen to weld with it.
    Real knowledge is to know the extent of one's ignorance
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  7. #7
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    HI
    Transformer welders have a very poor Power factor
    So the simple calculation of 50V x100A =5 kW & 5kW divided 240V = 20.8A does not apply
    The Pf of most transformer type welders is around 0.6
    The actual current drawn will be nearer 30A

    One also has to understand that two of the factor involved in a generators capacity are Engine power & Current rating of the generator

    It is the EXCESS current that causes overheating of the generator windings & burn out.]
    But the generator could also be rated in kVA [usually based on a PF of 0.6 ] such a a 5kVA generator would only have a cont current abilty of around 13A
    They may have a short time rating in excess of the continious rating but that may only be seconds to a few minutes


    PeterQ

  8. #8
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    Quote Originally Posted by Marc View Post
    Remember that the KW claimed by the generator are also embellished so, think 25% less at best.

    Whitey180, the inverter works on lower volts not 50 like the small transformers, still you are probably welding at 160a x say 25V (guess) = 4KW
    A 10 amp circuit breaker carries 10a x 240 v = 2.4 kw You need a 20 amp circuit breaker and of course the corresponding heavier wiring if you want to weld with any consistency.
    If you welder is starved of juice, your weld will be poor and you never understand why. I had a MIG 250 transformer that was giving me poor results and for some time I put it down to being a novice with MIG even when I have 40 years of stick welding. Eventually I worked out that the factory had supplied the machine with 2mm lead and a 10 amp plug just to appeal to the home market. In the back of the instructions manual in small print it said that if you want to get the most of your machine you must change the lead to 6mm and a 32 amp plug. I did so and it is a different machine. It welds like a 3 phase machine.
    I remember doing a job for a friend out in the sticks. They had home power but the tension was way low almost 200V. I tried to weld with a small transformer but the result was very poor and my machine overheated and I had to stop all the time. You can weld with a generator but limited to how much juice you can get out of it. Most people who weld that way use diesel or petrol generators that produce DC straight from the gen to weld with it.

    HI Mark
    Yes
    To get the rated output from any welding machine, both the machine power cable & the actual MAINS wiring[to the socket outlet] must be heavy enough to carry the MAX current without excessive voltage loss in the mains wiring.
    That current is not a simple volts Amps calculation as pointed outin previous post
    THe actual length of the total mains input cables is the determining factor for the cable size .
    Of course excessive lengths of welding cables have a similar effect

    PeterQ

  9. #9
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    Quote Originally Posted by Whitey180 View Post
    a razor weld stick, think it goes up to around 200amps and at around 160a doing 2 sticks in a row will trip a 10a overload on a power board.

    Oh that's a dc inverter model. I can have a look tomorrow for you and see if it has how many kW it draws.


    Hi
    The rated kW is usualy not the max input kW
    It is the continiously rated power with out overheating [low duty cycle]
    That is how they can sell them for use on 10A 240V, if used for too long witout a spell ,they will burn out or cut out


    PeterQ

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