Generator for welding

[ThePiglet]

I've got a 'toy' welder which I want to do a spot of work on the boat with. I don't have access to any power on my mooring and I don't want to keep bothering the very nice people at Avoncliff, so I figure I need a generator to make some for me.

The specs for my welder are in the image below, I figure a 3Kw cheapie would do the job but I thought I'd run it past the opinion of the experts you lot before money is spent...

 

[Guest TerryL]

I've got a 'toy' welder which I want to do a spot of work on the boat with. I don't have access to any power on my mooring and I don't want to keep bothering the very nice people at Avoncliff, so I figure I need a generator to make some for me.

The specs for my welder are in the image below, I figure a 3Kw cheapie would do the job but I thought I'd run it past the opinion of the experts you lot before money is spent...

 

 

It will depend on what sort of welding amperage you need but for full power and allowing for losses a 4KVA generator would be needed for continuous use, you might get away with less but could risk overloading.

Edited September 7, 2008 by TerryL

[Big Steve]

That spec plate clearly says 12amps 230volts max, a 3kva genny should run it no bother.If it doesn't , just turn the power down a bit. The problem might be the starting current.

 

My welder will do 180 amps @ 55v output, but runs off a 3kva generator provided I keep the output at less than 60 amps. That's enough for small jobs, but wouldn't do for anything structural on a narrowboat. However the spec on my welder does say "generator friendly" I think this means the start current is controlled in some way, probably a big inductor in the line.

Edited September 7, 2008 by Big Steve

[ThePiglet]

Thanks,

After looking around at options, I think it might be more worth while if I save for an extra month and go for a super silent 4.2kva.

I don't do structural. I want my boat on the water, not below it

[colin stone]

My little inverter welder is max 120A and runs off my Victron 24/3000/70 inverter quite happily - and the Victron quite happily runs it!!

[Justme]

A 3 KVA will not run that at full power. Read up on KVA compared to KW they are not the same. Also welders have huge start up currents. The welding forum I use would recommend a min of 5 KVA.

 

 

Justme

[Big Steve]

The mains input is quoted as 12A 230V, that IS kVA, 2.76 to be exact. I accept the start up current is a different kettle of fish.

Problem with a 4.2 k is lifting the thing.

[Justme]

The mains input is quoted as 12A 230V, that IS kVA, 2.76 to be exact.

 

 

Nope thats KW.

 

 

Will you be using it at full wack?

 

If so you problem wont be the genny (well it will but not as big as this) but the duty cycle of the welder.

 

You will spend ages with the genny running but the welder shut down due to over heating.

 

Justme

[ThePiglet]

If I'm butchering 3-4mm steel then I usually do use it on the higher setting to get a reasonable penetration.

I don't tend to do long welds, it's not shut down on me yet.

 

I was thinking about the power factor issue, if it's just a big transformer and rectifier, how can it be anything other than a PF of 1? Or something... I confused myself

[Justme]

If I'm butchering 3-4mm steel then I usually do use it on the higher setting to get a reasonable penetration.

I don't tend to do long welds, it's not shut down on me yet.

 

I was thinking about the power factor issue, if it's just a big transformer and rectifier, how can it be anything other than a PF of 1? Or something... I confused myself

 

 

But the genny wont have a PF of 1. Thats why the are specked in KVA & KW's. The start up surge happens when you strike the arc. Its the time you need the power avaliable & any struttering will cause a bad start to the weld. Dont use any auto throtle on the genny to reduce wear / fuel / noise as the delay in the genny spinning faster will cause problems.

 

So

 

Will it work? Yes

 

Will it work well & not give you a hard time? No

 

If you are skilled at welding then you might cope with the start up problems, if you are a learner then you realy dont want /need any thing thats going to make life harder for you.

 

Post your question on http://www.mig-welding.co.uk/forum/index.php

 

 

Edited to add

80amps is not realy enough to weld 3 or 4mm to 3 or 4mm steel

 

Justme

 

My little inverter welder is max 120A and runs off my Victron 24/3000/70 inverter quite happily - and the Victron quite happily runs it!!

 

 

 

Inverter welders are a different ball game & the inverter (victron) will be 100% ready to supply power (unless on standby which it wont be cos the welder will be turned on before the weld is sparked up) but a genny of the same size wont be as it needs to increase the engine revs to make the power needed.

 

 

Justme

Edited September 10, 2008 by Justme

[Timleech]

Inverter welders are a different ball game & the inverter (victron) will be 100% ready to supply power (unless on standby which it wont be cos the welder will be turned on before the weld is sparked up) but a genny of the same size wont be as it needs to increase the engine revs to make the power needed.

 

 

Justme

 

Not strictly, the revs will be usually supposed to be constant. Trouble is with small generators there's usually a momentary drop in revs when a big load comes on, it takes a moment for the governor to increase the engine power to get the revs back to where they should be.

 

Tim

[Big Steve]

Nope thats KW.

 

It's 12 amps at 230 volts max. that's 12 x 230 = 2760 KVA. If you put a ammeter on it and measure 12A, and the voltage reads 230v then it's KVA. It's only KW if you take the power factor into it. If the power factor is , say .8, then the plate would say 2.2KW (.8 x 2760)

 

If I'm wrong. I'd like you (or anyone ) to explain why, please.

[Big Steve]

I just read through this lot again and thought I'd had a little more cr*p.

 

Transformers are inductive and so have a very poor power factor, but this has to be corrected by adding capacitors to bring the PF back towards 1. In Industry this is strictly adhered to as a poor power factor will cause huge swings in current on the transmission lines with overheating problems on the lines. Not so strict on dometic stuff 'cos it's not a huge machine is it? Also industrial electric meters measure KVA so it's in the users interest to have the PFclose to 1. But domestic meters measure KW, so it doesn't matter much to you. However it will matter to a small generator, so the KVA of the welder must be less than the KW of the generator. Starting the weld will also be a big problem unless the gennies got a bit in reserve.

 

My small inverter welder is easily driven by my 3KVA generator when running at 60A, and this is enough (for me) to butt weld 3mm steel together provided the edges are bevelled a bit. I don't get great penetration, but if it needs to be stronger, just give it a second blast from the other side.

 

I picked up my welder from a chap on that mig site mentioned above, it's not a toy one and was an expensive model, but on offer. It's great. I could never weld with a transformer welder but this inverter welder is magic. Something to do with it being DC I'm told.

[ThePiglet]

Would it be better to run it from a 3.5kW inverter rather than a generator?

The only issue with this is having enough battery juice and the startup current.

Edited September 11, 2008 by ThePiglet