choosing a generator??

[tomcat404]

Evening gents

At the moment i am renting a barn to house my projects and finish my latest build. Great location and the owner is spot on. I have a small generator 2.8kva suitable for lighting and small tools at the same time.

I would like to use my new 255A mig welder (single phase)/ plasma and pillar drills etc.

The only problem is that the whole farm has only a single phase supply and the local utility are currently demanding a premimum for any upgrade of the PMT ( pole mounted transformer)

So i need a suitably sized generator!!

From my initial calculation a 7.5kva will suffice ( i think) with the starting load from the welder but the AVR ( auto voltage regulator) sensitivity will reduce the cycle time by 50%?

Any advice would be appreciated?

Mig welder specs are:

P MAx 11KVA

I1 =52A

I2 @ 20% is 250A @60% 145A @ 100% 110A

U2 @ 20% is 26.5v @ 60% 21v @ 100% 19.5v

thanks in advance

[TheRecklessEngineer]

Are you actually going to use your welder at full power?

Welders are pretty dirty in terms of power. You'll want about a 50% oversize I'd have thought (educated guess, by no means gospel)

[tomcat404]

I don't have any immediate plans to use it on full power? The max i will be welding is 8mm for about 20 seconds at a time and the rest is welding 2" tube?

my uncertainty is with the AVR as contrary to what they are supposed to do they do vary from manufacturer to manufacturer?

I did try it for a complete laugh with the little generator and before i even saw a spark the world went dark even my old hobby mig at 155 clarke special didn't work!

[nickwilliams]

If you are going to buy a generator anyway, why not get a three phase one?

If you don't mind risking buggering the generator when you accidentally turn the welder up too far then buy one which is rated about the same as the welder max input. If you want everything to work like you are on the mains though, you need at least 15kVA, and 25kVA would be better.

Go for something big and old: there is no substitute for rotating mass when it comes to providing the grunt needed to start a large motor or react to the fast changing demands of a welder.

[BogMonster]

You could try and find an old Lister with a brushed alternator on it, they are much better than the brushless AVR sort, used one in the farm garage (HR2) for quite a few years but they are old now, so you may not have much luck. Otherwise, as said, oversized is the way to go. You'll not want to buy AVRs too often as they are a few hundred quid for a decent generator!

[Blanco]

I second the old lister suggestion; a few years ago I was given an old searchlight generator (1942!), the engine is superb. The alternator was wired for single phase only but we weighed it in and it paid for an xmod 22.5KVa one! I have just looked and they are now out of stock but there are other ex mod suppliers, the build and quality of the mod stuff is superb, sadly its not as cheap as it once was. Might be worth a look though.

[tomcat404]

I might have found a nice 27Kva........... only 200 miles away !