Can anyone give me a simple way of making sure a petrol generator is rated correctly for what I need? I'm not sure what the KVA and other ratings mean and which are the most important.

What I could use it for is:

1. Powering tools and lights in a garage. All the stuff we use for our builds.

2. Powering an air compressor in my van for my mobile body shop business

3. Powering a MIG welder (Clarke 151TE)

I appreciate that there will be different specs and costs. Just want to get a feel for what is a reasonable cost vs spec and what is likely to be too much (I guess no 3!)

TIA

Ben

I would use a petrol or deisel compressor and use air tools or battery stuff. The welder needs a good supply or as soon as you strike an arc, the genny will slow and you'll lose the power you need to start the weld and drive the feed motor! I have a 3.5KVh genny and it stuggles to keep up with the MIG. The arc welder is OK!
Find out the size of the motor of your compressor.

This is what i suspected. The current compressor is normally run from 230v mains and i'll be keeping it until it gives up the ghost. Can then investigate petrol. Can't get the motor spec tonight, but reckon its propbabaly 2.5hp. Do you need a monster genny to run one of these?

2.5 HP electrical is about 1.865kW. So a genny rated at above that should work but it also depends on if your compressor has an unloader for starting and what sort of electric motor it has.
Another downside of the genny/compressor combo is the genny will have to be running all the time as well as the compressor. Rather noisey!!

KVA is just kilovolt amps, so if you have something that needs 240 volts and 10amps to run then you need 2.4 Kva. (assuming the gen manufacturer is not overstating what it can really produce) The problem with electric motors, it depends on the type, but they require a lot more current to get them going than just running, could be 3-4 times, so if the motor needs 10 amps to run then a 2.4Kva set won't be able to start it up. Hence a petrol powered compressor is probably a better bet.
flourescent lamps have similar power demands.

That's great info. Thanks.

So if i was to get a genny just to power tools and lighting in a garage. What would you recommend for the spec?

Also, are the "suitcase" type much quieter/worth the extra cash? Seem to be able to get chunky 'site' style one for less than a fancy honda 'suitcase'.

Cheers

If you have to work near the genny, get a quiet one. Also consider where you'll be using it. If you're outside someones house with a noisey genny, they'll soon complain!
As for powering your lights...it depends on what lights you have and how big they are!! Fluorescents take a lot of puff to start but then use very little power. Halogens and normal filament bulbs use a fairly constant power but are less efficient. Running fluorescents with a genny can cause them to strobe and cause headaches!
Power tools? A typical angrygrinder is about 600w? Same for an eleictric drill. A charger for the battery stuff takes a lot less but needs a long time to recharge stuff!

If you are going to buy one of the Chinese ones, then get the highest rated one you can afford as they are all grossly over-rated IME.

Check out http://www.gopower.com/content/companyinfo/faqs/faq_selector.php for tips on selecting suitable generator rating.

Makro have a 2.3KVA petrol genny for £99+vat and a diesel 1.9KVA for £179+vat. I can't recommend these as Ive never used one! A chum bought a Wolf genny rated at 850w (IIRC) and it was a load of rubbish. To be fair it cost £25 new from some discount DIY place but it wouldn't run a 500w grinder under use. As soon as any load was put on the grinder, the genny slowed down! It was fine for lights and it was a compact little thing!

Thanks guys. Seems like battery tools and 12v lighting for the garage and a petrol compressor for the van then.