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How many KW generator do I need? | 14 comments (14 topical)

Re: How many KW generator do I need? (3.00 / 0) (#4)
by Farmer on Tue Oct 19, 2004 at 09:28:21 AM MST

My real question at the heart of it is how much power will I need to run a 220VAC arc welder? When I buy one it is going to be a heavy duty one, not some light weight consumer model.

On the occasions when I need to run the welder everything else can be shut off.

I mentioned the loads from the house only to communicate that the house loads will be pretty light. I plan on eventually building either a wind or a hydro system to keep the batteries charged, but that takes time. In the short term I can run everything off the diesel and have plenty of power with less work.

Because of the altitude I will lose about 21% of the engine's rated horsepower.

Therefore I was thinking of using a 20/2 Listeroid and a 12KW FuKing head. Is this going to be too much generator and drink me out of house and home?

Re: How many KW generator do I need? (3.00 / 0) (#6)
by zmule on Tue Oct 19, 2004 at 10:16:46 AM MST

If you take 20% off the 20 HP that leaves you with about 16HP at your elevation. You should be able to produce a steady 8KW with that set up. According to the specs on Metro's website, the 20/2 runs at 1050 rpm. It might be fairly noisy at that speed. That same engine running at the 650rpm "quiet" speed is rated at 12HP. You can see the specs here: http://www.metroexporters.com/pages/metex/dieselslow.html I do not think there is a significant penalty by running a bigger head, just the extra cost of the larger unit. You could probably get by fine with a 10KW unit. I think the rating on the Fu King heads is continuous so a 10KW can surge to 12 or even 15KW without too much trouble. You have to check the spec plate on the welder you plan to purchase and run the equation (V X A = W). I don't think you can simply say: I have a 200 amp welder that uses 220 volts because you would get some rediculous answer like 44KW. I am sure there are folks on this board who know way more about this. For arguments sake I have a big old Lincoln 200 amp AC/DC arc welder that is probably like the one you want to buy. I usually weld at around 90-100 amps and it is on a 15 amp 220V breaker that has never tripped. So it is using less than 3.3KW.

[ Parent ]

Re: How many KW generator do I need? (3.00 / 0) (#7)
by Farmer on Tue Oct 19, 2004 at 10:55:21 AM MST

My 2 HP single phase 115V motor draws 16 amps according to the spec plate. 115V*16amp = 1840 watts continuous. The starting surge of course is more than that, I don't know how much more.

Your Lincoln welder is the type I intend to purchase. So lets build in a saftey margin and assume I need 4KW to run a welder.

The Metro 20/2 running at 650 RPM makes 12 HP but when derated 20% for altitude only produces 9.6 HP. According to the chart at http://www.power-co.net/mighty_yanan_generator.htm I should run a 5KW head.

If in fact there is not a significant penalty in running a larger head than needed I can run a 10KW head. That way if I need more power at some point in the future I can, change the pulley on the generator head and run the 20/2 at the full rated speed of 1050 RPM.

The 10KW head would also be good if at some point I moved the generator to my other off grid property at a lower elevation.

Now I understand the reasoning behind why John recommended buying the 20/2 with a 10KW head.

[ Parent ]

Re: How many KW generator do I need? (3.00 / 0) (#8)
by zmule on Tue Oct 19, 2004 at 12:36:43 PM MST

Exactly, now we are thinking along the same lines. If your 20/2 is rated to run at 1050rpm then slowing it down is just a matter of ordering a set of governer weights from the 12/2 and installing them. Then you have the flexibility to run at higher rpm's later if you like. I plan to keep an extra set of weights and an appropriate sized pulley for the generator so I can change the speed and the output if necessary. You cannot do this with a 12/2 because the flywheels are different for the slower speed. In other words, with Lister types, it is usually OK to slow one down below rated speed but not to speed one up it because the larger diameter flywheels will exceed a safe rim speed and may fail (explode)see this link to know what I am talking about http://engines.rustyiron.com/flywheel/index.html. If you look at some of the pictures of the different types of Listeroids available you will see a different flywheel on the higher speed engines than the slower ones.
The unit you describe should put out a solid continuous 4.5KW and spike much higher. It might just be all you need....and it may just last forever.

[ Parent ]

How many KW generator do I need? | 14 comments (14 topical)

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