Bandmill run by generator

Using a diesel generator to provide electric power to bandmill. January 16, 2002

How large a generator do I need to run one of these 15 hp three phase motors that power most electrical bandmills? I want to set up a bandmill operation at a remote location and was thinking it would be more efficient to run a diesel generator and provide electric power to run the mill. The setup costs would be much higher, but the advantages are great:

1. No fumes when sawing inside.
2. Less noise.
3. Less cost to run in the long term. A heavy-duty diesel generator has a much longer life span than a gas motor.
4. Electric lights for camp.
5. Run an electric edger in the future.
6. Small electric belt to remove sawdust at the end of the day.

Forum Responses
The full-load current at 230V is about 38 amps. That would be 8740 Watts. But you have to allow for a starting surge of at least that much again (which will be more than enough to take care of the other loads).

Short answer: 20kW

From contributor B:

When you find out what you need, let me know. I have an Onan diesel generator with 499 hrs. 230 volt, 52 amp, 3-phase. The fella that bought it thought it would be big enough to run my 25hp Wood-Mizer, but it doesn't have enough amps for startup. So now we sit on this beauty with no where to use it. I could probably power the township I live in with it, though!

I run a Timber Harvester with a 25 horse 3 phase on it. I would never get a fuel-powered motor on a machine in the future. I am set up stationary, and if that is what you are going to do, then it is a very wise choice. I guess if you had the right setup, like TH has at the shows, it would work for portables. I run a Volvo generator, putting out 175 kw. That is way more power than I need, but I use 1 gallon of diesel an hour. That is costing me 94 cents an hour to run. I am in a temporary shop right now, but once I am in my permanent shop, I will hook everything up. I have a transformer to go from 480 volts to 220/110. I would highly recommend a bigger generator than you need, because bigger is always better. My generator was $20,000 used. It was worth every penny. I have plenty of room to grow into it. I think you have to go by amps, and average is one amp per horse.

Contributor B, 52 amp should be big enough to run your Wood-Mizer. There is something you might check... We discovered, after running our 25 horse electric Wood-Mizer for two years, that they are wired from the factory for 440, not 220. Amazing how much our performance increased when we rewired the motor. We thought the claim they could cut 60 feet a minute in 12 wide red oak was just a sales pitch. It actually will cut it.

In one of my reference books, there is a conversion of about 750watts to 1 hp. I can check, but I believe roughly 1KW per hp will suffice with a bit of a load factor. You don't want to run a generator at full capacity all the time and, conversely, you want to be able to load it to capacity occasionally for other maintenance reasons.

Just to give you an idea what we're running off of a 230 KW gen set:

125 hp at the headsaw, 75 hp at chipper, 75 hp at hydraulic pumps, 50 hp on edger, 10 hp blower, and 10 hp on conveyors. We also use it to supply whatever lights we need, and heat and a/c to cab. Total of 355 hp, run on 440 volts. We think we are close to our limit.

With your setup you could probably get away with a 50 KW gen set, with a lot to spare for growth.

Your 15 hp motor draws 746 watts per hp. That equals 11190 watts. Taking power factor and eff. at .8 equals 13988 watts. Starting load is no less than 3 times running load. So rounding up requires a generator set of 45 kw. This will operate a smaller motor 5 to 7 1/2 hp range, if you start the larger motor first.

A friend of mine bought a gen set to do exactly what you want to do. He later went back to a diesel engine on the mill, because the generator used a lot of fuel, as it's always under load. The engine on a mill is only loaded in the cut. He sawed a lot of logs every day, and said the gen set idea was a bad one. Of course the best way is to have 3 phase brought in, but that isn't possible for everyone.

If you have a lot bigger generator than you need, then it isn't under load.

Contributor B, some quick figuring of the volts and amps for your Onan generator indicate that it is a 15 KW machine. Your 25 hp mill motor requires 18.5 KW for full load operation. If you needed to operate your mill away from power you could mount a 5 HP B&s. engine on top of your 25 HP electric. With a slip belt you could bring the motor up to speed, then apply your generate power to the motor. Your Onan would handle most of your sawing needs.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor B:
A generator is always better because you can place it far away from your working post. However, remember that when you read the electric motor plate and see 15 hp, you really need a 24 hp generator at least, not counting any other motors around. That is because the power factor of the altern electricity and also the efficiency of the motor.