generators

snowman · December 20, 2008, 12:20:39 PM

I need a generator capable of running a wood master and dust collection system. Woodmaster takes 40 amps,dust system I'm not sure of.Want something big enough but not to big for purchase price and gas use reasons.Generator specs give wattage not amps which leaves me confused.Anyone use a generator to run stuff like this? If so your comments on size and even make would be great. Thanks

Ernie · December 20, 2008, 01:13:24 PM

If this is any use to you

Many years ago I learned P=IV P- power in watts I= current in amps V= volts. If what's left of my memory is correct.

dolittle · December 20, 2008, 01:43:53 PM

Yes, P=ExI 40 amps times 240 volts=9600 watts and lets say a 15 amp dust collector at 240 volts=3600 watts. Add the two=13,200watts or 13.2kw. Motors draw more when starting so you have to allow for that also.

snowman · December 20, 2008, 02:28:05 PM

Since posting this I have been doing some research and am becoming concerned, very concerned.Honda has great site on estimating power needs.Code on my motor is E. That means multiply HP of motor by code number. Code number is 41.6 So 5 hp X 41.6=208. That is voltage required to start motor. 208x230v=47,840 watts.That is supposed to be watts required to start motor. No generator can do that. This can't be right, can it? I sure hope someone says , relax snowman, I run mine on such and such a generator, no problem, or someone corrects my math. If not, anyone wanna buy a woodmaster? CHEAP? :D

Radar67 · December 20, 2008, 02:54:40 PM

Dolittle is on the right track for your needs.

W=VxA
Watts = volts x amps

that is the formula you need to use to determine what your requirements are. Remember to add for the initial start up requirements. Usually double what the motor requires, sometimes triple.

If everything is 240v like Dolittle figured for, I would use a 15 to 20 kw genset, but that's me.

Dave Shepard · December 20, 2008, 04:45:39 PM

There are generators that will do 25 Megawatts, if you want. ;)

I run a 15HP 3 phase Wood-Mizer on a 25kw set. It will run about 33 HP worth of electric motors. A 40 amp draw puts you at somewhere near a ten horse motor, but that's a WAG. :D

Voltage is voltage, it's the amperage that changes. I don't think that the 15 HP on the Wood-Mizer draws much at all, the genset doesn't even make a noise when you start it. However the 7.5HP on the sawdust blower will draw about 140 amps to start.

Here is my genset running the WM. I'd recommend a lightet unit, mine weighs about 3 ton. ;D

thedeeredude · December 20, 2008, 05:02:59 PM

Doesn't the woodmaster have a soft start motor? I had a router that had that and it was nice, didn't jerk your hand when you turned it on.

dolittle · December 20, 2008, 05:07:20 PM

snowman are you needing single phase or three? A 5 hp single phase motor on 230 volts has a full load current of 28 amps.

srt · December 20, 2008, 05:30:55 PM

Starting current on motors tends to run between 7 and 10 times running current. Has to do with the developement of counter electromotive force and a few other things I no longer really remember what they mean. I'm not saying that you shouldn't be concerned and size your generator correctly, but that there are many things being run by generators that if you do just that little bit of math, you would think they could never start them.

So, I feel certain you can get a reasonable gen set to do what you want.

snowman · December 20, 2008, 06:14:31 PM

Quote from: dolittle on December 20, 2008, 05:07:20 PM
snowman are you needing single phase or three? A 5 hp single phase motor on 230 volts has a full load current of 28 amps.

It's a single phase motor.I know zip about elec as you can probly tell :D. Anyway I've been reasearching more and on motor it says FLA-21 which apparently means fully loaded amps =21. The wood master site says 30 amps. Maybe that means need 30 amp recepticle is needed? Beats me. By the FLA number I'd need a 5,000 watt gen to run this but the surge wouldn't be enough so I'm thinking 10,000 with 13,000 or so surge.I really shoulda researched this BEFORE buying the wood master. Kinda put cart ahead of horse I think. :D Just had a thought, maybe if I call wood master monday they know the answer. Maybe I spent all day at this stupid puter for NOTHING! >:(

moonhill · December 20, 2008, 06:27:24 PM

For longevity keep in mind some run at 3600 RPM while others run at 1800 RPM. It depends on how the generator is wound. Common sense tell me the 1800 RPM unit will last longer, it is turning at half the speed. Experience also verifies this. The 3600 RPM units will come apart after a while. I, as of now, have two gennys, An older Continental L-head and a newer Miller welder, both around 10,000 watts. I choose the welder for its cost compared to a similar generator only, and I can weld with it. Volts X Amps is Watts, is a rhyme to keep in mind.

Something else to keep in mind is do these items start up at the same time? Or can you control when they start up? If they start at the same time that needs to be figured in, if not you could squeak by with a smaller unit.

Tim

scsmith42 · December 21, 2008, 11:52:14 AM

Snowman, your assumptions regarding needing a larger generator are correct.

When running off of a generator, always start your highest hp motor first, and then start up subsequent motors in order of their current draw (largest to smallest).

Not all generators are the same - one manufacturs 13KW generator may start your load, and another's may not. I'd try them out before purchasing. Generally you'll need something that is rated for the breaker size specified by the manufacturer of your equipment, and generally it's a good idea to upsize this a bit - say 25% - 50%.

I think that you're going to need to get something at least the 15 - 20KW range.

Re the fuel consumption, a friend of mine that is a generator mechanic tells me that it basically costs the same in fuel to produce 10KW from a 25KW generator as it does to produce 10KW from a 10KW generator. The reason being that the 25KW genrator is running at partial capacity and it's not demanding a full fuel load.

He also stated that the maintenance required is reduced with you run a generator at partial capacity versus 100% rated capacity. He recommended being somewhere in the 50% - 70% range in terms of demand versus capacity.

Hope this helps.

Scott

Dave Shepard · December 21, 2008, 11:58:01 AM

Interesting information regarding the fuel consumption. I tried to talk to the technician from CAT about fuel usage of different sized generators and loads, but he wouldn't be pinned down, and generators were his forte. >:( >:(

dolittle · December 21, 2008, 12:50:26 PM

Both my backup and backup-backup generators turn at 1800 RPM and I believe there is less repairs that a 3600 RPM unit but you pay a lot more. My bigger unit is liquid cooled and coupled to a 4 cyl Ford and is not shy of sucking down the propane. If you are running all day make sure you get a good unit. Personally I would not buy less than 20 KW.

snowman · December 21, 2008, 01:31:05 PM

I'm obsessed with this issue and am spending all day today on puter too.Snowing out and 3 degrees,good day for it.I found a Voltmaster PTO gen for $1,300 that is rated 12-15K. The site says it will start a 7.5 code G motor, way bigger requirement than my 5hp code E. Next question I guess is, PTO generators, pros and cons. Can't wait till this weekends over and I'm waste deep in snow falling timber. Much easier really. :D

DanG · December 21, 2008, 01:33:40 PM

I'm a little confuzzed here, which is nothing unusual. ??? :

First off, what are we talking about running? Woodmaster is a brand name, so I'm wondering, Woodmaster what? For the moment, I'm assuming it is a planer. Correct me if I'm wrong, but wouldn't the power(wattage) requirement stated on the machine be the power required at maximum load? Where does the 40 amp figure come from? If that's the circuit capacity recommended by Woodmaster for this machine, wouldn't that include the current required to start the motor? Isn't the starting power requirement on a motor listed as what it takes to start the motor at full load? Would you likely be starting a planer motor at full load?

I'm not going to give out any advice here, 'cause I ain't qualified, but I will say that if I had a machine that required 40 amps at 240 volts, I'd just look for a genset that had such an outlet on it.

This is a great discussion on motors and power, but I'm afraid some of it has pore ol' Snowman wringing his hands in despair. :D :D :D

Don_Papenburg · December 21, 2008, 02:02:48 PM

DanG , Go ahead and give advice this is the internet you don't have to be qualifide to give advice on the 'net ;D ;D

scsmith42 · December 22, 2008, 12:39:48 AM

Snowman, one other stat to be aware of is that you'll need at least 1.8 HP per 1KW of generator output.

Thus, a 10KW generator should have at least an 18HP motor driving it.

If you want to use a 15KW PTO generator, you should have at least 28 PTO hp powering it.

The 1.8 number is a minimum, I know some folks that size 2hp to 1KW or more.

moonhill · December 22, 2008, 07:45:01 AM

When using the PTO on the tractor, the tractor is not available for other uses. I would find it a drag to swap implements every time I needed juice. Generators are like buildings, they are never big enough.

Tim