Electric Motor Question for Sawmill

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CuttingEdge
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Electric Motor Question for Sawmill

Post by CuttingEdge » Sun May 21, 2017 4:08 pm

I am making a homemade sawmill and want to go with an electric motor to power the bandsaw blade. With my log trailer it is just easier for me to bring my logs to the sawmill then try and bring my sawmill to the woods.

I know very little about electric motors except they perform more work then a gasoline engine does at a given horsepower because they have constant torque. So my question is, what is the ratio of electric horsepower to gasoline horsepower? In other words, I know most bandsaw mills run a 13 horsepower gasoline engine. What size electric motor do I need for the equivalent power?

I am 10 miles away from the nearest 3 phase line, so it must be a single phase motor, but what other attributes? I look in the supply center catalog and a 3 hp electric motor might cost $179, or it might cost $579...what exactly am I looking for in an electric motor?
I have no intention of traveling to my grave in a well manicured body; instead I am going to slide into heaven with a big power turn, totally wore out with busted knuckles, jump off my dozer loudly yelling, Woo Hoo, another Shepard has just arrived!

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Stan Disbrow
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Re: Electric Motor Question for Sawmill

Post by Stan Disbrow » Mon May 22, 2017 6:05 am

Hi,

An electric motor needs 750 Volt-Amps per horsepower. To get 13 HP, you need 10 kVa, which is 45 amps at 220v single phase. So, you really need 3 phase power for a motor that large, which would be 15 amps per phase.

These size motors are common enough in 3 phase. They are not in single phase. You probably have to source one of those huge open frame motors from prior to WWII to find one. They are slightly smaller than a 420 crawler. At single phase, the wires have to be pretty fat to not overheat with 45 amps passing thru them.

Or, stick with an engine. Yanmar makes a cute 3-cyl, 18 HP diesel. ;)

And, electric motors work backwards, torque wise, than a fuel engine. They have max torque at low RPM and it drops off as it speeds up.

Stan
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shinnery
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Re: Electric Motor Question for Sawmill

Post by shinnery » Mon May 22, 2017 11:19 pm

Get a three phase converter. Run a three phase motor off single phase power. Google or Wikipedia has lots of information on them and also Wikipedia has a big page on horsepower.
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Stan Disbrow
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Re: Electric Motor Question for Sawmill

Post by Stan Disbrow » Tue May 23, 2017 6:52 am

Hi,

It takes a 3 phase motor of greater HP than the running motor to make a rotary phase converter. Essentially what happens is you connect the single phase 240v across two of the three windings. Plus neutral, which actually gets you two-phase power. They generate magnetic fields which cause power to generate on the third phase windings. So, this makes for a motor-generator.

The problem is, that 2-phase power is 180 degrees and 3-phase is 120 degrees, and that does not quite line up. So, there is loss, which means you need greater HP in the rotary converter than the running motor requires. But, it is a low cost solution.

Stan
There's No Such Thing As A Cheap Crawler!

Have: '58 JD 420c 5-roller w/62 inside manual blade
Have: '78 JD350C w/6310 outside manual blade
Useta Have: '68 JD350, '51 Terratrac GT-25
Also Have: 1950 M, 2005 x495, 2008 5103 (now known as 5045D)

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CuttingEdge
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Joined: Wed Sep 03, 2014 5:13 pm
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Re: Electric Motor Question for Sawmill

Post by CuttingEdge » Wed May 31, 2017 2:10 pm

I apologize to everyone because I did not explain myself well enough.

I knew you could not get a 15 HP electric motor in single phase, just because catalogs do not carry them, but I was told that an electric motor's rated horsepower at say 5 HP, can do more than say a 5 hp gasoline engine because it is constantly under torque and not robbing power on the intake, compression and exhaust strokes making it less efficient. That is easy to comprehend...

I can get a 7 horse power electric motor, so would that equate to a 15 hp gasoline engine? I am cheap so a 5 HP electric motor would be even better! :-) I just know that horsepower is a poor way to compare different motivators. For instance a 12 HP steam tractor could pull a 7 bottom plow where today our 185 hp tractor struggles doing the same thing.

I only use 15 HP gasoline engine as a reference point because I know most commercial bandsaw mills use that size motor. I really would rather use electric as it eliminates clutching, noise and vibration issues.
I have no intention of traveling to my grave in a well manicured body; instead I am going to slide into heaven with a big power turn, totally wore out with busted knuckles, jump off my dozer loudly yelling, Woo Hoo, another Shepard has just arrived!

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