Gasoline Versus Electric Motors for Powering a Sawmill
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Sawmillers discuss a mill's power needs and the differences between gasoline and electric motors. August 29, 2006
Question
I have been reading in the Knowledge Base on gas versus electric power with great interest. Will a 20HP 3PH 3460RPM motor effectively power a 42" circular sawmill if I use 4 matched belts on V-belt pulleys configured to run the saw at 550RPM? Posts seem to indicate an electric motor will produce twice the HP of a gas engine and the mill was originally sold as needing 35 to 40 HP. Am I way off? I am just getting into sawmilling, as I have inherited my dad's mill and am using an Allis Chalmers WD PTO to drive the mill now. Thank you for your input. I am impressed by the knowledge out there!
Forum Responses
(Sawing and Drying Forum)
From contributor R:
I'd say if your mill needs a 35hp gas motor to run it, then the electric 20hp would work. Electric is 2 1/2 times gas.
From contributor I:
If the saw deserves 40 hp, then give it 40 hp. How many horses does your Allis Chalmers have?
From contributor R:
Electric motors have more torque at the same horsepower rating. Here's a discussion of the reasons.
Power Comparison Between Electric and Gasoline-Powered Bandmills
From contributor A:
There are all kinds of reasons out there. I do have two mills exactly the same, except one has a 20 hp gas and the other has a 7.5 electric. The electric to be the same, as the gas needs to be 10 hp. The 7.5 hp can not keep up with the 20 hp gas now. The reason for this is the gas engine produces a power stroke every two revs. The electric produces power every rev of the motor. It is plain and simple as that.
From contributor O:
Allis Chalmers WD has 35hp, the WD45 has 45hp.
From contributor E:
Contributor A, do you have a single cylinder 20 hp engine on your mill? If you have a twin, then you do have a power stroke on every revolution - even more if you have more cylinders. An electric motor is producing power throughout the entire revolution. There is no time that it is running off a flywheel's inertia.
From contributor A:
You bring up a very good point. Yes, it does have twin cylinders. But there are other things to consider. There is a lot more friction loss in a gas engine. The efficiency of a gas powered engine is about 33%, diesel engine is about 36%, and electric motor is very close to 100%. More to think about… I just know what I stated before.
From contributor G:
You are putting 35hp in the mill at 540rpm with the tractor. With the electric motor, you will have 3460 rpm out of the motor that you will have to reduce to 550 rpm. What will happen is when you load the saw, it will slow the motor down too much and the motor will run hot. With a 1800 rpm motor, you would have better luck. It is not the size of the motor; it is how fast you saw for the depth of cut. If the log moved slow enough, you could saw with 1 hp.
From contributor F:
The old timers used to figure 2 to 3 hp per tooth of an insert tooth blade with a kerf of about 5/16 of an inch. The commercial mills still are close to this figure. A 50 inch blade with 48 teeth is being powered with a 125 hp motor or using a 671 diesel with about 200hp. I think that you will find that you are way underpowered using a 20hp motor.
From contributor J:
When you state that your mill requires a minimum of 35 - 40 hp for the blade size of 42 inches, remember this is a minimum... The secret to circle milling is rpm's and power. A smaller gas engine will power a mill, if you are willing to monkey around sawing and just creep along. If you really want to saw, you have to have enough power so when the saw cuts into the log, the rpm's don't fall and heat the blade. The quality of the cut is way better when you can feed a constant rate, instead of backing off. The smallest electric motor I have seen on a 48 inch mill was 75 hp, and I use a 125hp Hercules on a 52 inch blade.
