Power for an Electric Bandmill

      Information on the power requirements of electric bandsaw mill motors. April 19, 2006

Question
I am a cabinetmaker and I am considering buying a small mill to start milling my own lumber as a hobby. I have looked at several mills and have been reading this forum for information. It seems that the bandmills that I have looked at are all gas powered. I suppose that this is for portability. I have also read that a 10 horse electric motor will work better than a 10 horse gas. I would be interested in an electric since I don't need portability and find that electric motors are much more reliable, but can't find any information on them. Any education on this topic would be greatly appreciated.

Forum Responses
(Sawing and Drying Forum)
From contributor A:
I received information from Woodmizer on their LT15 mill, which is available with a 10 hp electric motor, at a slightly higher cost than a gas engine. From what I read, Woodmizer is one of the best.



From contributor B:
Talk to your power company. You will need authorization to use it. A 10 HP single phase motor is a big load, and may cause flicker on you neighbor's (and your) power. My power company (PSNH) ran a simulation and determined that I could use the10 HP Woodmizer electric motor without bothering my neighbors, but the flicker would be pretty bad on my circuits. I ended up abandoning the idea, and I decided to locate the bandsaw mill further from my meter and panel. If you have 3-phase, things get much easier. Also, I think the 10 hp single phase motor added $400 to the base price of the LT15. Here is an email from my power company:

"I understand that you would like to start a 10 HP - 240 volt single phase motor on the 348X2 Circuit in Lyman. I will need some of the motor nameplate data to run a motor start model for this motor. Specifically, I will need the following information:
The NEMA Class or Frame of the motor.
The RPM at which the motor will be operating.
The Locked Rotor Amperes of the motor.
Does the motor have any reduced voltage or "soft start" capability.
If so, what type and how much. This is normally quantified by either a
percentage of in-rush amperage reduction or a listing of specific Per Unit
Machine Base Impedances. Sometimes this capability is listed as the amount
of capacitance which is introduced during the motor start-up
process.

When considering a large single phase motor there are two concerns which must be addressed. First, the motor start cannot affect other PSNH customers by introducing visible flicker on our lines. When I receive the information above I can model the motor start at your location on the PSNH electric system and check whether the start is visible to other customers through voltage flicker. The second area of concern is the flicker you will experience at your house or shop as a result of the motor starting. Ten HP-240 volt motors generally result in significant and very visible voltage flicker on the load side of a secondary transformer. There are some things which PSNH can do to help limit this flicker but it is virtually impossible to eliminate this flicker altogether. We can discuss this further in the future when I know more about the motor. Thank you for your help.

Second email:
I have run the system model on the start of your proposed 10 HP Single Phase 230 Volt motor on PSNH's electric system at the proposed location on Quebec Road in Lyman. Your proposed motor may be started on PSNH's system. I will follow up this email with a formal letter which will approve the operation of this motor. The letter will further state that this recommendation is based upon a computer model of our system designed to predict system response. This model is supported by motor size and starting data which the manufacturer and you provided to PSNH. Although PSNH does not expect this motor installation to have a negative impact on our system, should this motor installation not meet its proposed starting parameters and proceed to have a negative impact on our system, (this may include, but is not limited to, customer complaints) you will be responsible to rectify the situation. Please remember that the model which I have run examines the PSNH system response to the starting or inrush current required by your motor. The model does not predict the effects of this motor on the secondaries which run to your house or the branch circuits within your house. Single phase motors of 10 HP are the largest single phase units manufactured and are problematic due to the amount of starting current which they require at 230 volts. Remember, we are talking inrush amperage here, not Full Load running amperage. Inrush amperage generally comes and goes within the time frame of a fraction of a section to several seconds depending upon the starting characteristics of the particular motor and machine which is starting. No motor is capable of starting at anywhere near its full road running amperage whether loaded or unloaded. Loaded motors such as compressors start "harder" or require more inrush amperage to get up to operating RPM. Unloaded motors will approach locked rotor amperage levels at start-up as they work to overcome the inertia of the rotating mass of the motor.

Your 10 HP TEFC motor will likely have a locked rotor amperage of around 258 amperes at 230 volts. It will draw this level of amperage only at start-up or as it approaches locked rotor in a "stall" type situation. Your electric system will see this level of amperage flow for a short period of time - again only a fraction of a second to several seconds depending upon the starting characteristics of the motor/machine combination. This is generally not a concern as far as conductor or line breaker heating is concerned. The concern lies in the fact that line voltage drops when high levels of amperage flow over the line. A sudden voltage drop on your secondaries of only 2.5% will be visible to the eye. A voltage drop of 4% to 5% can generally be classified as irritating. This rapid voltage drop which is seen by the human eye as a flicker in incandescent lighting and other electric devices is known as voltage flicker. I do not know all of the electric characteristics of your home layout in Lyman. I know that you are served by a 10 kVa transformer of approximately 2% impedance. The average home in your area is likely served, between the transformer and the house, by 150 feet of #2 aluminum Triplex service wire. Utilizing these parameters for the low voltage side of your motor circuit,PSNH can predict that you will see voltage flicker approximating 21%. PSNH can aid you by stiffening the secondary portion of this equation. We can install a 25 kVa transformer of approximately 2.2% impedance and increase the conductor size to 1/0 Triplex. This combination will result in voltage flicker of approximately 11%. If 4/0 Triplex is installed in place of the 1/0 Triplex (your service entrance must be capable of withstanding the weight) the flicker amount can be reduced to approximately 9%. This high level of voltage flicker is the reason PSNH sometimes requires and customers often desire some type of "soft" starting device on a single phase motor of this size. In the final analysis, as long as you are not affecting any other PSNH customer, you can create as much voltage flicker on your system as you are comfortable living with.



From contributor C:
I have a 10hp on my Turner mill. It uses a 40 amp breaker, the same size as most electric stoves, and I've had no problems with it.

Here's my Turner mill with a 10hp electric motor on it.


Click here for full size image



From contributor C:
And when you kick it on the lights dim in the house for a few seconds, but after its on I just leave it on till I need to change a blade.


From contributor D:
To contributor C: How many amps does it say on the motor plate that, that motor is drawing?


From contributor C:
Here's the specs on the motor
Specifications: L3711T
Catalog Number: L3711T
Specification Number: 37F344W578
Horsepower: 10
Voltage: 230
Hertz: 60
Phase: 1
Full Load Amps: 40
Usable at 208 Volts: N/A
RPM: 3450
Frame Size: 215T
Service Factor: 1.00
Rating: 40C AMB-CONT
Locked Rotor Code: H
NEMA Design Code: L
Insulation Class: F
Full Load Efficiency: 82
Power Factor: 98
Enclosure: TEFC
Baldor Type: 3744LC
DE Bearing: 6307
ODE Bearing: 6206
Electrical Specification Number: 37WGW578
Mechanical Specification Number: 37F344
Base: RG
Mounting: F1


From the original questioner:
I don't think that power will be a problem for me. I hooked up over 70 hp of power to my shop this week. I would be putting this in my yard at my shop. 3 phase is not problem either. I am wondering what mills are available with an electric motor? Are they mills that a hobbyist can afford? I am a cabinetmaker but I like to read this forum as much as the others. I hope you don't mind me asking the simple questions.


From contributor C:
My mill was $3400 and the motor was $700


From contributor E:
The Wood-Mizer LT15 is available with 10hp single phase or 3ph motor. Wood-Mizer also offers the LT40 Super and LT70 mills with 25hp 3ph. We've been sawing with the LT40 Super with the 25hp motor for the past three years and have 2,400 hours on it. It's been great not having to deal with a fuel engine.


From contributor F:
I have Woodmizer LT40HD with 15hp 3phase. It is 1994 mill and I converted it to electric four years ago. It was very simple to do and a huge improvement.

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