The Forestry Forum

General Forestry => Sawmills and Milling => Topic started by: nathandcasey on September 05, 2019, 02:40:13 PM

Title: One 10HP motor, or 2-5hp motors
Post by: nathandcasey on September 05, 2019, 02:40:13 PM
So, Iím planning on building my mill, and Iím noticing that it is significantly cheaper and lighter in weight to use 2-5hp motors instead of one 10HP motor. Is using 2 motors with one helping the other using a double pulley actually the same as using one-ten hp motor? Iíve been in the motor-deciding phase for a long time because I canít make up my mind! Help me! Thank you!
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Crusarius on September 05, 2019, 03:07:39 PM
Interested to know the outcome on this. I do know that with cars when you add a second engine they get quite a bit faster. I would think with sawmills it would be the same deal. I dunno if it will equal 10hp though.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: muggs on September 05, 2019, 03:45:22 PM
two 5s should equal one 10. Motors is what I do. But remember you now have to buy two motor starters.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Crusarius on September 05, 2019, 04:10:09 PM
I would think 1 motor starter to start one motor and the motor to start the other motor. Have one start before the other.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Den-Den on September 05, 2019, 05:08:10 PM
I have some doubts that you are comparing equal quality motors.  Rigging two motors on one load is possible but there are several opportunities for things to go wrong.  Hard to imagine that total cost would be lower unless you already have the motors.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: nathandcasey on September 05, 2019, 06:32:51 PM
Okay, so I was at work when I typed this and forgot one critical detail. The motors Iím referring to are electric motors. Now letís see where the conversation goes. 😅
Title: Re: One 10HP motor, or 2-5hp motors
Post by: TreeStandHunter on September 05, 2019, 07:08:12 PM
I think it is clear off the go that you are talking electric. I canít imagine that you will be happy with that setup, if it were ideal there would be mills manufactured that way. The ease of having 1 motor and it costing slightly more too run than 2 smaller motors (the amp draw canít be that much more) will be worth the hassle of figuring out how to design 2 motors into a system that will be easy to maintain. 
Title: Re: One 10HP motor, or 2-5hp motors
Post by: SawyerTed on September 05, 2019, 07:41:27 PM
Twice the motors, twice the electrical wiring/devices, twice the mechanics to make them work together = many more ways for Murphy's Law to be applied.

In other words, keeping it simple with one motor reduces the number of moving parts, electrical connections and reduces the things to adjust, wear and/or break.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: sawguy21 on September 05, 2019, 08:26:19 PM
X2 I can't see it working unless both motors are perfectly synchronized which is unlikely.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Southside on September 05, 2019, 08:44:59 PM
Any slight deviation in RPM or belt tension will result in a reduced net gain.  Now if you could put two motors via a transmission system and clutch into your input shaft then perhaps you would see the gain, but then you would have a parasitic loss to overcome, so in the end even if it works in theory I don't see it working in practice.  
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Don P on September 05, 2019, 08:50:07 PM
I saw a circle mill one time running 2 20hp three phase motors, it worked well and one thing that seemed like a good idea was he had set them up to pull on the mandrel in opposite directions, balancing the side load on the mandrel bearings. There is a substantial difference in price as single phase motors go over 5 hp but check on the built cost difference. Locked to the hertz on the grid I believe they are synchronous.

10hp 3 phase motors are cheaper, it might be worth exploring building a rotary phase converter out of one to drive the other. Edit Duh-huh, the rotophase would need a 20 to drive the 10. But once it is spinning it can drive another motor, (blower, edger)
Title: Re: One 10HP motor, or 2-5hp motors
Post by: donbj on September 05, 2019, 09:04:13 PM
It can be done but is it worth it money wise and mechanically. Back in my working days I worked on a large dragline that had four 1250hp,yes 1250hp, electric motors on the drag, and four 1250hp motors on the hoist. They were paired two to a gearcase with one gearcase driving the front of the drag drum and the other case driving at the rear of the drag drum. Same for the hoist.

The propel system was two 500hp motors on each side of the house connected to the propel gearcases that drove the large eccentrics for the walking shoes.

Anyway, a little off topic but if it can be done large scale it can be done small.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Hobby_Saw on September 05, 2019, 10:10:10 PM
I've had this same discussion over the last year or so, to decide if I should replace the gas engine on my homemade mill. The disclaimers-- I am not an engineer but I talked to one , along with a couple of top notch industrial electrical contractors and we came up with this.
The complexity has already been addressed. Two starters would be best but once one is started the other could probably be switched on once up to speed (we never actually tried). Our plan was to have one motor drive a single V belt to one groove of a 3 groove pulley on the other motor and drive the blade with the other 2 grooves. One motor will always be a little stronger/ more efficient and so drive with most of the power but the other will increase its load share as the stronger slows due to load then they should team up as needed.  So-- one will carry most of the load until the other can "catch" up. We planned on using 2 amp meters to monitor the load sharing of the motors. 
I rebuilt the gas engine and regained it's former power and so we never got past the theory stage but it was a fun, thoughtful exercise!
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Woodpecker52 on September 05, 2019, 10:36:38 PM
You will find the more horsepower the better!! At a minimum 14hp.  On hardwood my 14 is ok but would be nice to have 22-24.  but for a hobby 14 is ok.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Don P on September 05, 2019, 10:51:07 PM
10HP electric is about the same as 25 HP gas, and rock steady rpms.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: ladylake on September 06, 2019, 06:10:08 AM
  Do you have 3 phase, if not 2 single phase motors is a good idea to get some extra power without having to use a phase converter. I think 3 phase motors can be bought cheap but you need a good phase converter.  Steve
Title: Re: One 10HP motor, or 2-5hp motors
Post by: luap on September 06, 2019, 12:23:19 PM
It can be done. I helped a friend do this on a fanning mill. I only did the mechanical work of mounting the motors, boring sheaves, keyway etc. He did the electrical after consulting an electrician. The smaller motors were available for less cost than the single. He was very happy with the results. also as mentioned the starters were less also. He already had a collection of sheaves, so no cost there.  
Title: Re: One 10HP motor, or 2-5hp motors
Post by: longtime lurker on September 07, 2019, 05:18:14 PM
The main advantage of using two smaller motors vs a single larger one is at starting. Being able to sequentially start smaller motors requires a lot less current draw. Think of it like hand cranking a motor - it takes a lot less effort to crank two 4 cylinders geared to the same shaft than it does to crank a single 8 cylinder for the same output.

Other than that its a PITA way to setup.

Look at your electrical situation and if you can swing the 10HP comfortably go that way. And I say comfortably because if you have just barely enough starting current you'll be forever replacing soft starts. A good VFD is also an option that will better handle marginal starting currents. They (VFD's) are expensive only once.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Crusarius on September 07, 2019, 09:19:24 PM
I am usually against electric clutches, but with this setup I think that be the way to go. Keep the motor running just disengage the clutch to stop the band.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: nathandcasey on September 20, 2019, 11:23:58 AM
Thanks everyone for all of your help. After searching around, I got a brand new 3-phase, 10hp Baldor motor for $250 and a 42a, 25hp rated VFD for 180. After looking around so much, I think I'll be more than happy with this setup.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: btulloh on September 20, 2019, 11:51:50 AM
Those are good prices. $180 for a 25hp vfd is a rare bargain I think. 

Sounds like youíre all set. Keep us posted. 
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Al_Smith on September 20, 2019, 01:52:05 PM
With a VFD you can "soft start "it .My shop has a 5 HP convertor I made which is running a total load of 6.5 HP .The start circuit will start all three motors plus the convertor at the same time .I got me some big old capacitors on that thing . 8).
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Crusarius on September 20, 2019, 04:24:32 PM
Where did you score those deals? great prices. Especially for the motor.
Title: Re: One 10HP motor, or 2-5hp motors
Post by: Randy88 on September 26, 2019, 10:20:43 PM
Dual electric motor drives are done all the time in my area, where larger hp's are required on single phase power, so dual 7.5's or dual 10hp can be started individually and get more hp than one 10hp single can.     Grain bin draw outs are all dual drives and many load out augers as are some direct drive dual fan bin fans.   

Not sure why you'd want dual 5's though, you can start one ten on single phase power unless likes already been stated, you had the motors. 

Curious where you got a vfd that cheap?