Thinking of customizing new mill to be electric driven

Al_Smith · February 27, 2012, 01:27:57 PM

I've had very good luck with building rotary converters .As rule on 240 volts the capacitance is 7.5 MF per HP for the run cap .Below line voltage you add capacitance and above you decrease .

It's always been a point of arguement or discussion as to the cost effectiveness of rotarys but truth be known properly built they are in the neighborhood of 92 percent .

As an example a 10 HP rotary will start up that size of motor and run up to 3 times that amount of multiple motors or in this case 30HP .

Under load as generating the third leg of three phase they draw about 1/2 the running current of the motor or as a 10HP that would be around 12-14 amps .25 amps would be about the load of a 10 HP as use perhaps as power for a mill .Giving around 40 more or less as the combined load on the single phase line .

Now of course this is just one mans opinion on things but a three phase motor is certainly more trouble proof than single phase .It has a much higher starting torque and used they are pennys on the dollar compaired to a large single phase motor .

They have no start switch to arc and spark .As been already stated about the only thing to go wrong with them is the bearings which last almost forever .

FWIW VFD drives are costly and inefficient .If you don't have the correct type induction motor in use with a VFD it will not last long .Besides all that there really is no reason a person would need to have speed control on a sawmill that I can think of .Set the drive pulley size and call it a day .

Woodchuck53 · February 27, 2012, 09:03:07 PM

Evening Frank, How are you? Well all this is still in the thinking stage and I welcome all arguments for or against. The 7.5 that is on my small lathe and grinder are fine and would add the end mill to it as soon as I get around to wiring it. It's the dual air compressor that is worrying me. All are right the swapp to a pair of single phase motors will really hurt the budget at this time. I will eventually have to bite the bullet and do something as the old diesel air compressor is not totally owned by me.

As for now my blasting and painting has been small potatos and all my own needs. But I am still thinking of my future plans and am leaning toward a good Temco unit big enough to handle it all.

I wish I had enough money to bite the bullet and bring 3 phase into the shop and mill.
But we will see. Thanks again. Chuck

Logginsteve · March 03, 2012, 03:38:45 PM

Good discussion, thanks!

I spoke with a middle manager at my power provider. He is waiting for me to send him specific specs so an engineer familiar with my line can make an informed opinion about viability.

I've run into the rotary convertor + 3Ph motor vs. 1ph motor debate in other forums while doing research. It seems, like so many things, that there are pros and cons to each. Not surprisingly those pros and cons vary depending on what the planned use is.

From what I've seen, it seems that if the only thing I plan on running 3Ph is the mill, then it probably makes sense to stick with a 1Ph motor. The argument for this is simplicity, lower starting cost, and low probability of practical problems down the road that exceed the rotary/3Ph combo. Now, if I was in need of running more 3Ph motors... seems to me that the argument swings back over to favor a rotary convertor because you're leveraging that investment against the savings of several applications.

BTW, I have once again changed my mind and am going with a slightly smaller mill. This means I only need a 7.5HP electric motor to replace the 11HP gas motor. The specs I need to match are:

The Honda 389cc GX390 Series
Net Power Output: 11.7 HP (8.7 kW) at 3,600 rpm.
Net Torque: 19.5-pound-Feet (26.4 Nm) at 2,500 rpm.
PTO shaft rotation counterclockwise (from PTO shaft side).

I have to look again at motor options, but it wasn't hard to find the right HP and RPM. What I have had trouble finding (easily) are the torque ratings. Obviously very important for a sawmill.

Oh, and I was already steered clear of VFDs in a couple of places. For a sawmill application it seems a no brainer bad idea.

Steve

Woodchuck53 · March 23, 2012, 06:38:03 AM

Morning all. Well I did it this past hitch home. I found a used Temco 50 hp in Freeport, Texas. Fellow brought it up and met me at a motor shop. We wired it in and spun it over and it runs nice and quiet. This model has 2 50 hp idler motors and 2 seperate panels on the same skid package. We set an inline switch and hooked up a 50 hp motor from stock and spun that up. I noticed no draw down or noise from any thing so i paid him off and took it home. I hope to wire it in to my shop this trip in and power up the lathes and big air compressor.

I think this will do for me now and maybe later bring in the power from the front utilities. Will get pictures and post the set up as soon as I can. Any other particulars some one wants to know can pm me later. Stay safe.