LumberJocks Woodworking Forum banner
4K views 17 replies 13 participants last post by  lanwater 
#1 · (Edited by Moderator)
Seems this is a constant subject of debate here on LJ. I thought I would add a little to what I posted on a motor thread and post it with a lot of search tags.

I have been doing mostly motor and control work for 43 years. I don't know much about plugs & lighting and really don't much care about it. Anybody can install outlets or hang light fixtures all day. The little bit of that type of work I have done was enough to last me a lifetime. ;-)) If you have more than 3 % voltage drop when starting your motors, you will see it flickering incandescent lights. If it is 5% or more, you will probably see it in fluorescent lights. Depending on how far you are from the transformer that serves you, some slight flickering may be unavoidable when motors start.

The bottom line on single phase motors; @ 1 hp & above consider wiring 220, 230, 240 (what ever you want to call it, your preference, its all the same thing).

If there is a noticeable lag in starting the motor of any size or voltage, it will eventually be damaged by that starting pause. It may take many years for it to show, but it will be damaged. The current goes up from 5 times to infinity during that starting pause. It is already at lest 5 times the running current during starting unless you have a soft start. High current means more heat; more heat means insulation break down; insulation break down means short circuiting in the motors winding; that, of course, means the end of the motor's useful life.

There is really no reason for any properly made electric motor to ever fail with the exception of the capacitor or starting switch on single phase motors or the bearings on any motor. Properly started and loaded, they will, literally, last forever.

A watt of power is a watt of power whether it is at 120 single phase or 480 3 phase. From a power bill standpoint, it does not matter which voltage you use.

The little bump or bumps on your single phase motor is the capacitor(s). One for capacitor start and 2 for capacitor start capacitor run. It just gives the motor a little push in the right direction to get it started.

Capacitors can be checked with a multi-meter (VOM) or, a small DC current such as a 6 volt battery series. They definitely will hold a charge. You discharge them by shorting across the connections with a screwdriver. What ever happened is ok ;-) Even if you jump, it is still ok ;-)) Most capacitors these days, have a built in resistor to take care of any remaining charge, but don't rely on it.

To check a capacitor you charge it with a voltage from a VOM or a few batteries. Watch for a faint little spark when you short it if you used 3 or 4 batteries to charge it. It is good if you see a spark. With a VOM, place the leads on the terminals with the meter on the ohms setting. Leave it for a minute or 2. Watching the meter, reverse the leads, if the meter shows little blip, the cap is good; if not, no good. Watch close, because you can easily miss it. Old analog meters with a needle movement are much easier to see than the new fancy dancy digital meters. Matter of fact, they are better for most trouble shooting applications of power and motors. Digitals have a habit of misleading you if you are not aware of how they operate. Most cheap digital meters will not show the capacitor as being good because they do not react fast enough. Meters like Fluke which have an analog bar on the display will show you what you what you want to know.
Capacitors can be replaced with another that is close in size, does not have to be exact. The voltage rating has to be as high or higher or it will short out.

If there are oil caps on the bearings, put a few drops of Rislone in there once a year with a few drops of light machine oil. About the only thing you can to a motor to destroy it is over load it, over lube the bearings or over stress the bearing by running things too tight or at an odd angle. Remember just don't over do it and it will last longer than you will. Few = < 5!!!

Reminds me of a burned up motor I found in a steel plant. The motor had zerks on the motor bearings. This was an old 25 hp +/- from the 60s or earlier. They greased the machine every shift, including the motor ;-(( Grease must be a very good heat conductor because it was packed full and no air could circulate to cool it ;-))

Standard disclaimer: This is not intended to make the novice an electrician. The intention is to inform you enough to know if the electrician you are using knows as much as you do now and enough about motors to be trouble shooting them.
 
See less See more
#2 ·
Great subject Topamax also great tip :) Another thing to consider working From working in industrial maintenance is to Properly size the circuit bigger than normal as such in my case running 50 amps out to a back fed sub panel with a 50a breaker and feeding 20amp Breakers separately for my larger Hp motors as a capacitor start induction motor rated @ 15 amps will pull 17.5 for 5-6 seconds during start up !!!! By doubling the voltage you cut the amps in half :) lessening the overall load on the motor which also in turn contributes to the healthy life of the motor :)
 
#4 ·
Thanks Topomax.
I did know some of this, YET I am guilty of doing things in my shop. (Out of necessity) The long extension cord I use is my pet peeve.
The little shop I have now was previously used to store a car only. It had 1 light bulb hangin (litterly hanging by wires) from ceiling and 2 electrical 110 volt plugs.(Each on its own 15amp fuse) The power comes from the house (shared with bathroom circuit) into a double fuse panel in shed. The shed is about 15 feet from house.When she uses her hair dryer and I am trying to cut on table saw, I am walking to house to re-set breaker.
 
#7 ·
Great post, I use to think 120 was all one needed in the shop but with a lot of the motors being able to be connected to either way. I have opted to wired for the 240 voltage instead for those motors that have that capability. Thanks for the great information on capacitors and voltages.
 
#10 ·
I've swapped all the machines that are capable of 220 over. I have a question on 3 phase, I've been looking for some additional machines for the shop, a lot cheaper in 3 phase and see all sorts of voltages listed as 3 phase. One that confuses me is 220 3 phase, is that right? Is there machines that have dual voltage 1 and 3 phase?
 
#13 ·
Three phase has an extra wire; one more than 220V, single phase, which has two hot, one common and one ground. You would need an electrician for the 3-phase wiring. As for the last question, I'm not sure. Topamax might have the info here. BTW, Top, thanks for the tutorial on electric motors.
 
#14 ·
3 phase "comes from the pole" so it may or may not be available to everybody. Too bad because many of the nice used machines are 3 phase. As for converting single phase to 240v, it does seem to make the machines run smoother (it might be in my head). Some machines (not all) will require changing the factory switch ($$$!). I know that to be true for my Delta contractor saw and jointer.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top