band saw

[Dick]

Does anyone have an idea why the notor on my band saw runs BACKWARDS? I just replaced one brush, (one is all they had), and the motor runs backward! I did take the motor apart, amnd possibly re-assembled it with the fields physically reversed,but, I don't think it would make any difference. On other motors, I have changed the brushes on many motors, without any trouble. The fields are permanent magnets, and for this reason I suspect it is reversed, and that it is the reason the motor runs backwards. I'll check, tomorrow, for this condition. All comments welcome.
Dick

[coop]

Any switches on the motor? I had a switch problem on an electrical equipment and all that was wrong. The switch turned to the wrong direction. Boy did I feel dumb after someone showed it to me.

[Dick]

Nope, no switches involved. The motor was removed from the stand, and no wiring moved. Just the end cap, with the brushes inside. If it were a wiring problem, no problem. I have done that all my life. I repeat, I suspect permanent magnets have been inadvertantly swapped end-for-end, and the motor runs backward. I put the brushes in and tried the power. That is when I saw the thing running backwards. I just shut it down, and closed the shop, (shed), because Havig beenoutdoors for 3-4 hours, I am blind as a bat! Manana, I'll work on it.

BTW, have you ever woeked with Presto Photo Impact? It is very much like Photoshop. I found it on this unit, after installing a camera, One of several, in fact.
Check the New finds...
Dick

[coop]

I know when you touch magnets they only attract in one position and repell the opposite. Maybe you have one/both turned the wrong direction? Figuring out which one may be a task, but I would switch them both rotating 180 degrees and see if this helps? That's the only varible I can think of. Maybe someone else will have another idea.

[Steven]

Turn it upside down

[carlb]

For one thing try just replacing the original brush that you removed. Faint chance only one is touching now. Normally if you chage brushes on any motor you should ALWAYS do both. I don't know what else you may have done but just try remembering what you did and reverse the process. Hopefully you kept the original brush. Also, explain if this is a standard 110/120V AC, 60 Herz, 1 Phase motor. Not all such motors are reversible you know so don't run it until you've found the problem. I highly doubt it is the magnets.
Good Luck.

[smed]

Could you have possibly reinstalled the armature backwards?

[Dick]

Thannks for all the responses!
Now, The field(s) are magnets, fixed in place. THey were not removed.
The saw stopped because only one brush was making contact with the commutaror bars. No circuit for the current to flow.
I finally got (A) new brush, today. They said there are noe more. It was installed, and the power applied. The motor turned, and was adjustable, as it is supposed to do, except, it turns backwards! That is precisely why I think I must have reversed the fields, inadvertantly, because there are no markings opf any kind, and not having worked since '81, I forgot to put punch mark to locate the parts positions! Dumb move, but repairable. I didn't look at the complete wiring, nor do I have a manual, but I'll bet that there is a rectifier somewhere, that coonverts the 110 V ac, to lo voltage, DC. That way, it doesn't have to have copper wire field windings, as do the ac motors. I'll lay you 3:2, that when I physically rotate the shel;l, end-for-end, and put it all back together it will rotate in the proper direction, and I can get busy, making more boxes, (not like the big one I posted a photo of), but small boxes that hold about 150 flips, in three sections. I'll post a photo of what I mean, later.


Dick

[Dick]

Good thing no one took me up on that bet. I lost! I switched the shell, (fields) ene for end, and tried it, same thing,runs backwards. swapped brushes, no change obviously. They only carry current, and have nothing to do with the polarity. Does anyone remember how we used to "shock the fields" on a recip engine starter motor, (way back with the "Yoke-boats)? That is when the AMM was also the AEM. There was no such thing as an aircraft electrician. The mech was that, and more!
I did check into the wiring, and as suspected, there is a printed circuit board, and the motor voltage is quite low. I tried to measure it, but my voltmeter is not designed for small DC voltages. I should have kept on working for another 20 years, or so.
My options are becoming fewer: Modify the motor mount, and put an AC motor in place, find the way to shock the fields, or buy a new saw. Anyone have a small 1/3 HP motor "kicking around"?
Diick

[eagames]

Silly questions...

In any case rotating the end won't change the polarity right?

Assuming the motor is DC (because it has fixed magnets) then you should be able to reverse those motor wires and the motor will be rersesed right?

The only caution is if one side is tied to the chassis ground so first ohm both leads to the chassis and if neither one is tied to it just reverse the wires.

Won't that work?

[Dick]

ED, I haven't done any trouble shooting, yet. The only thing done was demount the motor, and, (after pulling the end cap, i noticed that one brush looked like it might have snapped in two, so I naturally dis-assembled the motor. Which as you surmise, is a DC motor. MNone of the wiring has been disturbed, and that is why I am confused as to why it runs backwards, when nothing has been disturbed.
I do intend to dig into the whole thing. I don't have a manual, or any diagrams, but that is no problem. I have had to makd "service, and parts Manuals" before, on Machine tools, while working as an industrial Mechanic, Or Millwright, working for Kaiser Steel, in '79, and various machine shops since. That is why I said I would "modify it" if necessary! I was just looking for an "easy way out"!
Dick

[Dick]

ED, The saw is running as it should! It was too much of a job to try and remove all the wiring circuitry, so as to troubleshoot it (on the table, etc. SoI recalled seeing the leads were quite long, and strung aroung the perimiter of the end cap. I took the two wires loose fri, the connectors, and just swapped them. The wiring indicated an isolated circuit there so there shouldn't be any problem. There wasn't, and the mootor now runs as it should, Thanks to your suggestion. I would have done the same thing, as a last resort, eventually, but I had done everything normally done to change the direction of rotetion, except change two phases, because this is not a 3-phase ac motor. Thanks for your,and any others, who also suggested various things.
Steven, I took your advice, and tiurned it up-side down, and it runs fine, but it gets heavy, after a while, not to mention the saw-dust in the eyes!
Dick

[errorfinder]

i believe egames is on the right track.i've been using DC Permament Magnet motors for 30 years.i build and race 'slot cars' including hand winding small amatures 1/64 H.O. and 1/32,1/24th scale.reverseing direction can be done through reversing 'feed' wires (pre) commutator. unless the Comm. has shifted on the armator shaft itself. that is ; the commutator could have (though unlikley) rotated while the stacks (stacks-metal plates wrapped in wire) on the shaft did not. this 'shifting is used to set the 'timing of the arm . faster time less torque.less time more torque {less 'speed' (RPM)}. if the Comm. gets beyond certain degree in it's relationship with the "rest o the works". it will set up new parameters ie. run "backwards from previous run state (direction).*though unlikey - most 'armatures are most often epoxyed /fixed to the shaft along with stacks. an overheating Comm.worn/skipping brush *(cause)could break down an epoxy bond and allow "new timing" .i''ll be on th e "look-out " for 1/3 HP DC.for ya...

[Bob P]

I have had the answer all along folks. THe motor is obviously suffering from Mechanical Doubling! (that's a good answer for everything).

I think I can find a source and get ahold of a 1/3 HP motor Dick. My question is...'Don't the AC motors used on almost all power tools like that have a large capacitor to aid in the initial starting'? Does yours have a large capacitor on the motor?? You say it is not a 3 phase motor, so is it DC or not? Might the problem be a diode or rectifier??

[eagames]

Sounds like a DC motor with a rectifier circ or diode outside the motor.
Most AC motors don't use the fixed magnets.