reversing single phase motors, particularily the HF 3x36 belt sander

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Forum topic by REO posted 03-28-2013 05:18 AM 6484 views 16 times favorited 24 replies Add to Favorites Watch
View REO's profile


929 posts in 2277 days

03-28-2013 05:18 AM

Several times in the forums I have come across references to wanting to reverse the rotation of a motor, or someone looking for a replacement motor and upon locating one discovering that the direction of rotation is wrong for their application. There have been some interesting ways that this problem has been solved, requiring rework of the motor mount or creative belting paths. I am hoping that this pictorial instruction will remove a little fear from the chore of replacing a motor.

First of all I would like to say that electric motors are not magical, at least not completely. There is one closely guarded secret concerning the main ingredient in ALL electrical contraptions: The magic smoke! As long as you don’t accidentally release this and don’t attempt troubleshooting and modification while the plug is in the outlet you should be fine.

Some tools/ supplies you may /will need:

wire cutter for cutting wire and nylon ties and tails
soldering iron and solder or small crimp connectors
nylon ties
super glue
liquid tape if you want to use it
shrink wrap should you prefer
continuity tester/ VOM/ Ohm meter (any one of the three will do) Dont use 110 volts and a light bulb!
screwdrivers and wrenches appropriate for disassembly

Electric motors have been around for a long time. The basic theory is relatively simple. Over the course of time the manufacturing process has been refined in order to keep the cost of production down and increase the rate of production in any way possible. One way this is done is by using the same parts where ever possible and putting the same parts in the same places so there are fewer places for error along the line in the manufacturing process. They are a smart bunch! They use the same parts and market them as different products! The fact is that most single Phase low voltage motors in a horse power family use the same parts internally. For the most part any single phase motor can be easily changed to be any combination of voltage and rotation. Some are very easy and some take a little work. None are out of the scope of someone who can successfully use a volt ohm meter and make a good solder joint. If you are not familiar with soldering a crimp connector will usually do anyway.

This particular motor required digging out the windings as the manufacturer did not want to make it easy. Believe it or not the motor was speced out as a single rotation single voltage as many are on todays equipment for liability reasons. This is another reason why customer adaptable motors are much more expensive its not just the cost of the few extra pieces of wire and or the landing pad for the spade terminals. The manufacturer has to pay more for the liability insurance for this type of motor.

Of course you have to start by getting the sander disassembled far enough to access both ends of the motor. you wouldn’t really have to remove it from the base but I did. Take the shroud off the back of the motor and using a pry bar between the motor housing and the CENTER portion of the fan slide the fan off the shaft. Make alignment marks on the joint between the front bell housing and the body of the motor and do the same for the rear bell housing.

after removing the four through bolts on the motor (still installed in the above picture) Use a peice of wood to protect the end of the cooling fan end of the shaft and lightly tap the end of the shaft. Typically the rear bell housing will stay in place and the front bell housing will separate from the main body. remove the front housing and the armature and set aside. tip the motor up on the rear housing.

In these two pictures the white tubes cover the connection points of windings to line and capacitor leads.

carefully cut the nylon wire ties and discard. Also cut the cords where needed to release the connection points so they can be worked on and work them up and away from the windings. Carefully use only your fingers no screwdrivers pens scales prybars, hammers etc.

slide the sock back to expose the soldered connections. The blue wire o the left connects to one end of one winding. the other end of the blue wire connects to the capacitor. The white wire on the right has three winding wires connected to it.

being careful to remember where the wires are being disconnected,Either cut or unsolder the connections at the white and blue wires. you should now have six loose wire ends. The white wire and the three winding wires that were attached to it and the blue wire and its corresponding disconnected winding wire.

Our goal is to reverse the connection of the winding to the capacitor. We know that the winding wire to coming from the right that was connected to the blue wire is one end of the winding. We have a choice of three on the right. Eeny, Meeny, Miney, Moe, which wire is it I don”t know?, but I know how to find out. Set your meter to ohms (the horseshoe looking thingy). touch one lead to the wire on the left. Touch the other lead in turn to each of the three on the right. You want to find one that changes the reading on the meter. The other two should show no change in the meter. If they do we have one of two problems one the motor was already bad or you are useing your fingers to hold the probes to the winding leads. Here I have determined that the one from the left(that used to be connected to the blue wire) is the other end of the wire that is bent toward the outside of the motor housing.

So I connect the opposite end to the blue wire. I cut one of the insulating socks in half and threaded that on before I made the solder connection.

Here you can see the completed and recovered connection of one end of the capacitor winding made to the blue wire and tucked back down against the rest of the motor windings. I have similarly tied the remaining loose ends together. the green wire is an extension of the wire from the left as it was to short on its own. the piece of green wire is just something I had laying on the bench.

everything back in place with a couple of wire ties to replace the ones I cut and discarded. the loose ands of the cord are glued to the windings with a few drops of super glue and a coating of liquid electrical tape to finish it all off.

Watch this spot one of the through bolts has to get between the wires and the housing. make sure that the opening where the armature goes is clear (no wire tie ends hanging out in the way etc)
reassemble in reverse order of dis assembly. put a couple drops of super glue on the shaft just before reinstalling the plastic fan. Test run the motor before installing the belt.

24 replies so far

View Woodknack's profile


12431 posts in 2583 days

#1 posted 03-28-2013 06:50 AM

Thanks Reo, never know when this will come in handy.

-- Rick M,

View macatlin1's profile


78 posts in 3146 days

#2 posted 03-28-2013 11:37 AM

Years ago (30+) I was working on a project in a remote location and we needed a reversable DC motor. We could order one but it would take too long for it to arrive. I picked up a cheap electric drill (non-reversable) at the local department store and because it was a universal type motor reversing the polarity of the DC would not change the direction of rotation. Quick fix was to wire a diode bridge between the armature and field windings so the winding always saw the same current direction. Worked like a charm and the diode bridge fit into a cavity above the motor. When we told the people back at the main office that we had jury rigged a drill motor, they told us it would never work and couldn’t be made to work and to stop wasting time, etc. We modified another one and sent it back to prove what we had done. But this one had the case epoxied shut…

View TheDane's profile


5552 posts in 3866 days

#3 posted 03-28-2013 11:47 AM

REO—Thanks … I may give this a whirl on my HF belt sander/sharpening rig!

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View ldl's profile


1135 posts in 2568 days

#4 posted 03-28-2013 03:17 PM

Gerry I was thinking of you when I read this. Might be something to consider.

-- Dewayne in Bainbridge, Ga. - - No one can make you mad. Only you decide when you get mad - -

View Kenbu's profile


33 posts in 2084 days

#5 posted 04-02-2013 07:25 PM

REO, very useful info. Thanks for posting it. Now, getting up the nerve to try it on my own sander… Actually, a DPDT switch would make it operate in either direction on command.


View runswithscissors's profile


2893 posts in 2228 days

#6 posted 04-03-2013 08:01 AM

I picked up a 3450 rpm, 2 horse 220v motor very cheaply sometime back, but the rotation was wrong for my application. I took it into a local electric motor shop, and they said it couldn’t be reversed. These guys have been around a long time, and I am confident they know what they are talking about. But maybe they meant that it couldn’t be done without rebuilding the motor. I’m still waiting to find a use for that motor.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View REO's profile


929 posts in 2277 days

#7 posted 04-03-2013 04:00 PM

runswithscissors I don’t understand your question/statement. Either you wrote to prove me wrong or you want to get the motor working for you. Witch is it?

View runswithscissors's profile


2893 posts in 2228 days

#8 posted 04-03-2013 08:28 PM

Sorry to seem ambiguous. I can see that you know what you are doing. I’m guessing that my motor shop simply didn’t think it was worth doing, or that it would cost too much in terms of labor.

Does it make a difference what type of motor it is? Anyhow, at this stage, my project got set aside for a while to work on other stuff, so I don’t plan to do anything soon.

Can you recommend a published source for this kind of procedure? I know you have illustrated it, but it might be difficult to find your post again in the future when I would need it. Or maybe I could just google it.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View mchuray's profile


81 posts in 3201 days

#9 posted 04-03-2013 11:24 PM

Ok, just so I have this correct. After I have separated the wires, I locate the other end of the winding with my meter then I connect the end of the winding that was connected to the white to the blue and the winding end that was connected to the blue to the white. The two loose wires with no reading is then connected to the blue? OR do I just connect the two loose wires back to the white? Or do I keep the winding wires and only move the two wires with no reading to the blue wire OR did I totally miss read the entire procedure. I’ll admit to being someone easily confused.

View REO's profile


929 posts in 2277 days

#10 posted 04-03-2013 11:32 PM

connect them back to the white. I was not clear on that. apologies.

RWS I will se what I can find. Most of the stuff you can find that is very discriptive is motor specific. On the fip side the mor generic one gets the more they have to know what is being discussed. I will look around as I get time and return to this post to freshen it up with new info on the subject.

View REO's profile


929 posts in 2277 days

#11 posted 04-04-2013 01:01 AM

Concerning the winding that HAS the reading. you are reversing the connections from white to blue. Reversing connections on ONLY that winding the other wires that were disconnected from the white are reconnected to the white along with the wire that WAS attatched to the blue. the wire that has the reading that WAS connected to the white dhould be connected to the blue. you should end up with three wires again connected at the white and one wire connected to the blue.

View mchuray's profile


81 posts in 3201 days

#12 posted 04-04-2013 02:26 AM

Now that makes sense. Thanks for the clarification. Am a wizz at soldering and got plenty of wire ties, now all I need is time.

View Kreegan's profile


1452 posts in 2350 days

#13 posted 04-04-2013 05:23 PM

Thanks REO! Very helpful!

View Kenbu's profile


33 posts in 2084 days

#14 posted 04-20-2013 09:52 PM

I just finished doing this mod on my HF sander and…it works! No, I didn’t doubt REO’s advice, just my own abilities. I followed the excellent directions and, once I had the wires re-soldered and tucked back into place and everything back together, I braced myself and flipped the switch. Lo and behold, the motor now turns the other way. Nice!

If i can do it, you can, too. Thanks again, REO for this great trick.


View b2rtch's profile


4868 posts in 3251 days

#15 posted 08-09-2016 10:37 AM

Thank you Reo,

-- Bert

showing 1 through 15 of 24 replies

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