DazeCars, Upgrading shop tools for variable speed

The obvious solution is to slow down the speed of the blade and my original plan was to use pulleys and belts to reduce speed but the band saw is so small that consequently there is not a lot of room to add parts, so I was not able to make the modifications I wanted to.

I then tried a router speed controller hoping it would work and it did slow down the motor some but not enough and it also reduced the torque of the motor. After doing further research I also learned that those speed controllers are hard on the motors and will shorten their life. With two failed attempts at slowing down the blade speed I was about to give up but then my brother told me about the DC motors in treadmills. They are high HP/torque and by changing the voltage you can change RPM but not loose torque.

I began researching how to make this happen and found lots of information on line, some of it good, some of it not so good and as I said above none of it was “complete”.

My initial research said “get a treadmill remove the motor control board and the motor, attach a potentiometer (pot) to the control board at the H, W, and L terminals and you are good to go.” However it was not even close to that simple. The first three treadmills I took apart had boards that were way more complicated which meant they did not have the H, W, and L terminals. I have now taken apart a total of five treadmills. Out of those five only one treadmill had the correct board, but before I got the correct control board I searched for other options.

Speed controllers:

To adjust speed, a lot of people using treadmill motors on shop tools are using a board called an “MC-60 speed controller”. A few treadmills come with these boards but if you are not lucky enough to have one come with the treadmill you are using for parts, they are available on eBay, and cost between $60-$100. I was trying to keep this project budget friendly and continued researching other speed control options and found a couple YouTube videos on treadmill motors where they were using a different setup to control speed. Their solution was to get an AC SCR voltage controller for about $15.00, wire a bridge rectifier to it and use this combination of parts to control the speed of the motors. An MC type board and an SCR voltage controllere are the two most commonly used ways to power a DC motor from a 110 AC outlet.

An SCR controller modifies AC voltage and then you must use a bridge rectifier to convert that voltage to DC. The MC boards use PWM, which stands for “pulse width modulation” These boards starts by converting the AC to DC and then pulses the DC current to reduce voltage.

While both the SCR and PMW type controls are effective at providing motor speed control there are some advantages and disadvantages of each. An SCR controller is significantly less expensive, has fewer parts so fewer parts to fail, is more robust, and is able to handle higher current motors, but it makes a buzz when running, and is harder on the brushes and commutator (the contact the brushes ride on). However both of these negatives can be mitigated as I will explain further below. PWM controllers such as the MC-60 are more expensive, wired from the factory with “soft start” (soft start can be eliminated but requires more components) have lower current limits, and are not as robust as their SCR counterparts, but they run silently and the motor runs “better” with a longer brush and commutator life.

So the question is, which is the correct choice, the SCR controllers or the PWM controller and the answer due to their advantages and draw backs is it will depend on your application and needs.

SCR voltage controllers:

First you need to know that you can not hook an SCR voltage controller directly up to a treadmill motor. A treadmill motor runs on DC and the output of an SCR controller is AC. This is easily fixed with a high amperage bridge rectifier. It will convert the AC to DC, more on that later.

Second not all SCR controllers are created equally. They come in many different wattages but I wanted one that would put out more wattage than I needed so that it would last longer. The highest one I could find was 10,000W peak with 5000W sustained. When you calculate it out 5000W at 110 V works out to be about 45 amps and most of these motors are 15-30 amps so the 10,000W controller is the perfect size. There are at least three different budget friendly versions available on eBay and Amazon ranging in price from $10-$25. I have several projects that will all need a controller, so I purchase one of each that way I could compare them.

I set up each of the three controllers and compared their brush spark. What I mean by brush spark is, on one of my motors I could easily see through the vent holes to where the brushes make contact to the commutator. At higher speeds >3000 RPMs this contact point would spark. This sparking action shortens brush, and commutator life so observing sparking is a visual measurement of the quality of the SCR controller, and eliminating that spark is a good indication of improving SCR function.

The first SCR controller is the most inexpensive and the old saying is true, you get what you pay for. This unit is noisier than the other two, makes the motor run a little nosier and was the worst when it comes to brush spark. Also the knob on the controller had to be turned quite a bit before the motor would start. I knew from my research that having to turn the knob quite a bit just to start the motor was going be an issue and I will address the solution in the section “Setting up the potentiometer for speed control.” Depending on which motor I was using the lowest RPMS I could get with this controller were between 450 and 500 RPMs

The second controller was only slightly more expensive than the first one and came with a digital display. It was slightly less noisy than the least expensive controller and the sparking at higher RPMs was almost the same as controller 1, but maybe marginally less. One advantage of this unit is that it started the motors at a lower RPM range 300-400 RPMs however you had to start at a minimum setting on the display of 5 to get the motor to turn on. Also one thing that could be a benefit or a problem depending on how fine a speed control you needed for your application is that increasing the display by 1 increased the RPMs by roughly 100 RPMs. It has the advantage of knowing how fast each setting will be without having to measure but the disadvantage of not having any speeds in between each 100 RPM increase.

I had been using controller number 3 on my band saw and was very happy with it. It was working well, however I needed to use that controller for another project so I decided to mount controller 2 on the band saw. I figured it would work well for set speeds depending on what I was cutting. In other words I could make a chart that told me what number to put it on based on what material I was cutting. I spent an afternoon making an enclosure for it, getting it mounted up and was happy with the install. That was until a couple days later when I went to use the machine. When I pushed a piece of aluminum into the blade rather than slowing only marginally like it hade with controller 3 it bogged down a lot, at least 1/2 to 1/4 the speed it had started at. I had to ramp the starting speed way up just to get a decent cutting speed once material came in contact with the blade. I am not sure what makes this unit different electronically but it obviously does not work well in systems where the motor is under a load. I replaced it with controller 1 and have been happily using my band saw ever since.

The third controller was by far the best of the three. It was twice as expensive as the cheapest one but came with an internal cooling fan, is completely enclosed, and of the three was the quietest and produced the least spark inside the motor. This is the SCR controller I would recommend unless you need the lower RPMs provided by controller two.

PWM controllers:

As I said above one of the treadmills I parted out came with the correct board to use as a controller. It had an MC-2000, which has almost everything you need to use it to control motor speed.

There are three terminals on the board marked L, W, and H and these terminals are what you use to control speed. All you need to do is get a variable resister, or potentiometer and connect its three terminals to the H, W, and L inputs.

When wiring one up the middle terminal on the potentiometer goes to the W and for the outside terminals one goes to H and one goes to L. Therese terminals can be interchanged depending on which way you want the nob to work. Attaching the H to the left terminal will give you a clockwise knob rotation to increase speed. Connecting the H to the right terminal will give you a counter clockwise knob rotation to increase speed. I tried several different potentiometer sizes from 10KΩ all the way to 500KΩ and they all seamed to work about the same. This controller runs quiet, there is little to no sparking inside the motor, and is an outstanding option except for the soft start.

Soft start means the circuit will not restart at the last speed it was set at. In other words if using the machine at 600 RPMS and you then shut the system off when you turn the system back on the motor will not turn on. You need to turn the potentiometer all the way down to the slowest speed and then when you go back up it will start slow and then increase as the knob is turned; great for a treadmill, but not for a shop tool. This can be fixed by putting a normally closed push button switch in line between the potentiometer and the H terminal to disable soft start. To use it, with the power off, push the button, effectively disconnecting H from the potentiometer, turn the main power switch on and then release the button which will reconnect h to the potentiometer. This will cause the motor to spin up to the speed corresponding to where the potentiometer is set. Others have used delayed relay timers in place of the switch but to me this is a more expense option with more to go wrong. IMHO the two button system is completely effective and the simpler way to go.

Motors:

As I said before I took apart 5 different treadmills and they had 5 totally different motors. They ranged in amperage from 1.5-3 amps and 1-3 horse power. All 5 of them were rated for about 4000 RPMS. Some were set up for clockwise rotation and some were set up counterclockwise. Good news is almost all treadmill motors are reversible by simply switching the + and – wires. There is an exception however where some motors are not reversible. To know if your motor is non reversible there is a simple test, rotate the shaft by hand in the direction indicated on the motor label. It should easily spin but will probably have a slight “pulsing” feeling as you turn it. Then rotate the motor the other direction if it feels the same it is reversible if it catches and turns much harder it is not reversible.

All treadmill motors come with heavy flywheels and depending on your application, you may choose to use them or not. Some flywheels are threaded on and some attach using set screws and keyways. If the flywheel is threaded on keep in mind the motor can only be spun one direction while using the flywheel, as spinning it the other direction will unthread the flywheel from the shaft.

Even though all these treadmill motors are basically the same and are setup the same way there are some wire differences to be aware of. The colors you may see are red, black, white, green and blue. The red wire is universal across every motor I have seen and is the + wire if you want the motor to spin in the direction on its spec label. The black wire or white wire is the - wire. There is no difference between black wires and white wires other than their color. They are the opposite wire to the red wire. The green wire is the safety ground. Some videos I have watched tell you, “You don't need the green wire so clip it off.” This is horrible advice. The green wire is there to ground the body of the motor to the body of whatever you are installing the motor on and to ground it to the ground prong in the wall outlet. Electricity takes the path of least resistance and if something goes wrong this green wire provides that path. If one of the power leads rubs up against the body of the tool and the insulation becomes damaged you have a situation where electricity can be flowing through the body of the tool. If the green wire is installed it will create a direct short and trip the circuit breaker. If the green wire is not installed, electricity accidently begins flowing through the body of the tool and you touch the tool your body may provide the path of least resistance resulting in electrical shock. The green wire is there for safety. USE IT. Blue wires are also safety wires, and again I have heard videos that say, “You don’t need the blue wires so clip them off” this is again bad advice. The blue wires go to a thermal fuse inside the motor and that fuse is designed to be part of the AC circuit between the on/off switch and the speed controller. If the motor over heats the thermal fuse trips cutting power to the motor controller. An over heating motor will burn up so by using this feature you help eliminate that possibility.

Switches, rectifiers, fuses, and circuit breakers:

Seams fairly strait forward, you need an on/off switch to cut power to the speed controller and from there you wire up the motor and you are good to go. There is more to it than that. First when using an SCR power supply you must, as I said above, use a bridge rectifier to convert the AC to DC. A bridge rectifier is basically a single component with 4 diodes inside.

AC which stands for alternating current gets its name because the two power wires alternate from positive to negative 60 times a second opposite of each other. A bridge rectifier takes that input from the alternating current and shunts all the positive current from both wires to one terminal and the negative terminal returns the current to both wires converting AC to DC. I used a KBPC5010 bridge rectifier which is rated at 50amps and 1000 volts way above what we are needing to run a treadmill motor. Again I went bigger to maximize life of the component.

It is important to know, when a bridge rectifier fails it typically shorts out across all 4 terminals. When I first started this project I purchased 5 rectifiers from a supplier and with all 5 when a load was applied, even though the voltage and amperage was way less than what the rectifier was rated at, the rectifier would fail shorting out all 4 terminals which in turn would overload the speed controller burning it out. This problem could have easily been avoided by adding a 20 amp fuse or 20 amp circuit breaker on the non common lead between the rectifier and the power supply. It is also a good idea to add a fuse or circuit breaker between the power supply and the on/off switch.

It is important to know that bridge rectifiers produce heat as a byproduct of them converting AC to DC. I recommend using a heat sink to help dissipate that heat. I made mine by cutting a section out of one of the heatsinks from a non usable control boards scavenged from the treadmills.

Proper gauged wire and AC LED indicator lights:

There are a couple of other safety things that I would recommend. The first (a good tip I got from YouTube) is an LED indicator light on your main power switch. When there is power being supplied to the speed controller the light will be on. This is nice especially if you don’t have the correct potentiometer in the controller. I say this because turning the knob down past the “minimum” speed could cause the motor to stop even though everything is still on. The LED as an indicator lets you know the system is still on and to shut it off when not in use. Failure to turn the power off when not in use could burn up the speed controller, the rectifier, and or the Motor.

One other thing to note is just because the power cord came with the tool you are putting the new motor on doesn’t mean it is up to the task of powering the new motor. When I first set up my band saw I used the original power wire and after the conversion I noticed it getting warm when running the saw. Upon further inspection I discovered the wire was way to small at 18 awg. 14 awg is rated at 15 amps and is the minimum I would use.

Chokes:

The most important thing for improving function and prolonging motor life is a large DC choke and you really need to run one (another good tip I got from YouTube but something I was able to verify by trying the setup with and without them). Some treadmills come with them. They look a lot like transformers but are not.

They have two wires, an in and an out and when attached inline between the positive terminal from the rectifier and the motor they will SIGNIFICANTLY improve motor function. I have again heard it said “throw them away you don’t need them” and while to some degree that is true it is again bad advice. When hooked up the choke reduces the noise produced by the power supply and motor by at least half. Not only does it reduce noise but it also eliminates almost all sparking inside the motor. There is a direct correlation between noise/sparking and motor life so if you have one why wouldn’t you hook it up to prolong the life of your motor.

Also there was one more observation that showed the value of the large choke between the rectifier and the motor. When I set up my lathe with one of these motors I did not originally use the choke. When I turned the lathe on with speed control set at slower speeds there was no problem, but if the speed control was all the way up to full and I turned the lathe on the 15amp circuit breaker for the wall outlet that system was plugged into would trip. After I installed the choke I could turn the lathe on at any speed and the circuit breaker would not trip.

There are also smaller AC chokes that you may find in some treadmills that are as simple as too wires wound around a ferrite donut, usually not more than 1.5” wide.

These are better for the AC side. You need to put it between the SCR power supply and the rectifier. With this combination you are "cleaning" the current coming out of the SCR with the AC choke and then once again cleaning the current coming out of the rectifier with the DC choke. The end result, clean power.

Setting up the potentiometer for speed control:

The last component we need to address is the potentiometer. This is the dial we turn to control speed. Same part that I wired to the H, W, and L terminals on the MC boards. The SCR controllers come with a potentiometer already installed however all the controllers I purchased, with the exception of the push button unit, had a potentiometer that is way to big. The result of using an over sized potentiometer is you have to turn the knob 1/3 of its total rotation before the motor comes on and then you only have the last 2/3 of the knob movement to adjust speed. This makes the knob very sensitive where very little movement makes a big change in motor speed. The advice I found on line was to use trial and error to find a potentiometer that will work for your application. However, this is again in my opinion, not good advice. There is a much easier way to get exactly what you need. To know what size you will need, start with the SCR controller as it came from the supplier with the over sized potentiometer. Wire the speed controller up to the motor, power the system on, and turn the Knob until the motor coms on. Mark the body of the controller so you know where the knob needs to be to turn the motor on. Then with the system unplugged remove the cover of the power supply and use a meter to check the values of the potentiometer at the marked point. Both of the knob stile power supplies I purchased had 500K Ω potentiometers installed. On the cheaper unit the potentiometer had to be turned to 120KΩ for the motor to come on. That means 120KΩ potentiometer will give you full speed control with that supply. The better supply with the built in cooling fan measured at 150KΩ at the marked point so 150KΩ potentiometer was needed to give full speed control.

But what if you don’t want full speed? All of the motors I have are rated around 4000RPMs at between 90v and 110V DC. The AC motor on my band saw was rated at 1700 RPMs and spinning a treadmill motor at 4000 RPMS would be more than double that and at the very least probably cause the tool to fail and more likely cause injury. If you allow the speed controller to have an option for full speed there is the chance that you will accidently turn the speed up to much. This danger can be easily eliminated. To do so I used my RPM meter and my volt ohm meter. Using the RPM meter I turned the knob on the potentiometer (Again the one that came in the SCR unit) until the motor reached the max speed I was looking for of 1700RPMs. I then made a second mark on the body of the power supply to show me the knob location for the max speed I was after.

From there I powered down the system removed the speed control cover and used the volt ohm meter to measure the potentiometer rating at the two marks: start speed, and max speed. As I said above start speed was 150KΩ and target max speed mark was 100KΩ. That meant I needed 50kΩ of adjustability and a minimum Ω of 100. This was easily achieved by putting a 100KΩ resister inline between one of the wires and one of the terminals on a 50KΩ potentiometer. Resisters (a potentiometer is a variable resister with its max being its rating and then it can be reduced down to 0) when wired in series add their values together. When the potentiometer is at 50KΩ the total of it and the 100KΩ resister is 150KΩ when the potentiometer is at 0Ω the total is 100KΩ giving me full adjustability between starting speed and my desired max speed.

I used some shrink tubing over the resister and terminal end to insulate it and give it some regidity.

One important thing to note before marking max and min speed so you can measure the Ω Get the motor mounted up and driving whatever it is going to drive. Belts and pulleys will absorb some energy and reduce RPMs. For example 100KΩ made a max speed of the motor I was using 2000 RPMS when nothing was attached to it but once hooked up to the band saw that same amount of resistance gave me a speed of 1700 RPMs.

Tips and tricks for using the RPM meter:

As I said in the beginning the RPM meter works by placing a piece of reflective tape on the rotating assembly. The Meter then uses inferred and the reflection from the tape to calculate speed.

If you are putting the tape on something silver (bare steel or bare aluminum) you will not get an accurate reading. A couple solutions are to use electritions tape around the rotating assembly (I did this on my lathe chuck) or take a black marker to the surface (I did this on my bandsaw wheel)

Hooking it up to my band saw:

Now with all the technical info out of the way lets look at how I put it all in to practice in the application of my 9” band saw

I started by machining a pulley out of aluminum to fit on the treadmill motor shaft that matched the belt that the band saw came with.

I then mounted the motor to the back of the saw in the same location that the original AC motor had been in. The treadmill motor was about the same diameter but almost twice as long.

The belt was then installed and I turned to wiring it up. I attached the SCR controller to the side of the saw ran the ac output to a circuit breaker and from there connected it to the rectifier. The power conection refered to ascommon went directly from output on the SCR to the rectifier. From the rectifier the positive wire went through a choke and from there to the motor and the negative wire went directly from the rectifier to the motor. With everything wired up I powered up the system, found my min and max as described above and replaced the potentiometer with the correct one in conjunction with a resister.

System works very well and I am extremely happy with it. I have used the saw to cut all kinds of things including steel.

This project was almost the same as the band saw project with one exception. On a lathe I needed to be able to reverse direction. Reversing the positive and negative wires between the rectifier and the motor easily does this. To accomplish this I used a DPDT switch rated at 30 amps. To hook it up I connected the motor to the two center pins on the switch. The positive and negative wires are then hooked up to the outside pins opposite from each other.

By doing this when the switch is set to one direction the positive from the rectifier goes to the positive on the motor and the negative from the rectifier goes to the negative on the motor giving you the listed rotation direction, but when you flip the switch the other way it connects the positive from the rectifier to the negative on the motor and the negative from the rectifier goes to the positive on the motor giving you the opposite rotation direction.

I will also be adding a digital RPM gauge to my lathe. On the band saw I marked speed values around the dial and then fine-tune based on cutting performance and sound, but on the lathe I need more accuracy so by attaching a digital gauge to the tool I will have real-time speed feedback without having to use the handheld RPM meter.

eBay:

One thing I did before disassembling my treadmills was to plug them in and test them. It was important to know if they worked so I would have the option to sell off non needed parts. On two of the treadmills I was able to take the working control boards out and list them on eBay. I sold the boards for $35.00 each. This is a good way to get back some of the initial investment of purchasing a used treadmill.

I have been using this setup on both my lathe and bandsaw for several months now and am very happy with the way they are working. I did run into one small issue. On both machines I had a bridge rectifier failure. These motors draw less than 30 amps at 0-110 volts and the original bridge rectifier I used was raited at 50 amps up to 1000 volts. Also the bridge rectifier I chose had been used by others with success. This coupled with the fact that my first batch of bridge rectifier all failed with little to no load leads me to believe there are some manufacturing issues with these parts. To fix the issue I went with a 100 amp 1600V bridge rectifier normaly used in a welder. It comes with a heatsink built in and only cost me about $7.00 from Amazon. This is a far beter option and what I would recomend in the future. As you can see below the 100 amp bridge rectifieris way bigger size wise than the 50 amp unit I started with.