# Circuit to allow triac/bridge rectifier based ac controller circuit with manual potentiometer control to be controlled by PWM

#### besligar

Joined Mar 9, 2023
28
Looking for circuit to allow triac/bridge rectifier based ac controller circuit with manual potentiometer control to be controlled by PWM. Details attached

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#### crutschow

Joined Mar 14, 2008
31,535
What will generate the PWM signal?
It will need to be isolated from the mains for safety, such as with an opto-isolator.

#### Audioguru again

Joined Oct 21, 2019
5,579
A user and a DC motor might not like the 100Hz or 120Hz severe ripple from the rectifier bridge.

#### besligar

Joined Mar 9, 2023
28
Was looking for a circuit to add that would replace the potentiometer providing 0 - 200k resistance to the circuit through an opto-coupled 0-5vdc PWM signal, which will come from what ever we want to control a dc motor with. The circuit would have to take it's power from the controller and respond to the optocoupled signal.

#### LowQCab

Joined Nov 6, 2012
2,920
What You need to do is to start-over.

All of the Motor-Control needs to be done with DC-Voltage,
AFTER the Bridge-Rectifier,
then it becomes relatively easy to implement PWM-Control.

Are You just tinkering around for fun and learning,
or does this Motor need accurate Control for use in a dedicated machine of some sort ?

Are You up to building your own DIY-Circuit,
or are You just looking for a Chinese-Module ?

What is the Motor mounted in, and/or, what was it removed from ?
What are the full Specifications of your Motor ?
What will the Motor be powering ?, (a full description of the Mechanical-Load ).
Do You need to be able to Reverse the Motor's Rotation ?
Do You need to control how fast the Motor accelerates, and decelerates ?
Do You need to have automatic stabilization/control/governing of the Motor's-RPM ?
.
.
.

#### besligar

Joined Mar 9, 2023
28
Re: LowQCab’s excellent comment – Some background…

Many, many moons ago….
I started converting an old heavy drill press to a mini-mill of sorts and then added CNC to it using Mach3.

I powered it with a DC motor from a treadmill and used the “AC 110V 120V 220V 230V 10,000W High Power SCR (actually triac) Motor Speed Controller Voltage Regulator” available for $37.50 coupled with a KBP5010 to power and manually operate the speed of the spindle with the potentiometer. I had very good control of speed manually with this hardware and it is very compact and economical. As well, it would start the motor at whatever speed was previously set, just activate the relay in Mach3. When I got tired of using a TACH to set the speed I set up a motor speed sensor to Mach3 which made setting the speed easier by having direct feedback in Mach3 display. The motor never complained about it’s juice. The obvious next step for this project was to have Mach3 spindle speed control through the 0-5V PWM output it provides. There is a fair size community of people using treadmill DC motors and the power/control boards from the treadmill to power many different projects. I acquired an MC-2100 board and motor from a treadmill, the board is not working right currently and I’m waiting on parts to finish the repair…that can be followed on another thread here. The process of fixing these boards made me realize there are many more DC motors than controllers from treadmills out there (I have three motors, one controller) so this cheap hardware is a good alternative to variably power these motors, in my opinion. I am not proposing one build this circuit. By buying the 10,000W controller and a 5010, all the heat sinks needed are there and, well, you just couldn’t economically start from scratch. That leads me back to LowQCabs initial comments…after “What you need to do is start over”…lol, don’t know you man, but I like your approach! His following comment gets to the point and where I hit blown fuses: “All of the Motor-Control Needs to be done with DC-Voltage. After the Bridge-Rectifier. Then it becomes relatively easy to implement PWM-control.” When I tried to use another controller for DC only to control the output of this setup, fuses blew, twice… so I thought better of playing with the DC output of this other than to run a motor or heater directly. I am targeting the use of DC motors, mostly from scrapped treadmills as a cheap source of powering them. Most of these motors won’t draw more than 2500 to 3500 watts I believe. I could very well be off track by looking to use the components I am to do what I want, that is why I started this chat. If we can start with a KBP5010, and get to an input for PWM with some circuitry, that’s even better. See pictures for reference. #### Attachments • 2.3 MB Views: 9 • 2.7 MB Views: 9 • 2.2 MB Views: 8 • 2.2 MB Views: 8 Thread Starter #### besligar Joined Mar 9, 2023 28 Also, the schematic we are looking at is my reverse engineering of the module, to the best of my ability. I had two, so I took one apart. #### MaxHeadRoom Joined Jul 18, 2013 26,685 You are much better off going with the MC2100 (PWM) controller, especially for a CNC application, requires a 20hz PWM control signal to run it. Strictly speaking, you do not require two DC bridges for DC motor control in a Triac controller normally. #### LowQCab Joined Nov 6, 2012 2,920 The are some guys in this Forum who know all there is to know about the MC2100-Treadmill-Motor-Controllers if that's what You decide to do, but I'm reluctant to recommend them because they release "The-Magic-Blue-Smoke" at the drop of a hat, or just at random. There's usually regular post in these Forums around every ~2 to ~3 weeks with somebody wanting help with patching-up their smoked MC2100 Controller. But they're cheap from China. There are much more robust methods of building a High-Power-DC-PWM-Motor-Controller, but it is somewhat expensive. Depending upon your resourcefulness, you might be able to build a premium, bullet-proof, Controller for ~$150 to ~$400 Dollars, with all the bells and whistles You could ever want. And when it's completed, you'll have much smoother power-delivery, ( quiet ), and around ~25% more Torque available, and reliable safety-features as well. Let us know which way you'd like to go ......... . . . #### MaxHeadRoom Joined Jul 18, 2013 26,685 I'm reluctant to recommend them because they release "The-Magic-Blue-Smoke" at the drop of a hat, or just at random. Like any piece of equipment, if you abuse it it often results in failure. They are one of the most popular used boards in a great majority of T.M.s, They have quite a bit of protection built in, for example, when starting a DC motor under load that already has a 10lb - 12lb flywheel attached, you cannot randomly apply full power. At every instance of Start, the processor signal goes into ramp up mode. Which is entirely necessary when dealing with something like a T.M. Also the O/L and fusing should also be kept in place especially when using it for alternative uses. The older SCR MC60 bridge version also had a great deal of safety features built in in order to protect against instant start. For the most part, they are easily fixable, the only down side in the MC2100 ver. is if anything happens to occur to the processor itself. #### MisterBill2 Joined Jan 23, 2018 14,261 Looking for circuit to allow triac/bridge rectifier based ac controller circuit with manual potentiometer control to be controlled by PWM. Details attached The challenge in using the control shown in post #1 is that the variable resistance is half of a phase shifting network, it is not adjusting a voltage. This means that a variable voltage in that position will not work. The way to use that speed control circuit as a digitally controlled drive would be by means of an ISOLATED analog digitally controlled resistance. OR, if the controller can provide a digital output signal, an ISOLATED D/A resistance converter. If that PWM output can deliver a voltage adequate tp drive LEDs, then it may work to have the LEDs illuminate a variable resistance photocell like the ones used in some of those light sensors that have a sun sensor and a thermally driven snap switch. Those sensors have a wide resistance range and an adequate current capability. Thread Starter #### besligar Joined Mar 9, 2023 28 The challenge in using the control shown in post #1 is that the variable resistance is half of a phase shifting network, it is not adjusting a voltage. This means that a variable voltage in that position will not work. The way to use that speed control circuit as a digitally controlled drive would be by means of an ISOLATED analog digitally controlled resistance. OR, if the controller can provide a digital output signal, an ISOLATED D/A resistance converter. If that PWM output can deliver a voltage adequate tp drive LEDs, then it may work to have the LEDs illuminate a variable resistance photocell like the ones used in some of those light sensors that have a sun sensor and a thermally driven snap switch. Those sensors have a wide resistance range and an adequate current capability. An LDR is where my first thought went on this, I know there is 2K-200K versions at 150V, 90mA which I suspect wouldn't cut it current wise? My problem is I don't really understand this circuit. In going down the path of repairing my MC-2100 I've gotten a bit of an education in components I knew little about before, but to follow exactly what is going on here, I can't reason it out. The bridge rectifier really throws me off. The DC output from it probably isn't usable to power the LED for the LDR as it's output is dependent on the POT setting, I think. If there is an LDR that would handle the current (any idea how much current?), where in this circuit might you get the power for a mini circuit of the LED which would vary it's brightness by the input of a 0-5V PWM? If there is an LDR that will work there, another option, and maybe the most reasonable, is to make a module powered at the breakout board end that the PWM signal connects to and the output of the module is two wires and an LED which would go to the controller and be enclosed in something with the LDR. It looks like the LDR is 200k @ dark and the module is off at 200k and full on at 0-2K so at least no inversion would be required. Thanks for your initial assessment, It helps me understand a little bit more about this puzzle. #### MaxHeadRoom Joined Jul 18, 2013 26,685 The difference between the Triac circuit and the MC2100 is like night and day, For Triac controller circuits see Fairchild AN-3006 and AN-3003. For a DC motor, add a bridge rect. between Triac and motor #### MisterBill2 Joined Jan 23, 2018 14,261 The LDR is mostly providing the trigger current for the SCR, and I doubt that the variable resistor in the manual control is passing 90 milliamps. Probably much less.. Thread Starter #### besligar Joined Mar 9, 2023 28 The difference between the Triac circuit and the MC2100 is like night and day, For Triac controller circuits see Fairchild AN-3006 and AN-3003. For a DC motor, add a bridge rect. between Triac and motor Downloaded and had a quick gloss through these, looks like great info! I'll spend some time in them. Hope to have some results Monday on the MC-2100 repair after Digikey shows up. Thread Starter #### besligar Joined Mar 9, 2023 28 The LDR is mostly providing the trigger current for the SCR, and I doubt that the variable resistor in the manual control is passing 90 milliamps. Probably much less.. That is great to know about the potentiometer current, I suspected it might not be as great as I assumed because the original is 2W and large, but mostly for quality and smoothness maybe, the 200 K I replaced it with is only .5W and works fine. There could be a relatively easy solution here. Or the unit that has LDR and LED encased together... #### MisterBill2 Joined Jan 23, 2018 14,261 I have not seen the LDR that I am thinking of in anything other than on/off daylight sensors, and those devices are at least 3/8 inch diameter. They could be illuminated by a series string of 2 or 3 LEDs, and even handle a bit of power. But the device would be so useful that I am sure somebody makes it.. Thread Starter #### besligar Joined Mar 9, 2023 28 I have not seen the LDR that I am thinking of in anything other than on/off daylight sensors, and those devices are at least 3/8 inch diameter. They could be illuminated by a series string of 2 or 3 LEDs, and even handle a bit of power. But the device would be so useful that I am sure somebody makes it.. I could be way off base but I ordered a kit with this (25 of each -$18.00):
Type--Maximum Voltage--Maximum Power--Operating Temperature--Spectral Peak--Light Resistance (10Lux)--Dark Resistance--Sensitivity--Response Time : rose and Drop

GL5506------100 (VDC)-------90 (mW)----------- -30 ~ +70 ℃------------ 540(nm)----------2~6(kOhm)----------------0.15(MQ / MOhm)-----0.6(min)-----------30 and 40(ms)

GL5516------100 (VDC)-------90 (mW)----------- -30 ~ +70 ℃------------ 540(nm)----------5~10(kOhm)----------------0.2(MQ / MOhm)------0.6(min)-----------30 and 40(ms)

GL5526------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------8~20(kOhm)----------------1.0(MQ / MOhm)------0.6(min)-----------20 and 30(ms)

GL5528------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------10~20(kOhm)----------------1.0(MQ / MOhm)------0.7(min)-----------20 and 30(ms)

GL5537------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------16~50(kOhm)----------------2.0(MQ / MOhm)------0.7(min)-----------20 and 30(ms)

GL5539------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------30~90(kOhm)----------------5.0(MQ / MOhm)------0.8(min)-----------20 and 30(ms)

GL5549------150 (VDC)-------100 (mW)---------- -30 ~ +70 ℃------------ 540(nm)----------45~140(kOhm)----------------10.0(MQ / MOhm)----0.8(min)-----------20 and 30(ms)

So the 5516 should give 5-10Kohm at full light and 200K at full dark, ranging in between on light intensity, I hope.
Next thing will be to play around with these on a breadboard to see what kind of resistive reaction I can get from different LEDs etc.

I attached an LED to the breakout board PWM output with a 100 ohm resistor and zero speed was 98%duty cycle and max speed was around 2% duty cycle at 200 Hz...so I guess I need to invert the PWM signal. I already have one I made to experiment with the MC-2100 PWM signal so when I get the LDR's I'll post some results.

Also, what you said above....could be I'll need way more light than a single LED driven directly by the PWM.
This might be the solution in that case: https://www.amazon.ca/dp/B07QGXY7F3?psc=1&ref=ppx_yo2ov_dt_b_product_details

#### Danko

Joined Nov 22, 2017
1,552
It is better to use this pair:

LDR: Light Dependent Resistor NSL 4960, 1 MΩ -->500 Ω, 500 mW, 320 V, 550 nm (peak).
LED: Super-Green LED (GaInN/GaN) RL5-G5023 3.5 V, 20 mA, 5000 mcd, 524 nm (peak).

#### MisterBill2

Joined Jan 23, 2018
14,261
That certainly is a lot of LDRs, and depending on the size you may be able to have two of them illuminating the one you use. If the PWM voltage is 5 volts then you can use two in series and no resistor will be required, unless you intend to run 100% duty cycle all the time. I am guessing that minimum resistance is maximum speed, but maybe not.
If you need more light then the PWM could drive the base of a single NPN transistor that you might have, or would cost you perhaps 25 cents for one. and that transistor could switch 5 volts at 100 milliamps or more, enough current to drive several standard LEDs, or one high powered one, with a resistor.