In this post I have explained a simple, accurate, high torque treadmill motor speed controller circuit which may be effectively installed in similar units for acquiring PWM controlled variable speed feature. The idea was requested by Mr. Samuel.
Technical Specifications
I've a treadmill whose power failed completely...it had been imported from china and it's like they can't help after negotiating with them..guarantee is only meant in their x-try.
So, am asking, how would you assist me in designing a power supply that will control speed and change of direction of the treadmill movement as well. I'm and forever will be glad for your work.
Looking into the specs of the unit, the switching relays are specified with 10A ratings. I also had a view of the motor and it was written 180Volts on it.
This is the information i got sir. They also had a cautionary notice that the T.Mill shouldn't be run beyond 2hrs continuously. I hope I've given the best for the best.Thanks sir. Stay blessed now and forever! best moments!
The Design
Here's a simple PWM based motor speed controller circuit which can be used for controlling a treadmill speed right from zero to maximum.
The circuit also provides an instant bidirectional stop and reversal of the motor rotation by a single flick of a given switch.
Another interesting feature of this circuit is its capability of sustaining and balancing optimal torque even at lower speeds ensuring a continuous working of the motor without stalling it during extreme low speeds.
The circuit of the proposed treadmill motor speed controller may be understood with the help of the following points:
Here the two 555 ICs are configured as PWM generator/optimizer for acquiring the required speed control of the connected motor.
Circuit Operation
IC1 works as a frequency generator and is rigged at around 80Hz, any other value would also do and is not anyway critical.
The above frequency from pin#3 of IC1 is fed to pin#2 of IC2 which is wired as a standard monostable. IC2 responds and starts oscillating at this frequency, forcing equivalent triangle wave frequency at its pin2/6.
The above triangle waves is instantly compared by the set potential at pin#5 of IC2 creating an equivalent level of chopped PWM at its pin#3
The preset or a pot positioned at pin#5 of IC2 forms a potential divider network for a selectable fixing of any voltage from zero to maximum supply voltage at pin5 of IC2. This level is directly translated through optimized PWMs at pin#3 of the same IC as explained above.
The PWMs are fed across two sets of NOT gates via an SPDT toggle switch.
The NOT gates which act as inverters provide the feature of instant toggling of the motors rotational direction by a mere flick of the SPDT switch.
The resultant PWMs from the selected NOT gates finally reach the transistorized bridge network that holds the motor between them for implementing all the specified features discussed above.
These transistors should be rated as per the motor specifications, and the voltage across this bridge should also be as per the motor requirements.
Video Clip:
Simplified Design
If you do not wish to have the reverse forward facility, then you can much simplify the above design by eliminating the lower section of the circuit entirely, as shown below:
The 10K pot can be used for the speed control, while the 220uF determines the soft start feature. Increasing the 220uF value increases the soft start effect and vice versa.
Controlling Through an External Power Supply
The above design could be also modified for enabling motor speed control through an external variable power supply, as shown below.
Pin#5 can be seen driven from an external 0 to 10V variable power supply, for example from a LM317 based power supply
If you do not wish to use an external power supply, the above treadmill speed controller design could be simplified even further, by adding a 1k pot at pin#5 of IC2, as demonstrated below:
The 1k pot will allow you to adjust the treadmill speed from 10% to 90%, and the C4 value could be experimented to add a nice soft start to the treadmill motor during the switch ON.
Construction Guide
Power Supply Section
15V DC Supply:
Ensure that the input power source delivers a stable 15V DC, because it is critical for the 555 timers and the IRF540 MOSFET operation.
Use a well-filtered power source to avoid the noise interference.
Zener Diode (D1 - 2.7V):
Provides a fixed reference voltage for the base of T1 (BC557 transistor) which gives stable operation.
PWM Generator (IC1 - 555 Timer)
The first 555 timer (IC1) is configured as an astable multivibrator, to generate a pulse-width modulated (PWM) signal.
Pin Connections:
Pin 1 (GND): Connect to the ground.
Pin 8 (Vcc): Connect to +15V supply.
Pin 4 (Reset): Connect to +15V to enable the IC.
Pin 5 (Control Voltage): Add a 10nF capacitor (C2) to ground to stabilize the PWM signal.
Pin 3 (Output): Outputs the PWM signal to the base of T1 (BC557 transistor) via R4.
Frequency Control:
Use R1 R2, and C1 to set the frequency of the PWM signal.
Formula for frequency:
f = 1.44 / [(R1 + 2R2) * C1]Where:
R1 = 180kΩ
R2 = 100kΩ
C1 = 100nF
PWM Adjustment (1kΩ Potentiometer):
The 1kΩ potentiometer varies the duty cycle of the PWM signal allowing the speed control of the treadmill motor.
Soft Start and Motor Driver (IC2 - 555 Timer)
The second 555 timer (IC2), is configured as a monostable multivibrator to implement the soft start feature.
Pin Connections:
Pin 1 (GND): Connect to the ground.
Pin 8 (Vcc): Connect to +15V supply.
Pin 4 (Reset): Connect to +15V to enable the IC.
Pin 5 (Control Voltage): Add a 10nF capacitor (C3) to ground.
Pin 3 (Output): Drives the gate of the IRF540 MOSFET.
Soft Start Capacitor (C4 - 10nF):
This capacitor determines, the ramp-up time for the soft start feature.
Larger values of the C4 increases the soft start time.
Adjust C4 using the formula:
t = 1.1 * R6 * C4Where:
R6 = 10kΩ
C4 = Soft start capacitor
Motor Connection:
The motor is connected to the drain of the IRF540 MOSFET with the source connected to the ground.
D5 (1N4007): Protects the MOSFET from back the EMF generated by the motor.
Working Principle
PWM Speed Control:
The duty cycle of the PWM signal generated by IC1 provides the average voltage applied to the motor.
Adjusting the 1kΩ pot, changes the PWM duty cycle effectively, controlling the motor speed.
Soft Start:
When the circuit is powered ON, the IC2 gradually increases the gate voltage of the MOSFET due to the charging of the C4.
This ensures that motor starts smoothly without jerks.
Overvoltage Protection:
The 2.7V zener diode (D1) ensure the PWM output voltage doesnt exceed safe levels for the transistor T1.
Relevant Calculations
Frequency of PWM Signal (IC1):
f = 1.44 / [(R1 + 2R2) * C1]For the given values:
R1 = 180kΩ
R2 = 100kΩ
C1 = 100nF
Substituting:
f = 1.44 / [(180k + 2 * 100k) * 0.1µF]
f ≈ 34.3 Hz
Soft Start Time (IC2):
t = 1.1 * R6 * C4For the given values:
R6 = 10kΩ
C4 = 10nF
Substituting:
t = 1.1 * 10k * 10n
t = 0.11 msIf a larger value for the C4 is chosen (e.g 1µF):
t = 1.1 * 10k * 1µF
t = 11 msAssembly Tips
Use a Heat Sink for the IRF540:
The MOSFET can heat up under heavy motor loads so Attach an appropriate heat sink.
PCB Design:
Keep the ground connections of the IC1, IC2 and the motor driver separate to avoid noise.
Testing:
Test the PWM output with the multimeter or oscilloscope before connecting the motor.
Safety Precautions:
Ensure proper insulation for all tthe high-current connections to prevent short circuit.
Using A Dimmer Phase Chopper Circuit
As rightly suggested by one of the dedicated readers of this blog, Mr. Ivan, a 180 V treadmill motor can be simply controlled through mains phase chopping concept, normally incorporated in all commercial dimmer switches for regulating home fan speed.
Shown below is a modified dimmer switch circuit design which can be effectively used for regulating a 180 V treadmill motor from zero to max:
Please make sure to use a non-polar capacitor for the one shown between the bridge rectifier.
Use the following type, 10 in parallel
10nos of 0.47/400V in parallel will make 47uF/400V non polar capacitor which may work like a decent filter capacitor for the motor.