Improving a Holmes HAWF2043 window fan

Recently I got a window-mount fan with two separate fans and several operating modes. The device has a built in temperature sensor and supposedly is able to switch the fan based on the termperature in the room. It has one button that cycles through all 13 modes: off, fan on high, fan on low, fan on high with thermostat set to 60, 65, 70, 75, or 80 °F, and fan on low with thermostat set to 60, 65, 70, 75, or 80 °F. I didn't test the thermostat modes, but I do not think they would have worked well because temperature sensor was located in the case and would have read a different temperature than if it had been further into the room. Additionally, the fan would be unable to tell whether switching on the fan would have increased or decreased the temperature and might have made the room warmer even if it wanted to cool the room. However, I liked the ability to adjust the speed (and thus the noise) of the fans.

To make the fan easier to use, I first bypassed and removed the control circuit in the fan. When plugged in, the fan would now run at full speed. The fan was then plugged into an inline light dimmer so that the speed could be adjusted continuously, from off to full speed. Later, the dimmer was modified to allow the fan to run more quietly at full speed.

Operation of the fan control circuit

The fan circuit board and wiring have been reverse engineered. The schematic is shown below:

gEDA schematic file

The red box on the right contains the fan motors and the TRIAC that is used to control the speed of the fans. Each motor is represented by two coils in a green box. Depending on the setting of the direction switch, the mains voltage is applied either to the right or left coil. The other coil gets its power through a capacitor, which creates a phase shift (delay). Since the two coils are mounted at right angles in the motor, this creates a rotating magnetic field, which causes the fan to spin.

When a pulse is applied to the gate of the TRIAC, it conducts between its two main terminals until the current reaches zero. By adjusting the time between the zero-crossing of the input voltage and the trigger pulse to the TRIAC, the effective power of the fan can be controlled.

Operation of the dimmer circuit

A dimmer was purchased to replace the internal speed control and microcontroller. This dimmer allowed the fan to be switched off completely and allowed the speed of the fan to be continuously varied. The schematic of the dimmer is shown below:

gEDA schematic file | Simulation of circuit

Like in the fan control circuit, the dimmer also contains a TRIAC. C2, C3, R3, R4, and R5 form a delay network that delays the mains voltage by an amount controlled by the setting of R4 (the slider on the dimmer). Once the voltage on C3 reaches about 30 volts, the DIAC begins to conduct and the TRIAC switches on. The variable phase shift allows the amount of the sine wave passed to the load to be varied, which in this case controls the fan speed. Additionally, R1 and C1 form a snubber network that is able to absorb pulses of current when the TRIAC switches off.

Description of the modification

The control circuit was removed from the fan and the wires previously connected to the main terminals of the TRIAC were instead soldered together. The fan could now either be plugged straight into the wall or into a dimmer to allow the speed to be adjusted. I also noticed that when the dimmer was set to "full speed", the output of the dimmer was not a perfect sine wave, as a small amount of the sine wave was still chopped by the TRIAC. The edge that comes from the sudden turn-on of the TRIAC would cause the fan motors to emit noise while it was running. By replacing R3 in the dimmer with a short, I was able to reduce the noise when the fan was running at full speed. This is because the capacitor C3 could charge faster and the TRIAC would fire earlier, making the output waveform closer to a pure sine wave. However, the noise is still audible, especially when the fan is running at low speeds. (Upon testing the original circuit, I found it was not much quieter). The final schematic is shown below:

gEDA schematic file

Comments

Post a Comment

Popular posts from this blog

Improving and calibrating the capacitive water sensor

Image
In a previous article, I explained a type of water level sensor that works capactitively and therefore passes no direct current through the water. When I wrote that article, I had already made two of these sensors and installed one in each of the two sump pump wells in my basement. These sensors have been working quite well for a long time, but they have a few issues. In this article, I will describe the improvements I have made to the sensor design and how I calibrated the sensors to allow me to determine the water flow rate and the volume of water the sump pump pumps each time it comes on. Introduction The two water level sensors I installed in the sump pump wells were equipped with nRF24L01 wireless modules. They transmitted measurements every 30 seconds to a Raspberry Pi, which recorded them to a database. This allowed me to visualize the water level in the sump-pumps in real time and see roughly how often the sump pumps came on. However, the water level followed this interest
Read more

Turn a buck converter module into a buck-boost converter with only two components

Image
In this article I will show how you can turn a buck converter module (like the one shown below), which can only output a voltage lower than the input voltage, into a buck-boost converter module, which can output a voltage that is either lower or higher than the input voltage. Buck converter theory The schematic of a buck converter is shown below: Link to simulation The components in the box, in addition to the feedback loop (not shown), are usually integrated into a single chip. A regular buck-converter works by switching current into the output capacitor through an inductor. When the transistor in the box is on, current can flow from the supply to the output via the inductor. The voltage across the inductor is \(V_{in}-V_{out}\) and the rate of change of the current is \(\frac{V_{in}-V_{out}}{L}\). When the transistor in the box switches off, the current in the inductor continues to flow, but now through the diode. The voltage across the inductor is \(V_{out}\) and the rate of
Read more

Self-starting inverter

Image
In this article, I will explain a circuit that can be used to automatically start an inverter when a load is connected to it and turn it off once the load is disconnected. This circuit works by biasing the output of the inverter with a low-current signal from the battery and waiting for a change in that signal. The circuit then uses a current transformer to monitor the current through the load. If there is no current in the load for a few seconds, the inverter is switched off. The inverter The inverter I am using is a modified square wave inverter. The voltage between the live and neutral terminals at the output looks like this: However, this diagram misses out on an important fact: the neutral of the output is not connected to the negative battery terminal. In fact, the modified square wave is generated by alternately switching the live and neutral terminals of the output to an internal high-voltage rail. As a result, both live and neutral are always positive relative to the nega
Read more