PhilHornby
Senior Member
I'm embarking on Phase 2 of my project to enhance the temperature control of a Dimplex Oakhurst heater. Phase 1, published HERE makes uses of the heater's Infra Red Remote Control functionality, and is a vast improvement on the in-built mechanical thermostat.
However, the Fan - when it is on - always runs at full speed and I was hoping I could improve on this. It is the fact that the fan turns on and off, that is as much a source of annoyance, as the fact that it always runs at max. speed. I am aiming for a constant, but much lower, background noise level.
The scheme I have in mind, is based on PWM modulating the heating elements to match the room's heat loss and 'somehow' controlling the speed of the fan to match. I don't know if this speed control would involve a simple matching of the average power applied to the heating elements, or if it would be necessary to monitor the output air temperature. As I delved into the workings of the Fan Heater section, I realised I've got other issues to resolve first...
It turns out that I know a lot less about the functioning of AC motors, than I thought I did
Here are some photos of the Fan and its motor :-
https://www.dropbox.com/s/sfmeims8bd4gkjg/20170719_211335.jpg
https://www.dropbox.com/s/r2q3bx2xp2e2s6u/20170719_211346.jpg
(The forum appears to be out of disk space again, so I can't upload them directly )
If anyone has any observations on said motor, I'll be glad to hear them.
My various googlings, lead me to believe that since I don't have a big, inertial load, the only workable scheme will be to vary the frequency of the AC voltage applied to the motor. If so, I envisage synthesising a suitable 'analogue' signal with a Picaxe and using that to modulate the voltage applied to the motor - derived (presumably) from the rectified mains input.
If that is correct, it gives rise to the following question: How close to a Sine wave, does the motor control voltage have to be?
I'm pondering the difference between using a Square wave, a Triangular wave, an RC-derived sawtooth, or the signals documented here: http://www.me.ua.edu/me360/spring05/Notes/Topic17-AC_Motor_Speed_and_Other_Motors_sv.pdf (synthetic sine wave or Pulse Density Modulation...).
A supplemental question: Why does this motor always turn in the same direction? Obviously this is a very important feature of a Fan heater motor, but how is it achieved? Is it an inherent feature of the motor design, or are the existing heater control electronics involved?
However, the Fan - when it is on - always runs at full speed and I was hoping I could improve on this. It is the fact that the fan turns on and off, that is as much a source of annoyance, as the fact that it always runs at max. speed. I am aiming for a constant, but much lower, background noise level.
The scheme I have in mind, is based on PWM modulating the heating elements to match the room's heat loss and 'somehow' controlling the speed of the fan to match. I don't know if this speed control would involve a simple matching of the average power applied to the heating elements, or if it would be necessary to monitor the output air temperature. As I delved into the workings of the Fan Heater section, I realised I've got other issues to resolve first...
It turns out that I know a lot less about the functioning of AC motors, than I thought I did
Here are some photos of the Fan and its motor :-
https://www.dropbox.com/s/sfmeims8bd4gkjg/20170719_211335.jpg
https://www.dropbox.com/s/r2q3bx2xp2e2s6u/20170719_211346.jpg
(The forum appears to be out of disk space again, so I can't upload them directly )
If anyone has any observations on said motor, I'll be glad to hear them.
My various googlings, lead me to believe that since I don't have a big, inertial load, the only workable scheme will be to vary the frequency of the AC voltage applied to the motor. If so, I envisage synthesising a suitable 'analogue' signal with a Picaxe and using that to modulate the voltage applied to the motor - derived (presumably) from the rectified mains input.
If that is correct, it gives rise to the following question: How close to a Sine wave, does the motor control voltage have to be?
I'm pondering the difference between using a Square wave, a Triangular wave, an RC-derived sawtooth, or the signals documented here: http://www.me.ua.edu/me360/spring05/Notes/Topic17-AC_Motor_Speed_and_Other_Motors_sv.pdf (synthetic sine wave or Pulse Density Modulation...).
A supplemental question: Why does this motor always turn in the same direction? Obviously this is a very important feature of a Fan heater motor, but how is it achieved? Is it an inherent feature of the motor design, or are the existing heater control electronics involved?
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