My application needs a controlled heater fan situation, which means it should move a reasonable volume of air. I also need to control both speed and direction of fan. Can anyone point me to information resource that preferably uses back emf for speed/direction sensing. Pref using 8051. Of course, have searched before asking. Thanks, Alistair.
Alistair George scrobe on the papyrus:
Brushless DC fans are generally not reversible. Internally they consist of a three phase motor and a small driver circuit, usually comprising three transistors forming an astable ring oscillator. Break one open and have a look.
There's a good treatise on brushless fan speed control here:
I built one recently using a MAX522 (DAC with an SPI interface), a TL082 as a level translator and a TIP122. I'll let you have a schematic it helps.
-- John B
Thanks John.
Since you have already been down that track, can you recommend any company that supplies reliable, low cost dc motors suitable for the job, pref china or similar low cost area.? Alistair.
Alistair George scrobe on the papyrus:
. .
Hi Alistair,
Yes reversible but you need to get access to the motor windings. That's not generally possible in a COTS fan with a brushless DC motor, unless you can find one with a removable impellor. The driver is generally built into the fan hub and only has three wires, +, - and tacho output.
In my application the fan I used didn't need to be reversed as it was in a small wind tunnel for testing RF mixer modules in a controlled airflow. I just needed to provide a DC supply which was controllable from 8V to 24V and used a standard brushless DC fan. Air velocity was measured with a hot-wire transmitter and temperature with some NTC thermistors. It all worked really well.
Sorry I'm not an 8051 man as I have used AVR's for many years now and can't comment on the ADC. I would recommend that you look at the PWM features of the ATmega32 for speed control and its 10-bit ADC is good too.
-- John B
Hi Alistair,
you really want to have a look at the Infineon devices, this could be the C868, C504 or similar. They also have very good application Notes
They have all dynamic links (almost impossible to link to anything). Hope it works:
If not
An Schwob
Hi, I started off with the idea of using a DC brushless motor, but found that they are too expensive (at least I have not found any motors low cost/Chinese suitable for household fan). An Schwob, the infineon solution looks really good, and appreciate your pointer. I will follow that up more. But I still have a problem with sourcing a cheap typical household heater fan, that can reverse as well as alter speed. So I guess it must be 3-phase motor, low power are common and cheap, so it seems that I need to get the info relating to motor type, and driver informations. From there I can work out logic methods needed for the application. All tips appreciated. Alistair.
...
I suggest you also do a search on the mechanical aspects of fans/pumps and propellers, as to get a reversible fan requires special shaping of the blades, some will hardly work at all in reverse direction. The blades are shaped for air/fluid flow in one direction only. The efficiency in some cases is very small in reverse direction.
You may end up with a different shape to what you were expecting.
--
Paul Carpenter | paul@pcserviceselectronics.co.uk
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A pair of fans pointing in opposite directions would be a lot simpler. Just power one at a time to get the direction that you want. Peter
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