Controlling brushless DC motors

[Catch66]

Hello I have started on my Air system controller for Solar

Air panel. I need advice as to Controlling speed of

12V DC Fan the type used on electric cooling of radiators.

Rheostats first came to mind. the ones on the older pickups defroster

but most of these motors ran brushes,I believe.

Any advice appreciated.

Thanks,

Chuck

[sPuDd]

Chuck,

   brushless DC motors are much like a brushed motor to drive.

Look up "Controller for Brushless DC Motor" at your local electronics kit store.

They should have a kit or pre-built unit that will do the job.

sPuDd..

[Basil]

I have a 38 volt dc ceiling fan that I conrol with a hair dryer coil. Hook one wire to one end and find the sweet spot on the coil for the amp pull or speed you want. Cheap works great but not much to look at.

[Opera House]

You didn't specify the size of the motor.  Multiple 12V computer fans can be controlled in the range of 8-12V.  You don't want to drop the voltage below 7V ever, rather turn off under 7V.  A temperature sensor made from several diodes in series would work with a LM431 amplified zener as in the ghurd (sp) regulator.  I'd vote for a simple on/off relay control.

[vtpeaknik]

What's wrong with running them at less than 7V?  I've ran 24VDC fans on as little as 6V.  (But not for very long as yet.)  I've also ran AC fans (little square ones, like they used in computers in the olden days) on a small fraction of the nominal voltage, to get a bit of air with no noise.  I've done that for YEARS on some fans and none seem to have been damaged.  Sometimes I used a transformer to lower the (AC) voltage, sometimes a capacitor in series (around 1 uF, depending on fan size, must be a high-voltage non-electrolytic type).  For DC fans: a 24VDC model directly on a 12VDC system, a 12VDC fan on a small PV panel designed for charging a 6V battery, or a 12V fan off a 12V battery via a resistor (around 30-100 ohms).

[Opera House]

The operational word is brushless.  The chips in these just stop working below a certain voltage.  About 6V many stop working.

A word of caution about putting cap in series with an AC motor, it just might burn up.  That combination forms a LC circuit.  At the right combination of capacitance and motor inductance, voltage on the motor will increase greatly.  I have a stock of nice 220V muffin fan motors.  At 2 or 3UF in series, the motor runs quietly with 180V from a 120V line.

[Opera House]

I just checked a couple recent manufacture 12V computer fan motors for start voltage. As you would expect, the smaller motors started at lower voltages. Lowest I saw was 3V, larger diameter 3 1/2 inch fans started between 4.2-4.8 volts.  Couldn't locate some of the older technology fans that I remember took more voltage.  In any motor there will be a voltage where it stops or effectively doesn't move air.  A controller should turn off at this point not to waste current.   With a switching regulator like a TL494, you can set a turn on point and a speed ramp up with temperature.

[Catch66]

Thanks,Opera House.

I'm using a J thermocouple sensing signal into a Watlow 988B controller with dc output,using 3 -32 volt dc SSr as relay.

I'm Wanting to regulate 12dc motors for fine tuning. of CFM final flow.

Thanks Again for information

Chuck