View Full Version : Brain blockage 36V to 24V

05-22-2008, 01:51 AM
i have a problem, i need to hook up some pc cooling fans.
One is 24V the other one is 12V both have 0.16amp.
I only have a 36 V power supply.

Has somebody a idea how to hook it up.
Maybe in series ?
Or should i use leds to ramp down the volt?

May be a litle off topic but how knows...

Best regards

05-22-2008, 02:11 AM
This should really be in the Sandbox, I think. It isn't relevant to the Propeller.


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Mike Green
05-22-2008, 02:36 AM
Ideally, if the fans actually draw the same current (0.16A), you could hook them up in series. In practice, this may not be true and, if one fan draws substantially more current, even temporarily, the other fan could be damaged. The answer would be to add a current limiter. You could simply add a fuse, maybe rated at 0.25A, but this might leave you with no airflow at all when you could have limited airflow under other fault conditions. Another answer might be to use a 3-terminal regulator (like an LM317) as a current limiter. The datasheets for this show its use as a current limiter using a single resistor to set the current limit. You'd lose a little of the supplied voltage, but with a 36V supply, you could lose a few volts without noticing.

T Chap
05-22-2008, 02:45 AM
Assuming this is posted under the Propeller section meaning you are familiar with the Prop, I wonder about using PWM to a PNP mosfet switching the high side which would then have a large cap on its output. Experiment with a voltage meter and the duty/frequency to get the desired voltage, use one mosfet for each voltage required. Sort of like a larger output DAC.

05-22-2008, 03:00 AM
Thank u , i have just tried it with the series link,
and it works.both run nice and smoth, and yes i am familer with prop and PWM to PNP or NPN.

Its just a quick fix, to get my CNC machine running today and not overheating.

I will go and get later some temp controled Fans system from a pc and a power converter to 12V

And sorry for the offtopic question.

Best regards