How to adjust power to a 12 v Dc car fan (Start v = 6.0 v, Input power = 0.36, input current = 0.03 amp) without using rheost

puu · Apr 7, 2015

How to adjust power to a 12 v Dc fan (Start v = 6.0 v, Input power = 0.36, input current = 0.03 amp) without using rheostat. This fan runs on an axillary battery in a car. Rheostat gives heat away by using full power!

Any small budget unit that can be attached to the fan with a knob out there?

Thanks
puu

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after your answers:

Big Mahalo to all of you for the speedy reply and suggestions
Aloha
puu

getochkn · Apr 7, 2015

Dropping voltage will produce heat. The electricity has to be converted to something and that's heat.

Eximo · Apr 7, 2015

Well you could use several types of circuits for this. They will all consume power, though no where near as much as a Rheostat or potentiometer.

I guess I would want to know the purpose of the fan to make a recommendation.

nukemaster · Apr 7, 2015

A switching based regulator will be best because it wastes much less heat(so little it will not even need a heatsink).

The problem is they are a bit more tricky to build(compared to a rheostat of even LM317 based regulator.).

Both have one bit down side, You will never get the full 12 volts without some kind of bypass because these regulators require some kind of minimum overhead(1-2 volts on many).

A switching PC fan controller may also work. A fully loaded battery is about 13.6 volts so keep this in mind.

Eximo · Apr 7, 2015

Yeah, a simple switching regulator circuit was what I was going to recommend. Was just looking at some transistors and diodes that would be inexpensive. I wouldn't be surprised if someone has a complete package already built that could be purchased.

Though if this is just a cooling fan to keep a car interior cool or something then I would just say a solar powered fan.

If noise is the issue, just get a quieter and/or lower power fan that runs at 12V.

Eximo · Apr 7, 2015

People are amazing:

http://www.amazon.com/SMAKN%C2%AE-Converter-Power-Supply-Module/dp/B00NICVEE8/ref=sr_1_1?ie=UTF8&qid=1428443051&sr=8-1&keywords=12V+to+6V+DC+to+DC+converter

ko888 · Apr 7, 2015

PWM controller for $5.98 US.

http://www.ebay.com/itm/DC-15A-12V-24V-36V-48V-72V-90V-Max-1000W-Motor-Speed-Control-PWM-Controller/231450981145?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20131003132420%26meid%3D1dc95f16463845fd97d758f54ed13fac%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D221021510531&rt=nc

The fan motor will retain its full torque since the voltage is not being changed.

leeb2013 · Apr 7, 2015

my vote for PWM too, almost no power lost. To make it yourself, look up 555 astable and FET switch.

puu · Apr 7, 2015

getochkn :

Thank you for your answer!

puu

puu · Apr 7, 2015

Thanks so much for your input!
puu

nukemaster :

puu · Apr 7, 2015

Thank you for your answer, it is a NB-Multiframe, used to distribute low noise air flow. Power comes from 12 v car battery fully charged + 13.4 volts and I do not want to destroy the fan with that voltage. Also nice to have the airflow controlled.

Eximo :

puu · Apr 7, 2015

Thank you for yuour answer, I do not see any knob to adjust the voltage on the fly, can only make a one time setup .

puu

Eximo :

puu · Apr 7, 2015

Thank you for the link, this looks good to me, hope I can make a mark on installation board that it never goes over 11.5 volts.

puu

ko888 :

puu · Apr 7, 2015

Thank you for your answer

puu

leeb2013 :

giantbucket · Apr 7, 2015

puu :

am I reading those numbers right? a 12V fan that only need 0.03A (30mA)? that's so little power that I wouldn't bother with anything more than an inline variable resistor. sure, in theory a switching power supply can do some nice stuff, but for that little power it's totally not worth the time and effort and cost.

nukemaster · Apr 7, 2015

about 50 ohms will cut an average fan down to about 7 volts(this changes depending on the fan in use. This is like the low noise adapter Zalman and Noctua send out with some fans). No speed control, but would slow it down for sure.

giantbucket · Apr 7, 2015

for this fan, a 150-ohm or larger would be needed since it's a low current (30mA). and it would waste a whopping 0.135 to 0.150 watts. like, a bit more than 1/8th of a watt. chump change.

nukemaster · Apr 7, 2015

Yeah, I started doing the math after and noticed that. I thought my math(ohms law and the formula for a resistor divider) must have been wrong.

giantbucket · Apr 7, 2015

could probably also use a 5V Zener instead of resistor - it'll drop a (relatively) constant voltage at any current

How to adjust power to a 12 v Dc car fan (Start v = 6.0 v, Input power = 0.36, input current = 0.03 amp) without using rheost

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