Gazoo Posted February 10, 2015 Share Posted February 10, 2015 I have a 12v DC fan that is speed (voltage) controlled by an outside sensor. When it's being fed the full 12v, it sounds as if a Turboprop B52 Bomber is getting ready to take off. I'd like to limit the voltage going to the fan to 9v so as to limit the noise (it seldom stays at full speed longer than about 15 seconds or so, so 9v should be adequate to cool things down). So the question is, will a 9v dropout regulator work for this? I assume that the regulator will limit the voltage going to the fan to 9v and pass through any voltage less than that to the fan so it can run at a slower speed. Is my assumption correct or do I need to take a different approach? Some sort of Zener diode circuit? Thanks, Gazoo Quote Link to comment Share on other sites More sharing options...
Omega-TI Posted February 10, 2015 Share Posted February 10, 2015 Below is a circuit that might do the trick for you I'd avoid the resistor method as you generate a lot of excess heat, which is why you have the fan in the first place. Quote Link to comment Share on other sites More sharing options...
+Schmitzi Posted February 10, 2015 Share Posted February 10, 2015 Hi, I use these adapters for years, from Sharkoon and from Revoltec. have them from 12V to 9.5V, to 7V and to 5V Volts. Use them in hundreds machines for years. Maybe that fits. http://www.ebay.de/itm/SHARKOON-LUFTERKABEL-ADAPTER-12V-9-5V-Reduzierung-/361206914077?pt=DE_Computing_Geh%C3%A4usel%C3%BCfter&hash=item54199c1c1d 1 Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted February 10, 2015 Share Posted February 10, 2015 What about just simple voltage divider? Quote Link to comment Share on other sites More sharing options...
Gazoo Posted February 10, 2015 Author Share Posted February 10, 2015 Hmm... maybe this needs further explanation as the answers so far don't answer the question. In order for the fan to start, it needs the minimum voltage required to keep it running, so a resistor might not allow that. And straight voltage regulation wouldn't work, which is why I am looking at a dropout regulator. What I'm looking for is if the voltage in is less than 9v, that the voltage out in the circuit equals the voltage in. If however, the voltage in is greater than 9v, the voltage out be limited to 9v. Is that clearer? I'm thinking that's what a 9v dropout regulator does, but I'm not certain. Gazoo Quote Link to comment Share on other sites More sharing options...
Tursi Posted February 10, 2015 Share Posted February 10, 2015 While I don't know the best answer to your question, all the 12v fans I have tried will start fine with 9v - I used to power them with 9v batteries for use in mascot heads. Quote Link to comment Share on other sites More sharing options...
Gazoo Posted February 10, 2015 Author Share Posted February 10, 2015 While I don't know the best answer to your question, all the 12v fans I have tried will start fine with 9v - I used to power them with 9v batteries for use in mascot heads. Yes. most of them will actually start with as low as 4 or 5 volts. Gazoo Quote Link to comment Share on other sites More sharing options...
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