Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!asuvax!ncar!gatech!prism!gt0869a From: gt0869a@prism.gatech.EDU (WATERS,CLYDE GORDON) Newsgroups: sci.electronics Subject: Re: Fan for my amp revisited Message-ID: <26613@hydra.gatech.EDU> Date: 18 Apr 91 13:26:44 GMT References: <1991Apr17.022927.7094@msb.com> Organization: Georgia Institute of Technology Lines: 26 In article <1991Apr17.022927.7094@msb.com> ritz@msb.com (Chris Mauritz) writes: >Someone was kind enough to send me a message saying that controlling >the speed of an AC fan was not as simple as adding a pot. OK, >how about I use a DC fan and siphon off power from the power supply This should work, but I see 2 potential problems: 1. The voltages in the supply are really high(generally 60v or so) for motors. You would have to build a voltage divider, usually to below 35v, and then use suitable regulators to get down to 12v or so, for most motors. There are regulators around which should easily handle enough current- I can't see this carrying more than 500ma.(try 7812 or 7912- positive or negative 12v) 2. A motor hooked up this way has the potential to backfeed brush noise to the supply and the amp. Use fairly large filter caps in the motor circuit bypassed with small caps (big: typically 3000u, small; typically 1u or so.)One of each is a good starting point.Although this should take care of noise, further methods may have to be employed in some cases (see filtering in many EE text or handbooks) Hope this helps. Gordon. -- WATERS,CLYDE GORDON-Georgia Institute of Technology Atlanta Ga 30332 ************* uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt0869a Internet: gt0869a@prism.gatech.edu