Where and how is it a good idea to power a 12v fan? - Page 1
Forum section: electronics / beginners

author: EvilHRcat
author_rank: Newbie
timestamp: December 16, 2014, 05:03:31 am
content: Hi,I have a 2009 vintage Onkyo TX-SR508 receiver that I just got done repairing with some new SMD capacitors. They blew because this thing gets HOT! I want to add a fan to the innards and wire it in so that it runs when the power is on. I have a full schematic and I have thought of 2 ways to do it:1. The HDMI switch board (which is what needed to be repaired) seems to run on 12VDC and has a total of 5 power wires coming into it: 2x 12v+ and 3x groundI could wire the fan onto one set of these. (See page25 attached)2. The main transformer has power supplied to it through a relay.I could re-purpose the innards of a 12v wall wart to power the fan. (See page24 attached)My questions are these:Are either of these a good idea?Which one is the better idea (Assuming I already have the innards of a 12v adaptor sitting around)?Would there be any drawbacks to either one?Is there a better idea that I just have not thought of? (I can scan in more manual pages if anyone wants to see them)Some additional information:I already have the fan I want to use. According to the manufacturer, it has the following specs:Voltage 12 VMax. Input Power 0.48 WMax. Input Current 0.04 A(and moves almost 80 m3/H of air)Thanks in advance!--CatbertPS I realize that I could just plug the 12V adaptor into the switched 120V outlet on the back, but that would just be UGLY and I don't want my stereo to be ugly...

author: Falcon69
author_rank: Super Contributor
timestamp: December 16, 2014, 05:12:53 am
content: I'm just learning this stuff, but, wouldn't powering the fan from that HDMI switch board possibly introduce 'noise' into the system?I would probably power it from an isolated source, like you mention in your #2 proposition.

author: Skimask
author_rank: Super Contributor
timestamp: December 16, 2014, 05:16:05 am
content: Just tap the 12v off the 12v rail40mA ain't nothing.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 16, 2014, 06:01:14 am
content: I'm with you that simply plugging the wall-wart into the outlet on the back would be an ugly kludge.But we don't really know anything useful about the 12V supply, either. I would be reluctant to power the fan from that source without better understanding.OTOH, you could just try it and see if the performance of the unit is showing any symptoms of power degradation.My preference would be to put the guts of the wall wart onto a little board which is appropriately securely mounted inside the case. Remember that there is power mains voltage coming in, so it isn't a good idea to be casual about this and just let it flop around.

author: SeanB
author_rank: Super Contributor
timestamp: December 16, 2014, 06:12:25 am
content: Connect the fan directly across C8950, where the noise it introduces will be filtered out from the other rails. As well change it to 470uF 25V low ESR, which will reduce the noise further.

author: ConKbot
author_rank: Super Contributor
timestamp: December 16, 2014, 12:37:13 pm
content: Quote from: Falcon69 on December 16, 2014, 05:12:53 amIf it were powering a linear output stage, then possibly. But this is just powering a bunch of switching regulators to feed digital stuff. So it shouldn't be problematic as long as the load isnt too much.

author: macboy
author_rank: Super Contributor
timestamp: December 16, 2014, 02:39:16 pm
content: Personally I would grab a 7812 (or 78L12) regulator, and connect its input to the rail that supplies the regulators (likely 12 or 15 V) for the op-amps and other linear audio circuits. Using a dedicated regulator should mean less noise fed back into the audio circuits, and no additional load (heat) in their own regulators. You could also get fancy and use a LM317 instead, so that you can vary the voltage/speed of the fan.

author: Kjelt
author_rank: Super Contributor
timestamp: December 16, 2014, 02:39:44 pm
content: There is no need to open up and modify your device. I have an Onkyo 5507 and yes it runs hot on the hdmi board as well.Just put a Papst 12V on top of the casing where the hot airvents are and put it on 9V (so it was not that superloud). Has been working over the last 3,5 years for me.If children are in the household, put an roster on the fan for finger safetyYou can power the fan from a wallwart and put a relais or fet in series that is switched by the 12V trigger output or buy a 12V trigger operated mainsswitch for the wallwart.PS: once a year do a dust clean up, the fan will attract more dust ofcourse and you need to clean it .

author: EvilHRcat
author_rank: Newbie
timestamp: December 17, 2014, 07:55:14 pm
content: Thank you all for your suggestions! I was going to sit down and do it last night, only to find that my cheap-o adjustable soldering iron didn't want to get hot. An angry phone call and 2 hours this morning resulted in a new Weller iron being shipped, but it won't be here for a weekIn the mean time:Quote from: SeanB on December 16, 2014, 06:12:25 amSeanB, how did you determine that value for the replacement cap? I read a nice steady 12V across it, so that looks like the most likely route to take, for simplicity sake, as well as for the additional filtering if offers.Quote from: Kjelt on December 16, 2014, 02:39:44 pmKjelt, I already had to open it once, doing so again is no big deal. This model (the 508) and several others from this time (the 606 and 804 model just to name a few) have a known problem with overheating the HDMI switch board and blowing caps (mine actually leaked some electrolyte). Your 5507 has a very different internal layout that is much more open. Im trying to bullet-proof this thing as best I can so that it doesn't happen again. Also, I live in the desert, where dust contamination is a way of life. ALL of my equipment gets opened up 3 times a year and cleaned out.When my new iron gets here, I'll be sure to upload some pictures of the completed repair. Thank you everyone!!--Catbert

author: SeanB
author_rank: Super Contributor
timestamp: December 17, 2014, 08:29:30 pm
content: 470uF is the next value up commonly available, and 25V is well above the 12V rail. Thus it will likely fit in place of the old one, and if it is older it will be close to replace anyway. Low ESR cap there will do the best to reduce any extra noise from the fan. While you are there check the rest of the caps as well and replace as needed.

author: Kjelt
author_rank: Super Contributor
timestamp: December 18, 2014, 03:55:26 am
content: Quoteare you sure you are not in the need of installing a water cooling modification?

author: EvilHRcat
author_rank: Newbie
timestamp: December 18, 2014, 04:49:04 pm
content: Quote from: Kjelt on December 18, 2014, 03:55:26 amOMG! If I could do this without my wife stuffing the receiver up my nostril, you'd better believe that would be the first option on the table!