# So I want to put a fan on my modem...



## Nordic (Dec 18, 2013)

... not because I need it, but because I want it.

The modem is a Motorola sb6121. I want to mount in externally, and it has an exact hole the size of an 80mm fan. What I need to know though is how to power the fan. I have read people have soldered the fan directly to the pcb, but I am not educated enough to know where this is. I also read others also used a more powerful psu cable.



Spoiler: Pictures




















Just so no one mentions it, the modem is mine, not the cable companies.


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## BazookaJoe (Dec 18, 2013)

Well one far safer & simpler way to do this is to simply use an external variable power supply to power the fan that you can gently glue with hot glue to one side of the device - I see it has sort of a ventilated mesh on each side.

The main reason I would go this way first is because it is a lot easier - its a lot less risky, and should you ever want to sell the device you haven't altered its guts in any way and you can just pop the fan off again as hot glue holds well but can also be removed rather easily.

Beyond this a variable power supply is a lot easier to control - you really don't want the fan on full power all the time, too much airflow can be as bad as not enough - as over time it can pull dust and mess into the modem blocking it up and depending on your environment even land up filling that dust and gunk with humidity that can corrode the guts of the modem.

Anything like one of these AC/DC power supplies is fine - any size - even an old cellphone charger (usually 5v) will do just fine.






With a variable adapter you can drop the voltage as low as possible ( Many 12v 8cm fans can run on as little as 3v although a few may battle to start on less than 5v )- this will keep the fan QUIET and make sure its only just creating a gentle breeze through the device to help it cool rather than using its guts like a vacuum cleaner bag and packing the modem full of junk.

OR if you have an unused cellphone charger even better - almost all of these put out around 5v now which is usually more than enough to run a standard PC fan nice and slow and quiet.

Its not quite as convenient as running it all off one power supply but its all pretty much just going to sit in a corner somewhere anyway 

However if you 100% want a self contained solution get me some better pictures of this : 





The ratings on the power brick, and the back panel where the power plugs into the modem and i can help you from there.

We can even do a DIY variable fan speed control if you like.


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## pr0n Inspector (Dec 18, 2013)

looks like that modem runs on 12v. you have to find a really slow fan or figure out a way to drop/control the voltage.

Personally I don't think modems and routers in general need active cooling. Put them closer to ground for cooler air if you want.


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## SaiZo (Dec 18, 2013)

pr0n Inspector said:


> looks like that modem runs on 12v. you have to find a really slow fan or figure out a way to drop/control the voltage.
> 
> Personally I don't think modems and routers in general need active cooling. Put them closer to ground for cooler air if you want.



Uhm, why does it need a "really slow fan"? Most fans either run 5v or 12v. Were you thinking of using a more silent fan, as the 5v types makes less noise? Or a discrete one inside the modem??
But otherwise, both my Motorola modem aswell as the Netgear modem used to run hot - but they did not take any damage from the heat.
Ofcourse the lifespan would be greater with active cooling, since heat is not a good friend directly.

Just a thought, why not also use a heatsink and adhesive thermal pad (or glue if there is any)?
Want to be able to turn the fan on/off? Get a small switch and solder it to the fan. And as BazookaJoe said - external power supply. That's a good option, I run my chassie fans on their own power source.


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## v12dock (Dec 18, 2013)

Hot glue to the power input of the device, I have done this several times


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## rtwjunkie (Dec 18, 2013)

Don't most modems have vents on the bottom?  The solution I used was to take small rubber feet, like on a tower (even smaller diameter rubber washers will do), and glue to each of the four corners underneath.  This raises it up, and with a ceiling fan that I have, enough air is circulated in the room that there is air movement underneath the router.  I don't have exact temps, but the hand touch from before and consistently afterwards differs from almost hot to the touch on top to just alittle warm.


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## de.das.dude (Dec 18, 2013)

get 50mm fans that are specifically made for this. ball bearing low sound ones will work great!


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## xvi (Dec 18, 2013)

Was going to say that the power supplies for most modems are somewhere around the normal voltage for a fan. I wouldn't trust my word alone (read: wait for a second opinion), but I believe most DC 12v fans technically can operate up to ~24 volts without completely blowing up. I wouldn't trust one myself more than 15v without extensive testing, but it's an option if you find it's actually a 20v supply or something.


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## Nordic (Dec 18, 2013)

pr0n Inspector said:


> Personally I don't think modems and routers in general need active cooling. Put them closer to ground for cooler air if you want.


I want to put a fan on my modem not because I need it, but because I want it. I am not doing this because the modem runs warm, which does not bother me. I am doing for fun. I have this uber slow running 80mm fan that is useless to me for almost every application, but would work just fine for cooling a modem. I saw that someone put a fan on their modem once and I wanted to do that for fun. I do plan on putting a heatsink in there also, not because it needs it but for fun.

At bazooka, I don't want to have two powercables coming from the modem. I also am uninterested in on off capabilities. I will get a better picture of that power supply area today.


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## JunkBear (Dec 18, 2013)

Make it simple. Look at the output power rate on the power supply of the modem.  So take double the resistance and you will basically get 6volts.  Here's the formula for that: 12V / Input Amps = Resistance in Ohms. Double that ohms and you get a resistance at electronic store rated 12V and that resistance. Solder a wire on the Positive of the power connector then the resistance  with a wire going to a 12V fan then the negative side of the fan wired to the negative of the power plug on the modem inside. You will get a 12V fan turning at lower rpm because of the 6V.


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## Nordic (Dec 18, 2013)

This fan is so slow I wouldn't want it going any slower.


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## JunkBear (Dec 18, 2013)

You need a power supply fan from a cheap power supply. To see the speed of the fan at full just plug it on car battery or car battery charger at 12v .. if its fast and Noisy thats the one you use to lower at 6v.


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## Nordic (Dec 18, 2013)

I have a specific fan I want to use because I already have it, and it is almost useless to me. Its 80mm which the modem just so happens to have a nice ventilation area 80x80mm.


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## Norton (Dec 18, 2013)

You could scavenge a fan from a stock AMD cpu cooler and run it off of the 5v from a USB cable. I did a similar thing a while back when I pulled the fans out of a busted laptop cooling pad...


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## Nordic (Dec 18, 2013)

So you guys are saying the fan in the picture I showed wont work?


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## pr0n Inspector (Dec 19, 2013)

I'm pretty sure any 12v fan will work if noise is not an issue. 80mm fans draw very little current, especially yours since it is slow. Just don't put a Delta on it those things eat more power tha nyour modem!


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## xvi (Dec 19, 2013)

james888 said:


> So you guys are saying the fan in the picture I showed wont work?


Oh, it'll work just fine if you wire it in to the power adapter, but I'd plug the fan in to a computer first to make sure it's not going to make too much noise. It might require some soldering to get reliable. Might consider a resistor in-line just to bring the amperage (and noise) down.


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## Nordic (Dec 19, 2013)

xvi said:


> Oh, it'll work just fine if you wire it in to the power adapter, but I'd plug the fan in to a computer first to make sure it's not going to make too much noise. It might require some soldering to get reliable. Might consider a resistor in-line just to bring the amperage (and noise) down.


I know it is quiet. It is such a slow fan it has no use for cooling computer parts.

As soon as my camera's batteries are charged I will get photos of the power area.


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## micropage7 (Dec 19, 2013)

why you dont put bigger heatsink on that, its easier
fan would attract more dust inside of it


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## Arjai (Dec 19, 2013)

Just do it! Use a little duct tape and electrical tape. Be sure to do a few shots of Whisky, First. Then, go online and up your fire insurance, sit back and enjoy another Whisky while enjoying the small sparkly show!!



P.S. crack a window, the smoke smells bad.


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## segalaw19800 (Dec 19, 2013)

why not use chip set heatsinks like


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## segalaw19800 (Dec 19, 2013)

by the way my motorola modem is SB6121 and my fan is mounted  on the side and wire to pcb it was e-z to wire thay way..... Dust is e-z to blow off from in side, out


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## Nordic (Dec 19, 2013)

micropage7 said:


> why you dont put bigger heatsink on that, its easier
> fan would attract more dust inside of it


I will be doing that too. Not because I need it but because I want to.


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## Nordic (Dec 19, 2013)

segalaw19800 said:


> why not use chip set heatsinks like


I have some heatsinks like this. I have even stated I plan on using a heatsink several time snow.



segalaw19800 said:


> by the way my motorola modem is SB6121 and my fan is mounted  on the side and wire to pcb it was e-z to wire thay way..... Dust is e-z to blow off from in side, out


That is exactly how I plan on doing. I just need to know where to "wire it too." It looks like you can help.


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## segalaw19800 (Dec 19, 2013)

Have fun


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## Nordic (Dec 19, 2013)

segalaw19800 said:


> Have fun


I am not educated enough to know where to wire them too. Where did you wire yours too.


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## segalaw19800 (Dec 19, 2013)

james888 said:


> I have some heatsinks like this. I have even stated I plan on using a heatsink several time snow.
> 
> 
> That is exactly how I plan on doing. I just need to know where to "wire it too." It looks like you can help.


... I need to turn off modem. and take some pic be back and will post


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## segalaw19800 (Dec 19, 2013)

in the pic you will see two small hole you route wire to the back of the pcb , and there , will you have to solder wire on the board like on the pic...    There enough solder you can use on the board already there


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## Nordic (Dec 19, 2013)

Thanks. That is what I was looking for this whole time.

I will update the thread with pictures when it is installed. I got the pcb out of the case now with the heatsinks on. Gosh the main processor heatsink is too hot to touch under load.


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## segalaw19800 (Dec 19, 2013)

let it cool down before you work on it... have fun


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## BazookaJoe (Dec 19, 2013)

I think this is all getting very off topic , OP asked  a simple question "*I want to do X because I want to and that's just that*"

So as soon as those pics come in OP,  I will tell you exactly where to wire , what to do  - and even suggest a very nice simple voltage limiter to tame that fan a bit - there are some great and really simple to use voltage regulator IC's that you can get for super cheap - or often even for free out of old power supplies, you may not need one on this project but they are super useful to know about.

More of a general note for others reading as I see OP has a very slow fan already : 

Fans running on full 12V don't just attract dust, they also make noise - and I personally hate fan noise - dropping the voltage can practically silence the fan entirely, and often cause it to take more than 300% ~ 500% longer between dust buildups. 

And you will have exactly what you wanted - because that's what modders do, and you don't need any more reason than that 

*EDIT : I seem to have been screwed by this new forum format - the last 3 or 4 posts simply where not showing :/ after I posted it reloaded and they appeared*

I was going to say in the meantime here is a pic of another board using the same connector showing the most typical wiring of these sockets






... but that's all a little redundant now I guess 

And to say anyone else looking to do this mod or one similar could also think about using laptop fans such as this :






Various fans like these are easy to get online for $2 ~ $4 , they are incredibly slim and can easily be applied to the inside of the side panel and create more than enough air turbulence to keep the device cool if you DO have one that is overheating *cough*NETGEAR*cough*...

And for anyone looking for a super cheap & easy 5v regulator :






These parts are all very very cheap, available in any electronics store or online by order, and can often be salvaged from old power supplies for free.

The 78*05* is a *5v* regulator but if 12v is too fast and 5v is  too slow you can get them in a range of other values such as the 78*07 7v* regulator and more.


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## Mussels (Dec 19, 2013)

USB powered fan. simple!


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## AsRock (Dec 19, 2013)

segalaw19800 said:


> by the way my motorola modem is SB6121 and my fan is mounted  on the side and wire to pcb it was e-z to wire thay way..... Dust is e-z to blow off from in side, out



That fan @ full speed with the 0.75A put though it ?.  And these modems can get a little toasty too if you have a good internet connection and even more so if you don't use air con in  the summer


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## JunkBear (Dec 19, 2013)

james888 said:


> I will be doing that too. Not because I need it but because I want to.


 
Sounds like a quote by a bitchy girl.


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## segalaw19800 (Dec 20, 2013)

AsRock said:


> That fan @ full speed with the 0.75A put though it ?.  And these modems can get a little toasty too if you have a good internet connection and even more so if you don't use air con in  the summer


 
Yea this modem get a bit too hot, it's was restarting most of the time, so I install a fan and few heatsink too cool it . now it run like a boss .... no more restart


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## Nordic (Dec 22, 2013)

The deed is done.
























...back to the hole whence it came.








This fan is so slow. I think it is under 1000rpm. Still though, I can feel a slight breeze coming out of the top vent. Do these modems run hot? Yes. Do they need anything more than stock? Not really. Were the heatsinks enough to keep it cooler than it was without heatsinks? Yes. Is the fan overkill? Yes. Did I have fun? I very much did so indeed.


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## BazookaJoe (Dec 22, 2013)

Putting unnecessary things into other things is why we invented screwdrivers dagnabbit!

Well done


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## segalaw19800 (Dec 24, 2013)

james888 said:


> The deed is done.
> 
> 
> 
> ...



In deed Well Done


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