fan size?

Discussion in 'Modding Forum' started by mikez, Jan 4, 2006.

  1. mikez

    mikez Network Guru Member

    i was wondering on what size fan i should put in my wrt54gs v4....i want it to stay cool since i plan on boosting the Xmit power. Should i use one 60x60x10mm fan? or go with two smaller fans?

    if you did this cooling mod...tell me what you used for a fan size.
  2. Cenreyn79

    Cenreyn79 Network Guru Member

    that depends on whether or not you want to do a steath mod or performance. the stealth option means 2 smaller fans hidden under the top grill and the performance would be to add on a large or large fan with the grill removed.

    im using a 70x70x15 with the grill removed and forcing the air into it.
  3. mikez

    mikez Network Guru Member

    i figured it out...
    i used a 60x60x10mm fan
    it moves a lot of air and seems to keep my wrt cool
  4. SteelersFANinMA

    SteelersFANinMA Network Guru Member

    I did mine stealth and also used a 60x60x10 mm fan that came off of an Antec Solution Plus CPU Cooler. I just unscrewed the fan from the heatsink and installed it to force air out of the WRT. I also used small heatsinks for the chips. I think it's the best size fan for a stealth mod. It does more than a great job of keeping the WRT cool. I also added a potentiometer to control the fan's speed, cut down on the noise, and reduce the load on the power adapter. I really don't need 100% of the fan's cooling power. I also used a drill to increase size of the vent holes on the top of the WRTto allow for more airflow, (can't remember the bit size off hand).
  5. BassKozz

    BassKozz Network Guru Member

    What size (height) are the heatsinks you used ? How much clearance do you have between the fan and the heatsinks?

    I just purchased these HeatSinks (14x14x14.5)
    This FAN (60x60x10)

    Will there be enough room (clearance) for a stealth installation???
    And are these heatsinks good?
  6. SteelersFANinMA

    SteelersFANinMA Network Guru Member

    OK, here is my experience modding my WRT54G v2. I used 10mm heatsinks. The 14.5mm height will be fine with the fan on all but one chip. The Ethernet Switch chip sits under a wire that goes from the mobo to one of the antennas. With the same size fan set up in the front right quadrant of the cover holes, there is just enough clearance for the antenna wire to fit between the 10mm heatsink and the fan. The wire is a bit stiff, but you may be able to work it in there. Also, I didn't have 14x14 heatsinks. So, yours just might fit perfectly.

    Copper is probably your best bet for heatsinks. I read that silver or platinum are better, but good luck finding and affording them. So, yours look good to me. Use a small dab of Silver Thermal Compound in between the chips and heatsinks. The sinks will probably come with a tape-like compound, but I've heard that it's not nearly as good. However, some say that it still works just fine.

    I also used a 60x60x10 fan. It is perfect for a stealth mod. If the screws that came with it have flat tips and are the same length as the ones I got, then you're in luck. I screwed the fan in from the inside of the WRT and they fit perfectly into the holes on the top of the cover. No sharp points or screw heads showing from the top of the router. I then drilled the other holes a bit larger which allowed more airflow, reduced stress on the fan, and also made it a bit more quiet.

    If fan noise is still an issue, add a potentiometer. I found that it was too loud to be in a main area of my home. The fan at full speed also cooled my overclocked WRT more than enough. So, I thought that being able to turn down the fan would save wear on the A/C adapter.

    I read at that you'll need at least a 3 watt, "pot." The pot will also have an ohm rating. Overclockers had a formula to figure out what ohm pot you'll need. I did the math and came up with a 100 ohm pot, but it didn't work like I wanted it to. I also tried 1, 10, 50 and 500 ohm pots and found that the 500 ohm worked the best. It was the only one that didn't shut off the fan with a slight turn of the nob, yet when completely turned down, still allowed the fan to rotate. This could be important if you overclock the router and have fears that the knob might be accidentally moved, resulting in a fried router.

    As for my experience overclocking my G v2...I didn't know to change the CFE. I'm no expert on that, but if you change the CFE/'s, you'll be able to recover from a brick with the reset button after a bad overclock. After gradually getting it up to 264/96, I decided to go for the glory and try 300/96. Well, I bricked it good. None of the debrickers have worked and I can't get it to respond to a ping. I successfully added a JTAG, but bought a GS v3 and haven't touched the G v2 since. One day I'll try to debrick it.

    If you don't know about this site, check it out. It has a wealth of info. and guides to mods. Most of the stuff you'll find will also work with 3rd party firmwares other than OpenWRT. I use Hyperwrt myself:

    PS: I think they took down any overclocking info. probably due to too many people bricking their routers. However, if you Google, "openwrt" & "overclock" you may still find it in the, "cached" links. I did a few months ago.

    Have fun and good luck! :rockon:
  7. BassKozz

    BassKozz Network Guru Member

    Thanks for the post SteelersFANinMA (BTW, I am a DolphinsFANinMA... I hate the pats)

    I appreciate the help... once the heatsinks and fan arrive I'll open up my extra WRT and start working, I'll keep you posted.

    I do have a quick question thou... you wrote:
    If I remove the tape, and use thermal compound (like THIS) how will the heatsinks stay in place? Is there any holes on the board to tie them down? What can I use to make them stick?
  8. SteelersFANinMA

    SteelersFANinMA Network Guru Member

    If you want, you could keep the tape stuff on there. Some say it works just fine. I used a razor to scrape the tape stuff off of the careful. If you use the compound, (yes, the stuff in your link is perfect) you'll only need a very thin layer. At first I actually used a bit too much even though I knew better, and had to wipe some off. If you let the compound set for a bit it actually holds pretty well. When the chips heat up, the compound will loosen. I haven't had any problems and didn't have to tie them down. If you're setting the wrt down with the feet on the table/wherever then the sinks won't move. If you want to hang the wrt or feel the need to shake it around then they will probably move. I'll assume that even the tape-like compound will loosen when heated. One person mentioned that they used rubber bands to hold the sinks in place, but again I didn't need them.
  9. BassKozz

    BassKozz Network Guru Member

    Thanks for the tips... I got the sinks in today.
    I'll post pictures when I am done.
    BTW, you said:
    Where did you get it?
    Would this work HERE or HERE2
    Are there any guides to installing this ?

  10. SteelersFANinMA

    SteelersFANinMA Network Guru Member

    The pots I got looked like the ones in your second link, (guitar pots). However, I didn't see any wattage ratings for the pots in either link. says you'll need at least a 3 watt pot. If you wan't to try one with a lesser wattage it shouldn't cause any damage, but you may end up having to test different amperages to get it to control the fan to your liking.

    Installing the pots was pretty simple, but it took me a couple of tries since none of them came with any instructions. There were 3 connectors on the pot that I ended up with. One will be the ground and you'll only need one of the other two for the positive connection. If you connect the wires wrong, your fan will spin backwards. So, look out for that as it will let you know how well you did.

    At first I went to several area Radio Shacks to get the pots. As I mentioned in one of my previous posts, I tried out many different amp and wattage combinations. They only had pots with a max of either 1W or 100K ohm ratings. None of them worked like I wanted and ended up finding, It happens to be only about an hour away from my home and about 10 minutes from my part-time job. I went there and bought whatever I couldn't find at other stores. I got my heatsinks from Best Buy and and the fan and Silver Thermal Compound from Circuit City. I did an online search of, but couldn't find the same pots. I'm sure that if you call/email them, you'll be able to get what you're looking for. The salesmen were very helpful and pretty knowledgeable.
  11. BassKozz

    BassKozz Network Guru Member

    I found out from the seller that the POTs he has for sale HERE are 0.5w 500ohm...
    That won't work will it? :cry:

    :clap: It's funny you mentioned you-do-it electronics, I love that place... right next to the needham towers off 128... I am approx 10-15mins away from there, I even have a GiftCert I need to spend there, I'll go there this weekend and see what they have for POT's and for supplies to build a JTAG.

    So you think the best POT to get is 3w 500ohm?

    Thanks for the help SteelersFANinMA :thumb: ,
  12. SteelersFANinMA

    SteelersFANinMA Network Guru Member

    Get a 500k ohm pot that is as close to 3w as they have. They also have a good assortment of knobs which will make the finished product look as professional as possible.

    You should be able to find everything for the JTAG at YouDoIt, but you'll have to improvise. The JTAG guides call for 12 pin ribbon cable & connector and a 12 pin male header. All I found were 14's or 16's. So, I just stripped some wires off of the ribbon cable to make it a 12 pin and you can easily snap off sections of the male header to make it whatever # pin you want.

    As far as the resistors and DB25 parallel connector with solder pads goes, if you don't like what YouDoIt...has to offer, you can get that stuff at some local Radio Shack stores.
  13. BassKozz

    BassKozz Network Guru Member


    Thanks for the update, I'll get to YouDoIt this weekend. :D

    This article seem's to contridict what you were saying about using a 3w 500ohm POT:
    Computer Power User-Customized Cooling

    It's saying to use one with 100ohm setting? not 500...
    What will the difference be between the two?

  14. SteelersFANinMA

    SteelersFANinMA Network Guru Member

    I settled with a 500k pot, but I wrote somewhere above that I was led to believe that a 50k to 100k pot would be what I needed based on the math in this article:

    If you can spare it, buy both a 100k and 500k pot and test them out. Let us know how it went and then return the pot that you don't want. They'll take it back. I returned a few myself. Just save your receipt and try not to completely destroy the packaging and you shouldn't have a problem.

    As for the difference. I found that a 100k ohm pot shut off the fan with only a slight turn of the nob. The 500k pot allowed for more control and when completely turned down didn't shut off the fan, which is what I wanted.
  15. Cenreyn79

    Cenreyn79 Network Guru Member

    Potentiometer Specs, as taken from Overclockers
    12 Volt @ .16 Amps (75 Ohms Base Resistance) = 2.92 Watts
    5700 RPM Fan

    3W 100 Ohm Pot + 75 Ohms = 175 Ohms
    12 Volt / 175 Ohms = .0685 A
    .0685 A / .16 A = .4285
    .4285 x 5700 = 2442.85 RPM at its slowest

    3W 500 Ohm Pot + 75 Ohms = 575 Ohms
    12 volt / 575 Ohms = .0208 A
    .0208 A / .16 A = .1304
    .1304 x 5700 RPM = 743.47 RPM at slowest
  16. BassKozz

    BassKozz Network Guru Member

    I went out and purchased 3 pots from YouDoIt, they are all 2Watt POTs though (they didn't have any 3w's available), is this bad?

    1- 2w 50ohm
    1- 2w 100ohm
    1- 2w 500ohm

    I am running tests now, let you know what I come up with, but from the looks of Cenreyn79's calculations and using his formula either 100 or 500 would work...

    Quick Question:

    For these potentiometers, when the resistance is set to max it is equal to the amount on the box (i.e. a 500ohm pot is 500ohm's when set to full resistance) but what is the resistance setting when it's set to min (or turned down all the way) ?
    Is it 0ohm ?
  17. BassKozz

    BassKozz Network Guru Member

    I forgot to mention I also purchased a new DC adaptor:
    12v 1.5amp

    The stock linksys adaptor is 12v 1amp, I figured the extra 500milliamps would be what I needed to run 2 fans, since each fan requires 160milliamps so 2 fans equals 320milliamps...
    So the router will be using 1 amp and the fans will eat up .32 amps leaving .18amps of legroom.

    Is this the correct setup?
  18. Cenreyn79

    Cenreyn79 Network Guru Member

    First Response:
    For each of those pots, if you were to turn it all the way around so that each pot is at its maximum resistance, meaning that it slows the fan as much as possible, it would be the pots resistance plus the fans base resistance of 75 Ohms.

    50 Ohm Pot + Base = 125 Ohms
    100 Ohm Pot + Base = 175 Ohms
    500 Ohm Pot + Base = 575 Ohms

    When these are reduced to their respective lowest levels of resistance, the fan will spin at its maximum rate.

    Second Response:
    From the documentation provided at OpenWrt and by Anachip, it should work fine. however. The router only requires 6W to run, so you'll end up with a lot of extra power.
  19. BassKozz

    BassKozz Network Guru Member

    How does a potentiometer's rated "watt"-age have to do with all of this?
    How does it get factored into the equation?

    The overclocker's article says to use a 3w POT, but doesn't go into detail on how it factors into the equation.

  20. Cenreyn79

    Cenreyn79 Network Guru Member

    Not really sure of the dynamics of it, but unless you have a pot that is less than the rated wattage, then the pot is pretty much useless. thats just a guess but from what i know, electricity will take the path of least resistance, and if the pot is rated too low then it will be bypassed.
  21. RonWessels

    RonWessels Network Guru Member

    Uh, no, not really.

    When current flows through a resistor (a pot is simply a variable resistor), there is a voltage drop across that resistor that is governed by Ohm's Law: V=IR, where V is the voltage in volts, I is the current in amps, and R is the resistance in ohms.

    The power consumed by any device is given by P=VI. Application of Ohm's Law gives some other forms: P = V^2/R = I^2 * R.

    The power consumed by a resistor is dissapated as heat. Essentially, a heating coil is simply a low-value high-wattage resistor. The power rating for a resistor is the amount of power that the resistor is rated to dissapate. Using too low a power rating means that the resistor has the potential to burn up and fail. Using too high a power rating simply means that the device is bulkier (and typically more expensive) than it needed to be.

    If it is true that the fan's resistance is 75 ohms, running the numbers shows that the maximum power dissapated by the pot will be when the pot is set to 75 ohms. This is under half a watt for a 12V supply. However, for your 500 ohm pot, this also represents only 15% of the available dissapation area (you're only using 15% of the physical resistance), so you'll need to scale that up to the full scale resistance so you don't get a local burnout. That winds up being 3.2W. Now, having said that, that's certainly pessimistic, because it makes the assumption that you can only use 15% of the heat dissapation capacity and that the rest of the resistor is not helping dissapate heat in any way, which is not true.

    Bottom line: your 50 ohm and 100 ohm pots are fine at 2W. Your 500 ohm pot is probably OK, but should have been a higher wattage for better safety factor.
  22. Cenreyn79

    Cenreyn79 Network Guru Member

    good call on cleaning me up. im shooting in the dark here.
  23. BassKozz

    BassKozz Network Guru Member

    Thanks for the clarification RonWessels :thumbup:
    Now I have to try and find some 3w 500ohm POTs, any ideas, online?

    So are you saying that I should stick with the stock adaptor (12v 1amp) or is it ok to use the one I purchased (12v 1.5amps)?
  24. SteelersFANinMA

    SteelersFANinMA Network Guru Member

    Hmm, YouDoIt only had 2w pots... I don't remember what wattage my pot is since it's not listed on the pot itself and I don't have the packaging any more. I think that this is why I settled with the 500k ohm pot.

    I do remember searching for 3w pots, but the only pots I found had very long knob shafts. :rofl: I didn't think that the router would look good with one of those sticking out of it, and good luck trying to find a knob for it.
  25. RonWessels

    RonWessels Network Guru Member

    @BassKozz, I'd probably stick with the pot you've got. Give it a try, it'll probably work just fine. That scaling up part really is pessimistic. Even if it fails, you're no worse off than you are now. It's not going to blow up or anything. :)

    @SteelersFANinMA, you realize that the long knob shafts can be cut down to size? They sell them that way because it's easier to cut long shafts shorter than to lengthen a short shaft.
  26. SteelersFANinMA

    SteelersFANinMA Network Guru Member

    OUCH!!! How could any man cut a long knob shaft? I'll never do it...NEVER!!! :grin:

    PS: Thanks for the info. I wasn't aware of that. :thumb:
  27. BassKozz

    BassKozz Network Guru Member

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