RT-AC87U/R: Cooling solutions

[shez]

Anyone tried water cooling it yet?


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[^Tripper^]

Add me to the list.

My 87 was never stable. Was constantly getting random reboots, missing radios and general flakeyness. A few months back, one of the LAN ports quit as well. Was gonna replace it but figured I'd tinker with it and see how it goes first.

I had a 12V, 70mm fan. I cut out an opening on the top and mounted the fan onto the 5G heatsink. Used the 5G heatsink as it is centrally located and the biggest one of the lot. Used a 12V fan powered via 5V to help keep noise levels down as I'm extremely sensitive about noise levels. I also took the opportunity to apply some new thermal paste that I had lying around, between the heatsinks and also between the SOC chip and the heatsink cover. Since I was in there, I also replaced the spring loaded plastic fasteners that held the heat sink in place. Was tempted to power the fan internally via the USB jack but decided not to. Instead I cut a smal hole out the bottom back casing and pulled the fan power cable through so I can power it via my USB power brick. I also used pantyhose as a filter to prevent too much dust from being sucked in (pantyhose makes a great filter. And the best microphone pop filter ever!)

Result? A rock solid router. Seriously. Have had it running for about 3 months now and it's been stable, no more random reboots. It may be the cooling or I may have knocked something about when i had it open (who knows?) but damn if it isn't behaving like the router it's suppose to be.

Why did I bother? Well, I live in Asia where it gets mighty warm and humid. The router never behaved right since getting it and was on the verge of binning it anyways. Don't know if what I did is the cause but the router is now working much, much better. Except for that dead LAN port.

It was a fun project to do and resulted a better performing unit. That's a great result!

 

[carpov alexandru]

I have a cheap laptop stand, i placed the router on it and connected it to the router USB. The results were amazing.
From 67C to 43C. That's a 24c DROP!!!
I tested using 2 1080p streams at the same time.
How high can the CPU temp go before it throttles?

edit: found alternative solution. i placed my router on top of my pc case, which has 2 top fans.

 

[Grisu]

nothing to think about below 70°C. And it wont throttle AFAIK, only fail or restart somewhere over 80-90°C.

 

[carpov alexandru]

nothing to think about below 70°C. And it wont throttle AFAIK, only fail or restart somewhere over 80-90°C.

I guess. It stabilised at 50c on top of my desktop fans.

 

[Grisu]

be prepaired that is may get a cold

 

[bsdsource]

So much valuable information you've learned over the years Grisu. I'm impressed.

 

[elorimer]

Sorry to resurect an older thread. I've had an 87U in a basement location (ambient 68F or so) sitting on a 120mm laptop fan, working fine for about 5 years. I've replaced it with an 86U now, so I wanted to repurpose it.

I've moved it to another location (ambient 78F) and it started to go all flakey on the 5G radio. The 5G chip hits 75C after about 20 minutes and then it shuts down connections. This has led me to look at the cooling, which is really stupid. I can see that putting it on a large laptop fan like before wasn't that great, since the bottom vents are on each side. I can also see that that would mostly vent out the sides. So the bottom of the board might be cooler.

I lifted the back almost vertically, so air would go out the back vents, and that helped a degree or two. I put the router on its side, so air would rise across the heat sinks, and that helped a few degrees. But we were still dealing with 70C or so and issues on the 5G.

I put a powerful fan plowing into the router from the left, across the 2.4g radio, across the 5G radio and across the CPU. That helped a lot, lowering the 5G chip to 52C or so, and the CPU to 60C. But this isn't really a long term solution. The router draws around 12 watts, and the fan was more.

I took the cover off, and it is clear there isn't a cooling path. There are just vents to let the internal air leak out in a disorganized fashion. But with the top off, the temperatures at idle stablizie around 56C for the 5G chip and 64C for the CPU.

So I put two 40mm 5V fans on the heatsinks and put them on the two 3.3v headers on the board, just resting there, and still with the cover off. That brought the temperatures down to 52C for the 5G chip and 62C for the CPU. It added around .1 watts to the draw of the router, which is around 12 watts. The fans are small compared to the heatsinks, so a lot could depend on where the sensor is, and if the fans were mounted in the cover pulling air across more of the heatsink, it might be better.

The little fans, cover off, aren't much worse than the big fan blowing across, so I'm thinking of mounting them in the cover and closing it up. First I'm going to see if the flakiness recurs in the makeshift mode.

This is replacing a 56u, and in truth with its lower power draw that puppy with its natural cooling flow is doing much better than the 87U.

 

[Grisu]

You have to remove heatsink and reposition it correctly including pad position.
5G should never go above 60°C even without any cooling, there is something wrong in your router.
Maybe a screw-holder is broken and so no proper connection to the pads.
Usually only CPU gets high temps, and can be easily brought down under 70° (which is very well done) with any even very small fan outside housing on backside, any little airflow will be good enough for that.

 

[elorimer]

Thanks. There was indeed something wrong. As you can see in the attached photo, the gooey pad under the heatsink was torn and folded up on itself, so the left part part of the heatsink wouldn't be making a good contact. I've evened it out and will see if there is a change.

There aren't screws, just spring loaded pushpins. Should I pry up the metal plate and see if something similar is going on with the chips themselves?

IMG_20200218_171909.jpg
4.3 MB

 

[Grisu]

I wouldnt in a first step, watch temps now and if radio chips are below 60°C without additional cooling then everything is ok inside under the metal shielding.

 

[elorimer]

I did open the EMI cans and there are two thermal pads that look to be in the right place. So I sealed it up and the 5G radio still went to 75C. I've put a 40mm 5V project fan on the cover. That seems to be holding the temps at 57C without any load where before they were 75C.

Not great, but better.

 

[Grisu]

Just be prepaired to be forced to change your router some day, maybe it will last till there are good Wifi6 choices to go on.

 

[Mare007]

Temperatures droped to 40C (2.4 GHz), 53C (5GHz), 53C (CPU) ± 3C
I used carton and 12 cm 12V fan, pluged into 5V USB ... and tested different variations ... (air direction, left-right position, ...) .... this one give the best results.