Calculate TDP?

[Bleek]

Does anyone know the equasion to calculate TDP?

I'm looking at running a AMD Brisbane at ~1.5GHz sub 1volt and wondered if I could get it near or under 20W TDP and therefore passive cooled.

This would be for a little, silent and neat media PC.

 

[Amonlym]

http://benchtest.com/calc.html

for example:

My laptop, clawhammer 3400+, stock TDP = 89w @ 1.5v @ 2200 mhz, i input this at the top. then i run it at 2000mhz, 1.175v, input this below and hit calc = 50w and 800mhz, 0.8v = 9w

or my X2, Stock TDP = 69w, if i remember rightly, from t-case-max calculator. 2400 @ 1.35 @ 69w running, for example 3100 @ 1.65v = 133w

 

[Bleek]

Interesting, the calculator would suggest I can run a dual core Brisbane at 1.5GHz 1v and produce circa 20W TDP.

I wonder if that's low enough for passive cooling (with case fans of course), perhaps I need to get closer to 10W for that.

 

[Hesky82]

If you have fans running anyway why not just use a large 120mm fan on the cpu cooler running at a silly low speeds, that only kicks in when temps rise.

Ive tried passive cooing on an old AMD single core Opteron 146 running just 0.9v and 2000ghz, temps still kept creeping up.

I say give it a shot, but dont be afraid to run a silent 120mm fan

 

[pcoltrane]

What cooler are you planning on running? It is no problem running a 20-30W chip passive with a Scythe Ninja as long as you have a little case airflow.

I have a couple of HTPCs running with only 2 x 120m nexus fans @ 500rpm (one exhausting from the case and the other in the PSU)

These are truly inaudible unless your head is right next to the case, even in the quietest of rooms. I often switch the thing off by mistake as its so quiet I assume it needs turning on!

Don't forget though that if you get the case fans this quiet you need to consider other noise sources like the Hard drive. Suspending / foam mounting drives is critical ... but you might also want to consider using either a laptop drive, or perhaps if you need more storage one of the WD 'green power' drives. They only run at 5400rpm so are significantly quieter than the quietest 7200rpm drives.

The antec cases are particularly good for building quiet htpcs because even the smaller cases still have a 120mm hole for rear exhaust fans. If you went for the NSK 2400 / Fusion case there is even a mini version of the Scythe ninja that should fit and combined with the well position fan holes allow you to run passively easily.

 

[Bleek]

Well this would be a custom case, VERY small and 100% silent, sealed surround, no venting with a clear air flow through the design. Think set-top box, stick it anywhere and hidden from view.

TBF Hesky 2GHz is far too much for my requirements and the Opty was never the coolest of chips, nice to see you got it stable at .9v... gives me hope for even lower at lower clocks.

 

[Hesky82]

Well the old San Diego's were 90nm and the Brisbane's are 65nm, makes sense for the new chips to run cooler.

Can you still get those Brisbane EE cpu's? they went as high as 2.2GHz with only a TDP of 35W!

 

[Amonlym]

well my laptop, idling runs without its fans on a cold day - so its possible.

as mentioned, get a big hsf.

voltage is most improtant to drop. frequency gives a linear change in power, but voltage is a exponential curve.

when it comes to cooling, remember a few improtant things: fin spacing needs to be greater, and you wan the fins in line with airflow, in truely passive this means the fins must be orientated floor-roof, not wall-wall.

 

[Hesky82]

That’s why the Scythe Ninja is a good passive cooler, air restriction is very low due to large fin spacing.
Im thinking a Ninja will be way to big for his custom case though.

 

[pcoltrane]

Well this would be a custom case, VERY small and 100% silent, sealed surround, no venting with a clear air flow through the design. Think set-top box, stick it anywhere and hidden from view.

TBF Hesky 2GHz is far too much for my requirements and the Opty was never the coolest of chips, nice to see you got it stable at .9v... gives me hope for even lower at lower clocks.

Have you considered using heatpipes to transfer the heat to the surface of the casing? There are some places where you can get the kit off the shelf to do exactly this.

I have a similar design drawn up in solidworks, but have never quite found the time to build it.

 

[Hesky82]

Same here, I’ve looked into incorporating the cpu and gfx cooling onto heatsinks that fit on the side of the case. If you use laptop hdd’s you don't even need a case fan!

Something like this...

 

[Bleek]

Well I'm an IT Project Manager, a specialist in Data Centre and Infrastructure, so I understand air flow, heat outputs, climates, enclosures of all scales etc.

My case design is quite radical in that there is very limited space, most of which is filled with a contoured foam/poly-composite, the case will be the heatsink for all components and will use a suspended wall cooling technology. Quite advanced stuff and not so simple to get right, but if it works it'll be ultra efficient and literally completely silent.

 

[Bleek]

Well the old San Diego's were 90nm and the Brisbane's are 65nm, makes sense for the new chips to run cooler.

Can you still get those Brisbane EE cpu's? they went as high as 2.2GHz with only a TDP of 35W!

Yeah I was looking at those, the 1.9GHz is under 30W at stock volts. I'm pretty confident those chips will run 0.75-0.8v at near stock speed which is very cool (literally) for a dual core. Even less if I can regulate the voltage lower. After some careful consideration 10W TDP is my aim. However I need to calculate other heat producing elements and create a model that simulates the outputs and efficiencies of my design.