New HTPC build, question about gpu power

[slayed]

I am putting together an HTPC build with the following (relevant) components:

i3-4130t
Noctua L9i
Gigabyte GA-H97-N WiFi
PicoPsu 160xt + 192w AC-DC Power Brick
2x4gb dr3 1600mhz
Kingston v300 120gb
80mm Noctua

I know that I am well covered power-wise with this set up but I bought the largest picopsu with the intention of adding a discrete gpu later on.

I have seen other users on here that have pushed these pico psu's pretty far (can't post links yet as this is only my second post but there is a certain thread called "what's the closest you've made/seen a system run to the limit of its PSU?" where this is discussed). They mention running 750ti's and cpus that are much more power hungry than my 35w TDP 4130t on picopsu's. This makes sense in terms of total wattage, but I don't see how they are getting enough amperage on the 12v rail to achieve this.

The pico psu spec is as follows:

I see that the 12v rail can only carry a max of 15A and should really only be carrying 8A for extended periods of time. However, everywhere I've looked I see people state that the 750ti needs a MINIMUM of 18-20+Amps on the 12v.

Are these aforementioned users simply building these rigs to show that it's possible to power them up, and then not stress testing at all, or are these builds actually functional? I would love to add a 750ti to my build but I don't want to compromise system stability/component health.

tl;dr: 4130t + 750ti + picopsu 160xt = house fire or success?

 

[CaptNumbNutz]

The reason you are seeing a requirement of 18-20+ amps on the 12v rail is due to the overall load on the system. They are factoring in people who use crap PSU's and the other things drawing on the 12v rail like the CPU and hard drives.

In your situation, you are sacrificing CPU freeing up a ton of amperage on the 12v line. Watts = Volts X Amps. The 750ti itself barely uses 60 watts. At 12v, that means the 750ti is only using 5amps. That is assuming it's only using the 12v rail. CPU's also draw on the 12v line (and the motherboard converts it down to around 1v). Your i3-4130t 35w cpu is using 2.9amps at peak load since it can't be overclocked.

5+2.9= 7.9amps total being drawn on the 12v rail. This doesn't include everything else like hard drives, etc. So yes, people do come close to exceeding the PicoPSU's 8amp max limit. It also has a peak load of 15amps. Notice it says for "60 seconds". Since everything is digital, and with recent tech most CPU's and GPU's are adjusting their clock speeds several times a second, it is highly unlikely you (with your hardware combo) could create a real-world scenario where the PSU is peaked at 15amps straight for 60 seconds. If you had an i5-4690K processor overclocked and had speedstep disabled so it was always at that overclocked speed, then I could see a scenario where you could max out a PicoPSU rather quickly. Most people don't disable speedstep also.

With these other rigs, I suspect the PicoPSU is not reaching peak load on all the other rails (3.3v and 5v), freeing some overhead on the 12v line due to shared circuitry. IIRC, the main draws on 3.3v is RAM and chipsets. The main draws on 5v are drives, be they optical, HDD, or SSD. With the small form factor systems that PicoPSU's are meant to go into, there isn't aren't many devices in them to begin with. I would dare say a Pico PSU is extremely overspec'ed on the 3.3v and 5v lines simply for compatibility purposes. That overspec may also be that the original PicoPSU was designed almost 10 years ago when low power SSD's weren't as popular and RAM/chipsets used more power.

Combine all this together with ample air circulation, I have no doubt a PicoPSU could push boundaries of it's spec sheet on a consistent basis. In your situation, if you were forcing a situation with max load both CPU and GPU, you would be at the 8amp max load with plenty of overhead to reach 15amps periodically. The Pico should do well provided you don't have a bunch of drives in that system too.


tl;dr:
4130t + 750ti + a couple SSD's + picopsu 160xt = success (just barely), don't overclock the GPU too much
4690k (overclocked and/or speedstep disabled) + 750ti overclocked + PicoPSU = possible fire

 

[slayed]

Thank you for the breakdown. Those calculations definitely make sense. I'm going to go ahead and give it a shot and will report back... either from my new and improved HTPC or from a laptop in a hotel room after I burn my house down

 

[slayed]

Follow up question, how would I go about testing this in a way that won't break anything?

I know modern components are usually designed to force a shut down if they are unable to get enough power, but is there any way this could go wrong? My plan is to plug the machine into my Kill-a-watt and then just run furmark/games/prime95 (individually, not all at the same time) for a few minutes or so. I'll be monitoring and logging cpu/gpu temp as well as checking the picopsu temp by hand.

I have a multimeter so I was thinking I could attempt to monitor amperage on the 12v rail while the machine is running but I'm not sure how I would go about doing this. Any suggestions?