12V Fan for cooling powered by GPIO?

There is a separate thread discussing a 3D printed CPU fan duct, and people over there are using a 3.3V line (with a possible control mechanism from one of the pins on the front-panel FFC cable).

I myself plan on using a this 15mm x 15 mm fan: http://www.ebay.com/itm/15x15mm-5V-Supe … 375815521?

But I am trying to minimize power usage since I want to use it with a battery.

Yes, I had seen the other thread about the 3.3v fan, but I'd like to recycle the 12V one I already have, rather than get a new one.

I also read the GPBB user guide -- https://www.kosagi.com/w/index.php?titl … User_Guide -- and looked at the schematic of the pin layouts, but I'm not sure if the 12V fan would work, since it seems that max pin output from the GPBB is 3.3V, and I would need at least 5V.

Have I misunderstood the GPBB diagram?

It appears you're correct that there's no 5V out on the GPBB. There IS 5V in, but that's downregulated to 3V3. I don't see 5V at all on the Senoko in my cursory glance through the schematic.

The UART connections don't appear to even have 3V3 going to them, much less 5V. As for FPGA pins... nothing obvious from a 30-second check.

I don't think there's going to be an actual 5V header to connect to- the board itself is 3V3 and lower, in general. You're probably going to be soldering a wire somewhere...

-The USB ports all have 5V going to them. Soldering to the 5V leg of one of the USB ports wouldn't be too hard (so say I- I don't know your skill level at all)

-The GPBB connector is fine-pitch, but there's a whole block of pins that are 5V coming from the mainboard (A36-A40). You could tack a wire onto that block somewhere.

-Another option is to take power straight from the AC adapter. I don't know if you have batteries or not, but I'm guessing not, since you aren't using the case. Anyway, that's over 12V, but you could build your own regulator board (or buy one) to drop it from 18V to 12V. Or a board to PWM it into the right range (that would also give you speed control).

I was talking about soldering straight to one of the pins (the 5V pin) on a USB port. That P_USB pin that's marked is for selecting the boot device, and doesn't actually have 5V on it.

If you want to butcher a USB cable, that should work fine. If the fan draws 230 mA at 12V, in theory it will draw something like 95 mA at 5V- and the USB port should be able to supply that. That assumes you run the fan at 5V, so the current it draws is proportionately less than at 12V.

The link you provided was discussing if you wanted to step up the 5V from the USB port to 12V. At that point the fan would draw the rated 230 mA, at the full 12V. That in turn means at LEAST 552 mA would need to be going in the 5V side (since P = I V, and power in has to be at least as much as power out), more if you account for losses. Since USB ports are nominally rated at 500 mA, that's why there's nominally a problem.

Now, the Novena (like a lot of computers) doesn't actually follow that part of the USB spec (at least I don't see it doing any current sensing on the 5V rail in my 30-second search): it just has the USB ports' 5V rails connected to a regulator, capable of providing 7A max (or so says the Novena schematic; I haven't looked up the parts or other limitations). So in theory you'd even be fine stepping up the 5V to 12V and using that. Since you don't need much airflow to keep the CPU cool, I'd say just use the 5V directly and save the potential headaches of drawing too much current.

tl;dr: You should be entirely fine wiring the fan straight to a USB plug and plugging it into the Novena.

@dbtayl: thank you for suggesting trying the usb cable.

I may do that first, since it doesn't mess with the board, and basically does what I want, i.e., get the fan working w/o introducing its own power connection to a wall socket.

@james_a_craig: I saw the notes on how to switch the GPBB to emit 5V, but I admit I didn't understand them.

I'm more interested in your second suggestion, about using the PCB pins on the front panel.

There, too, though, I'm not sure what should plug into.

I looked at the annotated picture of the board, as well as the one I actually have, but couldn't figure out which are the PCB pins.

Here's a low-res snapshot I took of my board just now:

http://i.imgur.com/JvjHSG7.jpg

Could you point out where the PCB pins are? I would appreciate it.

Ah, that makes sense... thanks for clarifying that!

So I'll start with the usb cable, and see how that goes.

As I get more expert i soldering, I might eventually trying stepping up the GPBB to 5V and using that directly.

Thank you again for all your help with this.