PC fan on 30 volts - RC-Monster Forums

Gustav · **PC fan on 30 volts -** 07.28.2006, 12:26 PM

I'm wondering if it might be possible to run one of the very slow 80mm fans on much higher voltage,some of the ultra quiet ones only spin 1800rpm on 12v.

Is this a very bad idea? I don't mind the fan dying,they're cheap,concern would be if it could short out and kill other stuff.i want a fan i can run straight off the main batteries from 4s to 8s.Are there some very small voltage regulators i could use instead.?

GeeReg · 07.28.2006, 05:30 PM

You could wire in some resistors or a potentiometer to adjust it if you want. 30v would kill it pretty quickly I think.

coolhandcountry · 07.28.2006, 05:54 PM

If you chat with metal man. He could probably tell you how to make a bec 12 volt version. That would be the thing you need. He made a 6v model.

MetalMan · 07.28.2006, 05:55 PM

Or you could use a linear regulator to drop the voltage. I think a single 12v regulator (7812, can be gotten at many electronics stores) should work since it should only have about 2watts to dissipate as heat.

Gustav · 07.28.2006, 09:41 PM

Thanks,there's a 78S12 aswell that's 2A output.

I'm confused though about how i would wire it up,they have 3 pins,wouldn't i need something with a -ve and +ve in and a -ve and +ve out?(like the UBEC) if so,how is that done? Is it obvious i know sod all about electronics?:005:

This guy runs his fans on 24vhttp://www.afrotechmods.com/fanmod.htm and i'm talking about a slow fan here,i would try it,only concern would be if there's any chance it could short out my batteries when it dies.

Was thinking about running a battery just for the fan,a camcorder battery or something,and having that and the fan just attach to the body.That'd keep the birds nest down a bit.Also thought about a 3s or 4s reciever pack,with the fan and UBEC coming off that.

I suppose the alternative would be to have planty of extra heat sink,some properly effective air ducts in the body and just never slow down.

BrianG · 09:53 PM

Looking at the chip so the lettering is facing you, from left to right, the three terminals are input, ground, output. Even though the IC can supply 2A, it will only need to supply what the fan draws. Small fans usually pull no more than 0.25A, especially the slow ones. It is a 12v fan? What voltage do you want to run it at? I wouldn't go higher than 20% higher than its rated voltage or it may shorten its life. You can figure out how much power the regulator will dissipate by the formula:

regulator_dissipation = (supply_voltage - fan_voltage) * fan_current.

When the fan dies, it will most likely open circuit. And even if it does short out, the relatively tiny wires to the fan will act as a fuse and burn up, or the regulator itself will burn up.

Gustav · 07.28.2006, 10:03 PM

Yeah 12v fans,i normally run 4s or 7s lipo and at first i was thinking about running it straight from the main batteries with no regulator.how would i wire up the regulator? i'm still confused about that.

Are there any 5v fans that can shift a decent amount of air?

BrianG · 10:28 PM

Wiring it is really simple - especially if you stick to 12v (you can wire a 12v regulator to provide more voltage).

- Run a small 20GA wire from + of your main battery to pin 1 (left) of the regulator.
- Run a small 20GA wire from pin 3 of the regulator to the + lead of your fan.
- Run a small 20GA wire from - of your main battery to pin 2 (center) of the regulator.
- Run a small 20GA wire from from pin 2 (center) of the regulator to the - lead of your fan.

Put a heatsink on the IC and use a thermal insulator pad. IIRC, the tab on the IC is common to the output pin and if it touches any negative lead, it will damage the IC.

I'd stick to the 12v fans as they will move more air and are far easier to find. You can use a fan from a computer video card, chipset fan, CPU, etc and those all use 12v.

07.30.2006, 06:55 PM

That looks like it will work a treat, so long as it stays on its wheels. :026:
Did you work out the size for the in/out.

Gustav · 07.30.2006, 08:14 PM

Nah didn't work that out,just did it,had these scraps of lexan left over from an undertray i was making for a g-maxx.Didn't take long so i won't cry too much when it gets destroyed:030: ,it's just 1mm lexan superglued together.

BrianG · 07.30.2006, 08:57 PM

Ah, a highly scientific "yeah, that looks about right" procedure? :dft012:

I did a little reading up on the venturi effect and it seems it needs a little more than a funnel. From the materials I read, you need an input funnel with a slope of ~30 degrees, and an output funnel with a slope of ~5 degrees (for least amount of drag). I think you also need a good amount of pressure forcing air into the input because otherwise the air will simply go around the restriction where it is easier to flow (around the hole instead of in it). It might work better at higher speeds since air doesn't have as much of chance to change directions and so is forced into the opening. IMHO, I think the only gain in cooling you will see is from simply having some air coming in directly onto the ESC and not from any venturi effect. Once you test this, try simply making a hole in the windshield with a panel that directs the air directly to the ESC (instead of a tube). I think the effect will be the same or better.

No matter the outcome, good or bad, at least you are trying something different! As for me, I'll just stick to using larger heatsinks. :)

Something else you might want to try; Simply blowing air onto a heatsink is not really air flow; you get eddy currents. A lot of OEM computer makers (Dell, Gateway, HP, etc) sometimes use a ducted system with a fan on the output to pull air through the hot device. For this to work, an air shroud must be fashioned around the heatsink so the air is targeted directly across the fins instead of simply going around them. And since the air is being pulled through (instead of pushed), there is a cleaner flow of air (read: less turbulent).

Good luck! It will be interesting to see how this all works for you!

Gustav · 09:30 PM

Yeah very scientific:005:

I agree,just channeling the air across the esc is what i'm thinking of doing.I was just messin' about really,it's kind of the way i think out loud.I think the air will probably manage to 'dodge' the scoop at these low speeds.

There's no direct route for air onto the esc on this truck unless i raise the esc to the level of the windscreen,that might be the best way to go,with a lexan 'box' between the windscreen and the esc.And maybe an exhaust channel straight out the back too.

I've got some heatsinks coming too and some thermal adhesive,i'd like to try to get away without a fan if i can and just use more heatsink and find the best way to channel as much airflow over it,like you say.

squeeforever · 07.30.2006, 10:05 PM

Is the heatsink on the MGM's removable? It looks to have screws that hold it on. Maybe you can remove the heatsink and put a larger one directly on the board.

Gustav · 07.30.2006, 10:09 PM

I think it's stuck on there aswell,i was just going to add to the heatsinks.

BrianG · 07.30.2006, 10:18 PM

Once you remove the screws, you can try gently twisting the heatsink as the thermal paste may have dried a little causing it to stick somewhat. Also, be careful with adding more heatsinks to the MGM. It looks like the current HS may be directly attached to the FETs which might put physical stress on the FETs if you add more weight.

That's kinda why I like the Quark a little more; the case is the heatsink and adding more doesn't physically stress the FETs.