PC fan on 30 volts
 

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.?

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

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.

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.

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.

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.

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?

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.

Thanks Brian,i get it now.

Just a thought here... if you want to run two fans, you could just hook them up in series and they would each see 15V which would be perfect for a little voltage boost.

I have seen some pc cooling stuff that piggybacked two fans together... and I have thought of doing that just to get more airflow on my 12V fans.

That is another solution as long as the voltage is 24v-30v. However if he wants something that will work with batteries below 24v (4s and 5s), then the regulator might be his best bet.

I'm been toying with the idea of using the venturi effect and doing away with fans altogether,i'm trying to figure out what ratio between input and output area of the tube i would need to tripple the air speed.If i could get a 60mph wind blowing over the thing every time it goes 20mph then i don't think there'd be much need for a fan.

Might have to be more like double the air velocity so the OUT isn't too small or the IN too big to be practical.dunno haven't figured it out yet,there's online calculators for it though.

Drag might be a problem though,as might ripping the body clean off at 50mph:005:

The problem with just cutting holes in the body is it opens out after it enters and the air slows down so we're not really getting all that much cooling at these relatively slow speeds,i think maybe what we need is a tube or tubes going to the areas we want cooling.

Gustav, I recon a couple of ice cream cones through the windscreen could do the job.....they would have to be double scoop size obviously.....
That just leaves you to work out how much to bite off the end.......:004:

Ive always run my fans on 16-18 cells ( knowing sod all too :027: ) The one thing I am sure of now, is the neon ones seem to last consideably longer than the standard fans.......I plainly have no idea why this would be, just though id pass it on.

That sounds a bit technical,so far all i've got is a fairy liquid bottle jammed in the grill with a plastic pipe stuck to it,it's sure to catch on.

Lol, sounds too complicated. Why not have a small tank of liquid Nitrogen? Or use a Peltier cooler?

Hmm,liquid Nitrogen,sounds like a plan.

What i really want is little mini watercoolers on the FETs,with a little pump to send coolant to a little radiator in the front grill.You're a technical guy Brian,can't you sort that out on my MGM? Oh and it needs to weigh less than 100 grams too:018:

Watercooled, eh? Let's see.

- Radiator
- Attach a 80mm, 12v fan to the radiator.
- Waterblock to attach to your FETs using thermal epoxy.
- Of course you need a pump.
- And lastly, you'll need some tubing.

However, I don't see this weighing 100g - more like 900g+.

IMO, just get something like this.

Yeah! Now that's what i'm talkin' about.

I was wondering how the cooling tubes on the shulzes transfer heat from the FETs,they just look attached to the sides of the PCB,Just a thermal compound or mat or something? Those little waterblocks would be the buisness though.

The FETs used in most ESCs I've seen are just a huge array of surface mounted devices (no mounting "tab"). Therefore, they mostly use the PCB traces as a heatsink. Since there are so many FETs, the PCB is nowhere near big enough.

Schulz apparently attaches heatsinks to the sides of the PCB where the traces end.

Other designs seem to have multiple FET PCBs stacked on top of each other with the heatsink on the top layer. Each layer has the PCB above it laying on top of the FETs so the heat transfers to the layer above it (that sounded confusing even to me). BKs and Quark seem to do this. They have to make sure that each PCB firmly touches the FET below it or the heat won't be conducted as effectively.

[Edit]: Personally, each design leaves room for error and some FETs aren't cooled enough. I would like to see a slab of Aluminum between each layer of FETs, maybe machined so there are little raised squares where the actual FET is to prevent shorts. Each slab is then attached to a heatsink on the sides. Each layer gets cooled more or less equally that way. Although, it would be substantially larger, weigh considerably more, and be more expensive...

I always think the stacked designs look like they must suffer with low surface area:volume ratio,i wonder how much hotter they are in the middle.

I think the designers rely on the fact that heat tends to travel from a higher concentration to a lesser concentration. The heatsink on top cools the top layer, which then "attracts" the heat from lower levels. I'm sure those lower levels must be hotter, but FETs conduct less the hotter they get, so they are self-regulating in a way. Of course there are limits, which is why some burn up.

IMO, they should add more heatsink area or more FETs. Adding FETs would do two things:
1: Increase current handling (duh :))
2: Decrease total output resistance, which in turn causes less voltage drop on the devices, which then reduces generated heat, and increases efficiency.

Ram air experiment thus far
 

Air goes in the scoop,then it's forced through a sort of letter box,then it narrows again at the end before it hits the esc.Self explainatory really,just look at the pics.I'll test it out,should work pretty good me thinks.:005:

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.

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.

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!

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.

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.

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

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.

Maybe the screws support the weight of the heatsinks aswell though,and they're screwed from the side aswell.i was just going to add some small ramsinks,not alot of extra mass really,thanks for the heads up on that though.

Most PC fans will run perfectly fine up to 15 - 16V, I've been running one in my 1:1 for amp cooling, and it's been there for about 2 years...

If you want a good, high flow 80MM fan, look for the Vantec Tornado... something like 80CFM at 5000 or so RPM, if I remember right...
they're thicker than the average 80MM fan... about 1.5 times, but other than that, they're wicked fans... I'm running two of them in my computer at the moment.... Crazy loud, though