Controlling the speed of an uber huge fan?

MikeHunt79 · 28 May 2007 at 20:19

I've got a 12v car fan that I'm planning to use to cool a car rad for watercooling. It's well over a foot in diameter (300mm).

Now it test it I hooked it straight up to my car battery, and it sounded loud as hell! I measured the current, and it pulls around 3 amps, which means it uses over 30watts! I want it spinning a bit slower tbh.

This current is a tad high for a fan controller methinks, so would it be worth just hooking it up to the 5v or 3.3v line on my PSU? Or is there a more elegant solution than this?

cavemanoc · 28 May 2007 at 20:42

Just wire it straight into one of the molexes:
1xRed and 1xBlack = 5v
1xRed and 1xYellow = 7v.

Try them both and see which suits best.

MikeHunt79 · 28 May 2007 at 20:49

Yea, I'll try that... But I think even on 5v, it's gonna be too loud... I'm gonna just have to try it, and see what happens.

The Halk · 28 May 2007 at 21:33

Interested to see how this one pans out.

In a years time will we all be doing 1 foot car fan mods?

cavemanoc · 28 May 2007 at 21:52

MikeHunt79 said:
Yea, I'll try that... But I think even on 5v, it's gonna be too loud... I'm gonna just have to try it, and see what happens.

The biggest problem is that below a certain voltage the fan won't have enough power to overcome the magnets inside it (so you'd have to hand start it

) It should be nice and quite at 5v - will be much slower than at 12v - does it still have the shroud that it came with? - they make a huge difference to airflow through the rad.

DampCat · 28 May 2007 at 22:16

i want pictures, this sounds brilliant!

MikeHunt79 · 28 May 2007 at 22:23

The Halk said:
Interested to see how this one pans out.

In a years time will we all be doing 1 foot car fan mods?

Lol, well for me this is making my watercooling rig smaller! :eek:

I'm using a house radiator right now, which isn't the most practical thing in the world. I plan to bolt the car rad to the side of my desk, so it shouldn't take up too much space. There's no way it would fit in a computer case.

Quite a few people have already done watercooling with large car rads tho... Most people use them passive or maybe bolt a few 120mm fas on there. I have yet to see one which uses the cars fan tho.

cavemanoc said:
The biggest problem is that below a certain voltage the fan won't have enough power to overcome the magnets inside it (so you'd have to hand start it ) It should be nice and quite at 5v - will be much slower than at 12v - does it still have the shroud that it came with? - they make a huge difference to airflow through the rad.

The fan is still in the shroud, and it's all bolted together (with rusty bolts). :cool:

I don't mind hand starting it, or if I had a way of varying the voltage, I could start it with 12v then reduce it down to an acceptable noise level.

It is unbeliveably loud at 12v tho... hopefully the fan will still run at a much lower RPM than intended, once it's spinning.

WJA96 · 28 May 2007 at 22:25

You need a high current PWM controller to tame that beastie. Search for mCubed T-Balancer.

DampCat · 28 May 2007 at 22:49

You *could* fit it onto the side panel of the case? 300mm isnt huge, shorter than a 120.3 rad.

MikeHunt79 · 28 May 2007 at 22:54

WJA96 said:
You need a high current PWM controller to tame that beastie. Search for mCubed T-Balancer.

Sounds good... I'll have a look. I'm guessing it will use a bit less current at lower voltages, but even so, it still pulls shedloads of power compared to a normal computer fan.

DampCat said:
You *could* fit it onto the side panel of the case? 300mm isnt huge, shorter than a 120.3 rad.

Well, I could... I took a guess at 300mm... but even if I did manage to bolt it to the side of the case, it would probably tip it over, as it's real heavy, even when there is no water in it. :eek:

I've already got 1/2" fittings on my case to allow for an external rad also, as I've been using so far with a steel house rad, so going to car rad will only involve a bit of pipe cutting.

WJA96 · 28 May 2007 at 23:13

MikeHunt79 said:
Sounds good... I'll have a look. I'm guessing it will use a bit less current at lower voltages, but even so, it still pulls shedloads of power compared to a normal computer fan.

So build your own controller;

http://casemods.pointofnoreturn.org/pwm/

Just change the MOSFET for one with a 50A+ power rating and you're laughing.

MikeHunt79 · 28 May 2007 at 23:37

WJA96 said:
So build your own controller;

http://casemods.pointofnoreturn.org/pwm/

Just change the MOSFET for one with a 50A+ power rating and you're laughing.

Any excuse to bust out the soldering iron.

I'll probably go for the 556 circuit, as I need to be able to take the speed down below 50%. Exellent link - thanks.

Cyber-Mav · 28 May 2007 at 23:37

WARNING, those car fans have a huge current consumption rate, don;t be surprised if it sucks up 30amps of current. :eek:

snowdog · 28 May 2007 at 23:58

Cyber-Mav said:
WARNING, those car fans have a huge current consumption rate, don;t be surprised if it sucks up 30amps of current.

He measured it :confused:

... 3 Amps... :rolleyes:

MikeHunt79 · 29 May 2007 at 00:14

snowdog said:
He measured it ... 3 Amps...

Well, to be fair I only did a quick test with a crappy multimeter and thin wires, just to check if the fan was working.... plus it was only powered for a few seconds as I think the neighbours were expecting a plane to come in to land!

When running next time, I'll use a 30A fuse to be on the safe side, and I've gotta clamp meter that goes up to 100a and I'll use some thick cable... 30amps is a fair bit. :eek:

If it's not raining tomorrow, I should be able to get reliable current readings at 12v, 7v, and 5v, so I know what I'm dealing with. Let's hope the PSU doesn't go bang! :eek:

squiffy · 29 May 2007 at 00:15

Stick your hand in it?