250mm fan

[Spec-Chum]

Hi all

I've got on of these:

left over from my bygone days of PC Case modding (UV Watercooling, looked awesome!).

Anyway, it's 250mm wide so seem ideal to cool the primary mirror.

What would be the best way to mount and power it, do yo think? It's rated at 12v 400mA, and I've got a feeling a 9v MN1604 isn't going to last 2 minutes

It's rated at 105CFM airflow at 12v, so 9v should still move plenty of air.

Any advice from you DIY gurus

Thanks

[jimmyjamjoejoe]

Although my fan is smaller, i used one of those "emergency phone chargers" to power it. It's basically a 2xAA battery box with a usb out. I just cannibalised an old usb lead and attached it to the fan.

Being just 3v on a 60mm fan, it runs slow enough to not cause vibrations, but still moves enough air. Experiments show you really dont need a large amount of flow to reach peak efficiency, i think it's around 25-30cfm needed for our non observatory sized scopes.

On 2x2000mah batteries i get about 8hours of operation.

I think you'd be alright on 6v tbh, so 4xaa @ 2500mah should do you ok. If you're looking for something a little more substantial though, maplin do a decent range of 12v leisure batteries etc. Though you'd probably need to add resistors because that beast running at full power will be a) a waste of power, noisy, and c) shaky.

As for mounting it, i know some people who have drilled holes in the cell and used rubber anti vibration plugs. Others use rubber bands through the fan mounting holes and looped them around screws on the side of the tube. It all depends on how it fits tbh. It might be worth building a kind of fan box that will just push onto the bottom of the tube and act as a baffle.

Personally, i used the bottom off a big rubber bucket. I just cut the bottom inch or so off of it, cut a hole in the middle and mounted the fan with sticky velcro. The whole thing slots rather snuggly onto the bottom of the tube and looks rather neat.

Hope that gives some inspiration.

[Spec-Chum]

It does indeed, especially the cool dude with shades on lol I assume you meant to type b )

I'll see what I can rig up with 4 aa batteries and see how it goes. It's surprisingly quiet to be honest, only runs at about 800rpm, it just makes quite a pleasant "whoosh" sound.

PS I'll attach with elastic bands, never though of that! I'll make something more permanent if it works ok...

[NGC 1502]

Wow that's a big fan to cool your mirror

Agree that attaching with stout rubber bands is a good idea, easy to find them and fit, and vibration transmission is very low.

Last time I did this, I fitted 3 bolts into the back of the cell, protruding from the cell surface, and attached the rubber bands to those.

Lots of different ways to fit a fan according to the mirror cell design.

Regards, Ed.

[Spec-Chum]

Well, I have Bob's Knobs and the lock bolts are quite long and reasonably tight, could try attaching to them. Assuming they don't move any, but I doubt it'll pull that taut.