Fans on your radios...which direction to blow the air?

[Rayjk110]

As we all have experienced with using Mobiles, they can get HOT sometimes.

I've got M1225's, Spectra's, and MaxTracs and Waris's that I use here at my desk, but I've been wondering....is it better to blow air TO the heatsink of the radio, or blow it AWAY from the heatsink? I've probably heard an equal amount of advice from each, but I'm just not sure as to which heat dissipation method is best.


Anyone?

[Hartley]

Hi,

IMHO, what you want is maximum airflow across the heatsink, so whatever arrangement accomplishes that is best. I would suspect it would be easier to direct the output of a fan to blow across the heatsink than to duct the input of it across the same area, but in a tight enclosure, either should work.
If possible, you should aid any natural flow (i.e., upward for normal convection) to aid the process.

73 DE Hartley

[jistabout]

Some of us were discussing this very thing awhile back.........



http://batboard.batlabs.com/viewtopic.p ... ek+cooling

[Bruce1807]

on the Quantro base stations there is a set of three fans that are external to the PAs.
Motorola blow the air up over the heatsinks of the 2 PA s.

[phrawg]

I wrote up a quite lengthly study on this subject a year or 2 ago.
Bottom line is FORGET BLOWING air unless it is a last resort.
Best cooling is ALWAYS acomplished by DRAWING air across
a heat disapating surface so that maximum heat transfer to
the air can happen. Properly designed cabinet cooling systems
never try to push cool outside air into a cabinet, they always
evacuate warm air from a cabinet. Phrawg

see the link 2 posts up to read about it.

[AEC]

As Phrawg pointed out, the best way is always move air FROM the cabinet/heatsink, and OUT of the enclosure.

This method has another advantage of NOT creating debris buildup on the heatsinks or anything being cooled(for the most part), and allows a filter to be placed at the entrance to the cabinet being cooled so that easy cleanup is effected without opening up the cabinet to remove lint, dust and tarantulas that have somehow snuck inside when your back was turned.

A second benefit from this method is: total cooling of ALL components, not just the PA.
Airflow is necessary to keep all the 'parts-in-a-can' cool and happy as well.

[N4KVE]

I had a UHF Maxtrac that I wanted to use for rag chewing on 70 cm ham. I got a small computor fan & stuck it to the cooling fins with automotive silicone sealer. Quick & easy. It blew & yes, dust would gather on the cooling fins, however the radio never got hot. While I believe all the posts above mine are all correct & true, my way worked. Radio never got hot, but once in a while I had to blow the dust away. My install took 5 minutes. While this might not be the best way for a PD or FD, it worked for me. GARY N4KVE

[tvsjr]

What works and what's optimal are, unfortunately, usually two different things.

Phrawg and AEC are right... the correct answer is to draw air across the heat sinks, not blow air on them. Think of it from a physics perspective. In one instance, you're blowing air on a fairly small part of the heatsink and hoping that you cool it enough. This has two flaws... one, you typically don't get the heat transfer you're looking for, and two, you create areas of hot and cold, drastically increasing thermal stress. In the other instance, you're attempting to create what could be described as laminar flow across the heatsink, allowing air to come into contact with the sink and be drawn across it, maximizing the heatsink surface area each molecule of air is exposed to and thus maximizing the cooling.

For Ray's purposes, either method will probably work. However, since he's young and trying to learn, doing things the Right Way would be recommended.

[Bat2way]

I wrote up a quite lengthly study on this subject a year or 2 ago. Bottom line is FORGET BLOWING air unless it is a last resort. Best cooling is ALWAYS acomplished by DRAWING air across a heat disapating surface so that maximum heat transfer to the air can happen. Properly designed cabinet cooling systems never try to push cool outside air into a cabinet, they always evacuate warm air from a cabinet. Phrawg

Your scientific basis for this eludes me. You might want to check Broadcast transmitters. They have a VERY powerful fan blowing air INTO the tube cavity, vented to the exterior, and they are properly designed. As you say, if you are evacuating warm air from a cabinet, where would the inlet air have to come from? It is from cooler outside air.

[tvsjr]

Those systems are forcing air into an otherwise-sealed box... they're flowing air across the tubes by virtue of the fact the air has nowhere else to go.

It's a different deal when you're dealing with a heat sink in open air.

[nh7cy]

why dont you just take two fans, attach them to the top and bottom of the radio and have one blowing air into the heatsink and one drawing the air out

if you think back to the simplest thing about fans and cooling is that fans do not blow cold air, its the fact that the air is constantly moving that makes for a cool surface

so if you have two fans, you are moving relatively more air, and at a quicker rate

also, for ideas, you might just look at the way the fans are configured on your computer

anyway, just my two cents

now if you REALLY had alot of time, you could run some copper piping into your radio and fill it with coolant..

[phrawg]

The answers all lie in thermodynamics studies and laminar flow
of air over a surface with minimal eddy currents disturbing the
thermal transfer to the airflow.

[tvsjr]

why dont you just take two fans, attach them to the top and bottom of the radio and have one blowing air into the heatsink and one drawing the air out

Because, if you're not careful, you'll get lots of airflow between the heat sink fins and not much actually making contact with the fins and thus providing cooling.

Suffice it to say... unless you understand the physics and can engineer an intricate cooling system to meet your needs... stick with drawing air across the sink.

[marsguy]

why dont you just take two fans, attach them Suffice it to say... unless you understand the physics and can engineer an intricate cooling system to meet your needs... stick with drawing air across the sink.[/quote]

The Wind In Vietnam doesn't blow.. It sucks!