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GR300/GR500 Cooling Fans

Posted: Sun Feb 22, 2004 4:57 pm
by kurt meltzer
I have a number of these repeaters deployed in dusty locations (utility closets, HVAC rooms, etc). Since the cooling fans run continuously, the heatsinks get all full of dust in as little as 6-12 months. They must be blown out with compressed air regularly. Ambient temps are reasonable at most of these sites and the heatsinks on PS and TX do not feel hot at all, even without the fan running (except when transmitting of course). I was thinking of wiring the fans to timers so they would start running immediately each time PTT goes low and keep running until repeater has been idle for 10 mins or so, then turn off. The duty cycle on most of these repeaters is such that the fans would thus run for a total of 3-4 hours per day, instead of 24 hours, and the dust would not build up so fast. Fans would probably last longer too. Has anyone ever tried this?

I can't find the post now, but I seem to recall one of the senior members here on the board saying the fans on these stations should always be left running continuously. If this is true can someone please educate me on the underlying theory. Thanks!

Posted: Sun Feb 22, 2004 7:25 pm
by Monty
I can't find the post now, but I seem to recall one of the senior members here on the board saying the fans on these stations should always be left running continuously. If this is true can someone please educate me on the underlying theory. Thanks!
Hi:


If you run your GM300's at or close to rated power, and the
area where the repeater is restricted, YES by all means have
the fan running 24 hrs a day.

The proper installation is to find a air conditioned area
that is well vented,

Also, be prepared to " Replace " the fan on a Anual basis, as
the 12VDC Fans do ware out.

We NEVER run any of our GR300's at rated power, on the
opposite, we run them at about 1/2 the rated power, and
they will last forever if treated well

Monty

Posted: Sun Feb 22, 2004 8:05 pm
by PRR
I would suggest a filter media in front of the fan. Mouser sells (in various sizes) a filter kit which is a plastic retainer matching the bolt pattern of the fan it's sized for, a low restriction filter media and a snap retainer cover to hold the filter in place. They're pretty inexpensive (under $9.00) and work very well. Very easy to clean. Extra filter media is available in five packs.

Place it on the outside of the GR housing for easy access. The only caveat is it MUST be cleaned regularly or the dirt build up will severly restrict air flow. Clean out the insides of the repeater while installing the filter kit.

If you don't want to bolt in the retainer, Just buy over sized media and place strips of the stiff half of Velcro around the fan opening and press the media onto it.

In any case, I also believe in keeping the fan running continuously: It's more efficient to keep a device cool and dissipate heat as it's produced than it is to cool off a device that has already built up significant heat.

Hope this helps.

Henry

Posted: Sun Feb 22, 2004 10:21 pm
by Will
Some of the later GR series with the DuraComm power supply have a tempature sensor on the TX heatsink that controls the fan. I also use a PIPO thermostat wedged in the heatsink near the PA transistor to control the fan. If the heatsink gets above 85 degrees, it switches on the fan. Also on some repeaters the fan is run at low speed until the thermostat kicks in.

Posted: Tue Feb 24, 2004 9:58 am
by kurt meltzer
Thank you very much for the replies. Monty, I agree the GR300/500 are quite reliable. I am running all the xmtrs at 1/2 power as you mention and have never experienced a single failure on any of them. A couple of these units have been in continuous service almost 10 years and the only maintenance I've done on them is replacing the fans every 3 years whether they need it or not (never had a fan fail in service yet), and of course, blowing out the dust every 6-12 months. Unfortunately I don't have a choice on the site locations. The ambient room temperatures at the sites are all within reason (80F or less year round), but some are pretty dusty. I'm sure dust adhering to the heat sinks reduces their cooling efficiency. I'm looking for a way to reduce dust buildup on the heatsinks and extend the interval between cleaning. I guess I'll try the fan timer approach on one of the stations as a test and see how it goes. Thanks again.