I have two Motorola GR500 repeaters, and for some reason, I got to thinking about which direction the cooling fan should be blowing. On both of mine, they are blowing INTO the repeater but asking ChatGPT, it said they should be exhausting the hot air OUT of the repeater. Which is right, or doesn't it really make a difference?
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Cooling fan direction on the GR500
- Thread starter Flameout00
- Start date
In most cases exhausting air out of an enclosure is more efficient. When my job was RF layout and packaging I tested air flow with clear plexiglass tops on enclosures and injected liquid smoke into the enclosure to watch the air flow and creation of eddies or dead spots. Air fans pointing inward were really bad except to cool an item directly in front of the fan where everything else heats up and suffers. Pulling air out of an enclosure provides much better cooling of everything in the enclosure and with radio heatsinks at the rear of a repeater enclosure a fan at the rear pointing outwards will pull lots of air past that heatsink in addition to removing heat in other areas.
That's some good information, thank you..
The GR500 enclosure itself doesn't seem very efficient though. It's certainly not air tight, but with the current situation of the fan blowing in, you can feel air being pushed out of all of the small openings, and hear the fan change pitch when going from open cover to everything closed up. I'm going to change it to exhausting the air out, and see how that works out
The GR500 enclosure itself doesn't seem very efficient though. It's certainly not air tight, but with the current situation of the fan blowing in, you can feel air being pushed out of all of the small openings, and hear the fan change pitch when going from open cover to everything closed up. I'm going to change it to exhausting the air out, and see how that works out
Looking at a picture of the GR500 tower I would not only pull air out of the enclosure, I would also cut some intake holes along the front sides around the radios to get a flow across the side of the radio then off the rear heat sinks out the back. If there are any vents in the back besides the fan opening I would block those as they will only provide an air bypass path that doesn’t help anything. You can’t vent a sealed enclosure, you need intake openings in a spot where it will drag air at good velocity across hot areas then out the fan.
I'm definitely going to do that. At first I though about venting from the side, but I think it would be better from the front, since the radio is mounted in that bracket. Venting the front should pull air across the radio better than the side would. Would it be beneficial to incorporate some type of air filter, or is that overkill?
That's a different enclosure than I was thinking, the tower version is what I was referring to. I would have to look that one over to get some ideas.
I guess that wasn't the best photo to use.
Maybe these will give a better idea of what it looks like
Maybe these will give a better idea of what it looks like
- Joined
- Aug 17, 2010
- Messages
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we had one in a rather warm location where we added a 2nd fan to exhaust so the 2 were in a push/pull config. i never measured anything scientifically but over the next few years the customer no longer was replacing or repairing the PA every summer. push the cool air in across the PA, pull the warm air out to get rid of it. i don't remember exact details, but we basically cut a hole and mounted a 3 or 4 inch DC fan to blow out. noise was not an issue where this was located so we did not do any type of thermistor control and just let it run.
Muffin type fans typically live longer running all the time vs starting and stopping from a heat switch. Its probably better to use a heat switch to stick a resistor in line to cut fan speed to about half at cool temps then short out the resistor when it gets hot for full fan speed.
Thats the wall mount GR series. Installed many of them in factories and other industrial locations. We would install filters on them to keep some of the metal or cardboard out of the enclosures. Yes not super efficient for cooling but we always had them on low power to avoid the PA dying.The desktop ones were very similar for cooling. They even made a front cover for the desktop that limited even more cooling. Personally I dont think any of those were designed for continuous use even though many sales guys thought that was the perfect sale.
The fan seems to be loud. Any fans that are quiet?
What size is it?
I just bought a used GR 500 repeater for GMRS and the fan seems to be loud. Any fans that are quiet?
I would have to check .
I usually look for the original fan model # and look up the mounting size, CFM and sound level. Then shop for similar size fans that will move the same or more air but with a much lower sound rating. And I prefer ball bearing or other long life type bearing. For 4" or 120mm fans I'm a big "fan" of this model. Its very quiet and has a long lead with thermistor you can attach to the radio heatsink and it will run the fan at a lower speed when cool then ramp up when the heatsink temp goes up but its still very quiet at full speed.
I have a lot of spare fans in different sizes that have high CFM ratings and will test those for noise and flow, then use a resistor substitution box to find a resistor value that will slow it down to a nice quiet level while still moving adequate air. In some cases I've used a thermal switch attached to a heatsink bridged by the dropping resistor so the fan runs quiet until the temps get high then the thermal switch shorts the resistor and runs the fan full speed. Typical resistor values have been between 10 and 20 ohms and a 5w resistor should be fine with most fans 4" or less.
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Thank you! I looked it up on the manual and found the information, I bought the repeater used so I will have to see if this is the original fan or replacement. It is moving a lot of air but very noisey. It has a high pitch noise.
So I took the fan out ,cleaned it up and it didn't make the same noise while being out of the case. Im thinking it is a vibration noise . I think I'm going to get some rubber washers and see if that helps.
