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Author Topic: On equipment cooling fans..  (Read 5680 times)
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KK4YY
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« on: February 17, 2019, 04:39:33 PM »

On equipment cooling fans...


1.   One big fan is better than two small fans. Why? When you have two, even identical, fans they will run at slightly different speeds. This produces a audible, and annoying, low frequency beat-note (or heterodyne, if you will) between them. The one thing that you don't need is to have even more noise coming from the fan.


2.   Some cooling fans are available with a thermistor placed in the air-stream that controls the fan speed relative to the temperature of the air it exhausts. The hotter the air, the faster the fan spins. The fan works to maintain a steady temperature within the enclosure in which it's mounted. It doesn't make any more noise than what is needed in order to do the job. This tends to stabilize circuits that are effected by temperature changes such as VFO's and other tuned circuits.

I have this one mounted in my DX-100 and the VFO drift has been noticeably reduced. https://www.mouser.com/ProductDetail/Orion-Fans/OA109AP-11-1TB03?qs=3YvpK%2Fz1cHxcjiK98FYxyA%3D%3D
I run mine on a reduced voltage of 105vac. Nice and quiet.
(The "03" in the p/n indicates that it's thermostatically controlled.)

3.   Fans work just as well in receivers that get hot.


Don
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k7mdo
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« Reply #1 on: February 17, 2019, 09:52:40 PM »

My Gates BC1-g has a large fan in the top that makes far too much noise for my small shack...  my first thought is to simply disable the fan as my usual "rag chews" on 75 meter are not long winded.  Does anyone think of a better idea.  It is really loud but is not a muffin... could replace it with a computer fan I guess but is it really necessary for operation less than full time? Ppiniopns?


Tom

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N1BCG
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« Reply #2 on: February 17, 2019, 10:29:19 PM »

The Gates BC1G has a cooling fan for continuous (CCS) 1kw operation. The 833s have enough surface area for convection cooling at amateur power levels and intermittent duty, particularly when used in a climate controlled shack.

You could also place a low speed fan, or fans, within the transmitter either under the four tubes or blowing across them.
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k7mdo
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« Reply #3 on: February 17, 2019, 11:08:09 PM »

Thanks, I had considered a small fan but just got to it yet.  The 833's do give off a lot of heat but the chimney effect of the cabinet should help.  I think I will disable the big fan as you say...  Tom
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K1JJ
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« Reply #4 on: February 17, 2019, 11:31:02 PM »

The 833A is a great tube, being a glass radiation cooled and a convection cooled tube. It can be as quiet as a mouse which is crucial for hi-fi AM work. . The "cool" thing is that it is a low-mu triode so that the various seals (fils/grid/plate seals) can see each other and still work well without taking off.  Thus they are easy to cool by mounting a quiet muffin fan right under the fils tube mounting and let it blow upwards towards the plate structure to cover all seals.

When I had a pair of 833A modulators, this method worked great for intermittent ham duty and stayed cool. They were dead quiet after using a 120VAC Variac to control a 120VAC muffin fan at ~1/2 rotation speed.  Inside a cabinet and they make no noise at all.

833As in RF class C are even easier to cool due to less heat dissipated, so the same method works FB -  though more care sould be taken for the tube elements not "seeing" each other.

813s are to a degree similar for cooling, though when running them in tetrode config they need better in/out signal isolation.

Even my tube PDM rig running quad 4D32s and quad 6LF6 sweep tubes use muffin fans. (500 W carrier)  In this case I have the muffin mounted on top of the cabinet blowing air directly down onto the tube glass foursome center. It covers all sides of the glass with no blind spots. This is counter-intuitive, since normal practice is to push air upwards with heat convection. However after running lots of tests I found that if there are holes around the base and the air hits the whole glass structure hard, the tubes stay cooler.. according to my IR temp gun.   Air flowing upwards doesn't slam into the glass like when the muffin is forcing it down and the hot air then spreads out across the chassis. The surrounding cabinet  has to be ventilated with holes, of course.  Try it and see.

Yes, temp monitoring is a great idea. I have a Chinese kiln temp alarm with big, bright LEDS that can be preset and uses a temp sensor hanging an inch above the tubes in all my rigs.  After losing a very expensive power grid ext-anus triode in GG 15 years ago, I saw the light.  I used a big squirrel cage blower. Warning: Never suck air out thru the tube bottom since the hot air from the plate will smoke the fil seals. Always push it thru the fils and then thru the plate. This was an effort to mount the blower and suck air outside the house to be quiet. It worked for a few months. But you already knew that.

T
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WBear2GCR
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« Reply #5 on: February 17, 2019, 11:32:33 PM »

One of the "tricks" I like to use to slow down "muffin" fans is to put a judiciously selected film
cap in series with one side of the line. I found that I needed to select the value carefully to get
the desired speed. Too much capacity and little or no effect, too little and no rotation.

I've been slowing down a muffin fan for my Valiant to the point where it is virtually inaudible,
and it provides sufficient cooling, for at least 10 years now. No heat, no resistors, works great.

Where there's ample space, putting in a too large fan or blower and slowing it down makes for a
rather quiet air mover.

        _-_-bear
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KD1SH
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« Reply #6 on: February 18, 2019, 09:52:08 AM »

I picked up a box of 220/240V muffins somewhere, years ago.  I plug one into 115V and sit it on top of my Ranger, pulling air up through the perforated case.  Almost completely silent, but it keeps the Ranger worlds cooler.  Works great for any classic rig with a perforated case, where you're not inclined to put holes in it.
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« Reply #7 on: February 18, 2019, 12:48:45 PM »

My favorite blower; picked up at my town dump's swap-shack for some as yet undetermined future project.  Maybe a pair of 8877's, or GS-35B's or 4CX1500's, or a trio of 3-500Z's?  Probably at least 1500 CFM at some impressive static pressure.  Thinking of mounting it in the basement (it's got a howl to wake the dead) and running PVC up to the shack.  Probably incorporate some sort of waste-gate in the pluming, so as not to push the tubes right out of their sockets.


* Blower_1.JPG (77.51 KB, 1280x960 - viewed 193 times.)
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K1JJ
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« Reply #8 on: February 18, 2019, 01:23:22 PM »

Cool looking blower.

PVC pipe as ducting.... unfortunately 2"-4" diameter PVC pipe sounds like a trumpet and amplifies blower noise like you wouldn't believe. I learned the hard way by installing my blower on the outside wall of the house and connecting it to the inside rig with about 6' of 4" PVC. It sounded like a machine shop.... even louder than the blower itself.  I switched to smooth fiberglass flex-ducting (on the web) and it was almost dead silent.

Even 1' of PVC pipe can add a lot to the noise.

Use flexible ducting material.  Find some that has a smooth inside, no ribs. Inside ribbed ducting (like some cheap dryer hoses) causes air turbulence and tumbling that produces backpressure components.... and more noise.

A smooth air flow with no acoustical echoing is the goal.  

Another suggestion - Tired of blower bearing whine noise, a few years back I went on a rampage and removed all rig blowers and brought them down to the local motor rebuilding shop to replace all bearings. It cost about $30 each, but what a difference! All of my blowers were used flea market worn-out pulls. After repair, be sure to test each one when you pick them up. I found one that was still noisy and suspected he didn't replace the bearings. I came back and it was silent the next time.

Brand new bearings go a long way to soothing the nerves....  Grin


T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

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There's nothing like an old dog.
KD1SH
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« Reply #9 on: February 18, 2019, 01:37:13 PM »

   Thanks for the tip on the PVC - I'll check around for that fiberglass stuff.  Flexible drain pipe is readily available at Lowe's and Home Depot, but it's ribbed, and I figured that at the very least it would cause a ton of drag to rapidly moving air.
   The blower is actually made for those "bouncy house" things for kids.  You can actually feel a noticeable thrust; if I were to put on roller skates, it would probably propel me around the basement.  It's got a metal mesh screen on the intake - probably a good thing if mounted in the basement - nothing like pneumatically firing a live mouse into your RF cage.

Cool looking blower.

PVC pipe as ducting.... unfortunately 2"-4" diameter PVC pipe sounds like a trumpet and amplifies blower noise like you wouldn't believe. I learned the hard way by installing my blower on the outside wall of the house and connecting it to the inside rig with about 6' of 4" PVC. It sounded like a machine shop.... even louder than the blower itself.  I switched to smooth fiberglas flex-ducting (on the web) and it was almost dead silent.

Even 1' of PVC pipe can add a lot to the noise.

Also, use flexible ducting material.  Find some that has a smooth inside, no ribs. Ribbed ducting (like most dryer hose) causes air turbulence and tumbling that produces backpressure components.... and more noise.

A smooth air flow with no acoustical echoing is the goal.  

Tired of blower bearing noise, a few years back I went on a rampage and removed all rig blowers and brought them down to the local motor rebuilding shop to replace all bearings. It cost about $30 each, but what a difference! All of my blowers were used flea market worn-out pulls. Brand new bearings go a long way to soothing the nerves....  Grin


T
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WB2EMS
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« Reply #10 on: February 18, 2019, 02:00:41 PM »

Quote
(it's got a howl to wake the dead)

I once worked on a piece of equipment that was part of the LAMPS helicopter systems. We always had an external fan piped in to blow through the real fan mounted on top for most of our work with the real fan disconnected. On the day we had to do a full on test run, I found out why. After they evacuated the building, we threw the switch and the thing fired up. OMG Shocked  The thing was a 110db siren! Two blades spinning like the dickens and wailing away. I asked how in the heck they had ever managed to choose *that* as the fan and the answer was it moved the required amount of air, and mounted next to the helicopter transmission, no one could hear it over the other noise.  Grin
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KD1SH
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« Reply #11 on: February 18, 2019, 03:23:09 PM »

   Fan/propeller noise is an entire science in itself, especially in the aviation world.  A lot of aircraft still use propellers, and much work has been done to keep them acceptably quiet for use at airports, which often rules out designs which otherwise would be very efficient at moving a lot of air.  Jet engines, too, and not all of their worst noise comes out the exhaust, but the intake as well.  I've heard some relatively small jet engines - specifically the little J-69 engine used in the Air Force's T-37 trainer - whose exhaust was quite tame even at full takeoff power, but when taxiing around at idle the compressor inlets would give off the most ungodly banshee shriek I've ever heard.


Quote
(it's got a howl to wake the dead)

I once worked on a piece of equipment that was part of the LAMPS helicopter systems. We always had an external fan piped in to blow through the real fan mounted on top for most of our work with the real fan disconnected. On the day we had to do a full on test run, I found out why. After they evacuated the building, we threw the switch and the thing fired up. OMG Shocked  The thing was a 110db siren! Two blades spinning like the dickens and wailing away. I asked how in the heck they had ever managed to choose *that* as the fan and the answer was it moved the required amount of air, and mounted next to the helicopter transmission, no one could hear it over the other noise.  Grin
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KK4YY
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« Reply #12 on: February 18, 2019, 06:06:05 PM »

There's another *trick* that I've done with the 12VDC fans in riceboxes. These fans usually don't run at all unless a high temperature is sensed in the power amplifier area. I've added a series dropping resistor to the circuit so the fan runs, slowly, all the time.

Sometimes, to get the fan to run slow enough to be very quiet, the resistor selected is of too high a value to get the fan to start from a dead stop. To cure this, I put an electrolytic cap across the resistor which, at power-on, looks like a low impedance effectively shorting the resistor to kick-start the fan. At power-off the resistor discharges the cap, resetting it.

Also, depending on the specific circuit the manufacturer used, blocking diodes may need to be installed so nothing shorts when the fan is called up to run at full speed.

I have the fan in my TS-440S running at all times. Even just in receive mode the rig would get quite warm, but now the slowly turning fan keeps it cool.

I've done this mod to a 2M FM mobile rig that had the RF power module fail. The manufacturers, in a race to make their rig the smallest, skimped on the size of the heat sink. From the heat, the module substrate cracked, nearly invisibly, and open a trace. I needed to put the module on a hotplate to repair it. Having the fan run, even slowly, helped prevent future failure (along with lowering the output power just a tad).


Don
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« Reply #13 on: February 18, 2019, 07:01:10 PM »

Cool thread  Grin

Regarding "equipment" fans:

Start your mods and "tricks" with a quiet fan! I have a large box chock FULL of box fans, "whisper fans", 12V, 120V, 220V, Gates BC1-T fans.

They are all loud even at similar watts/volts and CFM compared to one:
It's the Rotron WR2A1:

https://www.ebay.com/p/Comair-Rotron-Whisper-Case-Cooling-Fan-WR2A1-115volts/1624612965

Moves lots of air at 120 volts, no mods really required..

It was used in EVERY control room, and transmission facility at CBS Television and were absolutely reliable and quiet!

Shhhhhhhh...
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K1JJ
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« Reply #14 on: February 18, 2019, 08:50:41 PM »

Cool thread  Grin

They are all loud even at similar watts/volts and CFM compared to one:
It's the Rotron WR2A1:
https://www.ebay.com/p/Comair-Rotron-Whisper-Case-Cooling-Fan-WR2A1-115volts/1624612965


Hola Jeff!

Heard you on with your new HB 4-1000A X 4-400As last week. Vely nice sounding. How is that working out? Are those modulators in tetrode or triode config?


Yep, Rotron is a high quality and sought after name in fans and squirrel cage blowers....

There is a certain Rotron squirrel cage that the QRO linear builders talk about... quiet with big back pressure specs. I always wanted to try one years ago but they were always listed at several hundred $ on the web, sometimes $500+ each if you could even find one.  Do you know the model number?  I have a need for one if I can find a reasonable deal.

T
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« Reply #15 on: February 19, 2019, 09:09:57 AM »

Hey T,

This be the Rotron blower still commanding big $$ :

https://www.ebay.com/itm/Rotron-Squirrel-Cage-Fan-Blower-PN-413-AS-3100-rpm-115-vac-2a-Quantity-1/282101893884?hash=item41ae954afc:g:2wUAAOSw3wVag9iC:rk:1:pf:1&frcectupt=true

And to answer the transmitter question, AB1 Tetrode  Wink
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KK4YY
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« Reply #16 on: February 20, 2019, 02:19:27 PM »

The measured impact of finger guards on fan noise! Shocked

This, and other fascinating application engineering information disclosures can be found here.

http://www.comairrotron.com/sites/default/files/files/COMAIR%20CATALOG.pdf


* impact of finger guard.png (543.53 KB, 517x358 - viewed 202 times.)
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« Reply #17 on: February 21, 2019, 06:43:30 PM »

I think I'm done with fans as much as possible (except for low volume low speed) and use only large low speed blowers from now on. They just can't be beat for low noise and working against pressure. What, if any, are the advantages of fans?

I have been using blowers surplussed from old VAX6000 computers. OK they seem to be hard to find these days but there are some here and I'd put one up against the Gates fan any time.

I admit this kind is intended for mounting so the shaft is horizontal and the inlet is on the side, but the one on the transmitter has been placed up there with the inlet on the bottom and has been run hundreds of hours with no slop appearing.

They are 24V and move a ton of air. The inlet is 10" diameter and the outlet is open, radial flow. At 11-15V they are almost silent. There's one on top of the 4-1000 transmitter where it removes hot air from the RF deck and entire cabinet. It's quieter than the two blowers inside the unit serving the 4-1000 and 3-500Z pair.

Very recently I mounted two 8 core PCs, a 100W/CH amplifier, and a crypto miner in a 4FT enclosed rack. A 10" hole was cut in the back door and one of those blowers put there to suck air in. On the outside is a standard residential type pleated HVAC filter setup and it all keeps the rack slightly pressurized, stops cat hair and dust entry. The exhaust is on the sides and front, down at the floor. The gear may try its best to circulate hot air in the rack, but the blower keeps pushing cold filtered air in and so air must go out.

Not telling anyone what to do but the lack of extra noise is wonderful.


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