julian@bongo.UUCP (julian macassey) (04/07/89)
Here in Los Angeles we are currently going through a heat
wave. It is in the hundreds during the day and plummets to the
low seventies at night. My 3b1 lives with me in an ancient
apartment with no air conditioning so we both swelter together. I
do not have enough power available (25 Amps 110V total) to slap
in a small air conditioner.
The other evening I cam home and sat at the console, suddenly
the cooling fan revs suddenly dropped. I thought the fan was
about to stop and my heart damn nearly did. That is how I found
out that the Unix-pc has a 2 speed fan. Regular noisy for regular
cooling and super noisy for super cooling.
This was a revelation. I mailed Jim Gottlieb (jim@denwa)
about this and he told me that yes indeed, there was a two speed
fan and it was controlled by a thermistor, possibly on the Power
Supply board.
Recently on this group there has been discussion about
ripping out the installed DC fan and inserting an AC fan from Rat
Shack. Obviously unless modifications were made, any change to an
AC fan would loose the 2 speed feature. It could be done, I could
do it with a bit of fiddling - schematics would help though.
Obviously for a margin of safety, as a single speed fan, the AC
fan at single speed would have to shift as much air as the DC fan
at high speed. Unless your computer lives in a luxury
airconditioned room. Beware of airconditioned offices, they often
kill the air over those hot August weekends to save energy.
So it would appear that some care should be taken over the
cooling fan thing. This brings me to a concern that I have had
since I first turned on my 3b1. I think it runs too warm.
Whenever I put my hand behind the machine I feel warm air coming
out of the fan vent, no matter what speed the fan is running at
or whatever the room temperature. Yes my un-airconditioned dump
also has no heat and it gets to the mid forties in the winter. I
believe as far as electronic equipment is concerned, exhaust air
should not be warmer to the touch than ambient and heatsinks
should never get uncomfortably warm. The reason for my heresy is
that heat kills electronic components - sooner or later. So if
you hate fixing stuff, or just having it die, keep it cool.
I am seriously considering throwing another fan (AC) in
series with my installed DC fan, just to increase the airflow. If
I can get an AC fan that really pushes wind, I will remove the DC
fan and replace it with the super AC fan. This will also remove
some of the load from the Power Supply which will further help
with cooling - assuming the fan is powered by the Power Supply.
As far as I know, there is no current source for replacement
power supplies. This makes keeping the thing cool and alive for a
long time all the more important. Also when power supplies die,
they have a nasty habit of doing it in a vindictive way and
taking expensive boards with them.
Any thoughts and suggestions re cooling and power greatfully
received. If you have messed with the fan, I certainly would like
to hear of successes and failures, tips and traps.
Yours
--
Julian Macassey, n6are julian@bongo ucla-an!denwa!bongo!julian
n6are@wb6ymh (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495alex@wolf.umbc.edu (Alex Crain) (04/08/89)
In article <157@bongo.UUCP>, julian@bongo.UUCP (julian macassey) writes: > I am seriously considering throwing another fan (AC) in > series with my installed DC fan, just to increase the airflow. If > I can get an AC fan that really pushes wind, I will remove the DC > fan and replace it with the super AC fan. This will also remove > some of the load from the Power Supply which will further help > with cooling - assuming the fan is powered by the Power Supply. I replaced my DC fan with the biggest AC fan that would fit in the machine. It makes a fair bit of noise,but I got used to it. It probably costs me money (more current) but It presumably takes a load off the power supply, and I haven't found the machine to be warm to the touch since. Also the air comming out the back went from moderatly warm to cool. I also got the feeling that AC fans are more reliable then the stock DC ones, judging from the postings here. My AC fan has been in service for about a year without a blink. :alex Alex Crain Systems Programmer alex@umbc3.umbc.edu Univ Md Baltimore County umbc3.umbc.edu!nerwin!alex
motteler@umbc3.UMBC.EDU (Howard E. Motteler) (04/08/89)
In article <157@bongo.UUCP> julian@bongo.UUCP (julian macassey) writes: > > This brings me to a concern that I have had >since I first turned on my 3b1. I think it runs too warm. >I believe as far as electronic equipment is concerned, exhaust air >should not be warmer to the touch than ambient and heatsinks >should never get uncomfortably warm. Depends on the equipment: you could bake a potato (or a whole chicken) on the exhaust heat from some of the radio or TV transmitting tubes I used to work around. Now, you're not pumping kilowatts thru this little box, but you're consuming, say 150 to 200 watts, and *every bit* (well, at least 99%) of this power ends up as heat, and gets blown out the back. (Not true, you say? Where do you think that energy goes!) So "warm" is about right, for the exhaust air--the waste heat has to go somewhere. The other major energy consumer/heat producer is the flyback transistor(s) in the monitor, which should also feel warm. About the same as a TV... Heat sinks can run pretty hot--an old rule of thumb from my technician days was to moisten a finger (the thumb was already burnt) and give the sink a quick touch--if you get sizzle, things are too hot, but fast evaporation is ok. But beware of heatsinks in switcher supplies: some of them may be "hot" in more ways than one! > . . . heat kills electronic components - sooner or later. So if >you hate fixing stuff, or just having it die, keep it cool. Absolutely correct, but what's hot to you may be cool to an SCR that's rated to dissipate heat most effectively while running at 70 C. >If I can get an AC fan that really pushes wind, I will remove the DC >fan and replace it with the super AC fan. This will also remove >some of the load from the Power Supply which will further help >with cooling - assuming the fan is powered by the Power Supply. I think even the cheap R.S. AC fans are rated at more CFM than the stock DC fans can give on "high"=12v. On low the stock fan(s) are fed about 9-10 V at 100 to 150 ma. If you're really worried, you might put a *pair* of AC fans in, acting as exhaust fans, in both fan slots. (In "parallel"-- not in series!) -- Howard E. Motteler | Dept. of Computer Science motteler@umbc3.umbc.edu | UMBC, Catonsville, MD 21228
julian@bongo.UUCP (julian macassey) (04/09/89)
In article <1886@umbc3.UMBC.EDU>, motteler@umbc3.UMBC.EDU (Howard E. Motteler) writes: > In article <157@bongo.UUCP> julian@bongo.UUCP (julian macassey) writes: > > >If I can get an AC fan that really pushes wind, I will remove the DC > >fan and replace it with the super AC fan. > deleted stuff > If you're really worried, you might > put a *pair* of AC fans in, acting as exhaust fans, in both fan slots. > (In "parallel"-- not in series!) > > -- > Howard E. Motteler | Dept. of Computer Science > motteler@umbc3.umbc.edu | UMBC, Catonsville, MD 21228 This appears to be a good idea. One of the first things that occured to me was to take the piece of foam rubber out of the fan slot on the left hand side of the machine and slap in another fan. Obviously, two fans would be twice as good. I mentioned this simple but brilliant mod to Gary Sanders n8emr@gws and he said "No". Here was his story. The early systems were shipped with two fans, but that caused air stagnation and hard disks were overheating and failing all over the place. So there is a reason you only get one fan, it is not because AT&T were too cheap to spring for a second fan. So judging from that and what I have read in this group, the tip seems to be: Go for a hefty AC fan and put up with the noise. Any suggestions for model numbers and sources? Or are all the 3b1 AC fans swapmeet specials. -- Julian Macassey, n6are julian@bongo ucla-an!denwa!bongo!julian n6are@wb6ymh (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495
motteler@umbc3.UMBC.EDU (Howard E. Motteler) (04/10/89)
In article <161@bongo.UUCP> julian@bongo.UUCP (julian macassey) writes: > [ regarding adding a second fan ] > This appears to be a good idea. One of the first things that occured to >me was to take the piece of foam rubber out of the fan slot on the left >hand side of the machine and slap in another fan. Obviously, two fans would >be twice as good. I mentioned this simple but brilliant mod to Gary Sanders >n8emr@gws and he said "No". Here was his story. The early systems were >shipped with two fans, but that caused air stagnation and hard disks were >overheating and failing all over the place. So there is a reason you only >get one fan, it is not because AT&T were too cheap to spring for a second >fan. So judging from that and what I have read in this group, the tip seems >to be: Go for a hefty AC fan and put up with the noise. This sounds like good advice, although I've been running for a year and a half with a 2 fan 3b1 with the 80 meg mimiscribe, and no problems. But then I pulled the "electrostatic shield" off the hard disk (along with the row of tin "fingers" in the back, and the monitor "ground finger"--it's still grounded thru the cable shield), so air can circulate around it a bit more freely. Warning: doing that may make the machine put out more RF noise, although mine shared a living room with a color tv, fm "wireless headphone" and various radios, with minimal effect. A US robotics modem I had put out far more RF noise. Actually, my motive was not so much cooling as (acoustic) noise: I'm feeding a pair of DC fans at reduced voltage, which draw a bit more air than a single DC fan, and only a little more current. Because each fan spins slower, the total noise is quite a bit less. The Miniscribe also had an annoying "ringing"--a resonance that I got rid of this by gluing a couple of quarters to the top of the case. A negative side effect of drawing more air thru the machine is that if you leave the keyboard off the shelf, more air gets sucked in thru the floppy drive, and it (or the whole machine, for that matter) can get gummed up with dust fuzzies faster. I did a number of experiments with different fan configurations, letting the machine run for a couple of hours each time, and then quickly popping it apart, to see if anything was getting too hot. I even tried switching the fans around to blow air INTO the machine, so that I could filter air being sucked IN thru the fan grates. (This worked, but not all that well, and blew warm air on your fingers... possibly a plus for typing, if your room gets a cold as you said :-) Probably the most important "cooling hint" for ANY user: DON'T BLOCK THE LITTLE GRILLE OVER THE POWER SUPPLY (below the monitor, on the right hand side). A sheet of paper laid here can get sucked down aginst the grill, blocking a direct airflow to all those hot little cooling fins on top of your power supply. -- Howard E. Motteler | Dept. of Computer Science motteler@umbc3.umbc.edu | UMBC, Catonsville, MD 21228
lenny@icus.islp.ny.us (Lenny Tropiano) (04/10/89)
In article <1886@umbc3.UMBC.EDU> motteler@umbc3.umbc.edu (Howard E. Motteler) writes: ... |> |>I think even the cheap R.S. AC fans are rated at more CFM than the |>stock DC fans can give on "high"=12v. On low the stock fan(s) are fed |>about 9-10 V at 100 to 150 ma. If you're really worried, you might |>put a *pair* of AC fans in, acting as exhaust fans, in both fan slots. |>(In "parallel"-- not in series!) |> I wouldn't put in *two* fans. I had this configuration with the DC fans, before I switched to the one AC fan. The two DC fans only put more of a drain on the 12VDC supply, and it dragged more dust through my machine. The left side of the full height "3B1" UNIX pc doesn't get that hot, and pulling more dust through the floppy only makes for more problems. The older PC7300's did have two fans, but they also had additional holes to pull air through that smaller case. -Lenny -- Lenny Tropiano ICUS Software Systems [w] +1 (516) 582-5525 lenny@icus.islp.ny.us Telex; 154232428 ICUS [h] +1 (516) 968-8576 {talcott,decuac,boulder,hombre,pacbell,sbcs}!icus!lenny attmail!icus!lenny ICUS Software Systems -- PO Box 1; Islip Terrace, NY 11752