Re: Exhaust Fan in IIe Internal p.s.

[Rubywand <rubywand@swbell.net>]

stephen e buggie writes ...
> 
> I still use IIe's at home and at the office.
> 
> Has anyone ever wondered about the sealed metal casing around the IIe
> internal power supply.  It gets hot, correct?
> 
> Over the weekend, I installed a CrowFred 2" exhaust fan on a IIe p.s.
> 
> I sawed a 2" diamter hole in the upper part of the casing, with 1/2" holes
> near the other end of the power supply.  I also installed a green LED lamp
> on the side of the casing, connected to the +5v DC line, inside the
> casing.  Colling air is now drawn into the IIe p.s., and it exits through
> the top.
> 
> The IIe p.s. is upside down so the air path is blocked by the botherboard.
> But ai4r goes around the board.
> 
> The +12v ppower to run the fan is tapped from large power points at the
> front edge of the IIe motherboard.   They are at the lower left front
> corner of the board.
> 
> It works!
> 
> The p.s. runs noticeably cooler. than with no ventalation.    I tried
> loading up[ all slots with large interface cards, and the p.s. eventually
> stalled (overload), foircing a reboot.  Thus, for a fully loaded IIe,
> Bugg-Power external p.s. is still needed.   But adding the exhaust fan
> migtht crank slightly better performance from the internal p.s. than is
> otherwise possible.
 ....

     Blowing air through the power supply is probably a good idea in terms of
extending component life, especially for electrolytic capacitors. It is not
likely to increase output capability because the supply has a set current limit
which, supposedly, is in line with running as a closed box-- i.e. you'll hit
the current limit shutdown before running into a thermal shutdown.

     According to standard specs, the IIe power supply is good for about 2.5
Amps on the +5V line. This is a bit more than the wires (+5V and GND) from the
supply can deliver without a noticable Voltage drop. So, if the total load on
+5 is, say, 2.3 Amps, you would be likely to experience glitching leading to
system bombing.

     A really stuffed IIe-- like one with an accelerator, extra RAM, SSC, mouse
card, printer interface, MockingBoard, disk controller card, and hard disk
would be likely to pull more than 2.5 Amps, trigger the current limit, and
simply shut down the power supply. There would not be time for anything to get
hot.

     So, as regards what you can stuff into a IIe, cooling the PS isn't likely
to matter much unless you fatten the leads from the unit and adjust the current
limit upward-- in which case you may _need_ the cooling to avoid damage and/or
a thermal shutdown.

     A better solution is to get a surplus PS with higher output capacity which
fits inside your IIe. By the time you get the new PS mounted, output leads
connected, and arrange for mounting the power cord socket and ON/OFF switch,
this can be a fairly demanding project.

     One of your Buggie Power Supplies offers a fairly quick, easy solution.
You do have to find a good, safe place for the external PS; but, in return, you
remove a major source of heating inside your IIe and acquire a nice chunk of
space you can use for further enhancements-- like, maybe, a larger speaker with
amplifier module or internal hard disk.



Rubywand