[Asterisk-Users] Qs about FXO/FXS cards

[Steven Critchfield]

On Mon, 2005-01-03 at 09:20 -0500, Andrew Kohlsmith wrote:
> On January 3, 2005 08:01 am, Bob Goddard wrote:
> > > As I said, I measured the variation on the relevant lines with a 100MHz
> > > DSO when running under load.
> 
> > No you didn't. What was the power load when the modules failed?
> 
> The actual current draw I did not measure -- I was looking for voltage sags or 
> swells on the +5V and +12V lines during load.

While this has stemmed from my semi-educated guess, I would be most
concerned with current instead of voltage. When I previously abused a PC
PSU it was driving a high torque 12v electric motor. The really high
torque motors would peak out at 5 amps during spool up. That would cause
a PC PSU to pulse between something like .5 amps and 4 amps. If the
spool up was controlled, I could keep the motor under 4 amps and the PSU
could drive the motor. I had no interest in the voltage because it was
the current that ran the motor.

> > That is a simple "find", a better one would be "find / -ls", you should
> > also try running seti on all processors at the same time.
> 
> yes it's a simple find but there would be significant disk/cache thrashing 
> when combined with a kernel complile, as I'd mentioned.

Okay, link this to my rambling above and you would see that by thrashing
the disk, you are actually keeping the spindle spooled up and not
measuring the spool up draw. My guess is a spooled down machine getting
a random incoming call that then must generate ring and spool up the
HD(s) to start writing logs at the same time on a questionable PSU.   

> > If your motherboard requires 5amps when your psu can only supply 4, then
> > you're going to have trouble.
> 
> Yes I completely agree with you here.
> 
> > This IS a problem, just that it may not be in your case.
> 
> I am willing to bet that my case is the more general case here -- The TDM 
> current draw just is not a big draw, or at least it should not be -- 
> certainly no more than a HDD during heavy seeking or a video card during some 
> intense gaming sequences or even some of the larger data acquisition/DSP 
> cards I've used in the past.

As far as I know, with the exception of a couple of video cards that
resorted to an external PSU, all video cards have to draw from the PCI
or AGP bus. This means the TDM card is likely to draw more than the
graphics card.  Heavy HDD thrashing uses less power than the spooling up
of an idle drive. 

I'm also starting to wonder about specific phones now as well. While
this next bit of rambling is not asterisk related, it is phone related
and something to consider. While out at my mothers house, she had a
phone next to her PC that wouldn't ring and when used would cause the
DSL to drop out. I happened to buy a new cordless phone for her and
replaced a phone that was working elsewhere in her home. After putting
the new cordless phone in, the phone by her PC started ringing properly
and was able to be used without dropping the DSL.  
-- 
Steven Critchfield <critch at basesys.com>