Compaq (off topic) - test-drb@ccmp.vtda.org

20 Jul 1998

The thing powers up off the keyboard, like a mac. I tried powering it
off a PC SMPSU, otherwise loaded by the PC from which it came. The
PSU was working fine, and I got correct voltages, even the right
voltages on the external power connector on the laptop (I connected
the wires to the battery terminals). And now matter how many times I
pressed the on button, the #*%^)!$ thing wouldn't start. Ideas?
...
 Surely you mean 170mA here. It's normal to charge
at the C/10 rate, at 
least when trickle charging. And I'd give it about 14 hours to make up 
for losses in the battery (you never get the energy out that you put  in).
...

> If the 'float voltage of the battery goes over the 12v figure, that  will
...
 > cut down the charging current. The _best_ thing
would be a  milliammeter
...
   on the PS
output, and a variac controlling input of the _big_ PS. 
Wait a second. I thought he was using a PC power supply. Those have 
internal regulation. Hanging one off a Variac won't do a darn thing  apart 
...
 from test the line regulation of the PSU.

> 
> Now, as to whether or not you can get away with the 'big PS' on the
> laptop instead of the battery? If at all possible, don't try. The
> battery is providing an imense ammount of conditioning to the  incoming
...
   power flow.
(There are amazing ammounts of garbage floating on top of
 the normal PS output. [everything from 'lightning induced spikes, on 
Every regulated power supply that I have ever seen has a fair amount of 
internal filtering. Now while it's not a good idea to only load one of 
the subsiduary outputs of an SMPS (and remember that in a PC PSU, the  5V 
...
 output is the main one, from which the regualtor sense
lines are  taken), 
...
 I think that noise on the output would be the least of
your worries.

> down to spikes from the local refrigerator turning on].) If you  _must_
...
   try, it
won't hurt to throw a few thousand mfd of capacitor across
 things. Voltage wise, you are probably O.K. 
There's probably 2200-4700uF inside the PSU across the 12V rail.

 Chuck 
-tony

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