I know  you know this.  Diode voltage drop depends on current.  If the router 
has times when it is drawing significantly less current, then the voltage drop 
will be less and vice versa.  I know everyone cites .6 volts for a PN silicon 
junction but it is more like double  that on many power rectifiers.  A common 
1N4004 has a 1 volt drop at 1 amp.  But only about .2 volts down in the 
microamp region.  


  From: "TJ Trout" <t...@voltbb.com>
  To: af@afmug.com
  Sent: Saturday, October 15, 2016 6:43:04 PM
  Subject: [AFMUG] dual psu with diode, ccr1036 wierdness

  to increase reliability on my new ccr1036 router, I decided to add a second 
24v psu and isolate the two with rectifier diodes. The factory PSU puts out 
about 24v, after the diode drop it's about 23 and change, I installed a second 
psu and adjusted the output to 22v or about 21 and change after the diode.

  I installed the router and started monitoring the reported voltage by SNMP 
logging, I noticed it started out at 23v and then has been slowly jumping down 
and back up to 22v any idea why it wouldn't just keep taking power from the 
source with the highest voltage?

  Is this going to be a problem? I was hoping to monitor for main psu failure 
by sending an alert below 23v which would tell me if the main PSU failed but 
for some reason this isn't working as planned...

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