View Full Version : Soekris boards and telephony power supplies
georgew
08-07-2003, 12:58 PM
Those of you using telephony type negative 48 volt power plants be aware that the Soekris has the negative supply side grounded on the board. This is only a problem when you bond the chassis ground to earth ground, such as when you install a lightning arrester.
-48v is a standard for much of the world for battery based power plants. -48v has a positive ground...
:?
sounds like you found out the hard way... both outputs on the the -48v westell power supply I have are floated to ground. I guess that wouldn't make it a -48v power supply, but that's what it says.
georgew
08-22-2003, 05:25 AM
If the power supply has floating outputs, either side can be grounded...
We have a large -48v power plant. I build to this standard because of the various power plant types, only +12v and -48v are well supported. +12v has advantages because it is better supported... However 48v is the highest nominal voltage rating considered safe to work on while live with standard metal hand tools.
I designed the power plant, and I have designed power supplies for modular systems... So that I didn't mentally complete the ground circuit before wiring it was pretty lame... When you work for yourself you don't document anything before you do it, so you run a greater risk of moving too fast.
But in general, when designing modular systems, float the circuit if possible... don't assume a negative ground power supply. The chassis ground does not need to be connected to the negative side of power...