| Products > Test Equipment |
| -48VDC power supply to power Symmetricom device |
| << < (3/3) |
| Scratch.HTF:
I've got some pointers for repurposing server PSUs including those for PoE applications: * Many are of high efficiency (typically having an 80 Plus Gold or higher certification) and have active power factor correction (APFC) which the APFC board may be separate in larger units. * Output is typically derated for lower AC input voltages. * Certain units (which may be designed for automated exchange without requiring the callout of a technician) do not have an IEC (computer type) input connector. * Starting of the main output (where the standby output is constantly enabled) typically requires a signal (which may be looped) on a certain pin (typically last mate (which connects last on insertion) for hot swap units) which typically has a pullup or pulldown resistor or for certain units, a command on the data pins (usually I2C as used by SMBus/PMBus/IPMB/AdvancedTCA/MicroTCA) for starting which also has pullup resistors to a +5V or +3.3V standby supply. * Outputs may be segmented and may have different current limits for each segment; for units supporting Power over Ethernet (PoE) applications (typically 48-54V) such as in network switches, this output is typically floating with a high value resistor connected between one side of the output and the chassis. * Electronic components are typically of high quality and rated for long operational life. |
| tverbeure:
--- Quote from: TimFox on July 15, 2023, 10:28:25 pm ---Usually, DC power supplies have a positive and negative terminal, and the user is allowed to ground one or the other. --- End quote --- I'm hoping that this is the case, but I want to be extra careful about that. Especially since the 10MHz output will go to other devices, and it's not clear if that output has its own transformer to make their own floating ground. --- Quote ---The Acopian supplies I suggested had neither terminal grounded, with a finite voltage rating between the terminals and the chassis (insulation rating). If you find a +/- 25 V supply, where the common is not grounded, you can use it as a nominal 50 V supply by not connecting the common terminal. --- End quote --- Good! I'll start looking in eBay. |
| iJoseph2:
--- Quote from: AVGresponding on July 15, 2023, 07:44:21 pm ---The 48V is a nominal voltage, I'd guess. We used to use 48VDC lead acid batteries to back up the power for telecoms switches, which of course in practice is around 54VDC at float charge levels... --- End quote --- That explains the output voltage on the Juniper power supply. Thanks! |
| ve7xen:
--- Quote from: iJoseph2 on July 16, 2023, 09:05:10 am --- --- Quote from: AVGresponding on July 15, 2023, 07:44:21 pm ---The 48V is a nominal voltage, I'd guess. We used to use 48VDC lead acid batteries to back up the power for telecoms switches, which of course in practice is around 54VDC at float charge levels... --- End quote --- That explains the output voltage on the Juniper power supply. Thanks! --- End quote --- The original PoE specification allowed for source voltages down to 44V, but the modern/higher power standards require either a minimum of 50V or 52V at the PSE, to account for the voltage drop over up to 100m of Cat5; 54V is a very typical choice. Powered devices must be happy to receive up to 57V. |
| Navigation |
| Message Index |
| Previous page |