-48VDC power supply to power Symmetricom device

[tverbeure]

I’m pretty sure that I just bought a Symmetricom OT-21 TimeSource that requires a -48V DC power supply… without having a -48V DC power supply.

So… where do I get such a thing? There’s surprisingly little info online other than expensive telecom grade new stuff.

Anyone who was able to solve this in a cheap way?

[TimFox]

Acopian makes high-quality DC linear supplies.
Their link:  https://www.acopian.com/linear-regulated-power-supply-models.html
They are not cheap purchased new, but I have seen many of these DC supplies on eBay.
an example:  https://www.ebay.com/itm/266234574920?hash=item3dfcd13848:g:9rcAAOSwQNJkSD2S&amdata=enc%3AAQAIAAAA4Lao48wC6ANyPJM%2B%2Br3mgOXWFqfOGc9ivjq1oIk1x7r9qxAN32Y8c%2FGeyi3IIwRLnE2DdVp2ci%2Fynf3NynPyWIdkavWRZugB5qrTEB6697eWbw0X5BExabQ6JKVJ4%2BeDRF66kfGbbArlIkccL1AdcOFzpqmFseMU7UTr%2FXkPbUelNd1MTEbyGlbZ7M%2FzayMXlmNHwcYXbrKM16QPyFQRc1TUbYMzarVrL8klgNMLm0MVekyEUlq%2FBJ2TZKtzudIO%2B76E78ToYqlHlAHJhKdD8V58tkIoPI9nEYtkI5bvCIod%7Ctkp%3ABk9SR_iPh6SrYg

Note that many eBay sellers of Acopian don't understand what they have and post the ratings by what they read by the fuseholder, e.g. 1/2A 250 V.
That makes eBay's sort by output voltage useless for these units.
Generally, the DC output voltage is two digits following the initial letter.
24 V is far more popular than 48 V, but you might get a deal on a dual 24 V supply.

[iJoseph2]

Anyone who was able to solve this in a cheap way?

I thought PoE edge switches were -48v, but ..

https://www.ebay.co.uk/itm/265994633767

.. that Juniper one's -54v.

I think the Extreme edge switches have DC-DC within the switch chassis so their power supplies are only +12v ..
https://www.ebay.co.uk/itm/364085635781

Is +48v 1amp any use? ..
https://www.ebay.co.uk/itm/364088948243

[tverbeure]

Thanks, that’s very useful!

I assume that I could use an +48V or +-24V supply, as long as they have a floating ground?

I have an E3631A power supply with +25/-25V and floating ground.

[wasedadoc]

On ebay I see a photo of the rear with the two power input terminals labelled '-48VDC' and 'RTN'. Also '1 Amp'.

[tv84]

Here:
https://www.digikey.com/en/products/detail/mean-well-usa-inc/NDR-240-48/7705223

[nctnico]

I’m pretty sure that I just bought a Symmetricom OT-21 TimeSource that requires a -48V DC power supply… without having a -48V DC power supply.

So… where do I get such a thing? There’s surprisingly little info online other than expensive telecom grade new stuff.

Anyone who was able to solve this in a cheap way?

Any 48V power supply that can deliver the amount of current required will do. Keep in mind that 48V is 48V. Only you'll need to connect the 0V of the timesource to + of the power supple and -48V to - of the power supply to get the timesource to see -48V at the power supply input. Looks like it need 1A. A cheap laptop brick style mains adapter will do just fine and these are easy to buy. Like this one for less than US$ 8 (special sale, so your lucky day) : https://www.newark.com/mean-well/gsm60a48-p1j/adapter-ac-dc-48v-1-25a/dp/44AC5091

[Gregg]

I have several telcom 48V power supplies in my storage that you could have cheap.  How many amps do you need?  You can PM me.
edit: I have two rack mount and some about laptop size plastic cased low amperage.

[AVGresponding]

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...

[TimFox]

Usually, DC power supplies have a positive and negative terminal, and the user is allowed to ground one or the other.
It doesn't hurt to check, especially if one terminal is actually labeled "ground".
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.
I have used dual Acopian supplies that contained two identical subunits, with all four terminals brought out for flexible connections.

[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]

Usually, DC power supplies have a positive and negative terminal, and the user is allowed to ground one or the other.

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.

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.

Good! I'll start looking in eBay.

[iJoseph2]

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...

That explains the output voltage on the Juniper power supply. Thanks!

[ve7xen]

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...

That explains the output voltage on the Juniper power supply. Thanks!

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.