-48VDC power supply to power Symmetricom device - Page 1
Forum section: electronics / testgear

author: tverbeure
author_rank: Regular Contributor
timestamp: July 15, 2023, 02:20:21 pm
content: 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?

author: TimFox
author_rank: Super Contributor
timestamp: July 15, 2023, 03:57:25 pm
content: Acopian makes high-quality DC linear supplies.Their link:https://www.acopian.com/linear-regulated-power-supply-models.htmlThey 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_iPh6SrYgNote 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.

author: iJoseph2
author_rank: Regular Contributor
timestamp: July 15, 2023, 05:26:06 pm
content: Quote from: tverbeure on July 15, 2023, 02:20:21 pmI 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/364085635781Is +48v 1amp any use? ..https://www.ebay.co.uk/itm/364088948243

author: tverbeure
author_rank: Regular Contributor
timestamp: July 15, 2023, 05:27:44 pm
content: 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.

author: wasedadoc
author_rank: Super Contributor
timestamp: July 15, 2023, 05:36:09 pm
content: On ebay I see a photo of the rear with the two power input terminals labelled '-48VDC' and 'RTN'. Also '1 Amp'.

author: tv84
author_rank: Super Contributor
timestamp: July 15, 2023, 05:59:03 pm
content: Here:https://www.digikey.com/en/products/detail/mean-well-usa-inc/NDR-240-48/7705223

author: nctnico
author_rank: Super Contributor
timestamp: July 15, 2023, 06:29:44 pm
content: Quote from: tverbeure on July 15, 2023, 02:20:21 pmAny 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

author: Gregg
author_rank: Super Contributor
timestamp: July 15, 2023, 06:41:09 pm
content: 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.

author: AVGresponding
author_rank: Super Contributor
timestamp: July 15, 2023, 07:44:21 pm
content: 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...

author: TimFox
author_rank: Super Contributor
timestamp: July 15, 2023, 10:28:25 pm
content: 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.

author: Scratch.HTF
author_rank: Regular Contributor
timestamp: July 16, 2023, 12:50:47 am
content: 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.

author: tverbeure
author_rank: Regular Contributor
timestamp: July 16, 2023, 05:45:30 am
content: Quote from: TimFox on July 15, 2023, 10:28:25 pmI'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.QuoteGood! I'll start looking in eBay.

author: iJoseph2
author_rank: Regular Contributor
timestamp: July 16, 2023, 09:05:10 am
content: Quote from: AVGresponding on July 15, 2023, 07:44:21 pmThat explains the output voltage on the Juniper power supply. Thanks!

author: ve7xen
author_rank: Super Contributor
timestamp: July 17, 2023, 06:55:01 pm
content: Quote from: iJoseph2 on July 16, 2023, 09:05:10 amThe 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.