Which computer equipment does use 42V? - Page 1
Forum section: electronics / general

author: 0db
author_rank: Frequent Contributor
timestamp: October 17, 2020, 03:30:30 pm
content: Yesterday I found a very massive lot of PSUs. They have two rails of 42V with 60A.They are marked "SONY/CISCO", but I cannot find any information about them.I am just curious: 48V is for POE, but ... what about 42V? And 60A ?!?I cannot imagine a computer equipment that requires so much current at 42V

author: Benta
author_rank: Super Contributor
timestamp: October 17, 2020, 03:49:34 pm
content: Could be in connection with a server farm with massive lead-acid battery backup. 42 V would fit in that scenario.

author: madires
author_rank: Super Contributor
timestamp: October 17, 2020, 03:53:33 pm
content: Those are most likely PSU modules for Catalyst 6500 switches.

author: Red Squirrel
author_rank: Super Contributor
timestamp: October 19, 2020, 01:12:04 am
content: Wonder if 42 is just the minimum it can take, sounds like something made to run on a 48v system, which usually floats at 54v. Usually used in telecom.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 29, 2020, 11:46:39 am
content: Those voltages are never used directly by computer hardware, and always go through an SMPS to get lower voltages. Therefore it's easy to make the hardware in such a way that a reasonable voltage range can be used.POE for example is not "just" 48V, but depending on standard it can range between 37 and 57V.https://en.wikipedia.org/wiki/Power_over_EthernetI'm not sure, but I think power supplies like that are also used as DC rails in 19" racks to provide power for all the units in the rack.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 29, 2020, 10:16:30 pm
content: Could be efficiency optimization by running the PoE at 42V except long runs which are boosted by individual boost converters.

author: nightfire
author_rank: Frequent Contributor
timestamp: October 30, 2020, 01:58:51 am
content: In Telco equipment and also ruggedized equipment (NEBS certified etc.) usually 48V components are used, as 48V is the most common way to power telco stuff due to some historical reasons. Also offsite container locations could be powered with a big battery pack instead of some sometimes flinchy 230V UPS.Some Switches and Servers have the option to order them with 48V PSU.So when their output is 42V, the input shoud be somewhat higher, which fits the 48V/Telco theory.

author: madires
author_rank: Super Contributor
timestamp: October 30, 2020, 09:48:39 am
content: Quote from: NiHaoMike on October 29, 2020, 10:16:30 pmPoE clients are usually powered by the local access switch (fixed ports and standard chipset). That means inexpensive 1000BaseT ports and short cable runs. Using a large Catalyst switch for that would be a waste of money.

author: nightfire
author_rank: Frequent Contributor
timestamp: October 30, 2020, 11:12:05 am
content: Depends- on some verly large campuses or office buildings, it can make sense to wire VoIP phones directly into one single switch to reduce latency. The Cisco 6513 was intended to do that, with a capacity of 13 boards- minus the two redundant SUP engines it meant 11 boards for 100 Mbit Ethernet/POE back then in 200x.