PC Power Supply 5V Rating - Page 1
Forum section: electronics / general

author: bobcat2000
author_rank: Regular Contributor
timestamp: February 16, 2021, 05:57:10 pm
content: I am trying to upgrade my 460W Dell power supply. I check the spec. It has a 25A 5V rating. So, I am trying find one that match the spec.I found only one Corsair CX model that has a 25A 5V rating that was within my budget. Many other brands only provide <20A 5V rating.My understanding is that CPU runs on 12V nowadays. The rest of the ICs still run on 5V (correct me if I am wrong.)What make the Dell motherboard different that Dell requires a 25A 5V power supply that motherboards from other brands do not?Thx!

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 16, 2021, 10:39:53 pm
content: Does it have a lot of USB ports (type A) or the capability to have a lot of SATA SSDs or HDDs? Those are the main 5V loads nowadays. In typical applications, less would be fine as long as you don't have too much stuff plugged into the USB ports. (Saw that problem with a development system that had a lot of smartphones plugged in for testing - machine would crash when deploying an app to many phones at once and the developers could not figure out why.)

author: bobcat2000
author_rank: Regular Contributor
timestamp: February 17, 2021, 01:14:48 am
content: The Dell has 10 USB ports outside, 5 SATA, 1 mSATA, and 1 mini-PCI inside.So, I do need a P/S that can push 25A 5V.Those 17A or 20A P/S won't cut it.

author: Monkeh
author_rank: Super Contributor
timestamp: February 17, 2021, 01:27:00 am
content: Quote from: bobcat2000 on February 17, 2021, 01:14:48 amDoubtful. Stick a clamp meter in there and see.Why are you replacing it anyway?

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2021, 01:29:41 am
content: Quote from: bobcat2000 on February 16, 2021, 05:57:10 pmAge? What motherboard and CPU?

author: bobcat2000
author_rank: Regular Contributor
timestamp: February 17, 2021, 01:41:01 am
content: It is a Dell XPS 8700 with a i7 4790. The PS is very compact but draw a whooping 8A from the plug. The Corsair CX may be too big in physical size. May not fit inside the case.

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2021, 01:51:52 am
content: Quote from: bobcat2000 on February 17, 2021, 01:41:01 amIs it operable or broken? If you can, I'd start measuring the actual currents rather than reading the labels. I suspect your 5A needs aren't that great.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 17, 2021, 01:58:38 am
content: According to:https://www.dell.com/community/Desktops-General-Read-Only/XPS-8700-Power-Supply-Replacement/td-p/4567328This one:https://www.amazon.com/CORSAIR-CS750M-Certified-Modular-Supply/dp/B00GH9NA0A

author: bobcat2000
author_rank: Regular Contributor
timestamp: February 17, 2021, 02:11:41 am
content: Oh! You side tracked me.I am not replacing the P/S.I am wondering why motherboards from other brands don't need that much power.The other MBs can use whatever.

author: Monkeh
author_rank: Super Contributor
timestamp: February 17, 2021, 02:13:19 am
content: Quote from: bobcat2000 on February 17, 2021, 02:11:41 amQuote from: bobcat2000 on February 16, 2021, 05:57:10 pm....

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 17, 2021, 02:15:27 am
content: Quote from: bobcat2000 on February 17, 2021, 02:11:41 amBut you started by saying you are trying to upgrade your power supply and that you have a Dell XPS 8700

author: wraper
author_rank: Unknown
timestamp: February 17, 2021, 02:53:29 am
content: You don't need high current rating on 5V rail. Chasing for 25A rating on 5V rail is lame, such rating written on PSU does not mean that PC actually draws it. Actually when looking at cheaper PSU models, high current rating on 5V rail usually is a sign of crappy or prehistoric PSU since they also have low current rating on 12V rail. Computers made in last 15 years consume little current from 5V rail, most of the load goes to 12V rail. I would be surprised if that PC draws more than 5A from 5V rail.

author: bobcat2000
author_rank: Regular Contributor
timestamp: February 17, 2021, 03:56:40 am
content: Oh yea. I said that I wanted to replace the p/s. Must be Tuesday. Can't remember what I typed.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 17, 2021, 04:50:10 am
content: Quote from: wraper on February 17, 2021, 02:53:29 amBudgeting 900mA per USB port and 1.5A per SSD (just looked at a random SSD in my collection, not sure how much peak current most draw under heavy I/O activity), it would not be hard to go over 5A at all. If the motherboard supports fast charging, that could be as much as 2A per port. (Note that USB-C with USB-PD uses a programmable voltage derived from the 12V line and does not load the 5V line at all.)

author: bobcat2000
author_rank: Regular Contributor
timestamp: February 17, 2021, 09:25:36 am
content: USB ~ 1ASSD ~ 1ASATA HD ~ 2AI have 10 USB ~ 10A1 SSD ~ 1A1 HD ~ 2A13A + other chips like memory, chipset, sound chip, network, etc in the motherboard.look like 25A is barely just enough if I hook up all the stuffs to SATA ports in the motherboard and the USB ports.

author: wraper
author_rank: Unknown
timestamp: February 17, 2021, 12:20:38 pm
content: Quote from: bobcat2000 on February 17, 2021, 09:25:36 amSATA HDD typically has <0.7A rating on 5V rail. Chance of populating every USB port with devices with such consumption is extremely low. You will need to populate every port with devices of high consumption, like charging smartphone, external HDD/SSD with no own power supply and similar. Not to say that as long as devices are within spec, they'll unlikely to pull such current.QuoteQuoteExcept most of it is not even powered from 5V.