What current can really delivery an atx 400w pc psu? - Page 1
Forum section: electronics / projects

author: Chriss
author_rank: Frequent Contributor
timestamp: January 26, 2020, 10:08:44 pm
content: Hi!I'm doing some reading on the net about atx psu.They write does an atx 400W psu can delivery only 23A on the 12v rail. Somehow I don't understand. What about the rest of the power?I=P/I so that mean 400/12=33.33A.So, how they come to 23A and so?Actually now I'm cuourious how much A can really delivery constantly the 12v rail on such of psu?

author: KaneTW
author_rank: Frequent Contributor
timestamp: January 26, 2020, 10:13:00 pm
content: Good ATX PSUs list max currents per rail. Example:https://seasonic.com/pub/media/pdf/consumer/datasheet/PRIME-ULTRA-Titanium-TR.pdfThe rest goes onto the other (3.3/5/-12) rails.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 26, 2020, 10:18:26 pm
content: The max power rating is usually for al outputs loaded at the same time, not only the +12V rail(s), but also -12V, +5V, +3.3V as well.

author: Chriss
author_rank: Frequent Contributor
timestamp: January 26, 2020, 10:28:18 pm
content: Thanks for the quick replay.I already checked the doc you shared.I'm a bit confused.Is it really true does lets say the Prime 1000 psu from that list can delivery 83A?If yes, hiw long can it delivery without to fail?Can that psu delivery lets say for 10h 50A without really to fail?

author: aheid
author_rank: Regular Contributor
timestamp: January 26, 2020, 10:36:47 pm
content: Seasonic is usually good stuff, as long as the unit has proper ventilation I would expect it to handle 80A for days (assuming minimal load on the other rails).Note that in most high end ATX PSU's the other rails are derived from the +12V rail, hence the ability to deliver all the power there.

author: Chriss
author_rank: Frequent Contributor
timestamp: January 26, 2020, 10:54:24 pm
content: So, an average psu of 400w could power let's say a 12v car wiper motor without problem?Could we say this as a conclusion of an analogy to poor man's understandings?

author: Mr. Scram
author_rank: Super Contributor
timestamp: January 26, 2020, 11:02:05 pm
content: Quote from: Chriss on January 26, 2020, 10:54:24 pmA car wiper motor likely has big windings and a healthy inrush current.

author: ogden
author_rank: Super Contributor
timestamp: January 26, 2020, 11:03:43 pm
content: Quote from: Chriss on January 26, 2020, 10:28:18 pmAt 12V*50A such 1000W supply can run 24/7 for long time. Size your supplies at <= 75% of nominal power. For "reliable DIY projects" I would consider 2nd hand server supply, thou out of the box they are screaming LOUD as hell.

author: Chriss
author_rank: Frequent Contributor
timestamp: January 26, 2020, 11:05:14 pm
content: Yea I know that but maybe the heating blower motor in the car ?

author: aheid
author_rank: Regular Contributor
timestamp: January 26, 2020, 11:25:30 pm
content: An ATX PSU is not designed to handle inductive loads like a huge motor. At the every least, you'd need extra protection to shield the PSU from the voltage spikes the motor generates, and the inrush current might trip the short circuit protection in the PSU so that would have to be deal with as well.

author: Nusa
author_rank: Super Contributor
timestamp: January 26, 2020, 11:40:08 pm
content: Quote from: Chriss on January 26, 2020, 11:05:14 pmProbably, but depends on the starting requirements of the motor in question. Also remember that any time you're talking automotive parts, you're really talking about 14V in normal operation, even if they can struggle along at the nominal 12V battery voltage.