ATX Powersupply as DC source for a LiPo-Charger - Page 1
Forum section: electronics / beginners

author: littleMax
author_rank: Contributor
timestamp: July 24, 2017, 10:03:34 pm
content: Hi,i have a LiPo-Charger that can be powered by a AC source it then can give you 100W on the outputsite, or you can power it by a DC Source and it than has 200W at the outputs. Many people in the RC hobby recommend to buy a certain typ of server power supply from ebay, that just ist the typical way many people do it.But i have an older ATX (20PIN) power supply lying around and why not use this.So i checked some stuff on how to turn them on, all say it is simply PS-On (Pin 14) to ground, but then my powersupply does nothing, the fan twiches shortly but then it stops.Then i read that it needs a load between the 5V and ground, so i did put a 12V 10W there. Still on PS-ON to ground only fan twitching.Tested it with an old nainboard that i had lying arround. ATX connector to the mainboard and PS-On to ground and it worked.I even bought a ATX-Tester and connected it to the powersupply, normaly this would turn on the PS and show me the voltages, but it didnt work (brought it back). It was this one:https://www.conrad.de/de/pc-netzteil-tester-renkforce-001503580-1503580.htmlSo now i dont know what my ATX-PS needs to keep running, can anybody help?PS: Pic of the atx-ps in the attachments

author: Nusa
author_rank: Super Contributor
timestamp: July 24, 2017, 11:22:19 pm
content: Quote from: littleMax on July 24, 2017, 10:03:34 pmI'm going to assume you meant to say 12 Ohm 10W resistor. That translates to a P = V*V/R = 5*5/12 = 2 Watt load. Which is somewhat shy of the 5W load recommended. Try a lower value resistor in the 5 Ohm neighborhood. Or parallel two 12 Ohm ones to get 6 Ohms if that's what you have.

author: littleMax
author_rank: Contributor
timestamp: July 25, 2017, 09:14:28 am
content: Oh ... i forgot to write that it was a 12V 10WBulb

author: tszaboo
author_rank: Super Contributor
timestamp: July 25, 2017, 09:25:30 am
content: I had an old AT PSU at home. I was young, I was using it to power projects. I was showcasing a project, when the damn thing started venting a capacitor. Smoke coming out of it, scarejump, running for the circuit breaker of the house. It wasnt funny. I dont use AT or ATX power supplies to power stuff anymore.

author: Nusa
author_rank: Super Contributor
timestamp: July 25, 2017, 10:08:12 am
content: Quote from: littleMax on July 25, 2017, 09:14:28 amThat's even worse. 10W at 12V means the bulb is a V*V/P = 14.4 Ohm resistor. So at 14.4 Ohms at 5V is a 1.7W load. Try 3 of those bulbs in parallel.

author: cowana
author_rank: Frequent Contributor
timestamp: July 25, 2017, 11:22:28 am
content: Quote from: Nusa on July 25, 2017, 10:08:12 amHowever when cold, the filament resistance will be much lower - I would not be surprised if the power was closer to 4 or 5W when powered by 5V.

author: littleMax
author_rank: Contributor
timestamp: July 26, 2017, 01:38:03 am
content: Quote from: NANDBlog on July 25, 2017, 09:25:30 amI dont want to power a elektronik Project. I want to power a LiPo-Charger which will output at max 6A @ 16,8V on two outputs so 12A @ 16,8V. Thats why i want to use my old/still working ATX-Power supply. I could buy this:switching power supply possible of 20A @ fixed 13,8V for 53€, but why?@cowanayeah thats what i thought to, the measured resistance is 1,6Ohm when cold, it should be more than enough. I just dont understand/know what safty measures prevent the PSU from staying on when if ground out Pin14/PS_ON...at the moment im thinking about screwing an old Mainboard to the wall where i charge my Batteries and pluging the ATX connector to it because then the PSU stays on.Does a mainboard that has nothing on it, only the stuff that is solderd on it, have a high load?

author: alm
author_rank: Super Contributor
timestamp: July 26, 2017, 09:15:37 am
content: Could be that it needs a load on both the 5V and 12V rails? Depending on the vintage. Seems like an easy thing to try.I am assuming you already have a LiPo charger with a 12V input? If the output is 12A * 16.8 V = 202 W, then I assume the input is 12 V at more than 16.8 A (due to conversion losses in the charger). And I imagine an old 200 W supply (depending on the age) may only be able to supply a part of that 200 W to the 12 V rail. What is the maximum current at 12 V according to the label? If it was cheap, then do not count on it actually being able to continuously supply the maximum rated current.

author: littleMax
author_rank: Contributor
timestamp: July 26, 2017, 10:50:54 am
content: I did post the label above it is rated for 420W Total and on the 12V Rail it is abele to carry 20A