24V + 5V from one ATX PSU? - Page 1
Forum section: electronics / beginners

author: Johntron
author_rank: Contributor
timestamp: August 17, 2015, 05:46:04 pm
content: Is there a way to get 24V in addition to the existing 12V, 5V, and 3.3V outputs from a typical ATX PSU? If so, how?My existing lab PSU doesn't provide enough power, so I've modified a 600W ATX PSU, and it's now supplying the 24V@1A I need to drive a solenoid between the -12V and +12V leads; however, I'm now at a point where I want to control my solenoid with a digital circuit, so I'm trying to find 5V to control an ATTiny85. Since there's a 12V potential between the negative lead of my solenoid (connected to -12V from PSU) and ground on the PSU, this means I can't just connect the ATTiny to the PSU's ground and 5V leads, right?I'd imagine there are a few answers to this question, so I'm really looking for a list of options and their tradeoffs. The project I'm working on – a modular pinball platform – is very ambitious (for me), so I'm trying to break it down into manageable tasks, so I can learn along the way.

author: singapol
author_rank: Frequent Contributor
timestamp: August 17, 2015, 06:06:33 pm
content: Just add a suitable DC to DC convertor. Tap from a voltage that has excess current capacity.

author: jeroen79
author_rank: Frequent Contributor
timestamp: August 17, 2015, 08:30:33 pm
content: How did you modify your ATX PSU?Just added banana sockets in place of the outputwires?A DC to DC converter could work but you would have to take into account whether it's output is floating or not.If it is not then you have to connect it to the ATX' -12V and it will only be able to deliver as much current as the -12V can sink.Another option is to get another AC to DC 5V PSU and use that besides the ATX PSU.Or use a second ATX PSU with it's GND connected to the first one's 12V.This requires that the second PSU's GND is in no way connected to the first's GND.Don't do this if this doesn't make sense!

author: Johntron
author_rank: Contributor
timestamp: August 18, 2015, 12:00:42 am
content: Thank you singapol and jeroen79. I just looked at the specs for my PSU, and found the -12V has a very low current rating of 0.6A. The 12V has a massive 40A available, so I think I'll just use an op amp to boost +12V to 24V - then I can use all the other supply voltages with not problems.

author: eilize
author_rank: Contributor
timestamp: August 18, 2015, 01:03:39 am
content: +40a on the 12v rail seem a lot.it remember me these chinse atx psu where they promise 30a on the 5v rail and 30a on the 3.3v railsomeone was doingserioustest and analyse it..it finished with fire and smoke ^^anyway , dc/dc converter is your best choice,(home made with a pic or premade with an ic)oh..and don't forget your load has to have a minimum value (or you voltage output shutdown<-voltage divider) if you don't regulate it

author: MarkF
author_rank: Super Contributor
timestamp: August 18, 2015, 05:04:35 am
content: Quote from: Johntron on August 18, 2015, 12:00:42 amYou can't boost the +12VDC to +24VDC with an op-amp.I recommend you buy a dc-dc boost converter like others suggested and remove the modifications to your ATX power supply. Look at this12V Step Up 24V Voltage Booster Power 24W @ 1A. There are higher current versions if you need something bigger. Just remember the 12VDC current limitations of your ATX power supply to drive the booster converter.Also checkout out thisATX PS Adapteror thisATX Breakout Board.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 18, 2015, 06:10:04 am
content: scrap a server. They put out upwards of 1Kw on all different voltages. Or a power amplifier. If you look for $1 stuff online to scrap then look for the model number and search that number to note the power consumption of the device, it is a guide to how massive the parts you'll get are.