Idea to consolidate all 5V / 12V power adaptors - Page 1
Forum section: electronics / beginners

author: stan001
author_rank: Contributor
timestamp: January 03, 2012, 05:10:20 am
content: Like many others, I have a lot of equipments like modems, wifi routers, NAS, switches, cordless phones that uses a lot of power adapters in multiple shapes and sizes , some SMPS and some are just heavy transformers that get really hot...I was thinking of getting a 12V SMPS (or PC PSU), probably 8-10A to power-up all these equipments directly and use LM7805 (for 5V) as most of the uses DC plugs in 5V/12V range and probably a few USB connectors for charging and powering my Arduino on 5V..Before I get started in my project, I would like some feedback on this matter as I have little experience dealing with power supply..1. Is this a good idea as I have not seen anyone doing it before ?2. Are there are potential danger of damaging my equipments using this method ?3. Will one faulty equipment affect the other equipments being power from the same source ?4. How to calculate the max power needed per equipments ? Some of the power supply does state the max output current..I can think that single point of failure would probably be the biggest drawbacks..Thanks for reading this posting..

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2012, 05:20:48 am
content: Quote from: stan001 on January 03, 2012, 05:10:20 amSurely the single location of the power supply is a bigger drawback? The advantage of power adapters is you can plug them in wherever they are needed. With a single giant power supply you would have to bring all your devices to the same place to plug them in.

author: vtl
author_rank: Regular Contributor
timestamp: January 03, 2012, 06:06:00 am
content: If you only use your equipment at a single location (for stuff like routers/modems) then it sounds like a decent idea. Youd be eliminating a lot of the loss from those cheap plug packs. But you'll have to use a switchmode DC-DC converter to make it worthwhile. An LM7805 will have to disspate a lot of power dropping from 12V->5V even at 1 amp. You'd need a huge heatsink and a number in paralell to power all your devices. Really unsuitable.If youre using an ATX power supply just use the 5V rail. Might be worth designing some circuitry for overcurrent protection because the ATX power supply will happily provide 10A without dropping voltage. Maybe you can split up the rails into smaller current limited protected rails. So you can still power many devices but still have the protection.I'd say theres potentially a decent amount of efficiency gain if you have a lot of devices running all the time.

author: Bored@Work
author_rank: Super Contributor
timestamp: January 03, 2012, 07:43:07 am
content: This idea comes up again and again, since the 1880s, when Westinghouse' AC won over Edison's DC. No, it is not new.Despite the wiring problems one of the bigger issues is you lose isolation between the devices.Just imagine you have a one device with an internal DC regulator on + of the power input, andthe - of the power input directly connected to the device's ground, including shielding of connectors. And imagine you have a second device which happens to have the regulation on - , and the regulated low side then connected to the device's ground and shielding of connectors. Now you connect them together, e.g. indirectly via USB cables both going to your PC, or directly, e.g. via Ethernet. And then watch the magic smoke coming out.Same for devices that split the 12V power rail and establish a virtual ground at e.g. 6V in the device.

author: slashguitar
author_rank: Contributor
timestamp: January 03, 2012, 07:49:07 am
content: It's a really nice idea, I might try it also. The only drawback I see is the noise from the power supply fanAlso most of the modems and routers I have run at 9V.I think the LM2576 ( adjustable buck converter) would be a good replacement of the LM78XX

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2012, 08:23:10 am
content: This is kind of the opposite of modern PC power supplies. I'm given to understand the newer designs route 12 V power around the board and down convert it locally to 5 V or 3.3 V where needed. This simplifies the main power supply since it only needs to provide a fat 12 V rail and it minimizes losses by avoiding the need to route high current low voltage supplies over longer distances.

author: ipman
author_rank: Regular Contributor
timestamp: January 03, 2012, 09:16:57 am
content: LM2576 is a good ideea of a buck convertor and there are fanless PC power supplies.But still, take care of ground loops, they will destroy allmost every low-power circuit until the PS protection will kick in at 20-30 amps.

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2012, 09:22:21 am
content: The good thing about a 30 amp power supply is it turns pretty much everything into a fuse...