Switching PSU, turn off at mains, vs off at low voltage side.  - Page 1
Forum section: electronics / projects

author: David97
author_rank: Contributor
timestamp: October 24, 2016, 10:43:03 pm
content: Hi everyone.My mum is technically blind. One eye is almost entirely blind, the other is in a bad way.The lighting around the house is really poor which doesn't help. So I'm wanting to put some led tape in a few key places.One of the places is the pantry, I'm wanting to put a strip on the bottom of every shelf. In total this will be about 1A at 12V. I plan on putting the switch on the door to turn it on. I want it to auto off after about 5 mins if the door is open for too long.I've been playing withmodules like this, since I figured it's way more effort than it's worth to just buy a already built timer. They seem to be working quite well, so I think I would be happy enough using it. I dont think I would use it for mains voltage stuff, since the isolation doesn't look good.This is the power supplyI plan on using.I am planning on breaking the 12V supply, and just leaving the power supply connected indefinitely. I figured that because this was a switching supply. the quiescent current will not be significant enough to worry about.Anyway, I'm wondering weather leaving the PSU continuous connected will still give a reasonable lifespan? And do you think the amount of power it draws while not in use will be enough to worry about?Thanks, David.

author: mos6502
author_rank: Frequent Contributor
timestamp: October 24, 2016, 11:23:27 pm
content: Easy way to test how much power the supply uses while idle is just to touch it. If it gets noticeably warm, it probably uses more than one watt. If it stays cool, it's probably less than a watt. But generally, those small switching PSUs have really low power consumption and you can leave them plugged in no problem. I've had USB HDDs that had their PSUs plugged in for years on end and HDDs died while the power supplies are still fine.The relay board should also work fine.But, the Sparkfun PSU you linked is pretty crappy. It'll probably not last long. I doubt it would even be safe electrically. I would try to find a brand name 12V only PSU from some kind of gadget, like a USB HDD or something.

author: David97
author_rank: Contributor
timestamp: October 25, 2016, 01:12:26 am
content: Thanks for the prompt response!I have been struggling to find a decent PSU. Ive had a look at some local stores, hoping that they would have something that would be electrically sound. Unfortunately, the only difference I can see between the ones I have found online and the local stores is the price tag. If they look like crap, smell like crap, and taste like crap, they are probably just expensive crap.I've even seen some of the cheapest ones having outstanding ratings, which are way too good to be true.Already gone through my box of old tangled together PSUs. Unfortunately, Ive used all the good ones up alreadyAnyway, do you have any recommendations for for decent brand name PSU, and and reputable sources for them?It's clear that the market is very saturated with fake and dangerous stuff.Thanks

author: David97
author_rank: Contributor
timestamp: April 25, 2017, 06:21:19 am
content: Well, I was cleaning out photos on my phone and realized that I hadn't got back to this thread. Thought it was kind of rude not letting you guys know how I got on. So better late than never.I ended up picking up a switch mode PSU locally. It's rated 7A, giving me a bit of headroom. I'm drawing 4.8A. Anyway, it's been working fine since Christmas, and been great so far. I ended up using the timer module I linked earlier, wired it to a switch giving about 4 mins of light when pressed. The PSU is constantly on, and I've just switched the low side. I haven't measured the quiescent current, but it stays dead cold.Here's a before and after of the difference it made to the lighting.Before:After:Thanks again for youre help! And Sorry I didn't get back sooner.