PSU rating - Page 1
Forum section: electronics / testgear

author: netdudeuk
author_rank: Frequent Contributor
timestamp: October 04, 2014, 07:03:59 pm
content: Is there any benefit in choosing a 5A over a 3A PSU for hobbyist use ? I'm used to using wall warts that don't deliver that much current but the difference between a dual (plus 5V) 3A PSU and a dual (plus 5V) is less than £20. Maybe lower percentage load on the PSU so more likely to last longer ? What does the typical (if there is such a thing) hobbyist use current wise ?

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 04, 2014, 07:09:24 pm
content: Quote from: netdudeuk on October 04, 2014, 07:03:59 pmThere is no way in the universe of answering that as a generic question. It depends on several critical details, none of which you have revealed.QuoteWhenever I would ask a question like that, my mother would reply with one of her favorites:"How long is a string?" or "How old is a duck?" or "When does the river come this way?"

author: jadew
author_rank: Frequent Contributor
timestamp: October 04, 2014, 07:13:15 pm
content: It heavily depends on what you do. Personally I rarely use more than 100 mA, but there was this one time when I needed ~5 A from a single supply and I didn't have it. Luckily 2 of my power supplies can deliver 3 A each and I was able to get by, using both of them.I'd say it doesn't hurt to go for the 5 A one, especially if the price difference is so low. Make sure that the 5 A one has the same current resolution as the 3 A one tho. In this case, I wouldn't sacrifice resolution for current.

author: SeanB
author_rank: Super Contributor
timestamp: October 04, 2014, 07:14:57 pm
content: No real difference, but there can be big variations in the quality and spec of the parts used. If you buy the 5A unit you are less constrained, though for most uses 3A is really overkill. Most commonly you will use a fixed voltage of 5V at 2-3A for a lot of the time, and then you might need a second rail of 15v at 1A max. For things with opamps you will need a -15V rail as well ( or some other rail in many cases) so you are not going to be straining either supply.The most common use for the 5A over the 3A is that the 5A can charge batteries faster, and in all cases the 5V rail will be limited to 1A internally from the 7805 they all use to generate it, less whatever the displays use.In some cases there is no difference internally between the 3A and the 5A version, especially on the low end where they cut costs to the minimum. In all cases open up and look for visible QC fails.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: October 05, 2014, 09:10:28 am
content: What would you look for besides making sure that the chassis is earthed (and without a soldered tag) ?Thanks

author: DanielS
author_rank: Frequent Contributor
timestamp: October 05, 2014, 03:04:18 pm
content: Quote from: netdudeuk on October 05, 2014, 09:10:28 amIf you have no idea what you are looking for, go check out lab power supply reviews and tear-downs on Youtube - Dave and others have done quite a few of those.You need to sort out your priorities and requirements before anyone can even begin to start trying to help you.5V 3A may be enough for you but for some people, 24V 40A is still not enough. Then you have turn-on transient, load transient, ripple, noise, output regulation, efficiency, current limit response, etc. to consider if those matter to you.

author: Fungus
author_rank: Super Contributor
timestamp: October 05, 2014, 04:38:00 pm
content: For "hobbyist" use you need to think about when things go wrong, not just when everything is right.eg. Short circuit protection can be very important.A current limiting switch is often good for the first time you try powering up a circuit (...but you usually need to go up to "lab" power supplies for that). It gives you time to put your finger on all the chips and see if they're overheating before you apply full power and release the magic smoke.Never run PSUs at full rating for long periods. eg. If youneed5A, buy 8A (or more).

author: netdudeuk
author_rank: Frequent Contributor
timestamp: October 06, 2014, 10:03:59 am
content: I've been considering this PSU -http://www.circuitspecialists.eu/power-supplies/bench-power-supplies/csi-3003eiii-bench-power-supply-0-60v-0-3a-linear-0-6a-0-30v-5v-fixed-output/I guess that it rebadged by various companies. Does anyone have an experience of it, especially from a safety perspective ?I could go for the Rigol DP832 but that costs twice as much.

author: rolycat
author_rank: Super Contributor
timestamp: October 06, 2014, 10:53:08 am
content: That CSI power supply is a rebadgedQJE model. The controls and displays look rather approximate, and reliability and build quality of those cheap Chinese PSUs is always a bit of a lottery.You might want to consider a used supply such as a TTi (Thurlby Thandar). They are British, built like tanks, and offer more resolution on the displays and controls.Kev (KJDS on this forum) currently has three TTi models for sale: the 2x2APL320QMD, the 2x3APL330QMDand the 2x2ATS3022S- you can generally get a discount on the eBay price if you buy directly via the forum, and he's a good guy.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: October 06, 2014, 07:01:32 pm
content: You'll never need a 5A power supply, until the day you need it! THEN that 3A supply looks a bit weedy, doesn't it? Also, remember that a twin, 30V 3A power supply can be used with its outputs in parallel to provide 30V at 6A, or series to provide 60V at 3A.+1 for a second hand TTI (other power supplies are available) over a new cheap chinese one. Plastic front panel? No thanks.TWO fans on the back of that CSI unit - is it a power supply or a HOVERCRAFT? How come my own TTI PL330TP 190W linear power supply manages without ANY fans? (big heatsinks, conservative design, that's how).My own TTI PL330TP (Metal case all round, yes please!) is no longer made but will outlast ME, and I wasn't planning on quitting, myself, any time soon. Didn't think about it at the time I bought it, but recent interests in electric model aircraft, testing battery>mains inverters, reasonably large LED lighting arrays, etc. have seen me call on all the watts available from my supply. You do really need to give some thought about what you might get into, one day.Sure, a cheap chinese power supply will probably work, for a bit, anyway; right up to the point when it blows up (or the series transistor within it fails, and it blows up your precious project, instead). I suppose you can always have endless fun waiting for this to happen. Or you could just buy one which probably won't. Queue: cries of support from lots of people whose cheap chinese power supplieshaven'tblown up - so far.Do take some time to trawl back through some of Dave's past videos on power supplies, and learn Dave's lessons.These are my opinions. Others' opinions may differ. My opinion is just that I am right, that's all.