5V DC PSU not delivering on specs - Page 1
Forum section: electronics / beginners

author: pwnell
author_rank: Regular Contributor
timestamp: February 15, 2024, 05:24:10 am
content: Is this normal? I bought this 5V 3A 15W DC power supply from Amazon:https://a.co/d/hAFgopuI hooked it up to my bench DC electronic load, it measured 5.22V at no load. When I draw 2A in CC mode it drops to 3.6V. Drawing 3A drops it to 3.0V and 9.0W.Surely this is not what is advertised?

author: mariush
author_rank: Super Contributor
timestamp: February 15, 2024, 05:35:31 am
content: Going over 5v is normal for such power adapters, some do it on purpose because it's assumed some voltage will be dropped on the thin wires between the adapter and the device... the cable has a resistance, so some voltage will be dropped ... V = I x R ...For example assuming cable has a 0.03 ohm per meter resistance and there's a 1 meter of cable that means you have two meters of wire between adapter and barrel jack, so at 2A of current you'd lose V = 2A x 2 meters x 0.03 ohm = 4 x 0.03 = 0.12v .... so the adapter will on purpose output 5.12v or more so that at 2A you end up with 5v at the end of the wire.Better quality adapters will have a sense wire going all the way to the barrel jack and the adapter will use that 3rd wire to measure the voltage at the barrel jack and adjust voltage dynamically to keep the voltage at the barrel jack as correct as possible.As for the other, most likely it's just a 1A ... maybe 1.5A adapter, falsely advertised as 3A ....

author: ArdWar
author_rank: Frequent Contributor
timestamp: February 15, 2024, 05:39:15 am
content: That's a POS for sure.On another note, I'd avoid amazon products with such a long product name at all cost. Just run away if product name contains a whole list of spec and application instead of, you know, product name....

author: pwnell
author_rank: Regular Contributor
timestamp: February 15, 2024, 05:39:57 am
content: So to increase the accuracy I shortened my leads from the dc load to the psu. I also switched to 4 wire mode. At 2A I get 4.48V and 9W. At 2.5A it drops to 4.3V, 10.7W. At 3A it is down to 4.1V and 12.5W, way less than the 15W advertised. So as you said probably some false advertising…

author: Jwillis
author_rank: Super Contributor
timestamp: February 15, 2024, 07:40:45 am
content: Has Amazon always being this bad?

author: tooki
author_rank: Super Contributor
timestamp: February 15, 2024, 08:12:31 am
content: Quote from: Jwillis on February 15, 2024, 07:40:45 amNope. Amazon used to be basically an online department store. Its prices weren’t always the absolute lowest you could find online, but they were consistently reasonable, enough so to make Amazon a great way to shop in a hurry: you might save a few bucks elsewhere, but not enough to justify the time needed to find another shop, register, etc.The beginning of the end was the introduction of Amazon Marketplace (=third party) sellers for things beyond books, music, and movies/TV. This led to problems with counterfeit name-brand products. But the real decline came when they decided to actively seek out Chinese vendors for Marketplace, to compete with eBay and aliexpress, which displace name-brand stuff with all this no-name crap.With the flea-riddled bazaar Amazon has become now, it’s now become a huge time sink, since finding what you want takes forever thanks to the ocean of junk listings. (It’s even worse here in Switzerland, where many Amazon items cannot be shipped. Some of them say that right on the product page, but others don’t throw an error until checkout. It depends on the seller, of course. What’s equally infuriating is that the search only sometimes lets you filter by global shipping, and even when it does let you, in any item with variants, if even one single variant by one single seller ships to Switzerland, the item shows up, even if the variant you actually searched for has no sellers for Switzerland. I have completely stopped using Amazon for anything but books, and use Swiss online stores for everything else.)

author: p.larner
author_rank: Frequent Contributor
timestamp: February 15, 2024, 12:14:26 pm
content: made in china explains it all!,just lying cheats mostly!.

author: Ian.M
author_rank: Super Contributor
timestamp: February 15, 2024, 12:33:36 pm
content: Photo of it failing to deliver 5V @3A, and back to Amazon it goes. You could write a s--tty review but Amazon will take it down or never post it if you return the item.

author: Ugur
author_rank: Regular Contributor
timestamp: February 15, 2024, 01:58:18 pm
content: We experienced a similar situation with Aliexpress. A friend of mine bought a phone fast charging adapter worth I think 40W.When he received it, he asked me to test it, but we found that it could only deliver 10W of power.We supported this with pictures and reported it.As a result, he returned the money. Without any explanation.What I understand from this is that not everyone understands this business, I will refund the money to those who do. Those who do not understand continue to buy this product.

author: MarkT
author_rank: Frequent Contributor
timestamp: February 15, 2024, 08:10:23 pm
content: Did you check the Amazon reviews, specifically the 1-star ones saying it was only 1A and came without the adaptors? Buy from a reputable electronics supplier is my advice, and a known brand of supply.

author: MathWizard
author_rank: Super Contributor
timestamp: February 15, 2024, 10:15:09 pm
content: Quote from: tooki on February 15, 2024, 08:12:31 amJust trying to put a search in a certain order, makes no sense on amazon. Every since I can remember, I never use 'sort by price', because they list so much other junk 1st. And sometimes your products of interest get cut from the list, just because you choose to sort by price.I still like amazon for some non-brand name stuff, but yeah if I had a lot more money, I'd get better stuff elsewhere.

author: Konkedout
author_rank: Frequent Contributor
timestamp: February 16, 2024, 05:22:15 am
content: Out of curiosity I looked at Digikey in USA. I find competitive units there are no more expensive (and some are cheaper.) Digikey is a bona fide electronics distributor which is much less likely to sell you junk. But I am not aware of any free shipping from Digikey.FWIW I used to design "wall warts" many years ago. For a 5V supply I would normally adjust the output to 5.15 - 5.20 at my circuit board output to help compensate for voltage drop in the output cable when operating fully loaded for example. So the 5.1V figure at light load seems perfectly OK. But the output voltage dropping below 4.75 at full load is inexcusable assuming that you are testing and measuring properly.

author: radiolistener
author_rank: Super Contributor
timestamp: February 16, 2024, 06:37:49 am
content: Quote from: pwnell on February 15, 2024, 05:24:10 amThis is some unknown noname Chinese PSU, usually such kind of PSU is very dangerous, because it can make fire or do electric shock and usually their rating is fake.It's better to buy raspberry pi PSU, it can handle 3A, but notice - it don't have ground terminal and it's output will have about 90 V AC relative to grounded equipment. I didn't notice it and it burned my USB DAC. Unfortunately there is no raspberry pi PSU with grounding terminal.Here is link:https://www.aliexpress.com/item/4000124439033.htmlI bought it in this store and it works ok.