12V DC 10A 120W Switchmode Power Supply  - Page 1
Forum section: electronics / general

author: metalphreak
author_rank: Frequent Contributor
timestamp: June 15, 2013, 04:49:35 pm
content: Bought a 12V 10A 120W switchmode DC power supply off ebay that arrived recently. Planning on using it to drive some RGB Led strips for a project I'm working on. It was only $12 delivered (10c/Watt!) so I was sceptical of how good it would be.http://www.ebay.com.au/itm/400469932749Chucked it on the DC load:Factory setting was around 12.3V so I adjusted the pot down to 12V. 10A out of it wasn't an issue. It didn't get more than a little bit warm in the short time I tested it. I will have to get out the oscilloscope some time to see how clean the output is. I managed to get 12A out of it without issue. Setting the DC load to 13A caused it to go into some kind of overcurrent protection mode. A bit of headroom is good and nice to see it has some sort of protection. Usually with these you struggle to get the rated output current.There is a 110/220V switch for these. It's a little plastic slide switchinsidethe case. You could probably flick it over with a screwdriver through one of the vents but I decided to take it apart to see how well it was made. Unfortunately I forgot to take any photos. Nothing amazing here - typical single sided board and components.My power meter says 145.0W input at 120W load. 82.7% efficiency. Not bad but not great either.1.09A current draw with a power factor of 0.52 (voltage reading was around 246V). Clearly there's no power factor correction here. Something to consider if you're putting multiple units on a single circuit.Voltage regulation was very good. No load voltage would increase by 10mV once a load was applied. Throughout the current range the voltage remained constant.As with all products from China, I made sure there was a good earth connection between the ground terminal and the case. Less than 100mOhm in this case. If you look closely in the photos I've got a croc clip connected to the case going to a multimeter with earth ground measuring AC voltage - just in case something failed and the exposed case went live.Pros:+ Very cheap+ Exceeds rated capacity (I would not recommend using it above the rated 10A for reliability)+ stable voltage output across current range+ overcurrent protectionCons:- The aluminium case is quite weak - one corner mounting point got banged up a bit in shipping- 110/220V switch located inside case. Also makes it non-autoranging- Poor power factor may be an issueUnknowns:? Reliability in the long term? Protection in case of component failureAnyone else have any good or bad experiences using these supplies? How do they compare to big name brand supplies (ie Meanwell)?There was no brand name on the case besides a sticker saying S-120-12 (which means 120W 12V)

author: Unknown
author_rank: Unknown
timestamp: June 15, 2013, 05:03:31 pm
content: I have a 24V version of this supply, and a smaller 5V version (that's not Chinese)... powered up fine, no issues, supplied enough current to test a touchscreen device I was trying to test.I didn't test it as thoroughly as you did, I don't have the equipment, but I'd reasonably trust them.The flyer that came *with* it was hilarious.. "Sending coupon is not kidding"

author: metalphreak
author_rank: Frequent Contributor
timestamp: June 15, 2013, 05:42:33 pm
content: Best efficiency if used at 3A or more. It draws around 4.5W with no load on the output. Make sure it's disconnected when not in use

author: Harvs
author_rank: Super Contributor
timestamp: June 16, 2013, 02:06:25 am
content: That is just ridiculously cheap isn't it. So I'm guessing there was nothing that stood out to suggest it wasn't safe when you opened it up? (clearances etc.)It would be nice to see some scope traces if you get around to it.

author: staxquad
author_rank: Frequent Contributor
timestamp: June 16, 2013, 03:29:20 am
content: Quote from: metalphreak on June 15, 2013, 04:49:35 pmI use a 12V 30A and a 12V 10A (looking like yours, $30 and $15) to power smart 250W battery chargersand another 12V 10A with a DC to DC converter for a spread of voltages at low current (have used it to power a 9V device).The 30A one's been working for years, the other two are more recent.They are low cost utilitarian power supplies that free up your better supplies from mundane uses.

author: metalphreak
author_rank: Frequent Contributor
timestamp: June 16, 2013, 04:32:53 am
content: Quote from: staxquad on June 16, 2013, 03:29:20 amYep. I'm thinking of buying a few more of various capacities for a few things. I've got a touchscreen iKarPC that's way to big to mount in my car, so I'm planning on using it as a lab bench PC. It runs off 12-24V DC and didn't come with a plugpack (has hardwire cable and cigarette outlet cable for vehicle installation). I'm always nicking my big linear power supply for charging lipo's on my turnigy charger as well, so one for that would be good.I'm about to hook up the scope in a minute to see the output quality. I'll take it apart again to grab some decent photos. Overall, I'm quite impressed at what you can get these days for a few dollars. I was planning on re purposing some PC power supplies, but these are a much neater solution (assuming you're somewhat competent at wiring mains voltage safely in an enclosure).

author: BravoV
author_rank: Super Contributor
timestamp: June 16, 2013, 05:41:57 am
content: Have few of these for years, yep, they're dirt cheap and reliable, these are actually Meanwell's clone.Suggesting to improve the main switching transistors thermal path since on mine, the original installation from the factory had a really poor thermal contact with the aluminium case, check yours, had one blew up on the transistors because of overheating cause it didn't have any goop on it and almost barely touch the metal case.Example quick fix on what I did by adding two shin-etsu thermal pads, and also a squeeze of thermal goop (gray paste that oozed out) between the inner and outer metal plates.

author: metalphreak
author_rank: Frequent Contributor
timestamp: June 16, 2013, 06:01:30 am
content: Some photos of the internals below.Transistor pairs are part no. 13007-2. There's an STPR1620 fast recovery diode on the other side. The control IC is a Texas Instruments TL494N PWM controller:http://pdf1.alldatasheet.com/datasheet-pdf/view/28818/TI/TL494N.htmlBravoV: Yep the transistors on this have a thermal pad between them and the aluminium frame. I think there's a bit of paste behind it as well. The aluminium plate actually has an indented part to make contact rather than an extra aluminium spacer. The clamp holding is seems pretty secure so there should be good thermal contact.Full 10A Load:3A Load:No Load:The caps are all 105C rated. Dongbaohe 220uF 250V on the input, and nichicon (if you'd believe it...) 1000uF 25V on the output (five of them in parallel by the look of it).[couldn't find a spare usb drive to use the screenshot option on the rigol]

author: PedroDaGr8
author_rank: Super Contributor
timestamp: June 17, 2013, 01:10:55 am
content: This looks really similar to the 24V Meanwell supply I rescued off a discarded incubator at work.

author: metalphreak
author_rank: Frequent Contributor
timestamp: July 20, 2013, 05:55:15 pm
content: QC Fail!Decided to grab a 24V 5A supply from the same place to power some LED lamps. About to start my usual load testing. Output voltage is fine, no load on it yet. It's been on for about a minute and I start to notice a bit of a smell and see some thin smoke appear. Tore it down to work out what was wrong with it. Ended up being quite simple reallyThese supplies all have a power resistor across the output to ensure there is some load on the supply when nothing is connected. The 12V one I previously tore down has a 470ohm resistor. This 24V one has a100ohmon the output. That resistor is dissipating almost 6W of power and certainly isn't rated for it. I'm guessing someone in the factory grabbed a 100ohm instead of a 1k resistorWill grab a replacement resistor and swap it out, then finish my testing

author: Phaedrus
author_rank: Frequent Contributor
timestamp: July 21, 2013, 04:12:08 am
content: Ripple is mediocre. If you need to run anything sensitive off it I'd build a pi filter, or at least pop a ~100uF cap or two across the output. Otherwise not bad for the price. I would advise checking out the quality of those caps, if they turn out to be some ultra-cheap crap like Fujhyyu or ChengX or something I'd consider replacing them if you've got higher quality spares available.

author: David_AVD
author_rank: Super Contributor
timestamp: July 21, 2013, 04:28:50 am
content: I've had a Mean Well clone literally go "BAM!" right next to me as it was powered up. Lots of smoke.Another one I saw radiated so much EMI that it killed all TV and radio reception in a house. It even stopped the ADSL modem from working!

author: nukie
author_rank: Frequent Contributor
timestamp: July 23, 2013, 02:26:58 pm
content: I like those thermal pads. Those silicone? paste, they go dry chalk after a few years, do they still work? The thermal pads coming out of an Intel Pentium II laptop still in great condition.