Are cheap ebay power supply worth the money? - Page 1
Forum section: electronics / testgear

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: June 18, 2013, 03:48:37 am
content: Recently I have been doing experiments that need a bit of umphhh.... Having a higher power adjustable linear supply would be very beneficial! Ive been looking at some supplys like thesehttp://www.ebay.com/itm/X5045-Pro-30V-5A-Digital-DC-Power-Supply-Precision-Variable-Adjustable-/370586966860?pt=LH_DefaultDomain_0&hash=item5648b45b4chttp://www.ebay.com/itm/Digital-DC-Power-Supply-30V-5A-Precision-Variable-Adjustable-Lab-Grade-/140675103345?pt=LH_DefaultDomain_0&hash=item20c0e3ba71http://www.ebay.com/itm/Precision-Variable-0-30V-5A-DC-Power-Supply-USA-Product-/280949385169?pt=LH_DefaultDomain_0&hash=item4169e367d1There all current/voltage adjustable under $100 with US shippers... Im not looking to run precision analog stuff off them, mostly bigger load items like motors, heating elements etc... and if quiet maybe low speed digital or imprecise analog stuff.... I think im more worried about these supplys blowing up than being noisy!What do you guys think of equipment like this?

author: Bored@Work
author_rank: Super Contributor
timestamp: June 18, 2013, 03:58:28 am
content: Some are okish, but far from great, for the money you pay, others are absolute crap. The problem: They all look more or less the same from the outside, but you can't judge them from the outside, they are essentially grab bags.

author: kerrinal
author_rank: Contributor
timestamp: June 18, 2013, 04:04:30 am
content: I think the description will help you much.If the seller is a fake or the production is a counterfeit.You can live the seller a negative feedback and hold the paypal fee.

author: Smokey
author_rank: Super Contributor
timestamp: June 18, 2013, 04:43:57 am
content: Check out the Chinese dual supplies that are rebadged by a dozen different companies like this:http://www.newegg.com/Product/Product.aspx?Item=9SIA1PK0JM2440I scored two on the ebay for 100USD each. They are killer since you can put the independent outputs in parallel or series for 60V at 5A or 30V at 10A. the ones I got were pretty beat up looking to start with and I beat them up more and they are still going strong. Nothing too precise but not bad for cheap work horse supplies.I always wonder who the OEM is for these things. They all seem to have a big oval power button in the bottom left that is usually green or orange.

author: jebcom
author_rank: Regular Contributor
timestamp: June 18, 2013, 05:06:12 am
content: I did a bit of online research on this several months ago. I wanted a 3A bench supply because sometimes I have the need for 2.5 A range. I learned that many of these look similar on the outside but they do come from several different manufacturers, and some are very bad. The Mastech seemed to have better reviews than most others, but they are far from the cheapest. I decided to go with the Mastech HY3005D, which has a rating of 5A. I figured I could trust it for 3A. I got mine new for about $100 from a California dealer on eBay, and it has been just fine. Not perfect, but not awful for a low-cost Chinese unit. The power transformer is a toroid with several secondary windings, and as I adjust through the voltage range, I think there are 7 ranges of relay clicks, to minimize drop across the output drivers. I have run it at 5A output for a brief test, but I trust it at 3A. Internally, construction and workmanship is OK; about what I expected. I'm satisfied.This is the current listing from that dealer for the model that I bought:http://www.ebay.com/itm/Mastech-HY3005D-30V-5A-Single-Output-Linear-DC-Power-Supply-Lab-Variable-NEW-/121086078044?pt=LH_DefaultDomain_0&hash=item1c314aec5c

author: LaurenceW
author_rank: Frequent Contributor
timestamp: June 18, 2013, 04:30:49 pm
content: RWGAST, it's difficult to give you a simple yes/no answer to your question "Are these cheap power supplies worth the money?" since i don't know how much you pay for your money!Personally - i would not trust these supplies, but i am quite willing to accept that my sceptism/caution may be over done. You must decide.As is noted elsewhere (and I concur), you cannot tell the quality of these supplies from the outside. Many fair and appalling supplies will even use apparently the same outer front panel plastic moulding, but have radically differing quality interiors. This will even change over time from teh same supplier, as they swap and change their own component suppliers.Power supplies can fail in a number of exciting ways. The bigger the supply, the more potential excitement! Often, the main output transistors will go short circuit, so dumping maybe 40V DC at up to 8 amps across your load. If that load is only a heater or motor, itmighteven survive that. An Ipod will not, however!!At the end of the day, you do get what you pay for. Cheap price will invariably mean cheap quality components and/or construction. You might getter better value and more reliable results from a branded second hand power supply? eBay is awash with those.

author: ignator
author_rank: Regular Contributor
timestamp: June 18, 2013, 06:54:29 pm
content: I purchased the 60V 5A version of this 6 months ago. Any adjustable supply can fail in output short circuit. If it's that critical you need a separate over voltage crow bar circuit.For the money, they do what you need for the hobby.My ONLY complaint is there is NO documentation of any kind of the inner workings. And I doubt if there are too many serviceable components. I have not opened mine (I bet that $17K agilent spectrum analyzer Dave did a tear down on is FUBAR), but I would guess the digital meters are integrated into the voltage reference to drive the switching power circuits. And there are no off the shelf components as these would be proprietary. If it ever fails, I would just buy another one.It's $63, you can buy a used, lab grade supply that's how old? And has the same guarantee.

author: edavid
author_rank: Super Contributor
timestamp: June 18, 2013, 07:07:58 pm
content: Quote from: jebcom on June 18, 2013, 05:06:12 amThat one seems overpriced to me... for the same price, you could buy the Korad programmable supply:http://www.ebay.com/itm/110888868115

author: edavid
author_rank: Super Contributor
timestamp: June 18, 2013, 07:09:10 pm
content: Quote from: ignator on June 18, 2013, 06:54:29 pmI think you are mistaken, it's probably a simple linear supply using very common parts.

author: bilko
author_rank: Frequent Contributor
timestamp: June 18, 2013, 10:08:09 pm
content: Here's the schematic for the Mastech 3005D. Most of the similar PSU's will be variations with some components added/snipped

author: calmtron
author_rank: Regular Contributor
timestamp: June 18, 2013, 11:26:46 pm
content: A couple of internal shots of my SAKO SK1731SL5A, which is similar to the ones mentioned (theschematicis very similar to the Mastech 3005D).Build quality is so-so, but it does provide the specified power and hasn't failed yet (3 years old or so). I wouldn't trust the specs for load/line regulation etc though.Sorry about the PotatoCam shots

author: nctnico
author_rank: Super Contributor
timestamp: June 19, 2013, 12:44:14 am
content: Did you look at this one?http://www.ebay.com/itm/ITech-IT6720-Programmable-DC-power-supply-60V-5A-100W-/22113285384360V may be handy every now and then. They are also available in 36V versions (as usual under several brands).

author: edavid
author_rank: Super Contributor
timestamp: June 19, 2013, 12:50:36 am
content: Quote from: nctnico on June 19, 2013, 12:44:14 amWay overpriced at $310!

author: iloveelectronics
author_rank: Frequent Contributor
timestamp: June 19, 2013, 12:58:28 am
content: Quote from: edavid on June 19, 2013, 12:50:36 amITech is a BK Precision company, so you are paying partly for the brand name there. You can't compare it (price-wise) directly with a no-name Chinese PSU.

author: jebcom
author_rank: Regular Contributor
timestamp: June 19, 2013, 03:02:13 am
content: QuoteMaybe; if you need a cheap programmable supply. But I try to operate on the Keep-it-Simple principle, so something that I have a chance of repairing is more valuable to me. I don't remember if I saw any reviews on that model, but for this purchase, I avoided anything that was not controlled by potentiometers.However, if this model has some positive reviews for quality and reliability, then it might fall into my general intention on this unit; that is to spend a bit more money than the dirt-cheapest in order to get something that works.

author: ignator
author_rank: Regular Contributor
timestamp: June 19, 2013, 04:21:28 am
content: Quote from: edavid on June 18, 2013, 07:09:10 pmYou are correct. Qty. 4 TO-3 output transistors that appear wired in parallel. These are mounted to a 2mm thick aluminum plate, with cooling fan.Also all through hole parts. 3 PWB assemblies. Front panel must be using some COTs LED panel meters.Pretty boring implementation. But these have been in production for a long time, and I would assume the bugs have been worked out.

author: nctnico
author_rank: Super Contributor
timestamp: June 19, 2013, 04:42:05 pm
content: Quote from: edavid on June 19, 2013, 12:50:36 amNot really. Its a switching PSU which can deliver a lot of current at low voltages and high voltages (with less current). And its lightweight and small. IIRC Mike (mikeselectricstuff) did a teardown of it.

author: electronupdate
author_rank: Regular Contributor
timestamp: June 19, 2013, 08:34:44 pm
content: A tear down and review video of the 3rd supply (GQ-305) you mention is here:The only real negative (other than very modest quality construction) is that the output can glitch rather badly when the supply is turned off.Quote from: rwgast_lowlevellogicdesin on June 18, 2013, 03:48:37 am

author: Smokey
author_rank: Super Contributor
timestamp: June 20, 2013, 09:50:06 pm
content: What are you doing turning it off? Quit taking breaks and get back in the lab!!!!

author: Unknown
author_rank: Unknown
timestamp: June 21, 2013, 09:05:40 am
content: In my opinion, you should save money until you can get something better than this... It's only a matter of time and you will get what you want: I saved up money at 200 eur/month, and after 1 year i got: 1.agilent PSU (u8002A) 2. Power meter (HM8115-2), 3. capacitance meter U1701B 4. fluke 287 5.oscilloscope hp54600B 6. another bit of money saved (which i won't use for test gear)