Brand new power supply blew up - Page 1
Forum section: electronics / beginners

author: b_t1ma
author_rank: Newbie
timestamp: January 21, 2021, 09:17:18 pm
content: So I just got my first power supply (Velleman LABPS3003) which I was pretty excited to use. It worked for a couple of days (was unable to connect anything because I hadn't gotten my banana cables yet), but all of a sudden when I power it on it flashes internally and blows the fuse. Fair enough I think. I replace the fuse, it works for a bit, then again, I turn it on and it blows up.I order some more fuses and try again. This time however the apartment breaker pops, and won't reset until I disconnect the power supply from mains (turning it off did nothing). Is it worth trying to fix, or should just contact the seller and ask for a replacement?

author: rsjsouza
author_rank: Super Contributor
timestamp: January 21, 2021, 09:42:52 pm
content: If the power supply did not suffer any damage that could have promoted these issues, I would have contacted the seller in the second blow and before buying more fuses...So yes, I would contact the seller and try to get a replacement unit or perhaps a refund.

author: wizard69
author_rank: Super Contributor
timestamp: January 21, 2021, 10:06:27 pm
content: I have to agree with rsjsouza above. A brand new device of any sort should not blow fuses, especially in this case when it wasn't actually doing anything. More bothersome here is that it has failed in such away that it blows the branch circuit protection breaker which in my mind might indicate a design issue or improper wiring at assembly time.

author: Fraser
author_rank: Super Contributor
timestamp: January 21, 2021, 10:10:52 pm
content: Sounds like an input EMI filter related failure due to a component manufacturing defect. As has been stated, ask for a replacement or refund. If you get to keep the dead unit we may be able to assist you in diagnosing the location of the fault.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: January 21, 2021, 10:16:39 pm
content: The Velleman LABPS3003 appears to be from the same factory as the Mastech HY3005D and there are often schematics available on the internet for Mastech PSU'shttp://www.mastechpowersupplies.com/3howdoigetsc.htmlFraser

author: Fraser
author_rank: Super Contributor
timestamp: January 21, 2021, 10:19:16 pm
content: This thread may also be of interest.....https://www.eevblog.com/forum/reviews/mastech-hy3005f-3-power-supply-teardown/Fraser

author: Fraser
author_rank: Super Contributor
timestamp: January 21, 2021, 10:23:53 pm
content: And the LED display version of the similar Mastech PSU.......https://www.eevblog.com/forum/reviews/lw-dqgs-power-supply-review-and-teardown-cautionsafety-risks] https://www.eevblog.com/forum/reviews/lw-dqgs-power-supply-review-and-teardown-cautionsafety-risks!!!/These budget PSU's are actually very common and come labelled as several different brands with just minor differences such as terminal posts vs 4mm sockets, LED Vs LED, different front panel plastics etcThe referenced single PSU teardown, above, discovered some nasty surprises including safety concerns. Note the issue with the mains cabling coming from the rear socket and passing through a cutout in an aluminium plate ! In transit the insulation of the wires can be damaged by their movement against the very sharp edges, causing an intermittent 'supply to earth' short situation. could that be the problem in your unit I wonder.By the way, Velleman do not make their own power supplies but are sometimes more expensive than competing power supplies that have come from the same factory. You might want to check the prices of similar power supplies, especially from Mastech.Fraser

author: james_s
author_rank: Super Contributor
timestamp: January 21, 2021, 10:59:04 pm
content: Does it have a 120/240V input selection switch? I've seen those arrive in the wrong position for the country to which the device is shipped.

author: Fraser
author_rank: Super Contributor
timestamp: January 21, 2021, 11:23:41 pm
content: The Vellerman unit appears to be similar to the Mastech HY3003 30V/3A model. I will see if I can find a schematic for it or the more powerful HY3005 30V/5A version.https://static.rapidonline.com/pdf/554309_v1.pdfHY3005 Schematic attached.https://elektrotanya.com/axiomet_mastech_hy3005d_high_res.gif/download.html#dl

author: b_t1ma
author_rank: Newbie
timestamp: January 22, 2021, 07:41:45 am
content: Quote from: Fraser on January 21, 2021, 11:23:41 pmThanks for all the information! I'll definitely take a look. I opened the case once and looked around, but couldn't find any visible damage on the cables, however.In any case, I contacted the seller about the issue. Hopefully, they let me keep the broken device so that I can do some debugging.

author: b_t1ma
author_rank: Newbie
timestamp: January 22, 2021, 07:45:20 am
content: Quote from: james_s on January 21, 2021, 10:59:04 pmThat was actually the first thing I checked. Had an accident when I was 12 where I switched a PC power supply to 120V, which blew it up completely. Scared the crap out of meBecame a habit to always double-check before plugging anything into the wall!

author: MarkF
author_rank: Super Contributor
timestamp: January 22, 2021, 11:01:27 am
content: Quote from: b_t1ma on January 22, 2021, 07:41:45 amThey will most CERTAINLY want the power supply back for the exact same reason.That is how venders improve their devices.

author: Fraser
author_rank: Super Contributor
timestamp: January 22, 2021, 01:57:11 pm
content: MarkF,Sadly such is not always the case. It depends upon the Vendor. Linear power supplies are heavy and some Vendors are just resellers who buy products in bulk. If the return of a faulty item is, in their view, not cost effective they will often just tell the customer to put the unit in the local recycling. The idea that a seller will inspect the faulty product or send it back to the manufacturer for investigation is what we might hope woukd happen, but on cheap mass produced products this is not usually what happens. It is just not worth their time and they accept some DOA or Infant failures. If the PSU had caught fire the situation might warrant an investigation by trading standards or Velleman but in this case the PSU will likely just end up in a skip either at the customers location or that of the reseller. Remember, Velleman are just badge engineering these things and the built in safety system, namely the fuse, did its job and disconnected power when the fault occurred. I may be wrong though and Velleman MAY take an interest in the unit as they are generally a good company who respond to customer communications. We shall see. It will come down to the resellers agreement with their wholesaler or Velleman on faulty equipment and recovery costs.

author: Fraser
author_rank: Super Contributor
timestamp: January 22, 2021, 02:14:33 pm
content: As a side comment on budget Linear type Lab Power supplies ......A common problem is damage in transit. Unlike a switching type design, a Linear power supply has a relatively large and heavy lump of metal bolted to the power supplies casing or chassis. If a linear power supply is dropped in transit it can suffer extensive damage as the kinetic energy contained in the heavy transformer, combined with deceleration forces upon impact with the ground can be significant. Such a drop can distort the casing, chassis or cause collateral damage to panel plastics etc. It is not uncommon to see budget Linear lab Power supplies returned from customers with a heavily distorted case bottom, detached transformers or smashed panel plastics. A bit of polystyrene foam cannot dissipate the energy created in a drop event adequately to prevent movement of the heavy transformer. I have seen toroidal transformers move on their single central bolt mount and sharp surrounding metalwork punch a hole through the outer insulation and damaging the outer windings beyond reasonable repair. I have also seen conventional E & I type transformers rip their mounting screws or other fixings out of the casing base plate. Much depends upon the quality of the power supply casing, the mounting method and the vertical distance that the package travels before impact with a solid surface.If a linear power supply is delivered by a courier or the mail, it is always worth inspecting the outer carton and any packing to see if there is evidence of a drop event. Smashed polystyrene is such evidence. Then check for distortion of the casing and transformer mounting points. If unusual distortion is seen, further investigation or rejection of the item is warranted. Personally, I would always open the power supply casing to inspect the interior for poor assembly or damage. Lab power supplies and UPS units are a relatively high fire risk so it is best to be safe rather than sorry. Also worthy of note is the fact that many home insurance companies consider laboratory test equipment ‘non-domestic’ and a fire caused by such a ‘non-domestic’ equipment can cause serious issues in the event of a claim. Hence why I have an electronics lab separate from my houseMention the word oscilloscope to an insurance assessor and they will likely define such as industrial or lab equipment, not covered under domestic house damage insurance for loss or cause of damage.Fraser

author: rsjsouza
author_rank: Super Contributor
timestamp: January 22, 2021, 04:37:42 pm
content: That is a very good post, Fraser.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 22, 2021, 06:19:18 pm
content: Sadly, Velleman/Mastech/etc. are the worst of the worst, they literally source the crappiest crap you can get from China then make 1000% profit on it (and the pricestillseems affordable). These supplies have stayed basically the same fordecades, they come under hundreds of names, and are always crappy. By being exposed to these supplies, you slowly develop PTSD/allergy and immediately recognize the look.Typical problems:* Blow up if voltage is present on the output when power turned off* Current limit does not work at all (noisy, jumping all over place, minimum way too high like 0.5A)* Current limit can't drop voltage below 1.2V or so, so current limit is bypassed!* Measurements show incorrectly, including the possibility of it showing 5.0V and actually outputting 20V* Noisy potentiometers, voltage jumps suddenly* Transformer tap relay thing oscillates on its own between ranges* Just blow up for absolutely no reason whatsoever* When they do blow up, they output the maximum voltage to your expensive once-in-a-lifetime projectThe funniest detail in this mess, IMHO, is just these crap supplies come in "deluxe" variety as well, including higher ratings, dual supplies with tracking features.Obviously, all the tracking features simply do not work at all.Due to being sensitized to such large number of such crappy supplies, I'm always expecting the worst when seeing any "new" budget supply, even if they look kind of different.I once had one which I got for free and I think it was the worst deal of my life.The best thing you can do is ask for money back and buy something else. Even if you are able to get a "working" unit, it blows up half a year later.Causing a fire is still quite a far stretch, IMHO.

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 22, 2021, 06:33:27 pm
content: That plus some old-fashioned mistakes like solder bridges, metallic burrs, that kind of stuff.

author: rsjsouza
author_rank: Super Contributor
timestamp: January 22, 2021, 08:43:02 pm
content: Quote from: Siwastaja on January 22, 2021, 06:19:18 pmYes, the issue is the widely scattered manufacturing quality. I have a Brazilian clone (Instrutherm) almost 20 years old and it had an issue with bad insulation between the 2N3055 collectors and the Earth GND, but otherwise it was manufactured with brand parts and hand picked bypass transistors (3x 2N3055).https://www.eevblog.com/forum/reviews/instrutherm-fa3005-(mastech-hy3005)-fix-and-teardown/