BEWARE NVVV Power Supplies - Very Sketchy Business Practices - Page 1
Forum section: electronics / general

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: February 02, 2022, 04:00:11 am
content: Back in June I received an 800watt / 65V Power Supply from NVVV AliExpress store.Recently I noticed the cooling fan comes on all the time and it heats up internally very quickly, so curious, I opened it up.What I found was a mess and a product that had been salvaged and I think may even be dangerous to use. See images below.BRAND NEW UNIT - Paid full price.Of course, It's out of warranty now so they got away with it clean. Never again.A photo of the entire board (top side)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 02, 2022, 04:22:22 am
content: Nice inrush protection!Lesson learned, don't buy from something very obviously trying to ape the MeanWell logo. They'd probably get sued for that... if they existed within any sort of legal jurisdiction that is.So, come on then, what's the rest of the circuit look like? I'm going to guess power dissipation from oversized transistors combined with insufficient drive!Tim

author: MrMobodies
author_rank: Super Contributor
timestamp: February 02, 2022, 06:44:27 am
content: Has that fuse been bypassed?

author: thm_w
author_rank: Super Contributor
timestamp: February 02, 2022, 11:15:55 pm
content: From your photo its not bypassed, they just repaired the vaporized tracks.But R1 discharge resistor has been removed.My guess its a returned supply, maybe customer applied 220V to a 110V unit?

author: John B
author_rank: Frequent Contributor
timestamp: February 03, 2022, 12:31:11 am
content: Maybe you can salvage the metal case and save a few dollars by installing an open pcb power supply from meanwell in there.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: February 03, 2022, 02:44:15 pm
content: Quote from: T3sl4co1l on February 02, 2022, 04:22:22 amRight?This is (a fraction of) the price we (in the USA) are paying for our lust for cheap (literally cheap) goods made in China. (The actual overall cost is FAR greater)Not even sure anyone in the USA still has the capability to manufacture power supplies.If that power supply went up in flames and burned my house down there is absolutely no way I could hold anyone accountable (other than myself)BTW...I THINK they changed their name toVISLONEnow

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: February 03, 2022, 03:09:40 pm
content: Quote from: John B on February 03, 2022, 12:31:11 amI added a photo of the full top side of the PCB in the OP.Can you tell me a bit more about R1 ? (Discharge Resistor)Do you mean to say that resistor was used to dissipate the energy stored in the large capacitors?If that was the case, wouldn't that potentially leave a large dangerous charge in the capacitors for a longer time?After sitting overnight, the two large capacitors (1000uF / 200v) were fully discharged.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: February 03, 2022, 03:27:33 pm
content: The Power Resistor marked 10watt 1K5J gets very hot at ALL times (even when the power supply is sitting idle doing nothing)So hot in fact that the cooling fan cycles on and off a lot to remove the heat.I am wondering if I could resolve this by adding another Parallel 10W 1K5J resistor to the existing one? (Or if there is a better solution)(I could not find a through hole, radial, wirewound resistor like this of greater than 10Watts)[ Specified attachment is not available ]

author: BrokenYugo
author_rank: Super Contributor
timestamp: February 03, 2022, 04:35:39 pm
content: These random name Chinese supplies are all dodgy, recycled transistors and caps, solder balls, transformers designed for copper wound with CCA, generally sloppy assembly, etc. That's how they're selling them for what's probably below the BOM cost to do it right with new parts. They're kits at best and even then the finished product is sketchy.

author: AVGresponding
author_rank: Super Contributor
timestamp: February 03, 2022, 05:18:48 pm
content: Quote from: ThermallyFrigid on February 03, 2022, 03:27:33 pmIf you add an identical resistor in parallel you'll just double the power draw and heat generated. If you add it in series, it'll halve the current and power dissipated.EDIT: That's assuming that it is a discharge resistor. 1K5 seems quite a small value for such, I'd expect in the tens or hundreds of K. Is it definitely 1K5 and not 1R5..? That would make it part of the inrush limiting and make more sense given where it's placed on the board.EDIT 2: R3 looks more likely to be a discharge resistor to me.

author: mariush
author_rank: Super Contributor
timestamp: February 03, 2022, 05:31:58 pm
content: What do you expect from a company that names itself NVV to confuse people and make them think it's Meanwell ?See meanwell logo, same red and close enough shape :https://www.google.com/search?q=meanwell+logoDiodesGoneWild on Youtube has teardown of such power supply, with components that were pulled from other power supplies ... dented capacitors that were "repaired" with wax to make them round again and then had new labels on them, recycled mosfets with cut leads etc etc

author: Jester
author_rank: Frequent Contributor
timestamp: February 03, 2022, 06:23:41 pm
content: Reminds me of that TV series junkyard wars.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 03, 2022, 08:33:49 pm
content: Wow, do they have the inverter supplied from one long-ass fly lead, wired to the output transformer with another (the two red jumpers)?Yeah, those things must switch slow as shit, to avoid any kind of overvoltage... there's no bypass cap near 'em either, at least not on top (and it seems unlikely they could afford a large enough ceramic on the bottom to be worthwhile).Wonder if it's a TL494 / KA7500 on the riser board, or something else.Looks like a current transformer and coupling capacitor (film) on the primary side as well, then also an aux supply (some ST? flyback chip?) and gate drive transformer. I doubt that means it's current mode in any meaningful way; more likely primary current is just used for latched faulting.Transformer looks like they used extra layers of tape between P/S, but no margin tape; the windings go fully to the edges of the bobbin, probably having dubious creepage. Probably okay to use with grounded output, but for isolated SELV (needs reinforced type) I'd be suspicious. Besides all the other things to be suspicious of, I mean.Also no litz wire used in the transformer, by the looks of it. So AC resistance will be pretty bad. Maybe it runs pretty slow (30kHz?), might not be terrible-terrible. Or if they used CCA, well...Output has reasonable filtering I guess, nice big fat choke (is that a green/blue marking on the cores, so, #52 powder probably?), lots of positions for diodes but just the one I guess installed here (probably the top voltage rating in the family so that's fine; probably all populated for 12V, etc.?). What the heck is the white box thing (C25)?No PFC on the input, so, 800W is all you're going to get out of the poor bastard before your breaker pops (expect PF ~ 0.5, 800W will use up most of a 120V 15A circuit), assuming it doesn't melt itself to pieces sooner of course. At least they have an NTC inrush with bypass relay, I guess? Think I see a thermistor elsewhere too, might be routed to a protection circuit or fan control. Of course with such insane losses, fan control is probably deleterious overall (better to leave it always-on so it's not cycling, risking getting stuck from the shite bearings also failing quickly?).Tim

author: MrMobodies
author_rank: Super Contributor
timestamp: February 03, 2022, 10:06:47 pm
content: They also make these ones look similar to a Meanwell in the video:https://cloud.video.taobao.com/play/u/3473172900/p/1/e/6/t/10301/309535369203.mp4Also look at this store and sellers ripping off the Meanwell logo even more:https://www.ebuy7.com/item/574533471604https://www.ebuy7.com/item/593879094238Mingwei power 800W switching power supply 12V24V36V48V60V65V industrial control centralized LED light bar to DCQuoteI see they also have pictures of the pcb which look similar in certain places:

author: thm_w
author_rank: Super Contributor
timestamp: February 03, 2022, 10:46:45 pm
content: Quote from: ThermallyFrigid on February 03, 2022, 03:09:40 pmR1 is to discharge the square gray capacitors, CX1 and CX2. Its not super dangerous, you might get a zap if you touch the mains leads after unplugging it, causing you to jump.They put that 1k5 power resistor in place of C25 capacitor for some reason. Maybe the supply needs a high minimum load to be stable. You could try removing it and measuring the output voltage, after removing it it may no longer be stable or be out of spec. Assuming you have the equipment and ability to do this.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: February 04, 2022, 05:18:09 am
content: Quote from: mariush on February 03, 2022, 05:31:58 pmYou know,I did not notice the rip off of the Meanwell Logo until you mentioned it. At least no conscientiously.I need to pay more attention.Yes, I love DiodesGonewild Channel.

author: MrMobodies
author_rank: Super Contributor
timestamp: February 04, 2022, 07:21:21 am
content: I think this video was posted by someone a couple of years ago somewhere on this board:I first remember DiodesGoneWild testing a dangerous powerhead with a coil element built in directly exposed to the water where he measured the voltage through the sprinkle in the bath with and without earth. Electric heated "suicide" shower PART 2 - test & measurementsyoutube.com/watch?v=jiErqUkw690

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: February 24, 2022, 05:33:03 am
content: I decided to repair the board.It was working but I don't like the shit job they did. Not sure how safe this design is but I need this PS right now until I can buy a better one.Working on cleaning up the damage and next I'll repair all the damaged traces.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: February 24, 2022, 06:43:06 am
content: Selling a product that falls far short of the product you are trying to copy.What would your parents say?

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: February 24, 2022, 03:47:11 pm
content: Quote from: Ed.Kloonk on February 24, 2022, 06:43:06 amThey would probably say......."If you spent another $100 to buy the quality components used on the better board to correct the quality issues, then considered the total cost including your original purchase price, you probably would have been smarter to spend the money and buy the better quality product to start with."That said.....I think everyone is "Guilty" of trying to get the things they need or want at the best price possible. Sometimes we play "Pay and Pray"

author: dbctronic
author_rank: Regular Contributor
timestamp: March 16, 2022, 02:14:34 am
content: I'll throw a few bucks for some standalone handheld thingy that I can just toss out if it fails, like a cheapo handheld radio. But, not for something like a power supply or test equipment that gets connected to other, possibly quite valuable circuitry. Something you've been slaving over for weeks is suddenly introduced to mains voltage or nasty big spikes... no thanks!

author: free_electron
author_rank: Super Contributor
timestamp: March 16, 2022, 03:16:36 am
content: Quote from: mariush on February 03, 2022, 05:31:58 pmthat was my knee jerk reaction too. The letters are spaced to trip up anyone believing this is a meanwell part.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 17, 2022, 03:17:16 am
content: Well,I went ahead and repaired it properly.I had to repair the Ultra shoddy work done by NVVV / VISLONE (It is my belief that NVV has changed their name to VISLONE - exact same product - exact same pricingIn addition to repairing the board damage, I had to replace both 40N50L Mosfets. They were from different batches and not the same.Anyway.....Powered it up and it works fine again. Maybe better. Voltage is rock steadyI wanted to fully test it before sealing the PCB with Green UV solder mask paint. Once I do that it will look almost new and should work better.I may add my own fuses to the PCB for added protection.Thanks for all the assists

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: March 17, 2022, 04:58:19 am
content: That large white ceramic resistor next to the capacitor and inductor sits at about 175F at idle.That's a problem.

author: MrMobodies
author_rank: Super Contributor
timestamp: March 18, 2022, 10:21:46 pm
content: Look to me like you did a better job with the cleanup than what they did to it at the factory.That'll put them to shame.

author: amyk
author_rank: Super Contributor
timestamp: March 19, 2022, 02:55:38 am
content: Quote from: ThermallyFrigid on March 17, 2022, 04:58:19 amNot a problem for the resistor; 65V across 1k5 is less than 3W, well within the 10W (assuming it's honest) rating. 175F or 79C is not too hot for a ceramic resistor; they're usually rated for over 100C.On the other hand, it will slowly cook the capacitor next to it, so you could try to replace it with a capacitor under the assumption that it was a minimum load resistor and you will always be drawing more than the ~43mA that it provides, or relocate it to a less heat-sensitive part of the case.

author: SL4P
author_rank: Super Contributor
timestamp: March 19, 2022, 11:27:46 pm
content: Quote from: ThermallyFrigid on February 24, 2022, 03:47:11 pm