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 My free Chinese bench power supply
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 Return to top of page · Post #: 1 · Written at 7:26:27 PM on 22 October 2014.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6172

Some time back I purchased a brand "X" el-cheapo 30 volt 10 amp variable bench supply for non-critical work. It failed to work out of the box; in fact it was going haywire with relays randomly clicking and the meters showing random numbers. I complained to the seller who requested a video of the problems. When they saw the video they agreed it was stuffed and, as they had no more in stock, refunded my money in total and told me to keep the unit for repair or parts.

Today I eventually got around to opening it up to find the transformer leaning backwards courtesy of a bent case beneath it. The PS came packed in some styrofoam that showed no signs of damage, and neither did the outer carton, so I can only guess this damage was done in the factory and they went ahead and shipped it anyway. Fantastic quality assurance!

Anyway, I removed the control board to find that the tilted transformer had dislodged a header connection. Once I fixed that, bingo, it worked.

These "generic" Chinese supplies have a few known problems, including a tendency for a voltage spike upon power up, and the meter circuits usually need to be calibrated.

I will put it through its paces before going to the trouble of fixing the bent case and transformer legs, and replacing the poor quality terminal posts.

So, with a bit of fiddling I may have scored a free low quality PS.

Apologies for the lousy quality of the photo. The camera on my phone will not focus.

Broken Power Supply


 
 Return to top of page · Post #: 2 · Written at 8:19:35 AM on 23 October 2014.
Maven's avatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 584

1. Voltage spike - is there a MKT capacitor across the AC supply, between the switch and the transformer? That's the usual spike protection, in my experience.

2. Phone camera focus - A lot of phone cameras don't have any macro setting and won't focus closer than about 60-100cm. They are also virtually impossible to hold steady enough for longer exposure in a dim light. Solutions include a)stronger light and b)shoot from further away, then use any basic photo editor to crop the picture back to the part you intended to shoot, and/or c) find the shutter delay on your phone app and prop or clamp the phone in position so your hands can be well away from it by the time it shoots.

Maven


 
 Return to top of page · Post #: 3 · Written at 8:26:52 AM on 23 October 2014.
DJ Oz's avatar
 Location: Central Coast, NSW
 Member since 18 April 2014
 Member #: 1554
 Postcount: 215

Yeah there was a comment I think in SC mag about a frequency Meter that was of very dubious make
on the Mains side...I think he mention it was a potential death trap

Doesn't surprise me mate that you scored a dude but with a little work one for Free is a good score, if you know its limitations and either correct or work with them

Good one GTC supplies I think you can never have too many of

Still I think its not good as how many people that are new to electronics would depend on supplies being built properly as they learn ...and as above you dont want a potential death trap either

Auto focus can be a real pain at times...that taken on your spiffy new Work bench ...looks great Smile

Cheers Smile


 
 Return to top of page · Post #: 4 · Written at 10:51:21 PM on 23 October 2014.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6172

Thanks for the camera tips, but this one is really not much better than a pinhole camera. It's on a cheap Nokia phone that has been dropped a few times. I bought the small phone because that's all I want in my shirt pocket, however it would have been nice to get a decent camera. I'll upgrade one of these days.

As for the power supply, I put it through its paces tonight and it ran pretty well. There was no power-on over voltage spike evident on the CRO screen despite numerous tests. Reportedly, the spike in these units is due to incorrect capacitance on the regulator chip resulting it being too slow to activate.

The voltage readings on the on-board meter were close enough according to my digital multimeter. For the want of a decent load I ran a quick 1 amp current test and tweaked the on board ammeter. The current limiter seems to be working.

So, I will go ahead and repair the bent case and upgrade the output terminals.

I'm not expecting miracles from this freebie, but it will be handy to have as a rough and ready linear PS on the bench.


 
 Return to top of page · Post #: 5 · Written at 10:29:53 PM on 5 November 2014.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6172

Okay, I've repaired and upgraded this unit and it's now on the instrument shelf above the bench ready to go when needed.


 
 Return to top of page · Post #: 6 · Written at 11:01:32 PM on 5 November 2014.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

I have been very guilty of not withholding comment on some stuff that I have scored, or has landed on the bench only for me to note that it is a death trap.

This is aside from "transformerless" live chassis sets which are intrinsically dangerous no matter what.

Most of my comment relates to what I consider lunacy, where a capacitor, that is not up to the current requirements, was placed on the mains to the metal chassis and metal case, on a transformer type apparatus with no earth wire (two wire cable)

If the capacitor leaks badly, is able to punch through,or the mains is inverted, there is every chance of the metal case becoming "Alive". How they got away with that I do not know? The current regulations require that if the metal can become alive, it should be grounded.

Mains approved "X" type caps are designed to fail open...... however!

Marc


 
 Return to top of page · Post #: 7 · Written at 11:19:17 PM on 5 November 2014.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6172

As per my first post in this thread, this particular unit is brand new, but damaged.

I upgraded the output terminals to more substantial ones (given that the supply is rated at 10 amps) and I made the flimsy earth connections to the case much more substantial, too.

Apart from those things it's pretty ship-shape inside.

However, aspects of the design leave a lot to be desired, including the fact that the 4 output transistors are on a plain sheet of 1/4" aluminium rather than a proper heat sink and the cooling fan runs continuously.


 
 Return to top of page · Post #: 8 · Written at 12:07:47 PM on 6 November 2014.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

Unfortunately there have always been people out there that think, or have been given bits of paper that say they are engineers.

It is only when they are released into an unsuspecting world, that we find out their level of incompetence.

Marc


 
 Return to top of page · Post #: 9 · Written at 12:56:55 PM on 6 November 2014.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6573

The root cause of all of the quality and design issues we face in this age is the issue surrounding self-regulation. Often, a manufacturer will just say something complies and seem happy to sign their lives away every time one of their process workers applies a compliance plate with the A-Tick and/or C-Tick logos and various other marks to 'prove' their product is mickey mouse.

When some of these products are opened up it is plain to see that no effort what-so-ever has been made to assemble the product with safety and longevity in mind. Based on previous experience, the last thing I'd do is purchase an appliance of any sort online where the product has to be direct imported by the vendor, unless the vendor is an Australian-based P/L or Ltd. company like Jaycar or Altronics. I'll admit I've been bitten too. I've also lost count of how many times I've read that someone has bought Product-X from the Shanghai Trading Post (fictitious company) for it to arrive in a state of disrepair or be electrically suspect - never mind the loose earth wire, try no earth wire at all, etc. Forums of all sorts are filled with stories like this so defective products are out there in large numbers.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 10 · Written at 1:08:48 PM on 6 November 2014.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 419

The root cause of all of the quality and design issues we face in this age is the issue surrounding self-regulation .......

Agreed ..... but I would add "cost" into the discussion also ...

I bet that I am not the only member of this Forum who tries to buy "quality" rather than "lowest price".

Cheers,
Ian


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Cheers, Ian

 
 Return to top of page · Post #: 11 · Written at 1:25:10 PM on 6 November 2014.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6573

I tend to try and strike a balance. The thing is, not everything that is made in China is rubbish though at the same time not everything that costs a million quid is the duck's nuts.

My own gut feeling often helps me with decisions I make on things and if I am served well by something I buy then I tend to favour the same brand when I buy again. My current laptop for example, a HP, is the fifth HP-built laptop I've owned over the years. HP is also my printer of choice and once owned a HP-branded smartphone (made by HTC). I would never buy a car that didn't have a lion on the bonnet and I've been squirting Fountain tomato sauce on my sausages for more than 43 years.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
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