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PS-305DM DC Bench Power Supply: Variable Linear 0-30V 0-5A, Are they worth a punt?

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crustytv
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Topic starter
 
psu1

Hi guys N gal, in answer to the topic title, in my humble opinion, yes!

I've been after a new bench power supply for a while and have been looking at these cheap Chinese ones you find on e-bay. They are many that come with different branding and features, ranging from £39 to about £52. I went for the one that has a switchable  A/mA current meter and one with the constant current and constant voltage indicators. I'm very impressed with it, I checked the output against my Metrix and it tracks very well. 

Features:

Power stability: < 0.2%+3mA
Load stability: < 0.2%+3mA
Ripple & noise: < 3mArms
Temperature: 0°C to 40°C
Relative humidity: < 80%
Input: 220V / 110V ± 10% 50Hz/60Hz (switch at the back)
Power stability: < 0.01%+3mV
Load stability: < 0.01%+3mV (Max. current < 3A)
Ripple & noise: < 0.5mVrms (5Hz-1MHz) (Max. current < 3A); < 1.0mVrms (5Hz-1MHz) (Max. current > 3A)
Temperature coefficient: < 300PPM/°C

Next we'll take a look inside.....

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Posted : 20/06/2018 11:32 am
ntscuser, PYE625, ntscuser and 3 people reacted
Marc
 Marc
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Hi Chris,

For the money it looks a good piece of kit.  ? 

PS, hope the cold clears soon.  ? 

Marc
BVWS member
RSGB call sign 2E0VTN

 
Posted : 20/06/2018 11:40 am
crustytv
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Topic starter
 

As promised the internal shots. 

The transformer is a fairly hefty beast, looks to be very well constructed. I'm equally pleased with the PCB's, I've seen some reviews of other clones where the print and soldering are atrocious, one example I saw had solder daubed on one of the traces in an attempt to beef up its current carrying capability.

However the one I have here all the soldering is good and the PCB's equally well constructed and not bodged. The only common critique across all is the Heat-sink just being a 6mm alu sheet. However it does have fan cooling and this does operate when required.

The case is really nicely finished and robust, even with the lid off, the unit is still very stable. Again I've seen other reviews where once the lid is removed the whole thing flexes and the end panels become wobbly. This unit has a cross member tying the whole thing together giving strength. The control fascia is very pleasing, all the control knobs and connections operate smoothly and the outputs nice and solid. There are pre-sets inside should you need to calibrate current and voltage.

Personally I think if you're up for purchasing one get this model. At £42 inc p+p with the CC, CV indicators and adjustable A/mA meter its an absolute steal. The supplied connection leads are just about OK, the banana ends are OK but I removed the croc-clips which were flimsy to say the least and added some quality EZ-Hooks, much better.

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Posted : 20/06/2018 1:54 pm
turretslug, ntscuser, turretslug and 3 people reacted
turretslug
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Interesting shots there, Chris- thanks for posting. I'd seen these things listed by lots of sellers and wondered about the quality, there is an element of  "too good to be true" about the price but this is very encouraging. Linear, too- so plenty of iron and copper for those shekels, plus (electrically) quiet and more chance of being straightforwardly fixable. I suppose it's a sign of the times that a bit of plain ally and a fan works out cheaper than lots of square cm of extruded finning hanging off the back. 5A is usefully hefty and might even spin up a typical receiver dynamotor enough initially for back-EMF to then help along (one of my criteria....).

The other day, I noticed an eBay seller doing new UK stock of these, labelled "110V" on the back, for a mere £22 delivered- I hummed and ha-ed, wondering if it had single or paralleled primaries for re-jigging, about a dozen sold during the next few hours but by time I'd decided to chance it, the sale was taken down. (I do have an ex-NOS military 230-110V 500VA autotransformer anyway, but equally I'm not a fan of clunkiness if I can avoid it!),

Colin

 
Posted : 20/06/2018 2:22 pm
PYE625
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Posted by: Chris

 There are pre-sets inside should you need to calibrate current and voltage.

 

A nice unit Chris. As a matter of interest, does it have calibration instructions in the manual? 

(Not that you should need to do that for many a year.)

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 20/06/2018 5:08 pm
Reelman
(@reelman)
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Get well soon Chris.

Looks a good deal and well enough made to last.

I was very lucky enough to buy two similar PSUs second hand at last year’s Finningley radio rally for about £8 each!

Incidentally the next Finningley rally takes place on 22 July, a good day out as next door is the Sandtoft trolley bus museum.

Peter

 
Posted : 20/06/2018 10:31 pm
crustytv
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Topic starter
 

A guest mentioned the following

Posted By: Guest

have a look at bigclivedotcom on youtube I believe he has one didn't end well

My response:

Well for a start Clive was sent a photo of one that had been left unattended running at 18V 8A load and the front had caught fire on their kitchen table. That's the one that "didn't end well", not the one Clive subsequently tested himself. What I find amazing is neighbours had to contact the guy who owned it as he had left his house and his alarms were going off. Perhaps we'll leave the question aside about leaving anything unattended for another time or thread. 

Off the back of this, Clive then bought the same one to bench test and do a video.

The only real problems he found were the mains plug earth pin was not full metal, it had a too large plastic shroud that when inserted into a socket resulted in the unit not being earthed. The second problem was the mains lead cable itself was copper coated plastic, a flame test on the bared wire showed it just disintegrated.  The one point he found and believed a possible candidate for the fire, were the test leads. Using a thermal camera the -ve lead banana plug was a hot spot, due to a bad connection. The wire had been poorly prepared and not secured in the plug correctly, the +ve lead was OK.

Finally both the unit that caught fire and the one Clive covered were SMPSU...... NOT the linear transformer version which is covered here in this thread. The mains supply plug earth pin is full metal. The mains lead core wires are full copper and the test leads were bared, soldered and tightly secured in their plugs.

Hope that clears up any confusion between the two units.

There are many reviews out there, as many as there are variants of these cheap PSU's, some are good,  some are bad. Nonetheless, it pays to be vigilant when buying anything and do your research before parting with cash. 

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Posted : 20/06/2018 11:11 pm
turretslug
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Copper coated plastic.....!!!! I'm endlessly astonished at what folk will fake to rake in a few bob (or possibly rather more in our globalised world). Someone must have made considerable investment in sophisticated industrial process to churn out km of copper-sprayed plastic string wire that looked convincing.

Picking nits, the mains switch appears to be single-pole- fair enough, there's probably loads of stuff like that in all our houses/workshops but the mains IEC receptacle wiring/earthing looks to be in non-compliant colours, I don't know if this is a trading standards thing or not, I daresay Rich (Sideband) is the one who would be able to comment definitively. TBH, I'm an accomodating pragmatist on this sort of thing- "if you're going to poke around inside mains electronics, you should have both technical and hazard awareness anyway etc etc"- but if a manufacturer has ticked the accustomed boxes with this sort of thing, it helps to give confidence that other aspect of a product are up to the mark.

If I hadn't scored a cosmetically excellent Farnell E30-2BT for a song at Dunstable Downs the other day, I'd definitely be interested in one of these. (This had one channel uncontrollably high, quickly traced to a leaky 1N4148 in the current limiter circuit. The diode was marked "TFK", I also got a steal of a Philips PM3206 'scope at the same event, this was fixed by replacing a 7912 in the PSU, also marked "TFK". Methinks that some quality control lederhosen need pulling up there....)

 
Posted : 21/06/2018 11:06 am
PYE625
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Posted by: turretslug

 

If I hadn't scored a cosmetically excellent Farnell E30-2BT for a song at Dunstable Downs the other day, I'd definitely be interested in one of these.

Similar thing with me, I got this beastie from work and it can sit at 30v 20A all day long. Although I certainly couldn't carry it all day long !!

https://www.radios-tv.co.uk/community/in-the-workshop/farnell-b30-20-psu/

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 21/06/2018 5:23 pm
Lloyd
(@lloyd)
Posts: 1897
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Looks a good piece of equipment! I’ve got a Goodwill Instek dual output power supply that looks like a bigger version of the one you bought, I got it for nothing from the place I worked in 2010 when it closed down. I think it was brand new, it still had its box and instructions. It has served me very well since then, and I’d be lost without it. It also has a fixed 5v 3A output, and the other 2 are 18V 5A. I also have a Wier 60V 1.5A power supply, which is very useful, but does keep overheating. 

I was hoping to get some nice TTi power supplies from work, they have been clearing the equipment stores of all the unused and faulty stuff, but they won’t let any of us near it!! Apparently they have to make sure it’s disposed of properly, for legal reasons, so they have to pay some company thousands to come and take it away, I was most disappointed!

 Regards 

Lloyd

 
Posted : 21/06/2018 7:00 pm
turretslug
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Posted by: PYE625

Similar thing with me, I got this beastie from work and it can sit at 30v 20A all day long. Although I certainly couldn't carry it all day long !!  > https://www.radios-tv.co.uk/community/in-the-workshop/farnell-b30-20-psu/

That's a no-messing beast! Long ago, I used to get involved with working on large professional audio mixing consoles- these stuck with brutish linear PSUs as everyone else shifted towards SMPSUs on the grounds of minimum noise. As with so many things in life, this was part truth, part "well, we've always done things this way". It certainly taught me to shed watches and rings before hands inside and it's become instinct before any electrical/electronic work. One plus point was that duff semiconductors could be easy to trace- there would be a few pitiful remnants of legs left sticking out of the board, but no actual transistor....

I've heard a few people being sniffy about Farnell products but I came to quite respect what they did as workaday test-bench stuff- from a bewildering array of all sorts of PSUs to 'scopes and quite sophisticated signal generators- quite possibly, there was some badge-engineering going on. One thing I would say that also applies to other British electronics is that while it might not have used the most exciting or ground-breaking technology, it's sturdily enough made- there must be some good metal-folding and fabricating shops up there in Wetherby.

 

 
Posted : 22/06/2018 4:19 pm
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