Statron 3231.1 Power Supply. - Page 1
Forum section: electronics / testgear

author: Kibi
author_rank: Unknown
timestamp: January 24, 2015, 10:17:13 pm
content: For his birthday, my younger brother hinted that he'd like a power supply, a 30V 3A 100W sort of thing. Now, there a lot of those Chinese PSU's that fall under a variety of brand names which can be purchased from numerous places. Some are OK, but you need to spend a bit more. A $50 one would probably be no good. I thought about building one for him, but I did not have the time. I wanted cheap and good quality (don't we all) so, the next stop was eBay where Kev (AKA KJDS) had another Statron in stock for a sensible price! What's more, it's about 200W (32V 6.4A) and it's made by the Germans!It arrived promptly and naturally I had to have a close look at it.Goodness knows what the previous owner did with it, it looks like it had been placed in the wake of an angle grinder. Oh well, I've never been too concerned with cosmetics.Right, let's get the lid off of it.Oh dear, a non-detachable power cord. Also, no mains earth. Strangely, it has a 4mm earth jack on the front. Despite displaying the double insulated symbol on the rear it's got a metal case. Any electrical appliance encased in a metal enclosure wants said enclosure earthing in my opinion. So, I detect a lovely little Saturday afternoon project approaching. I can kill two birds with one stone here:1. Get rid of that affixed power cable that snags on everything and follows you around like a lost puppy whenever carrying the unit about.2. Get the case earthed!!!!So, off to the workshops to see what we can do.I had a few options to choose from in the IEC 60320 range with regards to the power inlet socket. I had also considered the obsolete XLR-LNE connector due to initial concerns with space. The C6 would work, but C5 leads, although common enough, just aren't as handy as C13 leads, so I eventually figured that I could fit the C14 inlet with the vertical flanges in the space.Now, with that settled, I needed to remove the old lead and create an aperture to accept the C14 connector.Some scratching around in my die and punch set box was required to find the correct tool combination. It's a bit of a mess, I really ought to sort it out.Found it.Unfortunately, I don't have enough bench space to accommodate my die press in a permanent position, so I have to affix it to the bench with big clamps each time I use it, which luckily is infrequently enough not cause too much of a nuisance.So, I have removed the small metal panel below the heatsink and here I am aligning the tool. The thing with these punches is that they remove a lot of material in a relatively short amount of time which makes the job quick. However, due to this, you need to be sure of where you are cutting, as there is no going back.Wallop! It's done. I'd have to drill the screw holes later.Here I have mounted the C14 receptacle and connected up the wiring and employed an insulating boot to cover the whole lot up.Now, to make an earth point, I drilled a hole in the bottom of the chassis through which an M4 bolt could pass. Then I removed the paint from the area with a small section of emery cloth.Now, one of the earth wires from the C14 connector is terminated in a crimp terminal and bolted firmly down with a nylock nut and an internal star washer between the case and the terminal. Once fastened, I sprayed a layer of clear lacquer to prevent corrosion from compromising the connection.Upon offering up the rear plate, some of the wires proved to be a bit cantankerous causing the insulating boot to be pressed into an unfavourable position.I solved this by altering the course of some of the wires around the other side of the mounting post for the transformer.Now, given that the main enclosure is of steel construction and the front panel is of aluminium, I decided that galvanism may contribute to an unreliable connection at the interface of the two metals. In addition, the two are only joined by a few self tapping screws, which provide durable construction, but an electrical connection may, again, be unreliable.So, to overcome this problem, the second of the two earth wires originating at the C14's earth terminal will have it's other end terminated in a crimp on connector and bolted down to the rear of the earth terminal presented on the front panel.Here is a view of the whole of the PCB mounted vertically behind the front panel.Here is a side view with my modification applied.After re-assembling the product I thought it prudent to conduct some tests. Of course, I'd need a power cable. My brother only has a tiny work space, so I thought a shorter custom length cable would be helpful to him.I also took the time to construct some test leads. One set are standard 4mm to crocodile clips. The other set is terminated into an XT60 connector which is commonly used these days on electric models due to it's 60A capacity. My brother and I share a mutual interest in electric models.So, on to the tests. Let's start with Mr. HSE. We've got to keep him happy from time to time.Although I am confident in my own workmanship, it's nice to just go the extra mile, especially for my younger brother.Power lead OK. Please excuse the blurred image, I had neglected to check my camera's shutter speed.An earth bond test revealed 30m? at a 10A test current and 40m? at a 200mA test current. Very good.Insulation test comes out good too.A preliminary check of the meters reveals that they are perfectly accurate enough. I forgot to capture an image of the Volt meter accuracy check, but here at least is a comparison of the Ammeters.Now for some good old load tests. Behold, the load bank. In the below images I have actually overloaded the power supply with a 4? load with the voltage adjustments at their highest settings. You can see that it is in constant current mode passing close to 7A. This sort of condition did cause the current to drop rather steadily as you can see, in the time it took to take a photograph of the resistor bank, the current displayed on the multimeter (and indeed the PSU ammeter) had reduced. There is nothing to worry about here as this is an overload condition. Although the particular resistor array arrangement was only worth about 120W, it had not heated up enough to cause that much of a drop in current. The heatsink to which the resistors are mounted is massive.Even in it's overloaded condition, I could detect no appreciable noise on the output.What about operating the PSU within the constraints of it's advertised specifications. Crazy though such a proposition may seem, I thought I'd re-arrange my resistor bank in such a way as to present a 5? load to the PSU. A 5? load would drive the PSU to the brink of it's advertised limit at 32V. Indeed, 6.4A should flow and it does. Again, at this point my resistor bank is overloaded (two 10? 75W resistors in parallel). The mass of the heatsink is keeping the resistors from melting (or even warming up for that matter).It not only met it's specifications, but it sustained them for a good ten minutes before I decided that the pass transistor's heatsink was getting rather too warm. With forced cooling it'd probably be happy with that output all day, although the transformer hum at those power levels may begin to cause some irritation. The transformer does look man enough,but I do wonder about it's full load duty cycle. Despite my tests, I'd be staggered if my brother finds need to operate this unit above 50% of it rated output. for any sustained period of time.Overall I am extremely pleased. I hope my brother will be pleased with it. If he is not, he can offer it to me for my birthday.Thanks Kev for finding this unit and offering it up for sale.

author: Vgkid
author_rank: Super Contributor
timestamp: January 25, 2015, 12:11:01 am
content: Good job on the fix.

author: quarks
author_rank: Frequent Contributor
timestamp: January 25, 2015, 04:48:50 am
content: Well done

author: gwhaley
author_rank: Newbie
timestamp: June 14, 2023, 02:38:59 pm
content: Heh, a blast from the past! I have the same PSU, purchased from the same vendor!, around about the same time. I was using it just yesterday when doing some LED experiments. I thought I'd look around for a schematic, but your thread was the nearest thing I found... thanks for posting the thread. It inspired me to get the lid off mine. The voltage adjusts were being a bit flaky, jumping around a bit - a quick squirt of the contact cleaner onto the pots seems to have helped that!I'll keep your mods/upgrades in mind for the future. Mine too is a 3231.1 - they are now on model/version 3231.10 it seems - they look to have added the IEC power socket, and also an output enable switch to the front panel. Other than that, the unit (externally at least) still looks basically the same. And the only prices I have seen are... around the E500 mark! Wow!Oh, my unit also has the what looks like 'angle grinder splatter' on the front plate. I can't tell if it is splatter, or just corrosion over time. What does intrigue me is the use of relays internally, and you can hear them physically switching as you pass through roughly 9v and 18v on the output scale. I'm guessing it is maybe switching combinations of secondary windings on the transformer to alter the secondary side voltage to reduce heat generation and burden on the linear regulators as one moves through the ranges. Just a guess.I think I'll be keeping this unit then - and it's nice to have a chunky linear around now and then (particularly when I don't trust a heavy inductive load to an smps...)

author: ch_scr
author_rank: Frequent Contributor
timestamp: June 15, 2023, 12:12:19 pm
content: We have 100+ of these at work, with some running all day for years, and none of them new (by now...). Don't think you would ever see a fault with these in the home shop, if you got a new one (or refurbish one yourself).With that out of the way, a few "service notes", in the order of observed likeliness of the fault:- With use, the tap switching relays wear out. One is a 12VDC, the other a 24VDC coil.- The pass transistors (MJ15003) fail in time, if the unit ran many hours (think months and years) at high load.- On the tap switch PCB are three small electrolytics near the little linear regulator. Good idea to replace these caps on old units. One of them will fail, given enough time.These are the only "regularly occurring" faults observed, aside from the above mentioned noisy pots. The "calibration" tends to drift, good idea to tweak the pots on the front pcb and bring it back in.We've (each once) had a bridge rectifier fail and a bad contact in the line fuse holder. Aside from that, these units are rock solid. Relatively easy access to work on the "regular spots", too.