Power supply for harsh environments BP120B-D9-24C from Owen

I’ve already reviewed plenty of power supplies and devices made both in China and locally. But today I’ll be testing a power supply from OvEN, a well-known company that develops and manufactures industrial automation equipment.
Let’s take a look, take it apart, test it, heat it up, and draw some conclusions.

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Yes, I’ve already tested products from local companies such as Novatek-Electro (Odesa), DS Electronics (Kyiv), and Light Route (Kyiv), but those are Ukrainian companies. The first also manufactures its products in Russia, while the second has a local office there.
This time, though, it’s the other way around: the company is Russian, but manufacturing is also based in Ukraine—not just in Kharkiv, where I live, but practically within walking distance. It’s a little surprising their products didn’t come my way sooner :)


This power supply series is relatively old, but well proven. It includes three models with different power ratings: 30, 60, and 120 W. All the power supplies have a 24 V output, since that is essentially the standard voltage for industrial automation equipment.
The link goes to the Ukrainian website; Russian readers can go to the Russian site instead.

Here are the available versions. Apart from power rating and size, the models may or may not have a C suffix, indicating an extended temperature range of -40 to +70 degrees.


The packaging is very basic: a plain white box with no printing, just a sticker on the side showing the model and place of manufacture.


Besides the power supply, the box contains:
1. Instructions in Ukrainian
2. Instructions in Russian
3. Device passport
4. A screw for connecting the ground wire.


It’s unusual to see two versions of the instructions included. The individual device passport, however, is only in Ukrainian.
The stated warranty period is 2 years. The manufacturer also notes separately that it can provide repairs for 5 years after production ends.


The manufacturer’s website also provides a declaration of conformity, an industrial safety certificate, and an example of the results from an individual test. Mine didn’t come with one; I was told they don’t provide these with units made in Ukraine.


The instructions are available online; as usual, I’ll quote some excerpts from them below.



The look is “square, practical, good”—there’s no other way to put it—but it fits right in with industrial equipment.


1, 2. The input and output terminals are the “elevator” type. No complaints there, but they’re recessed quite far into the case, which is a bit inconvenient because you can’t see how far the wire or terminal has gone in.
3. On top, there’s a power indicator and an opening for adjusting the output voltage with a trimmer potentiometer.
4. The side label lists the basic specifications and serial number. The maximum output current is specified as 5 A; I’ll come back to that later.


The entire bottom of the case is a substantial aluminum heatsink with a clip for mounting on a DIN rail. The clip isn’t spring-loaded and has two positions, which is quite convenient. There’s a protrusion on the side of the heatsink with a threaded hole for connecting ground.


I liked the power supply’s design so much—especially the fact that it has not just a substantial heatsink, but one that extends beyond the case—that it even reminded me of a scene from a well-known movie. That’s more or less what I wanted to say :)


The top and bottom are essentially large ventilation grilles. That’s good in one respect—better cooling—but a clipped-off wire strand could easily get through those openings, which isn’t safe.


The power supply is relatively large, measuring 9 standard modules wide. The 30 and 60 W models are 3 and 4 modules wide, respectively.


The dimensions of the 120 W model, taken from the instructions.


And here it is next to standard circuit breakers and a Meanwell HDR-60-12 power supply. One advantage is that a power supply in this form factor fits in a standard electrical panel, unlike the MeanWell SDR-120-24, which has the same voltage and power ratings.


Of course, as always, I had to take it apart. Fortunately, this turned out to be extremely easy: just release a couple of clips on the sides of the case.


The first thing I noticed was the rather clever way the power indicator LED is installed. I've often seen light pipes, but this is the first time I've seen an LED mounted on the back of the board, shining through a hole in it.


The board is large and fills the entire area, but the design places it in a shallow recess, greatly reducing the chance of anything getting onto its underside—almost to zero.
Even at a glance, you can tell this is a single-ended forward-mode switching power supply with active PFC on the input. The large inductor on the left, the transformer in the middle, and the output inductor on the right give it away.


I should point out the full input filter, which isn't very common in “consumer” power supplies—except perhaps in relatively expensive laptop adapters and the like.


1. The input has a 3.15 A fuse and a thermistor. In my opinion, though, the fuse is a bit undersized and may not provide the required breaking capacity on an industrial power network. I could be wrong, since I haven't seen the datasheet.
2. There's also a 10 mm varistor rated for 430 V on the input. The voltage rating is fine, but they could have chosen a larger one to improve reliability and increase the chances of the fuse blowing successfully in an emergency.
3. Judging by the silkscreen, a heatsink was intended for the active PFC diode, but it wasn't installed. I'll say in advance that it isn't really needed there.
4. The input capacitor is a 150 µF, 420 V unit made by Nippon Chemi-con. Nothing to complain about here either.


1. The board is coated with protective varnish, which is great, especially for an industrial-grade device. A pair of Y capacitors have even stuck together. The capacitors are connected to the heatsink with a screw.
2. One of the screws that clamps the power components also provides an electrical connection between the output noise-suppression capacitor and the heatsink.


1. There are two optocouplers. If I've understood the circuit correctly, one provides feedback and the other is in the overtemperature protection circuit. Nearby are a couple of capacitors from a manufacturer I don't know, JB Capacitors.
2. The output has a pair of Nichicon 1000 µF, 35 V capacitors from the PW series, specifically designed for switching power supplies. But there's a problem: the installed capacitors have a rated ripple current of 1.95 A each (3.9 A total), while the specified output current is over 5 A. For comparison, the SDR-120-24 uses three Rubycon YXG capacitors rated at 2.23 A each (6.69 A total).


The labels on the magnetic components somehow remind me of the standard labels on some Soviet-era product—just as cryptic :)


To remove the board, you need to undo the five screws clamping the power components and the one screw connecting the midpoint of the Y capacitors to the heatsink. The board was also held in place by the protective varnish.
An insulating pad is glued to the heatsink, and, naturally, thermal paste has been applied.


It looks quite neat and even rather attractive, although the diagonal placement of some components is a little unusual. My only complaint is that there are traces of flux in places.


The high-voltage section: the PFC controller chip is on the left, and the power supply's PWM controller is on the right, with their respective high-voltage power transistors above them.
The PFC is controlled by an IR1155S, and the power supply is built around a UCC28C44 PWM controller.


The board also has high-voltage ceramic SMD capacitors installed before the rectifier and in parallel with the high-voltage electrolytic capacitor.


The low-voltage section: the upper leg of the power stage uses a diode assembly, while the lower leg uses a MOSFET, forming what you might call a “half-synchronous” rectifier. But as far as I can tell, there is no separate chip for controlling the MOSFET; it is driven by a separate transformer winding.


The control circuit uses a TL103WA chip, which is a dual op-amp with a built-in voltage reference, as well as a TL331 comparator, presumably responsible for the thermal protection circuit. The TO-92 temperature sensor is visible above and to the left.
There is also a 6 mΩ current-sense shunt on the right.
A quick look at the circuit showed that one of the optocouplers is in the feedback loop, controlled by the TL103WA, which implements CV/CC operation. The other is part of the output overvoltage protection circuit and is connected through a 27 V Zener diode. Overall, this is all fairly straightforward. The only slightly unusual things were seeing a MOSFET without a dedicated controller and a temperature sensor on the secondary side rather than the primary side.

Personally, I think it might have made sense to use a full synchronous rectifier here, although the load current is relatively low and the diode assembly handles it just fine.
There is no LC output filter, and the output capacitors are connected in the usual way, with one before the shunt and the other after it. Given what I wrote above about the capacitors, it would make sense to add a third one right after the shunt, but that's just me thinking out loud.




I connect the power and move on to testing.
The adjustment range is 21.97–26.32 V, and the adjustment is very smooth. They used a multiturn potentiometer, and there was a good reason for that, as I'll explain later.
With no load, the power supply draws a relatively high 3.5 W or so.


The manufacturer claims that the power supply will maintain a stable output voltage up to 110–120% of its rated output power, which for this unit means an output current of 5.5–6 A. Beyond that, it is supposed to switch to constant-current mode, but since the load is operating in CC mode, all we'll see is the power supply shutting down into protection.


The load test was performed at an input voltage of 230 V. The power supply delivered almost 140 W without any problems, then shut down into protection. The voltage remained very stable throughout. The maximum output current was around 5.8–5.9 A, which matches the specifications.


Since the power supply has active PFC, I decided to expand the test program a little and ran most of the tests at both 230 V and 100 V input.
However, the lower input voltage had no effect on output power or voltage stability.


The manufacturer doesn't provide an efficiency-versus-output-power graph, but does show efficiency versus input voltage and temperature. As you'd expect, efficiency increases as the input voltage rises.


I measured efficiency only at a 230 V mains input, and the results matched the manufacturer's figures quite well. The load power ranged from 10 to 140 W, so the horizontal axis is in 10 W increments.


I measured output voltage ripple at different load currents and input voltages, but it turned out to be almost independent of the operating conditions, so I'll summarize the results briefly.
I also tried measuring with the oscilloscope probe connected directly and with a filter made from 1 + 0.1 µF capacitors. There was a difference: without the filter, very short spikes appeared, with a peak-to-peak amplitude of no more than 80 mV, even under the heaviest load. This is because the power supply has no LC output filter, but in practice it doesn't really need one.

Here are a few oscilloscope traces; these and the ones that follow were taken with the filter.
Input: 230 V; load: 0, 60, and 135 W. High-frequency ripple is on the left, low-frequency ripple on the right.


At an input voltage of 100 V, practically nothing changed. The noise increased slightly, but only just enough to notice.
Load: 30 and 135 W.


At the very beginning, I mentioned that the power supply has smooth voltage adjustment, and also noted its maximum rated current of 5 A.
The point is that these power supplies can be connected in series or in parallel because they can operate in constant-current mode. But since load sharing is achieved solely through CC operation, without tying the feedback loops together, the best balance is achieved by keeping the voltages as close to identical as possible.

And this brings us back to the maximum rated load current. In parallel mode, the output current of one of the power supplies can easily exceed 5 A and will most likely hit its maximum current, set by the overcurrent protection threshold. For this power supply, that’s 5.8–6 A.


1. Power supplies often behave somewhat worse in constant-current mode, so I tested that mode as well.
For the load, I used three 10 Ω resistors connected in parallel, giving a total resistance of about 3.3–3.4 Ω. The power supply’s output voltage dropped to 19.7 V, so the current was around 5.9 A. But the unit performed perfectly: output ripple was no different from what I saw in constant-voltage mode.
2. As an additional test, I checked how the power supply handled a pulsed load: a regular TS100 soldering iron, which starts drawing about 2.5 A in pulses once it reaches operating temperature. I had no complaints here either; the unit behaved perfectly well.



And of course, no review would be complete without an important test: measuring the power supply’s temperature in different operating modes.
The test was run at an input voltage of 230 V. The power supply was lying on the table with its cover raised so I could take thermal images. Of course, you could say this isn’t entirely fair: the unit should be mounted vertically in a cabinet, not lying on a table. But the manual doesn’t specify any restrictions on its orientation, so it can certainly be used horizontally too, even though cooling will be worse that way.

Put simply, in my test the power supply gets hotter because it’s lying horizontally, but it cools better because it isn’t inside a cabinet, so the effects more or less cancel each other out. Also, I had the top slightly raised so the heatsink could do at least something.


Then I ran tests at 60, 120, 135, and another 135 W, with each stage lasting 30 minutes.
Thermal images taken at the end of the first three stages.


I ran the second half-hour at close to maximum power as an extra test, just to see how much the temperature would rise. The difference was about 5–7 degrees.

I can’t say I was very impressed with the test results. Yes, the power supply wasn’t in an ideal position, but the mains voltage was 230 V and the ambient temperature was around 21–22 degrees.
In the end, I measured about 50 degrees on the case, with the hottest spot between the transformer and the output inductor.
The transformer winding reached about 100 degrees, and its core reached 84–85. The inductor was a little cooler: 93 degrees on the winding and 83 on the core.


I started the next test almost immediately after the previous one, without giving the unit much time to cool down. But before describing the test, let’s look at the graphs in the product documentation.
On the left is the graph from the manufacturer’s website showing output power versus ambient temperature; on the right is the same graph from the manual. The differences are obvious: the left graph says the power supply can run at 100% power up to an ambient temperature of 70 degrees, while the right says that between 50 and 75 degrees, power must be reduced linearly to 50% of maximum.

You’ll agree these graphs are somewhat... different. In practice, the first one allows 120 W at 70 degrees, while the second allows the same 120 W only at 50 degrees—and just 72 W at 70 degrees. I think the manufacturer needs to be more careful with the information it provides. As I understand it, the graph on the right is the correct one.


So, I installed the power supply in a metal enclosure that had already been used for testing the Mean Well SDR-120-24.
The wires were routed outside and connected to an electronic load, set to 5.5 A, or 132 W.


There were no stages this time. I simply switched on the load for a few hours and went off to do other things.
The case reached about 55–60 degrees, and the area around the output circuitry was around 100. And there was nothing else in the enclosure besides the power supply.
Both the PFC inductor and the power transformer have spare room on their bobbins. I don’t understand why they didn’t use thicker wire or more strands for the windings. This would cost next to nothing, while slightly improving efficiency and reducing the temperature of these components. As the thermal images show, they’re the hottest parts.


This test was run at an input voltage of 100 V. Chronologically, it was the first one, but I decided to add it to the review later.
Here, the power supply was simply lying flat on the table. As before, the load was applied in 30-minute stages at 60, 120, and 135 W.

Thermal images taken after all three stages. You can see that the hot area has spread, and the PFC stage, input bridge rectifier, and thermistor have all heated up noticeably. This was expected: the thermistor and bridge rectifier heat up because of the higher input current, while the PFC stage is effectively running at full power.


1. To get a clearer picture of the temperature distribution, I had to cover the thermistor, since it was heating up to 125 degrees and the thermal camera kept shifting focus to it.
2. The PFC inductor winding heated up to almost 100 degrees, but what caught my attention more was the hot spot to the right of the input capacitor. Judging by the location of the hot spot and the other side of the board, the snubber resistors are heating up. I think it would make sense to increase either their power rating or their number.
3. And, as in the other tests, the output stage gets noticeably hot.


The output voltage’s temperature dependence was checked under the most demanding conditions, with an input of 100 V and maximum output power. And here I can say that the results are excellent:
1. No-load voltage with the power supply cold.
2. Under maximum load after warming up.
3. No load after warming up.

As you can see, the difference is only about 3 mV, which is especially useful when connecting several of these power supplies in parallel.


This next test was more of an impulse, since I hadn’t done anything like it before. Above, I wrote that this power supply must not be operated without grounding. Here’s why.
For safety, the distance between the primary (hot) and secondary (cold) side contacts is typically around 6–7 mm, which provides adequate protection against breakdown. Protective slots are also cut into the board for additional protection. The narrowest clearance on this power supply’s board is under the optocouplers, and there are no slots there. But attentive readers have probably noticed that almost all the power components are mounted on the same heatsink, and the distance from their leads to the heatsink surface is clearly less than 6–7 mm.
In this case, a breakdown could occur along the path: high-voltage component leads–heatsink–low-voltage component leads. Accordingly, the manufacturer specifies an isolation voltage of 1500 V between the heatsink and a component, and 3000 V (1500+1500) along the path described above, which makes perfect sense.

Just as an experiment, I decided to check the breakdown voltage between the heatsink and the power component leads under normal conditions. I took a heatsink and mounted a couple of transistors on it in the same package as those used in this power supply. I connected the leads of each component together so I wouldn’t burn it out.


To make the test as authentic as possible, I even applied thermal paste. The photo gives you an idea of the approximate distance between the leads and the heatsink.


The test was simple: apply 5 kV between the heatsink and one of the transistors; a breakdown should occur. Then switch the megohmmeter to the circuit between the leads of the first transistor and those of the second, where no breakdown should occur.
But “something went wrong.” In short, there was no breakdown at 5 kV along the heatsink-to-leads path with either transistor, and in the second case I even waited about 5 minutes.

I suspect the low humidity was a factor, since I have seen breakdown under other conditions and at a comparable distance.

But I’ll say this: in any case, this power supply must be grounded for safe operation!


Let’s sum things up.
First, the design. I liked it right away: a substantial heatsink, mounted outside the enclosure, is definitely a plus. The enclosure also fits in a standard electrical panel, which is nice, though the ventilation holes are rather large, so you need to make sure nothing gets inside.
I also have no complaints about the specifications or how well they’re met. I especially liked the output voltage regulation accuracy and the fact that the actual output power matches the stated rating.
Among the nice features, I’d point out the constant-current mode, rather than just overcurrent protection. This also means the power supplies can be connected in parallel. I’d also include the wide operating temperature range and overtemperature protection.

Now for what I think could be improved.
Personally, I wasn’t too happy with the heating, given the claimed extended temperature range, the product’s intended use in industrial applications, and the possibility of installing it in densely packed panels. It still runs rather hot. The active PFC is partly to blame, since it reduces efficiency. I also think the efficiency could be improved a little. For example, the MeanWell SDR-120-24 mentioned above is rated at 91%, compared with 86–87% for the unit under review, and it also has active PFC.
I also have some concerns about the temperature of certain components, which could be improved. And adding a third output capacitor alongside the two already installed wouldn’t hurt.
I also wasn’t too keen on the deep openings for accessing the terminal blocks. You can’t be 100% sure the wire is securely inserted, and some crimp ferrules for stranded wire won’t fit through the opening.


And, last but not least, the price. I think quite a few readers will ask why pay $110 for this power supply when you can get a Mean Well SDR-120-24 for around $35, with almost the same specifications.
Yes, these power supplies have very similar specifications, but there are also some significant differences:
1. Size—or, more precisely, form factor. The SDR-120-24 won't fit in every electrical cabinet. It's much narrower, but noticeably taller.
2. Temperature range: the SDR-120-24 is rated down to -25, while the one reviewed here goes down to -40, although I was told it had also been tested at -50.
3. It has a constant-current mode, which means the power supplies can be connected in parallel. There is a caveat, though: the SDR-120-24 also lists the following in its specifications:

but that doesn't mean it supports parallel operation.

Whether it's worth paying extra for all this is hard to say. I've just provided some food for thought. That's all for now; I hope you found this useful, and as always, I'm happy to answer questions and read your comments.