Sale of Mean Well SD-200B-24 converters

Not long ago, one of the blog's readers asked me to help sell some voltage converters. I thought, why not? Someone might find them useful, so I put together a short overview to explain what we're talking about.


The seller told me there are more than one or two converters—quite a substantial number, in fact. Some are new and boxed, while others are used but in good condition. All the details on prices, location, and how to get in touch are at the end of the article.
The link in the title goes directly to this model on the manufacturer's website.

So, we're talking about Mean Well SD-200B-24 voltage converters. First, I'd like to list the key features, because I think they're important.

1. Protection against overheating, overload, short circuits, and overvoltage—in other words, the usual set of protections you'd expect from a branded unit.
2. Galvanic isolation at the output, which gives you two things: the option to connect units in series and, most importantly, safety for the load even if the converter fails. I've explained before that when the power transistor in a cheap step-down converter fails, the full input voltage can appear at the output.
3. Passive cooling
4. The units have been tested at 100% load.


At a glance, these converters are easy to mistake for power supplies—which is essentially what they are, except that they have a different input voltage range. More on that later.


There are three converter series, distinguished by the letter B, C, or D. The difference is the input voltage range:
B - 19-36 V
C - 36-72 V
D - 72-144 V.

Each series also comes in four output voltage options: 5, 12, 24, and 48 V - datasheet

The units on offer are SD-200B-24 converters, with an input voltage range of 19-36 V, a 24 V output, and 200 W of power.


As I mentioned, this is essentially a power supply; even the block diagram is no different from that of a regular power supply.


By the way, Mean Well has a slightly more compact version, the RSD-200B-24, but this article is about the older SD-200B-24.


Converter dimensions.


Next are actual photos of the power supplies on offer, provided by the seller.
At least the new ones come in their original packaging.


The label. You can also see the trimmer for adjusting the output voltage. The specified adjustment range is 23-30 V, but I think you can probably set it lower as well.


The insides look nice. On the left, you can see that the transistor clamp has been unscrewed—that's from taking the photos :)


The input filter is genuinely comprehensive, and I can say that with a filter like this, it's perfectly safe to install the power supply in a vehicle—provided, of course, that it has a 24 V electrical system.


The converters are built around the rather old SG3525 PWM controller, and something tells me the voltage can be adjusted over a much wider range than the specified 23-30 V.


1. A 56 V varistor and Y capacitors on the input; they even included ferrite beads.
2. Three Nichicon 3300 µF, 50 V capacitors handle input filtering.
3. There are two optocouplers in the feedback circuit. I assume the second one provides overvoltage protection.
4. There is also an LM358 op-amp, with a trimmer resistor next to it. Most likely this is an overload protection circuit, perhaps even with CC mode, but that needs to be checked.


The power traces are reinforced with bus bars, and the soldering looks great.


The input uses a pair of IXYS 130N10T transistors, rated at 130 A, 100 V.
The output has two D92-02 diode assemblies, rated at 220 V, 20 A.

It appears to be a push-pull converter, which should reduce output noise. It also means that, with some modifications, you could get 2 × 24 V with a center tap at the output.


The transistors are clamped to the heatsink with an aluminum profile that houses a thermal switch for overheat protection.


I also found a graph in the datasheet showing how output power depends on temperature and input voltage.


The obvious question is: what can you use converters like these for? To start with, they aren't really suitable for portable applications, since they're fairly bulky. Otherwise:
1. For parts. It would be a shame to take one apart, of course, but sometimes it makes sense. These have quality magnetics and capacitors, for example.
2. To power a laptop or similar equipment in a truck. You get interference protection and better safety for the load.
3. To power other converters, such as cheaper QC/PD models. In a vehicle, this reduces the risk of those converters failing.
4. With some modifications, possibly as a charger for 24 V batteries.
5. To power audio amplifiers. Again, you get galvanic isolation from alternator noise and improved safety.
6. Your ideas.


After talking with the seller, we settled on a price equivalent to $10 for a new unit and around $5–6 for a used one. That seems reasonable to me, especially given the build quality. Prices are negotiable when buying several units.
The units are located in Medvedkovo, at 1 Startovaya Street, not far from Los station.
You can contact me here or call +79151294572 and ask for Vitalik.

More photos can be provided if needed, though I think the ones here are already enough to give you a good idea of what we're talking about.