BlitzWolf BW-S4 charger with an honest 50 W of power

Not long ago, I posted a review of an almost no-name charger (power supply) rated for 5 V and 7.2 A. As it turned out, the actual power was considerably lower. Today I have a model from the better-known (or perhaps simply known) company BlitzWolf, with a claimed total output current of up to 10 A.
Inspection, teardown, tests—as usual.


For a few reasons that I’ll explain below, this charger is rarely taken apart. That’s exactly why I decided to go a little overboard with the teardown, so there will be lots of photos.
But first, the usual introduction: the box, appearance, and so on.

Description and inspection.
The power supply comes in a small, rather plain-looking box. I’m not sure why there’s a perforated cutout for the power plug inside; the plug was packed separately.


The contents are just as modest as the packaging. They include:
1. BlitzWolf BW-S4 charger (power supply)
2. Power cable
3. Manual.



There’s nothing particularly interesting in the manual. I was more interested in the technical specifications. The manual tells users that the device can power up to six devices at up to 2.4 A per port, but no more than 10 A total. Of course, 2.4 × 6 is clearly more than 10, but I think charging three tablets and three smartphones at once is entirely realistic.
Unfortunately, the device doesn’t support QC. I don’t really need it at home for now, but it does support Power 3S, which is supposed to provide the maximum possible charging current to almost any connected device.
The power cable has a hook-and-loop strap for easier storage and connects to the power supply via the familiar two-pin connector.
Last time I wrote that I find it more convenient when a charger connects via a cable rather than plugging straight into the wall. That way, you can position it more conveniently, and it doesn’t hang from the outlet.


I’d call the dimensions fairly compact. It looks very neat, but glossy plastic is a source of pain and tears for perfectionists: over time, it’ll become unevenly matte and lose all its good looks. This is especially noticeable on a black case, so I recommend choosing a white one.


The power connector is on one end of the case, and a brief list of specifications is printed on the other.
There’s nothing on the bottom—not even feet, not even slippery ones. That’ll provide a few pleasant minutes of trying to keep the device on the table without it sliding away. In short, “the madness intensifies”; the marketing people are certainly earning their bread and butter.


The USB ports are on top of the case and covered by spring-loaded flaps. Neat and convenient.


Those little flaps also have an extra function: you can rest a smartphone on them while it charges. Spoiler: no, nothing overheats, and your beloved Samsung, Xiaomi, or iPhone will be perfectly safe.


Teardown.

Since this is a review of a charger—or, more precisely, a power supply—I naturally took it apart to inspect and analyze the circuitry.


This device is extremely difficult to take apart. No, that’s putting it mildly. This power supply simply doesn’t come apart properly. I spent ages working on it, hit it with a hammer, pried at it with a knife and various similar tools, all to no avail.
A couple of times I was ready to grab a thin rotary bit and just cut around the perimeter, but each time I stopped because I realized it would be hard to glue it back together afterward. I’m generally a fairly polite person and don’t swear often, but this one pushed me to the limit. In the end, I yanked harder and it finally opened.
As you can see, there are loads of clips inside, positioned so that there’s no way to release them without damaging the case. Some of the case is also glued together—more along the short sides, less along the long ones. You’ll see plenty more cut and torn plastic in the photos below.


To get the port covers out of the way, I simply removed them. They’re held in place by slots in the case and partly by the springy strips you saw in the previous photo.


I’ll hide the rest of the teardown under a spoiler so the review isn’t overloaded with information that most readers don’t need.


Testing.

To start, I tried checking how this device behaved with my smartphone and tablet, and comparing its performance with different cables and another charger.
Smartphone.
Standard USB-microUSB cable.
With the unit under review, the charging current was almost 1 A; with the other charger, 0.4 A (0.45 A without the tester).

The cable included with the power bank has no data lines and is only about 35 cm long.
0.98 and 0.91 A, respectively.


All right, let's connect the tablet.
First cable: 0.63 and 0.69 A.
Power bank cable: 0.62 and 0.44 A, which seems a bit low.

I grabbed the cable that came with the tablet.
0.6 A in both cases.


I tried connecting the tablet to my charger without the USB tester; it has a built-in ammeter.
First cable: 1.07 A
Power bank cable: 0.89 A.

The USB tester and the extra connector cause a significant voltage drop, so this test isn't entirely accurate.


I tried a second tablet. When connected to my charger, it usually draws around 2–2.05 A.
1. First cable: 1.33 A.
2. Second cable: 1.4 A
3. The cable that came with the first tablet managed just 1.18 A—not surprising, given its very poor quality.
4. The USB-to-barrel-plug cable delivered the highest current, 1.6 A, almost reaching the expected 2 A.


The reason became clear during one of the subsequent tests.
First, I decided to check the overload protection and the current at which it trips.
The protection tripped at 2.9 A, and normal operation resumed automatically. It's possible for the protection to latch, in which case it won't reset automatically. The manufacturer recommends disconnecting everything from the charger for 5 seconds, then reconnecting it.


To double-check, I ran the test again, this time setting the starting current to 2 A and increasing it in 0.1 A steps.
At an output current of 2 A, the voltage drops to 4.9 V. It drops further as the current increases, reaching about 4.85 V at 2.4 A.
Overall, that's fine: the specifications allow the voltage to drop to 4.75 V. But the cable causes an additional drop, so the device being powered gets even less.


I noticed an interesting effect during testing. With no load, the output voltage is 4.95 V. Under a light load, it rises to 5.06 V, then gradually drops as the load increases.


But let's move on to some additional tests and see how this device handles sustained operation under a heavy load.

Since USB connectors aren't designed for high currents, and the protection would trip before I could draw 10 A, I connected directly to the power supply's output capacitor.

First, I tested the power supply's output voltage, efficiency, and ripple.
1. No load: 5.1 V, which is quite good.
2. 2 A load: voltage dropped to 5.09 V, efficiency was 84%, and ripple was 70 mV.


1. 4 A: 5.08 V, 87% efficiency, 100 mV ripple.
2. 6 A: 5.065 V, 89% efficiency, 150 mV ripple.


1. 8 A: 5.05 V, 89% efficiency. Ripple increased noticeably to 200 mV.
2. 10 A: 5.04 V, 89% efficiency. Ripple was about the same as at 8 A: 200 mV.


Here's how it looks from the electronic load's perspective.


But I was much more interested in the component temperatures. This took quite a bit of effort, since the test had to be run with the device powered on, while checking temperatures with the case closed (or at least mostly closed).
I couldn't close the case completely, of course, so there was a large gap all around the perimeter—but I did the best I could.

The test lasted more than two hours: 20 minutes at 2 A, then 20 minutes at 4 A, and so on up to 10 A. Then I extended the test at maximum current by another 25 minutes. In total, the test at 10 A lasted 45 minutes.


At the end of the test, the thermal image looked like this:
1. Overall view with the case on
2. Board, top side
3. Board, bottom side. You can see that because the heatsink surface is mirror-finished, the thermal camera cannot measure its temperature accurately.


I also checked how the output voltage changes with temperature.
At the start of the test, I measured the no-load voltage, then measured it again after two hours of warm-up. The difference was just 0.02 V—a good result.



To make the results easier to digest, I put everything I measured into a single table, including the temperatures of:
the input capacitors, high-voltage transistor, transformer, synchronous rectifier transistor, and output capacitors, as well as the output voltage measurements and efficiency calculations.
I can say that this power supply passed the test with flying colors: temperatures, voltage stability, and efficiency were all at a pretty high level.


Back to the matter at hand—or, more precisely, figuring out what current this little box actually charges at. Above, I tested it with a USB tester, and the readings were far from normal. I also often see comments online along the lines of: 5 V is too low; it needs to be 5.3–5.5 V.
Well, folks, you’re right in a way. Not 5.5, of course, but 5.25–5.3 V wouldn’t hurt. But what actually happens?

Let’s use the same cables and the same charger, with an output voltage of 4.9–5.1 V, and connect it directly to the device, without a USB tester. Since I measured the power supply’s output under a 2 A load above, I can now determine how much current the device draws.
1. Large tablet, microUSB cable: 1.33 A with the tester, about 1.8 A without it.
2. Large tablet, included charging cable: 1.59 A with the tester, a little over 2 A without it. At a 2 A load, the power consumption was 12.1 W.
3. Large tablet, black cable: 1.18 A with the tester, about 2 A without it.
4. Small tablet + smartphone: with another charger, they draw 1.05 A and 1 A. With the USB tester, the readings were 0.63 A and 0.96 A, respectively. The combined current here came out higher than 2 A.

Conclusion: with a direct connection, and especially with a decent cable, 5 V is quite enough for normal charging. Still, as I said, I think 5.25–5.30 V would have been better, making the device less sensitive to cable quality.


Since the device is already disassembled, it would be a shame not to modify it.
The modification itself is very simple: just raise the output voltage a little.
As the tests showed, the output voltage is 4.9–5.1 V. I figured it would be better to set it to 5.25–5.30 V.
The modification isn’t really necessary; I only did it because the power supply was already disassembled.

There are a couple of resistors on the auxiliary board, R29 and R30. These resistors form a voltage divider that sets the output voltage.
The original values are 6.2 and 5.9 kΩ, so the manufacturer has already set the voltage slightly above 5 V, since the values would need to be equal for 5 V.
A quick calculation showed that to raise the voltage by 150–200 mV, I needed to solder an additional 82–75 kΩ resistor in parallel with R30. I happened to have an 82 kΩ resistor on hand, so that’s what I used.


As a result, the output voltage rose to about 5.25–5.3 V with no load and 5.2–5.25 V under load.
Let’s repeat the tests with the USB tester.
1. Smartphone: it was already drawing 0.96 A, and that’s what it still draws :)
2. Small tablet: it went from 0.63 A to 1.07 A.
3. Large tablet: it went from 1.33 A to 1.77 A.
4. Large tablet with the charging cable: it went from 1.59 A to 2.08 A.

In my opinion, the power supply can now handle even cheap cables, since it delivers a normal charging current even with the USB tester in the circuit.


And now, the conclusions.
In short, it’s a decent charger and it meets its stated specifications.

To go into more detail:
No complaints about the exterior, but I did notice a couple of very minor things inside: whitish marks on the circuit board. If they don’t affect performance, though, then everything is fine here too.
I was pleasantly surprised by the circuit design and the synchronous rectifier. The capacitors are from an unknown manufacturer, but they performed excellently. I was also pleased that the charger delivered 10 A without any trouble—and even more pleased to see that it didn’t overheat.
There’s an input filter to suppress interference. I couldn’t find an X capacitor, but the manufacturer partly made up for that by installing three inductors (two dual-winding ones of different types, and one in the filter capacitor circuit).
The Power 3S system works. Maybe not in 100% of cases, but it does work—that’s a fact, at least with my devices.

What can I find fault with...?
Well, to start with, the relatively high ripple level of 200 mV. In reality, things aren’t as bad as they might seem. The thing is, ripple was measured directly across the filter capacitors, but there’s a protection circuit after them that is essentially a low-value resistor, followed by ceramic capacitors. The actual ripple is about 1.5–2 times lower. It could be better, but it’s acceptable in principle.

The lack of an input thermistor can also be counted as a drawback, though there’s a bit of a nuance here too. Usually, the sequence goes like this:
The power supply is plugged into the outlet, and the voltage across the filter capacitor is 315–320 V.
Unplug it, and the voltage drops sharply to 80–120 V, then falls to almost zero over about 5 minutes.

Here, though, it’s different.
While the power supply is on, the capacitors are at the same 315–320 V.
After the power is switched off, the voltage across the input capacitors stays at the same level.
After an hour, it’s around 314 V; another hour and a half later, 304 V; two hours after that, 295 V; four more hours later, 280 V, and then it drops very slowly.
So if you switch the power supply on again after a day or two, there won’t be a large inrush current, since the capacitors are still charged.

I don’t know whether the manufacturer intended this, but it does help to some extent.

All in all, I liked the power supply. It could use QC, though I don’t need it yet. Otherwise, I have no complaints.
Actually, no, there is one quirk—I remember now. The power supply can quietly “buzz” when the current draw is around 200–300 mA. For example, you plug in a tablet and everything is fine, but near the end of charging, when the current drops significantly, it starts buzzing. Unplug the tablet, and it goes quiet.