Pure sine wave inverter, or how the Chinese have gotten too bold

Around the middle of December, I ordered several inverters. I decided to order a couple from a different store than usual. Naturally, I first read the reviews, where buyers showed that yes, it really did have a pure sine wave output. But things turned out not to be so simple.

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First, a disclaimer: everything I had to do was solely because of the seller’s audacity in cheating a bunch of people. I would NEVER do this (and never have before) if not for these exceptional circumstances.

Anyway, as I wrote above, I read the reviews. People didn’t just write about it; they also posted photos of the insides and an oscilloscope trace showing that there really was a sine wave at the output. And the photos made it clear that everything was OK.
What’s more, the product page even lists the features—and not only that, it’s in Ukrainian. The Chinese wouldn’t lie, would they?


There’s a table that includes my model, the smaller one. I cropped the table; there’s no point showing the rest. The important thing is that it lists a pump and an AC motor, both of which need a sine wave. The pictures also repeat several times that it has a pure sine wave output and supports heating boilers.


There’s even a sales pitch showing that our inverter is supposedly the most invertery inverter in the world, and all the others are just junk by comparison.


I ordered a couple. They came to about $88, even though just a short while earlier they were selling for $35–36 without any trouble. Well, all right: where there’s demand, there’s supply. That’s the market. A product is worth exactly what a buyer is willing to pay for it, so I have no complaints about that.


The first thing you notice is that the inverter clearly has a regular square wave at the output. I won’t comment on the build quality, but in this case that’s not particularly important anyway.


How can you tell from the outside whether an inverter has a sine wave output or not? It’s actually quite simple.
A sine wave inverter usually has two things:
1. A controller board that generates the sine wave using PWM.
2. A toroidal inductor.

By the way, the irony of fate: above is the seller’s example of a bad/good inverter. In my case, everything turned out exactly the opposite in real life. Even the casing of the supposedly “wrong” one is the same color as in his picture—but only the color matches; everything else is the other way around :)


Here’s the inductor and the board. It may look a little different, but it’s usually similar: lots of components, plus a crystal resonator (the shiny part on the right in the photo). Sometimes there are two boards: one like the one in the photo, and a smaller one that works in the primary 12–380 V inverter.
As you can see, the inverter I received has nothing like that at all—not even space for these components.



I won’t go into the details, but the board has space for a reverse-polarity protection circuit, though the components are missing. I have seen this exact board with the protection circuit populated, though.
But that’s not all. As you can see above, the secondary inverter’s transistors are pressed against the casing without even any thermal paste. How long do you think it’ll last like that?


As you can imagine, I wasn’t at all happy with this, so I opened a dispute for “not as described,” meaning that it had no sine wave output.

I had already decided on the refund amount: $68.36 out of the $88.36 I’d spent. In other words, I valued the junk I received at $10 each. That amount covered:
1. The casing
2. The fan
3. Terminals and wires
4. The board for spare parts, or maybe for some other project.

I think that’s more than fair.

So, step 1.
I attached a couple of photos and briefly described the problem (there’s a 500-character limit), but for some reason only two images were attached: one showing both inverters, and one comparing what was advertised with what we actually got. I immediately wrote that this wasn’t a malfunction: the insides were identical, and they couldn’t work as they should because they simply weren’t capable of it.


In the end, they politely told me to get lost: no return, no money.

Step 2.
All right, I attached an unboxing video and a few more explanations, and of course explained the problem itself.





AliExpress replied with a message and these options:
1. 50% refund
2. 100% refund, but return the item
3. Add evidence.


Naturally, I chose the last option, and here's why. Even if the seller refunded me 50%, he'd still break even at worst—and might even make a little money, since an inverter like this probably doesn't cost more than $22 wholesale.

Step 3.

Naturally, that option didn't work for me, so I added a photo from the reviews showing the internals of a proper inverter with the same power rating (thanks, kind stranger) and compared it with what I received.


But the main thing was to show that the inverter couldn't deliver the required power. This was easy: I made a small change to the circuit, and the inverter's power dropped by a factor of 10. Fortunately, reducing power is easier than increasing it.
There's no point explaining what I did. It won't help an inexperienced person, and anyone experienced will come up with at least five ways to do it.
Anyway, I got this result, recorded a video, and attached it to the dispute.


But another problem came up along the way. When I was testing it, I noticed a spark jumping across one of the resistors when I switched the inverter off using its own switch.
It's the gate resistor for one of the upper transistors in the output bridge. I replaced it, but then, after switching it off a few more times, the resistor on the second transistor burned out, followed by the one I'd replaced with a higher-power resistor. So there's a design flaw here that will show up sooner or later.


I also found a schematic for a similar inverter online. It shows that if these resistors go open-circuit, the transistor gates will be left floating. Still, apparently the leakage currents were enough to keep them from turning on, so all I got in the end was flickering lights.


At this point, AliExpress offered me these options:
1. A refund of $68.36
2. A full refund, but I had to return the item
3. My proposed option.

Since option 1 worked for me now, I agreed, but the dispute status changed to waiting for the seller's response.

Step 4.
After the first stage, I had already messaged the Chinese seller, recommending that he accept the dispute terms. He replied, basically, “No, we'll settle it through the dispute.” Well, fine then.
This time, the seller replied to the dispute in Chinese, saying, basically, “Only one device is shown.”

I thought, “You asshole, you know perfectly well you sent me junk, but you're still fighting this,” and messaged him again: “I recommend accepting my terms.” This time, he didn't reply.

And AliExpress really managed to surprise me. After the timer ran out and the moderator reviewed the evidence, I got an email:


Anyway, the dispute was closed, the money was refunded to my card, and the seller was penalized. I think I handled everything correctly.
There's another detail: before placing the order, I messaged the seller saying that if he wanted a product review, he should give me a discount, and I sent him a link to my blog. So he knew perfectly well what I do. He didn't reply, so I just bought a couple of inverters and reviewed them—and got my “discount.” In other words, I got what I wanted anyway, just not quite the way I'd planned :)

Some will say I ripped off the Chinese seller, that he probably has a family and is just doing what he can to get by. Others will say the seller didn't know anything and just shipped whatever he had. Maybe so, but the facts are:
1. The price was inflated because of the buying frenzy. I can't argue with that; I explained why above.
2. Blatant deception: advertising a pure sine wave and compatibility with boilers—even in Ukrainian—and then shipping junk that outputs a square wave...
3. Refusing to take responsibility. The reviews include comments saying the seller even submitted a video in the dispute showing him testing the inverter and claiming it had a sine wave. There are also reviews where AliExpress simply tells people to get lost. I recommend reading the one-star reviews; there's a lot to learn. Some are too full of profanity to quote...

Personally, I think I acted entirely fairly and correctly. As for the “modification” I made for the dispute, it reminded me of a scene from a well-known movie.


The saddest part of the whole situation is that there's a war going on in our country. Russian troops are shelling infrastructure, it's winter, and it's cold in the house. And then someone offers you an inverter that not only doesn't work properly, but can also fry your equipment (there are examples).
And that's not all. An ordinary person trying to save money won't be able to prove anything afterward. My case is more of an exception: first, I know what to do in this situation, and second, I'm used to standing my ground—and I did.

That's all from me. I hope this was useful, and I hope you never need to deal with anything like this.