[BK7231N/CB2S] Yet Another Noname Smart socket with BL0937 meter

I've purchased the cheapest no-name socket I could manage to get. One grim day it failed to power the load, HVAC in particular. So this story started...

As you see, the packaging is absolutely brandless, even no sign of Tuya. Except for the socket, inside there is a small startup guide with a QR code leading to download the standard Tuya Android app.

The socket case has absolutely no marking at all. (Sorry for hot glue, I've already opened it with a Dremel and diamond cutting disc, bastards had the plastic parts welded together, so some plastic had to go)
Sorry, I didn't take any photos from inside, but this is a pretty standard typical socket like this one.
The only thing I remember I didn't like at all is that there is no fuse or any other kind of protection in the power circuit, just a single open relay contact. MCU is a separate CB2S module without a protective screen, soldered at 90 degrees to the main board. Also, on the main board sits a BL0937 and a small switching 3.3v power source.
Since one of the RX1 or TX1 (I don't remember which in particular) is connected on board, I've desoldered it completely to flash OpenBK firmware.
The rest of the process is pretty straightforward and well-documented, I used a CH340 3.3v self-modified UART to USB converter and 115200 baud rate because faster speeds gave errors in the process of verifying when flashing firmware. DIY is typical, cut the 5v trace and solder LM6206N3 in between source 5v, output, and nearby ground:

Pin settings were extracted from Tuya backup firmware while flashing. For this particular socket, they are as follows:
[syntax:json] "pins": {
"6": "BL0937CF1;0",
"7": "BL0937CF;0",
"8": "WifiLED_n;1",
"10": "Btn;1",
"24": "BL0937SEL;0",
"26": "Rel;1"
},[/syntax]
P.S. Now about the fault. This is the relay that was faulty:

I've searched around for a suitable replacement but found nothing due to the miniature size and footprint of this little sucker.
It's probably easier to use the hardware in another project and buy a new socket!
By the way, I personally don't believe it can really stand 20 Amps of load.
So I've got nothing to lose and removed the relay's housing and cleaned its contacts, and voila, it's working again!
That's all, folks!

HZ32-1A3S-LH1... rated at DC 3V? Do I see correctly? That's new to me, I remember only seeing a 5V and 12V coil relays in Tuya products so far.
Let me google for HZ32-1A3S-LH1....
Hmm results are leading back to our forum, nice:

It must have been used in another Tuya product.

>>20617096
Yes, that's a 3v relay. There is no 12v/5v source on board and no 3.3v LDO either.
Google only HZ32-1A3S. The first link is to a Chinese supplier site, where you can get some info on those.
I've attached HZ32 datasheet pages from there in this post.
So according to page 2 here we have an HZ32 series, 1 = single pole, A = NO normally open, 3 = 3VDC, S = sealed type, L = 0.2W coil power, H = high contact capacity (and no explanation what it is and how it affects the characteristics), 1 = some custom ID.
The interesting thing is that all their relays according to page 1 are 1) black colored 2) rated 3/5A switching current with 10A absolute maximum flowing current.
I'm sure these white ones are a counterfeit product. Guy here you mentioned had a black relay case and "rated" 16 Amps - aaaand still it's counterfeit too. Real ratings are 5A switching, 10A max flow.
The maximum switching power is limited by 300W in the datasheet, be careful!

The only replacement relay I could find is a Fujitsu JV-3S-KT, datasheet on JV series is attached.
But it's not fully compatible by footprint, only by dimensions. And in my electronic sources its price is higher than or about the same price of the socket itself.
P.S. And how it comes that a relay of another well-known brand of about the same dimensions is also rated 5 Amps?... Maybe because it IS 5 Amps and these 16-20 (stakes rising, haha) Chinese-marketing-Amps are just bluff?
The manufacturer however rates these relays 150W maximum power.

Found the very similar one, it's American Zettler AZ7709-1A-3D 5 Amps and AZ7709T-1A-3D 10 Amps, datasheet included.
But they say that even for Version “T”: max power is 300W plus > 30VDC special precautions must be taken, ask the factory.
I like this socket less and less...

This is a standard issue with Chinese products. They try to be as cheap as possible and they even sacrifice quality and safety for that.
They also tend to skip interference filters, surge protection, etc. You can often see boards with unpopulated places for safety components.

No news for me, I've seen Chinese cheap switching power supplies since ATX and Pentium 4 in PCs and "compatible" chargers for mobile phones in the 2000s. But there, the filter components were mostly just unpopulated or bypassed with jumper wires, but were still there by (copyrighted) design! (except those who did redesign to the most cheapest possible ones of course)

And in this particular case, safety is a taboo word.
A fuse in the power supply circuit? Okay, we will install a 10 ohm resistor in series, which will probably blow after anything valuable is already fried to short circuit.
A noise/interference filter? No, we have no place for that, and that is costly.
A fuse in the power load circuit? Nope, live with it, hopefully the traces on PCB or your relay contacts will burn away earlier in case of a massive power load or a short-circuit.

I have only one question in the end:
Why all this ridiculous stuff is still produced? These don't pass any safety standards anyway, it's just cheap, but gonna blow up randomly.

Anyhow, I DO warn anyone getting here in this topic - NOT to buy anything like this socket for driving passive loads more than 150-300 Watts, AND if you accidentally bought it - return this piece of crap and redeem your costs immediately.
(well, except the case that you know what you're doing and going to use this hardware not as it is designed as a smart socket)

Hi,
I desoldered the relay, carefully cut the wall of the relay near the 220V contacts, bent one contact, and cleaned the burns with a glass brush. I put the contact back, and the relay works like new.

WBR
Gintas

Good job, that's a whole new level of repair. It's always better to repair than to replace. Still, I am curious to see how long will it last.