FAQ
TL;DR: Motor-driven Wi-Fi RCBO trips with 12.7 mA test current; “This thing isn’t a toy” [Elektroda, TurkeyMan, post #20365615] Stock Tuya firmware exposes 20+ datapoints, and UART flashing takes <10 min through four pads only [Elektroda, p.kaczmarek2, post #20365852]
Why it matters: You can turn a certified DIN-rail breaker into an open-source energy monitor without dismantling the safety side.
Quick Facts
• 2-pole (L+N) RCBO rated 20 A / 6 kA [Elektroda, TurkeyMan, post #20365615]
• Adjustable leakage: 30–100 mA via Tuya dpIDs 116-118 [Elektroda, as-2, post #21167561]
• Test resistor 18 kΩ ±5 %, 2 W metal-oxide [Elektroda, rusudanion, post #20808674]
• HT7017 metering IC, 8000:1 accuracy spec [Elektroda, p.kaczmarek2, post #20365852]
• BK7231T / CB3S Wi-Fi SoC @ 115 200 bps UART [Elektroda, as-2, post #21167561]
What sets the AT-Q-SMR1-20 RCBO apart from add-on smart relays?
It replaces the original mechanical breaker entirely, providing combined over-current, leakage and motorised switching in one 54 mm-wide DIN module. Energy metering, Wi-Fi and RS-485 are built-in, so no extra enclosure or upstream MCB is required [Elektroda, TurkeyMan, post #20365615]
Which main chips are inside and what are their roles?
BK7231T (CB3S) handles Wi-Fi; a Tuya-branded MCU drives the motor and reads sensors; HT7017 measures voltage, current and energy; MAX3085 transceives RS-485; PN6850 bucks mains to 5 V [Elektroda, p.kaczmarek2, post #20365852]
Can I flash OpenBeken or ESPHome without drilling the rivets?
Yes. Remove only the left cover, expose the CB3S module and use the four 2.54 mm pads (3 V3, GND, TX, RX). Solder fly-lead wires, power with 3.3 V USB-UART and flash in <10 min [Elektroda, TurkeyMan, post #20365615]
How do I perform the OTA (cloudcutter) hack instead of soldering?
Back up the full 2 MB flash, run Cloudcutter profile for “pqcmqh1ufgmalru0”, then push OpenBeken.bin via Tuya OTA. Several users confirmed success on the ZMB9-W variant [Elektroda, piotrszulc1, post #20817461]
What is the safest way to sniff UART traffic while the breaker is on mains?
Insert an opto-isolator between CB3S TX/RX and your USB-TTL; power the opto’s secondary side from the breaker’s 5 V rail. This keeps PC ground isolated and prevents USB damage [Elektroda, TurkeyMan, post #20369612]
My test button no longer trips—what should I check?
Inspect the 18 kΩ, 2 W metal-oxide resistor under the main board. A burnt part stops the 12.7 mA imbalance current, so the RCBO never sees leakage [Elektroda, rusudanion, post #20808674] Replace with same value and voltage rating.
How much current flows during the self-test and is it safe?
At 230 V the 18 kΩ resistor draws 12.7 mA, slightly above the 30 mA trip threshold yet far below hazardous levels [Elektroda, morgan_flint, post #20807990]
Does the RS-485 Modbus port work after open-source flashing?
Not yet. CB3S UART1 talks to MAX3085, but OpenBeken still lacks a Modbus driver. Community roadmap lists it as “planned” [Elektroda, TurkeyMan, post #20366523]
Which Tuya datapoint actually toggles the motorised switch?
dpID 16 (Boolean) controls the latching motor; dpID 11 handles prepaid lock. Send tuyaMcu_sendState 16 1 0|1 to open or close [Elektroda, piotrszulc1, post #20817699]
How can I make the breaker refresh voltage and current automatically?
Add a repeating event:
addRepeatingEvent 60 -1 tuyaMcu_sendQueryState- Save autoexec.bat
- Reboot. Tuya MCU now publishes every 60 s [Elektroda, p.kaczmarek2, post #21177104]
What protection limits can I customise through firmware?
You can set over-voltage, under-voltage, over-current, leakage, fire and surge alarms via dpIDs 101–118. Over-voltage range is 250–300 V; leakage 30–100 mA [Elektroda, as-2, post #21167561]
Known edge cases or failure modes?
1 % of users reported UART silence after flash because CB3S boot voltage was too low; reflowing the buck converter fixed it [Elektroda, TurkeyMan, post #20366523] Burnt test resistor is another common fault [Elektroda, rusudanion, post #20806738]
