Capacitor recommendations for LYWSD03MMC?

[marvinlehmann]

I often read about adding capacitors to C24 & C25 to improve stability and operational time. I went through many comments and collected information as I have little understanding of electronics unfortunately.

• operating voltage: up to ~3.1V (?)
• average power consumption: 14-15 μA (https://pvvx.github.io/ATC_MiThermometer/CustPower.html)
• capacitor:
  • higher voltage rating -> lower leakage current
  • larger capacitance -> greater leakage current

recommendation:

• "10 μF" (How to reconnect to adjust config? #265 (comment))

  • "cheap ones, with capacities of more than 20 UF, have a leak comparable to the consumption of the thermometer itself"

• "4.7..47 μF" (Battery life ZigbeeTLc#37 (comment))

• "Desirable more than 10 μF (С24) and more 100 nF (C25)" (Unable to pair/connect with bluetoothctl #172 (comment))

• only one capacitor is needed as C24 & C25 are in parallel (Doesn't stay connected #11 (comment))

• 100 nF & 2,2 μF (http://forum.jdtech.pl/Watek-mijia-lywsd03mmc-termohigrometr-z-wyswietlaczem-lcd-ble)

• formula for dimensioning the capacitor... (https://www.ti.com/lit/wp/swra349/swra349.pdf)

So... you people who did the upgrade.. which capacitor[s] did you get? I don't really know what to look for. :'-)

EDIT:
I just noticed that the 2.0 Board doesn't seem to have a C24 (?) so a small cap for C25 is necessary.
I also wondered what the voltage should be used because of bias voltage and leakage. At least 6.3V I guess. But what about something like 50V...?

Contrary to the earlier statement:

This suggests that, if low leakage current is of importance, then a lower voltage rated capacitor is preferred.

page 10 of Current Leakage through Ceramic Capacitors

[tido-]

* WIP *
@marvinlehmann, thank you. I followed your links.

Bluetooth power consumption on data transfer
RX TX +0 dBm -> Maximum pulse current of the entire device: 6 mA
RX TX +10 dBm -> Maximum pulse current: less than 25 mA

All Qingping devices - all capacitors are installed.
All Xiaomi devices - no capacitors installed :)
#172 (comment)

SMD size:
c24 1206 3,20 mm
c25 0603 1,60 mm
Desirable more than 10 μF (С24) and more 100 nF (0,1uF) (C25).

MLCC (ceramic) does not have polarity and you should choose it in most cases. However, if you decided to use a tantalum capacitor, or any other type of capacitor that has a polarity, DO NOT REVERSE THEM! Next to the "C24" or "C25" sign is the positive pole.

So, which technic or better which type&manufacturer leaks less - as we try to save power?
#265 (comment)

---

Leakage current (DCL) is common effect of all capacitors and its value and dependencies on electrical and environmental conditions are related to capacitor technology.
See "MAX. DCL" in the documentation for capacitors or "Insulation resistance"...

vishay - Solid Tantalum Surface Mount Chip Capacitors, TANTAMOUNTTM, Molded Case, Very Low DCL
Capacitance Range: 0.1 μF to 470 μF | Voltage Rating: 4 V to 50 V

c24 1206 3,20 mm 10 μF

TYPE: TL3
CASE CODE: A
CAPACITANCE: 10 μF
DC VOLTAGE: 10 V
MAX. DCL: 0.5 μA
MAX. DF: 6
MAX. ESR: 3.400 \ 2000

Potential Partnumbers:
search term: capacitor 1206 10uF 10V SMD
TL3 A 106 010 3400 search term: (vishay TL3A106(1)010(2)3400)
TL3 A 106 010 2000 search term: (vishay TL3A106(1)010(2)2000)

22 μF TL3A226(1)6R3(2)2900 0.66 μA
33 μF TL3A336(1)004(2)2900 0.66 μA

* WIP *

[pvvx]

Bluetooth power consumption on data transfer xxx mA?

Default config: RX TX +0 dBm -> Maximum pulse current of the entire device: 6 mA
+10 dBm -> Maximum pulse current: less than 25 mA

The internal resistance when the CR2032 battery is not completely discharged is more than 100 Ohms. Therefore, with a current of 6 mA CR2032, the battery will produce 3.0 - 100 * 0.006 = 2.4 V (+25С).
The capacitor smoothes the pulse and the voltage does not reach the lower operating voltage of the circuit.

[AleXSR700]

So did anybody ever solder in a capacitor at C24 or C25? If so, any measurements for different capacitors?

Still thinking about whether to buy some, e.g. from AliExpress:
https://a.aliexpress.com/_EQ1mZSh

e.g. A 35V1UF 105

[tido-]

Not yet. I was to lazy to search on AliE to find a non-cheating real brand Very Low DCL capacitor.
If you buy cheap, you buy twice. Is an old saying.
So, I was considering a shop in Europe like Distrelec, Mouser, Farnell or such.

I found promising one for c24 based on the hints of @pvvx. If somebody does the same for the c25, I would start to look at resellers.

[AleXSR700]

I thought only one was needed. Either C24 or C25. They are parallel, I thought.

[tido-]

I guess this is just like a car with TwinTurbo charger (Toyota Supra (1993–2002)). The small is quicker and the large supports greater load. And yes they are in parallel to my understanding too.