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User avatar
By rudy
#62556
I'd like keep the circuit for the solar cell disconnected until the SOC reaches a defined level to ensure the lipo decent discharge before recharge


Just to make sure I understand it correctly. What you have is a solar panel that will feed the TP4056. The TP4056 will connect to the LTC4150 charge/discharge pin. The LTC4150 will be monitored by the ESP8266. The ESP8266 will be used to interrupt the charging of the LiPo. And what you need is a way to stop the charging of the battery, (controlled by the ESP8266)

If that is all correct then I would suggest that you try using the Temp pin (pin 8) of the TP4056 to disable charging.

Connecting TEMP pin to NTC thermistor's output in Lithium ion battery pack. If TEMP pin's voltage is below 45% or above 80% of supply voltage Vin for more than 0.15S, this means the battery's temperature is too high or too low, charging is suspended. The temperature sense function can be disabled by grounding the TEMP pin.


Image

The above circuit should work. The top connection would go to Vcc/input of the TP4056. Z' would connect to the TEMP pin. Z would be the ESP8266 signal used to disable charging. A low on Z will make Z' a high. The TP4056 would disable charging, and a high would enable charging.

That would work but it would bot allow charging without the ESP working. If you want it to charge without the ESP running yet then the following would work as well.

Image
The ESP pin would go into the top of U1 (bottom ground). U2 would go into the TEMP input of the TP4056. If R2 was twice the size of R1, that should give you a voltage on the TEMP pin that would be below the 45% value specified above. That is with a high from the ESP. If the ESP output a low then the TEMP input would see a 0 volts and the TEMP function would be disabled and normal charging could take place.

R1 could be 10K and R2 could be 22K. The values don't matter too much as the ratio that you want.
User avatar
By AusUser
#62589
If that is all correct then I would suggest that you try using the Temp pin (pin 8) of the TP4056 to disable charging. - See more at: viewtopic.php?f=160&t=13745&start=4#sthash.kFnkw8eG.dpuf


Thats correct. And thanks for such a detailed response this sounds like a good options. Just to note the LTC4150 can be set to provide 3.3v output to the ESP8266. The solar panel will output 5V to the TP4056

As an alternative could I also use a 2N7000 or similar to do the switch?
User avatar
By rudy
#62623
AusUser wrote:
As an alternative could I also use a 2N7000 or similar to do the switch?


The 2N7000 may work. The problem with it is the Gate Threshold Voltage. It has a large range 0.8 to 3.0 volts. I have used them with 3.3 volt devices and they seem to work most of the time. But when I design a product for production I would us a 2N7002 instead. It has a specified range of 1.0 to 2.5 volts.