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Using BOD 2.7V AVR ATTiny85 as Li-ion 18650 4.2V battery discharge protection?
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beduino:

--- Quote from: Siwastaja on October 06, 2019, 12:43:15 pm ---And yes, integrated li-ion charger ICs should have temperature qualification check. If not, they are crappy and dangerous you just need to implement it yourself :).

--- End quote ---

Lets take a look at "reference" Li-ion charger 4.2V based on TP4056 with TEMP1 connected to GND which means disabled cell temperature sensing   ::)

However, on this PCB TP4056 Vin is 8Vmax, so we still might need somekind of DC-DC converter eg. with MPPT feature.
Anyway, if this is 1A capable cell charger (not sure 22? TP4056 PROG2 resistor value), Li-ion NCR18650A datasheet says that below 10 degrees (above 0 degs I guess)  to charge 0.25C instead of 0.5C, where C is around 3000mAh, so we need to  :-/O TP4056  PROG2 resistor to value to be below 0.75A recomended charge current and still this thing will try to charge full at level 4.2V, which I do not like.
We can replace PROG2 resistor to 10k to get 130mA charge current, but we can't set lets say 3.92V maximum charge voltage in TP4056.

So, as we can see sometimes, when you buy li-ion charger like shown above, you do not know what is going on inside unless you take it apart and dig into its ICs datasheets  :-/O


--- Quote from: Siwastaja on October 06, 2019, 12:43:15 pm ---Never just connect a 18650 cell to a 100mA, 4.1V CC-CV source. Check the voltage first. If < about 2.5V, discard the cell. If you want to implement the conditioning cycle, learn to do it properly. Yes, a 100mA current source is less likely to blow the cell up, than, say, 1000mA current source, but it can do it. All it needs to do is to plate the dissolved copper within the separator, and you have an internal short. This can happen at 100mA, given enough time.

--- End quote ---
We can cut using grinder PCB above exactly in half vertically and we have DW01A typical application circuit which probably does what you'are talking about, hovever with 4.3V+/-50mV overcharge and 3V overdischarge and some histeresis for those, I guess ;)


Conclusion is, maybe we could use this TP4056 PCB for charging to lower maximum Li-ion cell voltage around 3.9Vmax with charge current limited to 130mA by replacing PROG2 re4sistor to 10k accordingn to TP4056 datasheet and lower down charge voltage from 4.2V by adding not BAT85 which is my supprise has rather huge Vf drop at 100mA, but use instead eg. SS24 2A schottky diode where datasheets says around 0.3Vf at 0.1A at room temperature 25 degs  ::) Probably, it could be also good idea add 100uF capacitor before diode at TP4056 output, so it could charge capacitor instead of battery, but let oryginal DW01A circuit disconnect battery when overdischarged or overcharged?  >:D


We have still temperature sensing disabled (shorted to GND) in TP4056 on this board, but we have overdischarge and overcharge protection.

For the moment in my oryginal LM317 based circuit simply by changing BAT85 to something like mentioned SS24 with lower Vf @ 100mA, I think could do the job, but in the case to make charging & discharging more safe for battery (regardless of MPU BOD feature) maybe this micro usb TP4056 based Li-ion charging PCB could be usefull  :-/O ?

What, do you think?
beduino:
Update: R3 smd resistor is of course  marked "122" which is 1.2 kΩ for 1A charge current on shown above TP4056 based micro usb Li-ion charger PCB,
so by changing PROG2 pin to 10k we can have 130mA charge current   8)
Siwastaja:
Since you have an ATTiny85 in your system, you can also add voltage and temperature qualification with a trivial piece of software. Pseudocode:

if(readInternalTempSensor() > -5 degC && readInternalTempSensor() < 50 degC && readCellVoltage() > 2.7V && readCellVoltage() < 4.15V)
   enablePinHigh();
else
   enablePinLow();
beduino:
Yep, I have temperature sensing availablle in ATTINY85 MPU, but I do not like idea of using ADC and loose one of precious pins for this, so maybe it could be better add hardware protection with additional NTC temp sensor when needed in more critical application.

Anyway, meantime I've added to my oryginal LM317 based circuit 33k resistor in parallel to existing 2.2k and... nice 3.94V output from regulator very close to calculated 3.93V in this case ;)

When we do not take into account IADJ*R2 we are off around: 50uA*2.062k ~0.1V ,so I'm supprised how close to detailed design output voltage formula from LM317 datasheet real circuit is (without load)  8)


xani:

--- Quote from: Siwastaja on October 06, 2019, 12:43:15 pm ---Your issue is, you are assuming things and overlooking obvious advice, and trusting a well-known and widely debunked fake site (yes, their content quality has definitely gone up, but still, be careful.)

--- End quote ---

Care to elaborate ?  Haven't seen any "debunking" of it here (or maybe I search forum wrong) and while their articles could definitely cite their sources better they are mostly useful info
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