Electronics > Beginners

Li ion 18650 battery discharge

(1/7) > >>

VEGETA:
Hello,

I have designed a small board which uses 18650 battery to power a very very low power consumption circuit.

I measured the consumption about 0.250 mV across 13 Ohms limiting resistor... meaning about 20 uAs.

The board is designed to have a charger which charges the battery fairly quickly at 100 mA then I disconnected the battery and it is now powering the circuit.

I noticed some rather quick voltage drop for the battery, as follows:

format is TIME -> BATT VOLTAGE


--- Code: ---Thursday 01-6:
fully charged in-circuit
04:32 -> 4.188 ---> end of charging
05:07 -> 4.184
16:32 -> 4.171

friday 02-6:
11:31 -> 4.145

saturday 03-6:
00:56 -> 4.142
02:21 -> 4.142
04:17 -> 4.142
11:31 -> 4.142
charged for a bit.
14:46 -> 4.144
16:32 -> 4.143
21:41 -> 4.142

sunday 04-6:
18:53 -> 4.137
22:34 -> 4.136

monday 05-6:
01:12 -> 4.136
16:46 -> 4.134

tuesday 06-6:
00:43 -> 4.131

wednesday 07-6:
07:27 -> 4.126
16:43 -> 4.122
--- End code ---


I read there is quick self discharge at first but is it correct?


will it settle later on?

inse:
Have a look at the typical discharge curve of a LiIon  battery.
For most of it’s capacity it is around 3.6V

tunk:
No expert, but I think it's not initial self-discharge, but initial cell chemical stabilization,
and that it should take seconds or a few minutes. The simplest way to see self-discharge
is to not put a load on it and measure the voltage maybe every day or week. I would think
it's difficult to measure self-discharge in circuit with high accuracy. You could try to find
voltage vs state of charge curves (maybe in the link below), and then calculate how much
the voltage should drop with your load.

https://lygte-info.dk/

westfw:
You're counting ~0.05V as significant voltage drop?
Did your "charge" cycle include the full constant-current segment, or did it just stop when you reached 4.188V?

VEGETA:

--- Quote from: westfw on June 07, 2023, 08:06:38 pm ---You're counting ~0.05V as significant voltage drop?
Did your "charge" cycle include the full constant-current segment, or did it just stop when you reached 4.188V?

--- End quote ---

well, I thought it will probably drop from 4.2 to something like 4 or down to 3.7 over time and settle there for long time until it starts to be depleted from its capacitance.

my circuit taking micro amps should not drop the battery voltage like this each day... is this ok or wrong?


I wanted the battery to last for at least a year in this circuit but if it keeps dropping like this it won't. battery output is delivered to very low dropout LDO to deliver 3.3v then followed by a schottkey diode to final circuit (dreamcast internal cmos clock circuitry to keep time).

Navigation

[0] Message Index

[#] Next page