Hello,

I am trying to extend the life of a 3.6v lithium battery (LS 14500). I have looked into the buck-boost converter but it is not worth the energy waste during buck operation in comparison with the short time that the boost converter is working (from 1.8 to 2.4v). My circuit can work from 2.4v to 4v power supply.

I thought about using just a boost converter when the voltage is lower than 2.4v, but I didn't find any application similar, is this something viable? Is there another method to extend battery life?

Thanks

 

Such a strong discharge of the battery will greatly reduce the life of the battery.

 

It's not a rechargeable battery

 

Hello,

The battery is indeed not rechargeble.
See this page for details:
https://www.batteryjunction.com/plc-ls14500-ba.html

Bertus

 

Looking at the discharge curves (below - from the datasheet) there is very little energy left once the terminal voltage is below 3.1V never mind 2.4V so it really doesn't seem to be worth the effort.

 

I thought the same too, but in case I want to extend it, does anyone know how to build an efficient circuit to detect when the battery voltage is lower than a value (2.4v) and activate the boost converter?

Thanks @AlbertHall, but my real question is that in case I change the battery.

 

my real question is that in case I change the battery.

So what battery would you change it to?
Most batteries have little energy left once they get below their normal discharge voltage.
Adding a boost converter would likely add only a few percent to the life.

 

For example, alkaline batteries have a very different curve, the drop voltage is progressive.

 

Hello,

You could have a look at the LT1308.
How much current does the powered device need?
If the load current is less than 100 mA, the LT1307 can be used.

Bertus

 

Thanks @bertrus, have you used it before? I understand that it detects a fixed low voltage of 200mV. Is it adjustable?

 

If you want the longest battery life, then it may best to use a high efficiency converter all the time with the output voltage adjusted to the minimum for your circuit.
Otherwise at the high battery voltage during most of the battery life, you are wasting energy equal to the battery voltage minus the minimum circuit operating voltage times the circuit current.

 

The possible benefit: may be 3% of energy economied, may be 5%.
The more than sure losses: never over 90% efficiency but more probable the 85%. Thus 15% of permanent loss. Somehow I remeber a soviet ex-leader Gorbachow popular slogan from the past "the economy must be economical". He made a many foolish things, but this was rather wise one to memorize.

 

Just look at the graphs. The battery drops off so fast that I do not think it is worth perusing. I doubt you would cover your power losses in the boost circuit.
Change to a bigger battery would be my suggestion. Or add a small solar panel.

 

My point was that significant energy could be saved by using a converter even with a fresh battery.
If his circuit can work at 2.4V, then he can reduce the power by about 33% (not counting converter efficiency) if he drops the voltage from a 3.6V battery to 2.4V.
And that assumes his circuit draws a constant current.
If the circuit current is proportional to voltage, then the power reduction would be over 50% (proportional to the square of the voltage change).

 

Probably a good point.
My comment was aimed at him wanting to switch a converter in when the battery was about to die. I should have made that clear, sorry.

 

Understood, thank you everyone for your advice!

 

The only justification for using a step-up converter is that at low ambient temperatures the voltage drops significantly. This is the only way to justify the use of an overvoltage increase.

 

See