# Battery Charging Circuit efficiency

Joined Sep 28, 2021
181

Question: How efficient is this circuit in (%) that is useful output power/ input power to charge a battery? I am planning to build a 4.2V charger but with a much higher ampere limit by connecting the output pins of these same charging circuits together to provide a higher ampere with the same voltage (4.2V) ? Is this possible and I was wondering about its efficiency that is how much heat (%) is converted to bad power(heat)? Can just give an approximation if anyone has ever build this before

#### crutschow

Joined Mar 14, 2008
29,467
How efficient is this circuit in (%) that is useful output power/ input power to charge a battery?
For a linear charger (as this apparently is, although the picture tells me little about how that simple charger works) the power dissipated in the charger equals the voltage in minus the voltage out times the current.
I am planning to build a 4.2V charger but with a much higher ampere limit by connecting the output pins of these same charging circuits together to provide a higher ampere with the same voltage (4.2V) ? Is this possible
Possible, but a poor idea, as the circuit with the slightly higher voltage will try to deliver all the current.

I assume this is a Li-ion battery and those should be charged with a charger designed specifically for that purpose.
Otherwise there is a significant danger of overcharging the battery and causing a battery fire and/or explosion.

#### dl324

Joined Mar 30, 2015
14,306
I am planning to build a 4.2V charger but with a much higher ampere limit by connecting the output pins of these same charging circuits together to provide a higher ampere with the same voltage (4.2V) ?
If you're planning to charge Li-ion, a simple charging circuit will be dangerous because Li-ion batteries won't tolerate much abuse.

#### Audioguru again

Joined Oct 21, 2019
4,523
Why do so many people in India who are not educated in electronics post so many You Tube electronics videos?
The guy who posted this video does not know that his circuit has a very low output current and maybe does not know that 4.2V is a full charge.

#### bassbindevil

Joined Jan 23, 2014
372
Nearly all the 5V lithium chargers are linear, so it's not going to be any less efficient. But when you can buy a TP4056 module for less than a buck which provides a proper charging profile, LED indicators, and even a separate battery protection chip, why bother? (Those modules do lack the series resistor that's shown in the data sheet; about 0.5 ohm which reduces the heating in the chip significantly. I cut a trace and add a resistor.)