Does a battery need to be fed voltage greater than its output to charge, even with a diode?

Thread Starter

caitlinfham

Joined Aug 26, 2018
2
Hello, I was wondering if the statement "In order for a rechargeable battery to charge, the battery needs to be fed with a voltage greater than that it outputs." is correct. If so, would that statement still be correct if a diode was used to prevent the battery to be charged from discharging into the source that has a lesser potential.

Any help would be greatly appreciated,

Thanks!
 

AlbertHall

Joined Jun 4, 2014
10,582
It would be even more true if you add a diode.
Take a standard car battery. The normal battery voltage is around 12.6V but you charge it you need to feed it with 14.3V. If you add a diode between the charger and the battery then the charger must supply the 14.3V plus another 0.7V to overcome the forward voltage of the diode, so now the charger must supply 15V.
 

dendad

Joined Feb 20, 2016
3,625
Think of it as a water tank.
You cannot put more water into the tank unless the supply pressure is greater than the tank pressure. The diode is a one way valve so now the supply pressure will need to be even a bit higher as it has to open the valve too.
 

dl324

Joined Mar 30, 2015
11,932
Yes, the voltage used to charge a battery must be greater than it's nominal voltage; otherwise, current won't flow. If you add a diode, the charging voltage must be increased by the voltage drop of the diode.

If you specify battery chemistry, we can provide more detailed information.

The correct charging voltage for a lead acid battery is 2.3-2.45V per cell. A 12V battery has 6 cells with a nominal voltage of 2V each. So the charging voltage would be 13.8-14.7V. Not charging sufficiently "hard" will result in the build up of sulfation; which will eventually short the cell.

Some batteries tolerate improper charging better than others. Improper charging leads to early end of life.

batteryuniversity.com is my go to site for battery information. Here's the article on lead acid:
https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery
 

Thread Starter

caitlinfham

Joined Aug 26, 2018
2
Thank you very much everyone for clarifying. You've provided some excellent and insightful comments which I really appreciate. Nice analogy too.

Thanks again,

Caitlin
 

Yaakov

Joined Jan 27, 2019
1,612
Just to add a point which might be relevant:

A battery will charge up to the supply voltage of a charger but not above it, even if the chemistry is capable, at full charge of providing a higher voltage.

This is not contradicting the answers above, but adding something that might not be obvious.
 
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