# how to design 6v 4ah battery charger

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Joined: Aug 07, 2018

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how to design 6v 4ah battery charger
August 7, 2018 - 5:45pm

I am designing a 6v 4 Ah  Battery charger with automatic cutoff. But  I am confused to determine the cutoff voltage.

Charging voltage is 7.5 v. When the fully charged condition, How much will be the terminal voltage

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Joined: Aug 16, 2016

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Since the rating is 6V 4Ah I assume it to be a Lead acid battery.

Normally a Lead Acid charger will have a minimum of two charging modes Constant current mode (CC) and constant Voltage mode (CV). If you are charging the battery with a fixed voltage of 7.5V then it is called Constant voltage charging mode.

But a voltage of 7.5V for a 6V battery is very high. Remember that Lead acid batteries are made by combination of 2V cells. So, a 6V Lead acid battery is made by combining 3 2V Lead acid cells.

The maximum charging voltage for a single 2V cell is 2.3V. Hence for a 6V battery it should be (2.3*3=6.9V) around 7V only. This voltage is called the float voltage.

So your ideal cur off voltage for a 6V battery should be 7V