Automatic Battery Charger Using a Single Relay

Amazed to hear this! Yep that’s actually possible, you would need only one relay and a handful of diodes to make a simplest one relay automatic battery charger circuit.

How it Works


The idea struck me while trying to design the easiest possible battery charger circuit for one my clients.

The concept is simple; just raise the operating or triggering voltage of the relay up to the optimal battery charging threshold voltage by dropping the required amount of supply voltage to the relay coil, with the help of series diodes.The idea may be understood from the following points:

Take an ordinary relay, measure its triggering voltage by carefully applying a variable voltage across its coil.Now suppose the triggering voltage of the particular relay was about 9 volts, and also assume you want to raise its voltage to 14 volts, which may be your 12 volt battery’s charging threshold voltage.

We know that a 1N4007 diode drops about 0.6 volts across it, so if we add sufficient number of diodes in series with the relay coil would hopefully pull its tripping or triggering voltage to about 14 volts.

That means, 14 – 9 = 5, we’ll require 5/0.5 = 10 diodes in series to achieve this rise in the triggering voltage of the relay.That’s pretty simple and interesting isn’t it?The rest may be done with the help of the shown diagram…..your simplest single relay automatic battery charger is ready.

 

Automatic Battery Charger Circuit Using a Single Relay

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Comments

Swagatam said…
12v input will not charge a 12V battery
rohit choudhary said…
Please share a automatic cut off circuit so that , I can charge a mobile battery , with mobile charger.
Swagatam said…
you can try the second circuit published in this article:

https://homemade-circuits.com/2012/07/make-6v-4ah-automatic-battery-charger.html
Ahmed Elmasry said…
i take your idea and made this circuit :im75.gulfup.com/3SLo5.png
Ahmed Elmasry said…
hi i take your idea and make this circuit ...

im75.gulfup.com/3SLo5.png
Swagatam said…
Actually, I was wrong in acknowledging the zener idea, it won't work

It has to be done exactly as suggested in the diagram in the above article. 1N4007 or 1N4148 in series with the relay coil is the only correct way of doing it.
Swagatam said…
Actually, I was wrong in acknowledging the zener idea, it won't work.

It has to be done exactly as suggested in the diagram in the above article. 1N4007 or 1N4148 in series with the relay coil is the only correct way of doing it.
Unknown said…
Sir, thank you for sharing your idea on this simple circuit.
What components will be required if I need this same simple circuit to charge 48 volts battery made from 4 x 12. The battery AH is not important.

anticipating your quick response

Thank you once more
Swagatam said…
sorry this circuit is not recommended for a 48V battery because too many diodes will be required for the 48v operation .......moreover the design is not too accurate.
Farhan Ali said…
yes relay starts to switch on and off. i have made this circuit.this is due to disconnection. it order to overcome this connect 14v dc to battery positive terminal not through the NC of relay.
untung suharto said…
Hi, friend this is can workout well charge SLA battery?
Swagatam said…
yes it will work....

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