/Schematics/Power supply/Automatic battery charger

Scooter battery problems, anyone?

Why automatic? Because it automatically starts the charging procedure when battery voltage drops below a certain predefined value and stops after the voltage has risen above the maximum allowed value. Setup can't be easier, just connect two alligator clips to battery terminals and plug the device in mains. This way it can stay connected for months and the battery will never overcharge. This comes very very handy when you have a scooter or a real motorcycle that you don't drive during the winter time. Because we all know what happens to a battery when not used and especially during the winter.

You can download the schematics at the bottom of this page by clicking on red "download" button.


Device consists of two main parts; power supply with current and voltage regulation (2 x LM317) and voltage monitoring circuit with switching relay. The charging procedure starts when voltage drops below 12.6V, and finishes when it gets to 13.8V. These values are not fixed and can be adjusted with trim-pots. The maximum charge current can also be adjusted with DIP switches. Voltage is not that critical but it must not be below 13.85V so that the charging procedure can stop.



It is mounted inside a plastic project box with three LEDs: green – powered on, yellow – charging in progress, red – wrong battery polarity (switch + and -).


Schematics are from Info elektronika br. 41, only the PCB is adjusted for different relay and additional power regulators.

Author (sent by): RazoR

Download counter: 25,113

Rating: (2.84, votes 2476)


Date: 09-06-2010

Lokalna verzija ove stranice: Automatski punjač akumulatora


Bookmark and Share Comments (18)

comment [8]

the trick. constant limiting @ maximum current through the lm317 (1,5A) und constant regulation with a pot. sorry bro. you can do better. ;)

comment [7]

ly fallen down to the lowest voltage. and now you take the accumulator and use it, because, you think that the accumulator is full. the accumulator will be destroyed very quickly, because of the low voltage, when starting a scooters engine. sorry to say that: this device is bulls***. it would be better to keep the accumulator directly connected to a current limiteded constant-voltage charger at 13,6...13,8 Volts. you already have the needed parts in your charger ;) lm317 and a potentiometer. this will do

comment [6]

hi. "nice" thing, BUT what is the advantage of it? NONE. but wait, it is the opposit of benefit: the accumulator will drive cycles of charge-self discharge-charge-self discharge when out of use. this is not good for lead-acid or gel-types. You will never get the full capacity out of the accumulator, when you charge this way. for if the accumulator is charged, it will be cut off from the charger by a relay. then it stays and stays unused (letting the "ready-LED" glow) until that moment the voltage is near

comment [5]

Eagle Schem. Please? Hard to read + non-cohesive schems. Why not show what you did for the real instead of just the real layout?

comment [4]

"Is it possible to turn it into 6v charger for seal lead acid batteries?" It is possible quite easily. In magazine Info Elektronika number 41 there is description what changes to do for that. If you want that file send me an e-mail at razor_x@net.hr (but it is in Croatian language).
IP: n/a

comment [3]

I Loved It! This is a very good device, and I think I'll adapt it for other projects.

comment [2]

Awesome! Thanks! Is it possible to turn it into 6v charger for seal lead acid batteries?

comment [1]


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