# DIY Lead Acid Battery Charger Over Voltage Protection?

In this circuit, does it provide overvoltage protection once it is charged? That is I am going to use this to trickle charge a 6vdc rechargeable lantern battery. I dont want to overcharge it?

5 years ago
research into how 555 chip works. you should be ablo to hack the battery in there instead of the capacitor (with mods so that voltages match and it only charges and does not discharge etc)
motor137 (author)  110100101105 years ago
hack the battery in there?
5 years ago
see here how 555 is built (copy paste it there are spaces in the link)

now imagine that it is connected like in the generator circuit (lower in the page) and not single pulse circuit

the capacitor is connected to entries 2 and 6 and to the + thru 2 resistors

lets power on and see what happens

capacitor begins to charge thru 2 resistors

entry 6 - switches T1 on and connects entry 7 to - when capacitor goes above 2/3 vcc

capacitor discharges thru 1 resistor

entry 2 - switches T1 off and disconnects entry 7 from - when capacitor goes below 2/3 vcc

capacitor charges thru 2 resistors

now what we have to do is connect the 555 to a constant voltage source and fool it into thinking that the battery is a capacitor

imagine the capacitor is connected to 5 V. 1/3 of it is 1.6 V. 2/3 of it is 3.3 V

we want the battery to go between 12 - 13 V

so we want to give into entry 6 of the 555 exactly 3.3 V when battery is 13 V and into entry 2 exactly 1.6 V when battery is 12 V

lets connect the battery to a 358 isolator amp (to avoid disharging it thru the resistors) and to 2 voltage dividers

one takes 3.3/13 of the V and its output goes to entry 6 in 555

one takes 1.6/12 of the V and its output goes to entry 2 in 555

now instead of connecting any other link between battery and 555 we just use the output of the 555 (entry 3 or 7) to switch on off the charger

the 555 thinks that it really charges and discharges a capacitor to 1/3 and 2/3 of 5 V

in reality it switches on off a charger on a 12 V battery (the battery does not discharge thru the circuit when the charger is off. it just waits untill the battery falls to 12 V on its own)
12V5 years ago
does it use a 6.9v regulator and if not put one before the resistor(if it has one). otherwise the battery may gas and dry out!
motor137 (author) 5 years ago
Will do and thanks ALL!!
motor137 (author) 5 years ago
DIY Lead Acid Battery Charger circuit
lemonie5 years ago
Which circuit? L