The Simplest Rechargeable Battery Circuit (and Save the Planet Too)!!!





Introduction: The Simplest Rechargeable Battery Circuit (and Save the Planet Too)!!!

About: I like to invent and modify things. When i was 13 i fixed my dad's old Lancia Fulvia motor. I builded my first mod PC in 1991 using a mobo builded in a VCR box. I am first using all my inventions. I love eve...

Hallo to all.....

The idea came to me when i was ready to replace a battery cell in my alarm clock next to my bed. Even i am using the last 5 years only rechargeable batteries of the most types i considered how many battery cells people around the world throw away in a simple move like that i did now.....How meny disposed battery cells thrown away in each household? Who knows? But what if we had a rechargeable system to recharge batteries when the device is connected to an outlet and when we will need the battery (In a black out) this will continue working the device.So first we will have power continuity, second we will save money buying and dispose all the dead batteries, and third under normal conditions we can rechargeable any type of battery we like. My next question to my self was that this kind of circuit must be simple, cheap, realible, and easy convertible to recharge any battery cell and giving power to a device at the same time. SimpleEhhh????

So i tried to recall my studies from university and i reminded a very simple circuit which actually recalls all the science of electricity and every 1st year stuedent knows well.

Materials..... Cheap and Easy

>>4 diodes of 1N 4001 type for making the bridge which conncects to the transformer
>>a transformer 2x6 if you want to recharge batteries from1-6VDC or 2x12 for devices up to 12VDC (input 220VAC europe output 2x3,2x6,2x12 choose your one)
>>a 1000uF Capacitor, using it as a filter and elevator of the power
>>a Relay (6VDC if you will give power from 1-6VDC or a 12VDC if you like to recharge a 12VDC battery)
>>a resistor of 33 or 39 Ohm /5W (5W is ideal because the resistor cool down faster)
>>a diode of BY251
>>2 rca female for chassis
>>2 rca male
>>a prototype card or a perforated card, no PCB needed
>>a nice box for the battery recharging docking station appx12cm X 5cm X 3 cm ( in this box you will try to fit a transformer, the basic circuit , cables, the battery nest and your spirit! :D

All materials costed to me 12euro (15USD) The most expensive is the transformer.
Lets go now at the circuit design and i will explain to you....

Step 1: Explaining of the Circuit lets go to explain all theese Chinese things!
first of all the circuit is well separated is two sections the power supply on the left (green line) with the battery pack and the outline with the purple line

We take the transformer (220V europe make the calculations over Atlantic reader) and we connect it in a formation of diodes called bridge.This circuit is what a first year student learns and remember it for ever. Its the simplest circuit to achieve best reults, cheap and realible.Ok, if u like to transform from AC to AC again then the circuit remains the same u change the diodes of type 4402, 4403, 4002, ofcourse the transformer and the appropriate relay working in AC. The capacitor of 1000uF value is a filter and a choke to elevate the power. Connect the diodes to the capacitor and then this one at the line of the relay. Then the + pole of the device gets to the switch of the relay. At the + pole of the device we attach a diode or a BY251 and a resistor 33Ohm of 5 Watts (we prefer 5watts so the resistor isn't get hot when it works and cools down faster)

You will not need any PCB. Take a protorype or better a perforated card and just place the materials and do the connections. No particular attention needed (of course take all the precautions when using high voltage such as 220VDC are able to fry you in seconds and send next to your anchestors for ever)

from the + and - we will take line and we will drive it to 2 RCA female (chassis) The one male RCA connected here goes to the charge the battery and the other goes at the device where we will place a fake battery

Step 2: The Final Product....

So....please drop the soldering gun and pass me your beautifull years in University...Lets see what we got. Ok about the soldering and the connectrions even a 5 year boy could do it.....lets proceed to refine the product......Dont forget the purpose. Is to place a rechargable battery of any type, using a power supply instead the battery and if the years of darkness come we will use the rechargeable batteries......neet?

Of course u have a rechargeable battery (AA,AAA, any type even 6V). We will build a charging docking station for batteries and also we will make a fake one (battery) for the supplied device (clock etc) the fake battery i made it is wooden!!! with metal edges connected to - and + cables.

take a piece of wood and cut it till be a cilinder of the shape of the battery type you want...(AA,AAA).open a hole in the center of the wood and pass the 2 cables for + and - poles. At the end of every poly attach a bronze wire formating the - and the + pole.

Now connect the two edges of the cables coming from the wooden battery to a male RCA coneccting to a female RCA placed on the docking station. With that way goes power from the 220VAC to the wooden battery. Now place the wooden battery in the device you want (Clock).

At the docking station you have placed a battery charging nest of any type. Take 2 wires and connect one the + and the other to - pole of the nest and the other edges connect them to a male RCA connected to the one of the two female RCA's

U are ready my boy.....and be proud of it......That's it guys. Save the planet with less disposable batterries, recharging your battery cells for your clock, mouse, etc and when the end of the world comes you will be well prepared...........neet???

Good luck my friends.....please before go take a look of my pic and admire me...Don't Forget to Vote me for the Green Contest...........Thanks all voters

C u around all



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27 Discussions

What is that re2 in the circuit
Symbol shows an inductor but doesnt understood why

1 reply

Hallo friend,

1. Re2 is the relay for NC/NO contacts....the inductor is not something else than the inductor of the realy....In schematic just shown any functionl part of the circuit. Also this circuit is given as initial way to think about the abilities of this.

2...hahaha you may have right but when i made it I wanted to make you undesrtand that this circuit can charge any kind of batteries.

3....Yes of course. So forget the tranformer, the bridge and the filter and add the output of the charger in serial with a diode (or LED) and then to rellay. Be sure the charger pack gives you STABILIZED power......

Can i replace that left side circuit with a dc mobile charger ?

And what are those
Huge batteries connected down the cicuit
For ?

And what are those
Huge batteries connected down the cicuit
For ?

Charging happens when the relay is energized and the power comes in from the right side surrounded in Purple. Probably a switching power supply or other regulated (or not) DC supply. If you put a tap in there, when the power went off the batteries would supply the load making a slow UPS.
This circuit needs work though to do that.
A circuit very much like this one was written up in QST Magazine and it is used to provideemergency power to Ham Radios when the lights go out.

2 replies

hi dr bill.. where can I find this circuit you mentioned from magazine? I need a circuit to do just that!

QST magazine is put out by ARRL for Amateur Radio Operators.

I found this schematic in QST as part of an article. The circuit is slow because of the relay. The schematic is done in TinyCad, a versatile free cad program from SourceForge.

Becomes an Uninterruptable Power Supply when a power supply and a battery are attached.


Hey there. Can i simply replace a supercapacitor with a rechargeable battery? Or i must make some modifications? Thanks

This is a very 'nice' simple circuit. It would have been even better if there was some sort of connection between the bridge and the battery! But hey ho! we can't have everything.

1 reply

oups sorry you got right man! The real battery you charging is incuded in doted lines. The NC of reley gives + and NO gives - so them are going to battery you want to charge. The outlined battery is a dummy battery which you take the - from ground (charging battery) and + from relay
Actually that was my first attempt in electronics. Thanks for your humorous view

I build a better circuit for charging batteries Problem is that charges only 100mA batteries (like the wireless phones use) I charged also bigger Ni batteries of 300mA but it takes more time. 

You will need also Pack 100mA Wall transformer,  LED , 10K resister, 1N4001 Diode ,1000uF capacitor

Please before plug it to 220 or 110 V AC double check for any short circuit.


I have a question about the circuit - what is the purpose of the diode and the resistor in series? Is this to reduce the voltage from 12v to what is required by the battery?

I want to charge a NiCd power pack from a radio control toy and I think the voltage is 7.2V. I also have a power supply from a junked computer which I think can supply 12V. What type of diode and resistor is required?

With this type of circuit can the battery become overcharged? If so what what is the safe charging time?

Thanks for any help.

2 replies

You need that diode to prevent a switching power supply from tripping to 'off' when charging batteries and the resistor current limiter for charging to take place safely.

 you answered correct in your fist question. The resistors reduces the Voltages not the Amperes to do so you need any diode. For your 7,2 i will use a 6,1 diode (i am not sure if you can find in the market 7,2 exact and then using the Ohm's Law you have to calculate the available mA you need for your toy. Usually the NiCd batteries are in class of 800mA so 12V/0.8=15Ohms
I ve made this circuit to charge the batteries and protecting them for overcharging. Safe time is about maximum 120-140 min

HI Agis, sorry for the late comment, just read this today, question, what is the purpose of the relay? how does the battery charge? i dont see any connection from the bridge rectifier going to the batteries? i guess i am missing something!

2 replies

the relay supports the battery charging. when is charged (the Batt) then the rellay released and stoping the charging.....This cisruit is just a part of another circuit (to charge the battery for an alarm for example so also the relay can be connected to the missed cisrcuit....

i have a 120vAC-9vDC adapter, how could i use this to charge a rechargable 9v battery? would a simply attach the positive lead on the charger to the positive lead on the battery? that's what the diagram seems to do.while charging, will it continue to power the battery operated device? also (stupid question probably) does an LED work like a regular diode, as a "one way valve" for current?

1 reply

Not a LED but a regulate real diode like 5v1, or 6v1.and 9v1. It depends from the final power u want to have. For example if you want to have 9 volt then put a 9v1 Diode. U have to place always with in parallel with an apropriate resistor. For 9V u have to get a 220-360Ohm resistor. Of course u can place also a Led as indicator. The answer in the other question is what u suggested.