Introduction: How to Make an Automatic 12V Battery Charger

Picture of How to Make an Automatic 12V Battery Charger

Hey! everyone My name is Steve.

Today I'm going to show you How to Make a 12v Battery Charger

Click Here to See The Video

Let's Start

Step 1: Features

Picture of Features

Input Power

  • 110-220 v AC

Output Power

  • 1.25-24 v DC Adjustable at 8 Amps

Built-in Protection

  • Short Circuit Protection
  • Over Load Protection
  • Over Charge Protection

Charger Features

  • Constant Current Charging
  • Constant Voltage Charging
  • Full charge indicator
  • Charging Indicator

Continuously asked Questions

Q - Can I leave it overnight

A - Yes! For Sure this will not overcharge your battery just because we're using constant voltage there will be no potential difference to make your battery overcharge

Q - Why you are setting the voltage to 13.8v

A - Just because when a 12v battery get fully charged the voltage is 13.8v Google it for more information

Step 2: Gallery

Picture of Gallery

Step 3: Things You Need

Picture of Things You Need




Step 4: Stand Off Installation

Picture of Stand Off Installation
  • First, install the standoff "as shown in the image "
  • Do the same for SMPS and DC to Dc Convertor

Step 5: The Acrylic

Picture of The Acrylic
  • First, pull off the protective layer from the acrylic sheet
  • Now place your components " as shown in the image "

Step 6: The Drill

Picture of The Drill
  • Now use a marker to make the point for drill
  • Now use a 2mm drill to drill the holes
  • And now go for 3mm drill bit and at last counter shink all the holes " as shown in the image "

Step 7: Assembly

Picture of Assembly
  • Now use some screw to screw the board with acrylic sheet " as shown in the image "

Step 8: Wiring Diagram

Picture of Wiring Diagram

Step 9: Wiring Part 1

Picture of Wiring Part 1
  • Now solder the XT60 with Ammeter with some wire " as shown in the image "
  • And then use heat shrink tube to secure the connection

Step 10: Double Sided Tape

Picture of Double Sided Tape
  • I used some double-sided tape to hold the Ammeter and XT60 Connector

Step 11: Wiring Part 2

Picture of Wiring Part 2
  • And I Passed all the wire underneath the board till last and connected it to the converter output" as shown in the image "
  • And now I took 2 wire along with ammeter wire and connected it to the output of SMPS " as shown in the image "
  • And now I connected the ammeter wire and passed all the wire underneath the board till last and connected it to the converter Input

Step 12: Output Wire

Picture of Output Wire
  • I used XT60 connector with 2 alligator clip and wired it together and used some heat shrink to secure the connection

Step 13: Input Wire

Picture of Input Wire
  • I used XT60 connector and connected it to the Green connector for mainline input " as shown in the image "

Step 14: Final Assembly

Picture of Final Assembly
  • I used couple of screws to close the upper acrylic sheet
  • And used some rubber feet on the bottom

Looks neat

Step 15: Calibration

Picture of Calibration
  • Now connect the main input wire
  • In order to set the current, you need to short the output wire and now set the current with the potentiometer " as shown in the image "
  • now you need to disconnect the output wire in order to set the voltage and now set the voltage with the potentiometer " as shown in the image "

My Settings

  • Set the Voltage to 13.8v
  • And set the current to 1 Amps or more it depends on the battery size

Find out the current

  • Use this formula - Battery Capacity x 1/10 = setting


  • I used a 7 amp battery, now let's put the formula
  • 7 x 1/10 = 0.7 and here I set it to 1 amp " You can go for little higher current but not too much "

Step 16: Finishing Up

Picture of Finishing Up

  • Now just plug the battery and it's all set
  • You can see the ammeter it's drawing about 1A just because we have limited the current it is the safest way to charge the battery
  • And when the battery will get fully charged " This will automatically stop the charging " Just because we have limited the Voltage and there is no potential difference to overcharge the battery


  • Red Light - Charging
  • Blue Light - Full Charged

That's all for today guys!

Click Here to See The Video

You Just Made It

Thank you for visiting my Instructables

Stay tuned for next Projects


DylanT53 made it! (author)2017-12-02

I got all the stuff you recommended except that the SMPS is a AC main driven and capable up to 240VA power.
The volt-am-meter did came different from the picture looking at the PCB end. Using your diagram to hook up the circuit, the moment I connect the 2-wire (CT), the system will not power up. If I remove one of the CT wire (-ve), the system will boot up and voltage will have reading. I touch the -ve CT wire to the -ve of the SMPS, again the system shut with a spark. Remove and it powers up again.
I check the Aliexpress seller side and got this diagram attached. But still doesn't work. This time using this diagram method, the system did not shut down like previously. But I couldn't get the current adjusted. It remain at 0. When I shorted the output, spark and system shut again.

DylanT53 made it! (author)DylanT532017-12-07

If you have followed the link to purchase the VA-meter and arrive differently from Steve's, but like mine, then follow this hook up diagram.

BhavyaE (author)2017-10-01

I own a 1963 model Royal enfield bullet and want to use this circuit. I want to have two batteries and want to charge both of them (may be one after another). what modifications are needed to this circuit?

JohnC430 (author)BhavyaE2017-10-04

I am familiar with the Enfield rifle, but what the heck is a 1963 Royal Enfield Bullet? i am assuming it is a battery but why the Titile?

BhavyaE (author)JohnC4302017-10-04

If I were you, I would have quickly google it. It's a motorcycle manufactured in 1963

skiercraig (author)BhavyaE2017-10-01

It should not make a difference with two batteries in that each will only float to its own individual requirement. That being said I am assuming you are running both in parallel and not in series.

JohnD164 (author)2017-10-04

why do you guys keep praising this guy.... this is not a charging circuit this is just a lab power supply.. you can buy online that he added a volt meter display and a another circuit that is not needed.. this has no intelligent power management meaning its dumping 13.8 volts in and its over filling with amps think of a glass of water unless you shut off the current when it stops taking a charge and reaches that 13.8 volts this is done with math and a ic logic circuit... similar to lipo chargers but charge is on for 30 seconds then off on then off...

so this is just another instruct able by an indian guy thats wayy dangerous..

im not trying to be a jerk just showing you all the truth.. reason he put a volt meter display is to watch the voltage get to a set point then shut it off if you forget or walk away .. ever see a lead acid or glass mat explode.. its not pretty and it explodes with the ammount of force of a grenade..

you need a circuit that goes from full charge to top off to trickle then float.. and to do this you need inelegance that is nothing more than a lab supply... so stop praising him it should be removed from this site

CraigH23 (author)2017-10-01

#massimostep is correct up to a point. On the side of your battery you can see "cyclic use 14.1-14.4V",that is for deep cycle use. What you are doing at float charge (13.8V) is ok for say, a UPS for a raspberry pi, if you only unplug it for 5 minutes to plug it in somewhere else. You haven't taken more than 5% out, so you don't need absorption charge at the higher voltage. If you ran the pi all night you would be deep cycling the battery. Then 13.8V would only take the battery to about 80%. Batteries used like that might last 6 months then die. You might manually turn up the voltage till the battery voltage has been at 14.3V for half an hour. Note that due to voltage drop in the cables, what you see on your display will be higher than the voltage at the battery until the current comes down.

Nice instructable, nice production.

JohnC430 (author)CraigH232017-10-04

what he sees on the display will be what the battery is getting. at 14 volts there is hardly any current flowing into the battery so the drop on the wires is minimal. no more than a few 10's of millivolts. but yes it is a good idea to top it off at 14.3 volts once a week.

JohnD164 (author)2017-10-01

im sorry to say this but this is not a charger... all this is.. is a lab power supply that delievers constant current and voltage there is no chip on the output side that says cut off at 14.4 volts.... even if you place it at 14.4 volts and the battery tops off it will keep charging and charging and then blow up...

this has no output protection what so ever so thats why he put a meter on it to see when it gets to the voltage it should be.. dont walk away from this or you will be very sorry

JohnC430 (author)JohnD1642017-10-04

he set it to 13.8V and not to 14.4V. so no need to worry about over charge,

MicheleH14 (author)2017-10-01

Can a similar circuit be used to recharge using a small solar panel ?

kleetus92 (author)MicheleH142017-10-02

Sure, but it doesn't work well overnight.

JohnC430 (author)kleetus922017-10-04


JohnC430 (author)MicheleH142017-10-04

similar yes. he has the buck converter set for 13.8 VDC. if ur solar panel has between 16 and 24 Volts output then u can connect it and it will definitely charge the battery. you can also set the converter output current like he did to the max that ur solar panel will supply. you can connect it 24 hours. of course at night it will not do anything and then in the morning it will start charging again. there are chargers called MPPT chargers which are a lot more expensive, but this will do the job nicely. (The one he is using costs under $5). Dont expect too much current out of it though. the heatsinks are undersized.

templemain (author)2017-10-02

A lot of hard work went into making this project & video-photos, well done, very good for the limited time electronics buff. Why reinvent the wheel when you can purchase the parts ready to manipulate into any project you need rather than build from scratch. Other projects I would like to see but no one yet has really considered is TINY power supplies (9v usually) for test equipment that can be purchased like 'do it your self' oscilloscope, function generator, component testers, wireless relays etc that need a 9vdc battery or 12-6v battery pack. To have these devices work on a 5vdc input boost converter or off tiny mains devices would add to their usefulness and be a nice project for hobbyists. Keep up the good work.

Fugit185 (author)2017-10-02

Nice instructables but the mains side is risky, you should not use XT60 on mains side but wires and connectors designed for that usage. Also you need have way to protect mains cables pulled off i.e. so no force can be applied to connected cables.

maximzodal (author)2017-10-02

Terrific instructable! Instructions were very easy to follow and well laid out. A model of how to do an instructable.

Your use of existing otherwise difficult to make components is excellent and demonstrates a knowledge of electronics many electronic instructables lack.

My BatteryTender has given up the ghost and this is exactly what I needed.


you are most welcome

andrewty (author)2017-10-02

nice instructable.

Modern Lead Acid batteries do not suit >14V charging despite what some of the other comments say.

The correct charging voltage for the modern chemistry in a Lead Acid battery is 13.8Vdc, unless the manufacturer tells you otherwise.

The design uses a constant current pre-regulator.

That acts as a short circuit protector. It does not need another protection device.

Had this charger used a linear regulator, then it would become hot if short circuited and passing the set current into a near zero ohms load. But this charger is made up from pre-assembled switcher regulators.

They do not overheat when taken to their maximum.

I repeat, this battery charger is excellent and when used correctly will not damage modern Lead Acid batteries.

Well done.


TamasV4 (author)2017-10-01

Dude! What about safety? You almost touched the AC DC power supply!

Also I am not sure the XT60 rated for mains voltage. Input and output connectors are easily interchangeable and with human error you blow up the whole thing.

Cover the sides with plastic too, in this form is lethal.

RuiF2 (author)2017-10-01

Nice instructable!!! Can you please tell me the cost of this project? Ty

roughly about $15-$20

ZacWolf (author)2017-10-01

Thank you for the excellent source lists! To me it's always what makes or breaks a good Instructable! Well done!


pemazzei (author)2017-10-01

Very nice Instructable! Please, can you show the wiring diagram between the modules you used?

it is present there see the image

massimostep (author)2017-10-01

It can not work!!!!

nice article but the project can not work because a charger works with other principles!

a lead battery charging up to 14.4V afterdrive feeds to 13.8 to keep it charged.

if you charge the 13.8V battery it never reaches its charge !!!!!!

this you have accomplished is a POWER SUPPLY and not a charger!

inform yourself well before you disclose erroneous notions, do not always be superficial.

billbillt (author)2017-10-01


Kevanf1 (author)2017-10-01

So simple and yet so brilliant. Well done and thank you. I wonder if this could be expanded further? How about adding a conditioning or de-sulphating circuit to the design? This is just a thought as I have two commercially made chargers with conditioning circuits and they seem to be the trend nowadays. Yours is superb whatever :)

nic.bryan.73 (author)Kevanf12017-10-01

I think the idea with this one is that it doesn't need to condition the battery, because it's only charging it up to the max-voltage, not over-charging it.

der_fisherman (author)2017-10-01

I like your ideas, and due to you being careful in using 13.8 volts, your lead acid battery will last a hell of a long time, even if its not a full charge (which cuts the working life dramatically!!). Very similar to what I use (13.6 volts) on my own designs.

I switch my charger off automatically from the mains once the battery is between 13.6 and 12.6 volts. 12.6v is apparently where Sulfation starts according to some Battery manufacturers....

I am sure that your design will find a lot of very happy users here on Instructables, very well done!

Thanks for sharing.

About This Instructable




Bio: Hi my name is Steve and i'm a Creative and I got Technical skills i can build anything just stick to my account . I ... More »
More by Steve Willson Kujur:DIY 300 Watt 5.1 Channel Amplifier How to Make an Automatic 12V Battery ChargerFast Charging Anywhere
Add instructable to: