How To Make A Battery Charger (12 Volt)

How To Make A Battery Charger? We are referring to a 12 volt 45 AH charger in this guide. If you can not afford a battery or feel like making one on your home is more fun or cost effective over the long term, this guide will teach you how.

  • You cannot proceed without first figuring out what type of battery you want, especially the maximum charge voltage compatible for it.
  • The standard is a lead acid battery cell that can handle 14.4 volts. What you are going to make will resemble a circuit box in a lot of regards. This means components…
  • Get yourself a quality bridge rectifier. 25 A (amps) will be perfect. If you feel it is not small enough, it is alright for a bridge rectifier to be slightly bigger for a car battery.
  • The next step needs you to stop and learn the charge current required for your battery. With an automotive battery of 45 AH (ampere-hours), one tenth of that capacity will help you determine how many amps you need to charge the battery over a period of time. The equation commonly used goes like this: 45 AH = 4.5 A x 10 H [A: amps ; H: hours].
  • The above is a general rule of thumb, not a hard fact that every DIY car battery needs to follow. The charging time could vary based on the amps you know your battery can handle. This means the equation values to help you figure out the charge current for said battery will also change.
  • The biggest heat source in your battery will be the transformer. Is the one you are using prone to over-heating? A halogen lamp transformer is a good option. It can generally handle about 12 volts for a 60-watt power output. It will still be hot, a fact that is difficult to alter.
  • Cautionary Note: If the transformer over heats, its internal fuse will burn out and render the battery inert. It will take time to insert a new transformer. Basically, this component should be hot but not too hot.
  • A computer fan can be fixed during assembly to keep it cool. You will need to make a separate power suppy for the fan. A small wood box can hold the power source that keeps the fan going. This box can sit inside the overall ensemble. A good cooling fan demands 300 mA (milli-amps) to work efficiently.
  • The next component on the list is a bunch of silicon diodes. After you have fixed these as required, remember that the output voltage has to align with these power diodes. Classic or standard diagrams for these assemblies can be found online.
  • The diodes play a crucial role in helping reduce transformer voltage and keep it from over-heating. When you see apt diagrams to form your diode circuit, be sure to use at least two diodes in the bridge rectifier region.
  • All this will help you get the required power output to make for a functional 12 volt car battery.
  • For calculation’s sake, suppose you have an AC of 12.5 volts your DC voltage will be 1.4 times that value; in this case 17.5 volts [AC x 1.4 = DC]. This occurs on the bridge rectifier’s capacitor.
  • The output voltage should be manageable and not go beyond a limit. This means keeping the capacitor circuit at a sufficient size. It all has to do with the charge stored inside the capacitor.
  • The higher the electrolytic capacitor’s value the more the power output. Too much and it could ruin your battery, which is only a 12-volt one.
  • Finally, we have primary and secondary fuses.


Once you have put them all together, you have a workable car battery. Make sure the fan is on one side of the ensemble where air can easily go in. The transformer is an inch or so behind, where the air can cool it. All other components go where needed. Air has to be able to leave after passing along the setup else, it will accumulate and store heat.

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