Tricky 12V Battery Charger Circuit, tricky questions.#Tricky #questions


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Tricky questions

Tricky 12V Battery Charger Circuit

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Here is a crude but efficient tricky charger for Lead Acid Battery. It uses a 12 volt car bulb as current regulator and charge status indicator. The brightness of the bulb indicates how much charge is flowing into the battery. When the battery becomes fully charged, lamp turns off. If the lamp is staying on with full brightness for more than 30 minutes, it indicates that the battery is dead and is not accepting charge.

Charging current is obtained from a 15-0-15 volt secondary 2 Ampere step down transformer. Diodes D1 and D2 are rectifiers which can handle 3 ampere current. In order to give “Dirty DC” for charging, a low value filtering capacitor C1 is used. So that the DC voltage will have some ripples which is necessary for better charging of lead acid battery.

Tricky Charger Circuit diagram

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The trick of the lamp is interesting. A 12 volt car tail lamp bulb is used in the circuit. It is connected in series with the positive output rail so that current flows through the bulb into the positive terminal of the battery. From the positive terminal, current passes through the battery chemistry into the negative terminal and then returns into the transformer. So the current flowing through the bulb depends on how much charge is using by the battery. When the charger is connected to the battery, the lamp turns on only if the battery requires charging current. OFF state of the bulb indicates that the battery is dead. If the battery holds some charge, bulb will turns on. If the battery is partially discharged and holding 50% charge, bulb will light brightly when the charger turns on. Then the brightness gradually reduces and finally the filament appears as a red hot line. This indicates that the battery is fully charged. The bulb also restricts the flow of current like a resistor.

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Yes, one can use resistors and diode for limiting the current for charging the batteries. We can also provide high/low voltage cut off for the safety of the batteries. But, as this is a very simple charger (As the name suggests), I have not gone to that extent.

PS : I AM that good

V. Sambath kumar

Well done V.Sambath kumar

You compensated for too high of a voltage from your transformer and DC supply, and too much current, and also managed to find light bulbs that did what you wanted. You are either very good or very lucky.

I have tried many light bulbs, in series and in parallel, and combinations, to give me the exact voltages and current I wanted for various stages of charging. I have rarely found bulbs to do exactly what is ideal for use as a visual indicator.

The main reason my bulb setups haven t worked like described, and like you described; being dull and bright and off, at the correct times, is because I alter the circuit for the different stages of charging(change bulb sets) AND I have been charging batteries in various conditions.

Under conditions of a basic single stage charging, of a good condition battery, you can indeed get a bulb setup that goes out at the correct time.

A way to improve your charger so that you have a better indicator, and control of the charging for various types of batteries, and for batteries in good to poor condition, is to add three things in place of light bulbs.

Add a variable resistor, to replace the bulbs, so you can make adjustments for all conditions. Add both a volt meter and a current meter as excellent indicators of state of battery, state of charge, and rate of charge, and for doing proper stages of charging that are best for these batteries.

When I get the parts and am done building my charger, I will be able to: use it to charge virtually any type and size of flooded battery, 6 or 12 volt(made two secondary coils in the transformer I rewound), create 4 charging stages(3 most of the time), and use it to restore batteries in poor condition of sulphate build up. I plan to add overload protection and reverse polarity protection and a fan to keep the transformer and circuity cool.

Sounds like you have the skills to do this too if you wanted.


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