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Can I use 220-12v,1.5 Amps Stepdown transformer along with 12V 2A (KBP200) bridge rectifier to build a charger for 12v, 7.5AH battery or I should use transformer with Higher output, maybe 15V

Mahendra Gunawardena
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opeolluwa
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    What type of battery are you planning charging? Is this a Lead Acid battery. If this is a Lead acid battery then the 15V might work better. What is your peak voltage? What is the voltage drop across the bridge rectifier. – Mahendra Gunawardena Feb 23 '21 at 13:05

1 Answers1

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You will need more than a 220V:12V transformer.

Fullwave bridge rectifier output:

$$ V_{DC} = 0.637\ V_{MAX} = 0.9\ V_{RMS}$$

This is the generic formula (textbooks), which gives you 10.8V. Higher current may cause < 10.8V. Lower current > 10.8V. As in: the actual voltage depends on the load current.

From Full Wave Rectifier.

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The peak voltage of a bridge rectifier has two diode losses (Forward voltage of diode depends on current).

If you do the ideal math:

$$V_{MAX} = V_{RMS} \ \sqrt {2} - 2 V_{F\ diode} = 12V \times \sqrt {2} - 2 \times 0.7V = 15.6V$$

which seems enough to make a 12V charger, but that is peak voltage (top of ripple), while actual voltage depends upon load current. Essentially if there is no load current, then maximum DC voltage is 15.6V.

StainlessSteelRat
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