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Charging circuit 4 AAA NiMh
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mach7
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« on: January 08, 2013, 10:43:28 AM »

Hello everyone!

I am trying to charge 4 AAA NiMh rechargeable batteries with this simple circuit. Do you have any suggestions for better results? The resistor is getting really hot during charging. Is that normal? I use a 12V, 2A transformer.

Thank you.

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Relayer110
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« Reply #1 on: January 13, 2013, 06:03:11 PM »

What is the voltage of the NiMh batteries? I hope not 1.5V each...
Regards,
Relayer
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Hero999
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« Reply #2 on: January 15, 2013, 05:18:01 PM »

The battery voltage is not the problem. The main issue is the charge current is too high.
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KevinIV
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« Reply #3 on: January 16, 2013, 07:51:23 PM »

The circuit shows a wall transformer and not a rectified AC power adaptor. So the resistor would need to be in series with the batteries. A half wave rectifier has more ripple, but the 1000uF capacitor with a 1Kohm resistor may charge the batteries slow enough. You probably have a regulated AC power adaptor. So change the resistor to a 2Kohm.
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Hero999
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« Reply #4 on: January 17, 2013, 11:56:20 AM »

The resistor is in series with the batteries.

A capacitor is not necessary because the battery doesn't care about the ripple current.

I agree, increase the resistor to 1k to 2k to limit the current to something more sensible.
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KevinIV
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« Reply #5 on: January 17, 2013, 06:27:46 PM »

The resistor in this half wave rectified circuit is in series with the capacitor and battery. If you change the resistor to reduce the charging current, the battery could take a week to charge. If the resistor is in series with only the battery, it will charge in a fraction of the time.
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Hero999
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« Reply #6 on: January 18, 2013, 05:22:36 AM »

You're wrong, whether the resistor is in series with both the capacitor and battery or just the battery will make little difference to the charging time.
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