Chargng a tiny PP3 9V 200mah battery

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Chargng a tiny PP3 9V 200mah battery

Postby Burgerman » 16 Jan 2023, 23:06

Its a bit perverse using a 1344 watt, 40A and 32V capable charger with a 3KW power supply to charge a minute 200mA battery somehow.

But amazingly you can wih the PL8.
This battery is the tiny 9V PP3 out of my multimeter.

Charging nickel metal hydride rechargables isnt easy. Theres 2 ways. Both are Constant Current.
1. charge at its rated capacity, at the 15 hour rate for 20 hours. This works by charging so slowly that the overcharge doesent matter. And it needs an overcharge as charging these is not anywhere close to 100% efficient. More like 70%. So that means this 200mAh battery would be sat for 20 hours at 1 fifteenth of its capacity. So 200 div by 15 = 15mA.

2. Or a better way, where all cells are healthy and at a similar state of charge is the delta peak method. Which the PL8 does. As you charge at approx 1/2C or in this case 100mA at a constant current the voltage steadily rises. At the point the battery or each of the cells are full, they begin to warm up. And this causes the voltage to stop climbing. And as they start to get even warmer the voltage begins to fall very slightly. The charger detects this few mV drop and ends the charge.
It only works with GOOD connections, clean terminals, healthy low impedance cells.

See below. Remember current is constant at 100mV. You can see that charge ended where the charge voltage begins to drop. I included the profile.
Attachments
NiMH 9V PP3 (7S) 100mA.PS8
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PP3-9V nmh.jpg
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