Electronics > Beginners
How to charge NiMh batteries?
tszaboo:
You cannot charge NiMH with CCCV charger, because the voltage curve will go down at the end of the charge.
Buy a dedicated charger. Best are the ones that have different charge current for AA and AAA. They cost literally 5 EUR/USD.
macboy:
--- Quote from: Andreas on September 10, 2019, 09:08:17 pm ---Hello,
I would use 1.4-1.45V/cell as voltage limit (@20 deg C) and a diode to prevent discharging in case the power supply (mains line) fails.
So total voltage including diode ~3.4-3.5V. Depends on room temperature: with higher room temperature you have to decrease voltage.
(~3mV/deg C and cell)
Current can be increased to ~0.15A (C/4) with voltage limit.
with best regards
Andreas
--- End quote ---
--- Quote from: MosherIV on September 10, 2019, 08:55:16 pm ---NiMh can be charged with CV.
2 cells in series gives 2.4V
Set the psu to 3V and limit the current to 60mA. Should take about 10 hours to charge.
If the cells state the max charge current, you can set the current limit to that.
Keep an eye on cell temps, if it gets too hot to touch - stop immediately.
--- End quote ---
NiMH (and NiCd) are never charged with constant voltage, but always with constant current.
If you charge at a slow rate, then it is safe to overcharge them without damage. So a common easy way to charge cells of either chemistry is at a constant current of 1/10 the capacity (C = 600 mAh so use 60 mA in your case) for 14 hours. This is also used as a conditioning charge for brand new cells or to help refresh old cells.
If you want to fast charge (which I doubt) then you can increase current up to at least 1C (600 mA). Then, you need to monitor BOTH the voltage and temperature of the cells. After reaching full charge, the cell voltage will drop a few 10's of mV, and the cell temperature will rise. Detecting either condition is used to terminate the fast charge. You should also terminate charge after approximately 1.4C worth of charge. So if you are charging the 600 mAH cell at 600 mA, the safety timer should stop the charge after 1.4 hours.
It is very easy to use a good CV/CC lab supply to charge these batteries. Set the voltage to double the nominal pack voltage, set the current to 1/10 C (60 mA), and charge for 14 hours.
Giuss:
I charge them at 1/10C (a simple LM317 as constant current regulator) without problems
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