SilverFoxCPF
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Re:Trickle charge pros & cons - 2007/06/16 04:32
Hello Gb,
NiMh batteries like to be charged up and used. Holding them via trickle charging at 100% charge makes them loose their vibrancy.
The self discharge rate of our current cells had greatly reduced over the rates that occurred when NiMh cells were first released for consumer use. Healthy cells now have around a 0.7 - 1.0% self discharge a day at room temperature. This works out to around a 20% loss a month.
This means that your 2200 mAh cell, after sitting in the drawer for 30 days, has discharged down to 1760 mAh. This is still plenty for most uses, so there is really no reason to keep cells on the charger for extended periods of time.
Cells dry out when exposed to trickle charge rates for extended periods of time. They also tend to form larger crystals that add to the internal resistance of the cell during discharge.
As a matter of fact, you are better off to store NiMh cells discharged, and charge then up just before you use them. Just make sure to do a charge/discharge cycle around every 30 days to keep them vibrant.
The modern NiMh cells can handle trickle charging, but you will get better performance, and your cells will last longer, if you don't trickle charge.
The BC-900 trickle charges at a little over 5% of the rate it charged at. For example, if you are charging at 1000 mA, at the end of the charge it will trickle charge at around 60 mA. After charging at 500 mA, the trickle charge rate is around 28 mA.
The C9000 applies a top off charge of 100 mA for 2 hours after a charge, then trickle charges at 10 mA.
The C8XX series of chargers trickle charge in the 8 - 10 mA range.
These Maha chargers are probably suitable for leaving cells in them for an extended period of time, but I still don't advocate it.
The best bet is to store cells discharged, and cycle them once a month. If you have sudden needs that arise often, pick up a 15 minute charger. 5 - 10 minutes in a 15 minute charger will bring your cells to a charge level that will be adequate for most spontaneous events.
Tom
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