Originally Posted by gmclam
I have read articles on the issue of properly detecting end of charge voltage as just posted, but yet to see issues related to it on the batteries I use. My issue is to get the longest life out of the battery, and as long as you don't overcharge, I don't see how a charge rate of 0.5C helps that (compared to a slower rate).
Most everyone thinks that way, but they fail to take into account aging / capacity loss and internal resistance. The delta-v provides the most accurate end of termination signal regardless of battery state, whereas simple timing at low currents may work fine initially for brand new batteries, but that timing changes as they age - and if not adjusted by the consumer by measuring things like internal resistance, the battery is overcharged. What consumer has the gear to measure that?
Perhaps this may help - consider that early on the engineers at Maha consulted some of those in the Candlepower forum group for feedback on proper charging. Advice from Silverfox is highly recommended, although there is a litany of other knowledgeable members.
A look at slow charging
Note that the only timed charge cycle on the C9000 is the break-in. When you use the normal charge mode, and manually throttle the current too low (under 0.5C), there will be no delta-v termination signal, and the C9000 will fall back to other methods like temperature, or a termination on a high terminal voltage, like 1.48v per cell - which is a bit of overcharge.
In other words, you are now overcharging your cells by forcing the C9000 to fall back to other termination methods when you place them in anything but the timed break-in mode. Temp and battery terminal voltage are just two of the fallbacks - there are more, but they are proprietary.
Essentially, unless you absolutely know the percentage of discharge of EACH of your batteries, know the internal resistance value, and accurately calculate / offset the timed charge based on those parameters, the higher-current delta-v method (the signal comes from the battery itself) will net you longer life-cycle use.
Another tip: over the years, many charger and even battery manufacturers have mistakenly called 0.1C a trickle charge. It is not and is a slow-charge, which slow-roasts the electrolyte if left on long term. A TRUE trickle is 0.01C of current. Guess what - the Maha C9000 knows the difference, and when charging is done, leaving cells in the 9000 won't hurt them since it applies VERY low current - ie a true trickle.
Tip #2: Maha knows about the Peukert effect. When the delta-v termination signal is received from the battery, you can still put in about 100ma or so more capacity with a gentle top-off. Maha doesn't mention it, but it will supply about 60ma for two hours after the "done" indicator lights before falling to about 10ma trickle. Thus, if you absolutely need to have that last little drop of capacity, wait for two hours if you happen to actually catch the "done" indication light up.
One thing consumers fear is heat - and rightly so. But there is a difference between hot and too-hot-too handle. Nimh when charging is exothermic, and it is normal to feel warmth. If you can't hold them in your hand without immediately dropping them, then you have problems. This fear of any amount of heat also leads to the slow-charge-is-always-best mindset, not knowing that slow-roasting your electrolyte is a bad idea as well.
Basically, charge at a reasonably fast rate, let the delta-v do the signalling, and be done with it for best overall results.