linnix said:
Here is a different opinion:
http://www.greenbatteries.com/bachfa.html#charger damage
Many battery manufacturers do not recommend long term ( months at a
time) trickle charging.
Who the hell is talking about leaving the battery in the charger
months at a time? Powerstream says, in the part of the quote you
snipped " To preserve battery life the best practice is to use a
timer to prevent overcharging to continue past 13 to 15 hours. "
If trickle charging is used then the charge
rate should be very low or only intermittent. The best smart chargers
will only send an occasional pulse charge to the battery once it is
charged. They do not apply a continuous low rate of charge. Some
battery resellers state that applying a continuous trickle charge of
about 1/10th the battery's capacity is not harmful. However, we have
not seen any battery manufacturer condone the practice.
That is fine as the trickle charge part. But for fast charging, you
would need burn 20W on the Lm317 and 10W on the resistor.
You want to talk fast charging, post a circuit - don't
pervert mine, which is intended for slow charging: C/10.
as well as a termination method.
Helloooooo ... the timer *is* the termination method.
Powerstream does *not* recommend a timer "as well as"
(meaning in addition to) a termination method.
They also say that they can't find a
good enough termination method based on dV/dt.
Irrelevant. Nothing to do with slow charging. You claimed
NiMh cells don't like slow charging. That's just plain baloney.
Both Powerstream and Greenbatteries recognize it as a viable
method. Neither claims NiMh cells don't like slow charging.
Both talk about improper charging being the culprit - however
it is arrived at. If you charge improperly, whether it is a
fast charge or a slow charge, you can damage batteries.
The best method is
based on dT/dt. So, you need to add a thermosistor to a micro with A2D
as well.
The op did not ask for the "best" method. He asked for
the simplest: "what is the simplest design for a charger?"
His resistor divider is likely simplest - but as you
point out is likely to cook his batteries. A light
bulb in series would be a candidate for simplest, but
requires a regulated voltage which is not as simple
as the LM317, cap and resistor. And those three parts
work whether the supply is regulated or not, and don't
require a light bulb. You want to add analog to digital
conversion, a thermistor, a micro and who knows what else.
That takes it far away from simplest.
Your ideas belong under another heading - perhaps
"best NiMh charger". And the idea that NiMh cells
don't like slow charging - well, it's hard to say
where that idea belongs.
Ed
