Hi again,
Andrew:
Well, i noticed that he was using voltage regulation, but it is sort of a
voltage limit type circuit, so it will work up to the age of the cells
where they can be fully charged before 1.5v is reached. Once the
internal R increases they will no longer fully charge. That was my
main concern. Yes, i guess we should be thinking of ways to detect
end of charge too.
eimix:
Ok that's good, just keep in mind that you may have to raise that
voltage in the future when the cells age a bit more.
What kind of circuit are you comfortable with, can you use
LM339's or would you only want to use small transistors?
(This is for the end of charge detect).
Perhaps this is a bit better explanation...
If you limit the voltage across a cell yes the current will
eventually decrease, from 2amps down to 50ma or so,
or even lower, but that doesnt mean the cells are fully
charged. This is because the cells do not have a repeatable
voltage characteristic, unlike lead acid or Li-ion cells, which do.
This is why there are many chips designed just for charging
NiMH cells, and the way these chips work is totally different
than an 'ending voltage' detection scheme.
Here is a short list of charging schemes used with different
battery types:
1. Voltage detection with current limit: Lead acid, Li-ion
2. Minus delta V: NiMH,NiCd
3. Minus delta T: NiMH,NiCd
4. Max T: NiMH,NiCd
5. Timed: NiMH,NiCd
Max T (temperature) is often used as a backup to other
types of charge regimes also.
Timed, which is max time, is also often used as a backup
to other charge techniques, just as a fail safe in case
something else goes wrong with the charge process.