[This is in addition to the previous post]
Hello again,
I've taken a little more time to look at this and
i've been able to find at least three different
approaches to the problem of keeping an eye on
several cells at once.
Approach #1 is the most straight forward and is going to
work the first time it's turned on.
#2 is a little more tricky.
#3 is the most advanced and therefore may require a little
R&D time on the bench, but uses the least parts for the
most cells.
#4 (which i didnt show) would require PIC programming,
so i dont know if many people would go for that.
My personal favorite is probably the approach that stems
from sampled data theory (#3), but i like the simple #1
too because there's no chance it wont work. I've even
built and tested something very similar to #1 already
for one Li-ion cell, and it worked the first time it
was turned on too.
---------------------------------------------------------------
The following is an Overview of three approaches to
undervoltage protection of NiMH cells in series
---------------------------------------------------------------
Not including the MOSFET which is optional...(see below)
[1]
Straight forward differential amps and open collector comparators...
Parts per cell: 1 chip + 4 resistors
Other parts: one voltage ref diode + 3 resistors
[2]
Voltage difference reference diode...
Parts per cell: Ref diode chip + 3 set resistors + one-half op amp chip
[3]
Sampled data theory approach...
Approximate parts for up to eight cells:
a. 5 resistors + op amp or voltage ref diode
b. two CMOS analog switch chips (16 pins each)
c. CMOS binary counter chip
d. oscillator (single chip or chip + 4 resistors + cap)
e. small cap
Approximate parts for up to sixteen cells:
a. almost double of that for eight cells.
For all approaches:
Note that the MOSFET is optional because there is always the
possibility that instead of turning off the circuit there
could be a single red LED turned on, which would indicate
to the user that the light should be turned off as soon as
possible.
Another possibility is to have a red LED for each cell...
where the ones that light show which cells are low.
This would be pretty neat
and very functional.
Comments/ideas/suggestions or just what sounds best to you?
Take care,
Al