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[Reply #30 on:]

Nope, leastways I can't think of a way to use zeners.

If you just want to drop the voltage down the easiest way is to use 45 voltage dividers, all set to provide the best range possible for the voltage at that point in the battery string.

The voltage divider approach obviously loses resolution the further you need to drop the voltage - I don't know what resolution is needed here, but there must come a point where the voltage is so high that it isn't possible to achieve enough resolution.

I was thinking with the zener something like connecting each battery junction to a zener and then through a voltage divider to ground, the idea being that the zener would drop the voltage by a known constant amount to bring the voltage down to a range that can be measured, with no loss of resolution.

By the time you have several cells in series all with varying voltages the range of values that needs to be measured could easily exceed 5V hence the voltage dividers to reduce the range - still some loss of resolution due to the voltage dividers used for that, but nothing like as much as there would have been if dividers were used to drop the full voltage down to 5V.

[Reply #31 on:]

Works for me!  This is the easiest solution for hardware.  Calibrating it using a DMM in the code will take some time and effort.

[Reply #32 on:]

I get the zener idea now (told you I was slow), but if each voltage divider is tuned to the voltage surely there's no loss of resolution anyway.

We haven't heard from the OP since post #7 so as is often the case we're talking to ourselves, still it's good to bounce some ideas around.


______
Rob

[Reply #33 on:]

Hello
Would the temperature coeff. of zener/avalanche diodes skew the accuracy ?
http://users.tpg.com.au/users/ldbutler/ZenerDiodes.htm
jolphil