T i m wrote:

On Thu, 21 Sep 2017 10:45:21 +0100, The Natural Philosopher
wrote:

snip

If only you could apply the same amount of energy to helping us
resolve this (and what must be to you, 'brain as big as a planet'),
simple *energy* measurement issue as trying to defend the indefensible
(Linux or leaving the EU) we might all get on faster! ;-)



The fact that I have a degree in electrical engineering

You say ... ;-)

and a huge
anount of experience in using lithoum ion batteries in model aircraft

;-)

Yeah, I was a 'sponsored' RC car driver so because of that I know all
there is to know about Nicads and NiMh .... (not).

completely precludes me from offering what would instantly be shouted
down as 'an opinion'.

Yes, but if you had an EQ as big as your IQ you would be able to offer
*information* around my question wouldn't you?

But I will give you a hint.

Ohms law.

No use whatsoever mate as it's a linear relationship and this isn't a
linear problem.

I think we have established that the relation between terminal voltage
and current at a given state of discharge is a linear one.

If you want the *derived* quantity of remaining capacity *at a given
current* for a given state of discharge this can simply be a look up
table and is little or nothing to do with what the battery *has* been
doing, depending only on discharge state, not how you got there. So you
need no other measurements to estimate remaining capacity at a given
current. Specifically it does not depend on how Peukert's law has
applied during the use of the battery up to now, only on how you use it
in future. You could automatically estimate remaining endurance (to a
given future state of discharge) for the prevailing current at the time
of measurement, but you still only need a look up table for capacity
against current and your present state of discharge plus present current
consumption.

You could use an approximation to Peukert's law to calculate capacity at
a given current on the fly, but there is no advantage to doing so as the
future behaviour is apparently not affected by how you have treated the
battery except as represented by current discharge percentage. And, as
the currents you are using are well within the range for which capacity
is published interpolation would be easy. If the 'k' you can calculate
is actually is constant you could program the Peurkert equation, but a
look up table for capacity for each amp of current per battery up to ten
might be even easier.






As you know all there is to know about LiPo (as the chances are you
*wouldn't* be using Li-Ion in RC aircraft as they are too heavy) you
would know that whilst Peukert's Law also apples to them in theory,
you would also know it is pretty well cancelled out by the increase in
efficiency found as the batteries heat up in use (proportionally to
the current drawn).

So, what with you having a degree in electrical engineering, into
using your (Linux) laptop as a typewriter (writing code for the likes
of Gridwatch?) and like debating things so what's not to like? ;-)

So, cummon, have a go at being the solution, you know you want to. ;-)

Cheers, T i m


--

Roger Hayter