>The phone is required to maintain approximately (depends upon testing
>method) 1500 ohms of AC impedance during ringing.  Since the ringer
>voltage is roughly 100V, wouldn't it be fair to say that I'm entitled to
>about 67mA of current during a ring per phone?
>
>At any rate, I should be able to charge a large cap by drawing a few mA
>between calls with circuitry sleeping until a ring occurs.  After that
>everything would wake up and run until brown out occurs as the cap is
>drained.  It appears this would likely violate part 68 requirements for
>a telephone device, but I think it should work in theory.  What say ye?

My (admittedly very limited) understanding of POTS system is that the
ringing current is purely AC, and the bell is typically coupled through a
capacitor so it does not load the line, You will need to do the same into
your rectifier. However this may also give you a chance to use a suitable
transformer to step down to a suitable voltage to rectify, simultaneously
giving you isolation from the phone line. In the USA an ordinary mains
transformer may be suitable. However if the exchange and local phone are
both modern electronic items the ring voltage may be different, even if it
is an analogue phone line.

The current that determines if the phone is off hook is DC current
(originally the current required for a carbon microphone), which used to be
detected by a relay in the exchange, which is in series with the supply
voltage to your line. Lifting the handset made the DC circuit, causing the
relay to pull in and making the voice connection. It is for this reason that
the bell is AC coupled to the line.

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