"T i m" wrote in message
...
On Thu, 21 Sep 2017 21:43:31 +0100, "Ian Field"
wrote:



"T i m" wrote in message
. ..
Hi All,

Not a 'repair' question as such but I was thinking of using an old
skool 250uA FSD moving coil panel meter to read the 10 to 15V DC range
(a lead acid battery charge / discharge indicator), next to a 0-30A
Ammeter (inc shunt etc).

I was thinking of using either a voltage reference such as
LM4040DIZ-10.0 or could I get away with a simple zener (BZX55C?) with
associated resistor(s) please?

Most people just use a Zener and maybe a few normal (or SB) forward volt
drops to trim the offset.

Ok.

I was thinking the TL431 programmable Zener could be calibrated to exactly
what you need - but it needs a minimum current through it (possibly 1mA or
so).

Well that's ok?

You can probably incorporate a TL431 into some kind of bridge circuit with
the movement spanning the 2 arms, but it will almost certainly need some
kind of power supply.

Because the reference voltage will be too close to the minimum voltage
expected Ian?

The TL431 is actually a comparator with its own built in 2.5V reference.

In closed loop operation, that's as low as the cathode goes - you can
saturate it in open loop operation, but "Vce-sat" is around 2V.