On 22/04/2021 17:21, Paul wrote:
Dave Plowman (News) wrote:
In article ,
Â*Â* Fredxx wrote:
On 20/04/2021 20:02, Cliff Topp wrote:
All modern cars will have an amount of quiescent current draw to power
things like the alarm, the clock, the radio presets and so on when
the car is parked up and switched off. I've seen it written somewhere
that around 50mA can be considered 'normal'.

My question is - if the quiescent current draw is 50mA (0.05A), how do
I calculate voltage drop per hour?

For instance, if I park the car up at 10pm and the battery is showing
12.5V, with a 50mA draw overnight what will the voltage be at, say,
9am?

This is an article I feel might be useful for you.

Â*https://batteryuniversity.com/learn/...tate_of_charge


Good article that, Fred. I knew by experience taking a spot reading of
lead acid voltage of little use. But didn't know the makers reckoned it
had to be left unused for 24 hours.


But that doesn't tell you enough about the situation,
to be celebrating a single reading of OC voltage.

It's comforting reading the voltage and seeing a
"normal" value after it's settled. But that's not
a diagnostic as such.

It does give an indication of the state of charge. That is better than
nothing.

The Smart Charger has more means at its disposal
of determining battery health.

Your car doesn't charge it chock-full. And if you
didn't find it full, what would you conclude ?
(Battery ? Alternator ? Voltage regulator ?)

Most smart alternators only charge up to 90% in normal use.

The usual criterion is the car won't start.

The Smart Charger has more opportunities for making
measurements, than your car does. The car doesn't
have a desulphation cycle,

It's normally called an equalisation charge, and is more suited to
stationary use, and used to stir up the electrolyte to prevent
stratification.

it doesn't use pulse
charging (where the relaxation can be measured
after each pulse).

If you know the capacity of battery then charge current at constant
voltage is a good way to determine a specified state of charge.

Pulse charging is generally used to increase battery life and decrease
charging time.