On 24/04/2021 00:29, Dave Plowman (News) wrote:
In article ,
Fredxx wrote:
On 23/04/2021 13:43, Dave Plowman (News) wrote:
In article ,
williamwright 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?

Couldn't the manufacturers fit a separate small battery dedicated to
supplying the quiescent items? One that would last maybe ten days.
With a user option to decide whether it should steal power from the
main battery when it became depleted?

Not too many would be keen on a car which still sort of starts, but
has to be taken to a garage to have all the things that rely on a
memory reset? Nor would it be a small battery. Up to 50 mA is a common
quiescent drain. Work out the size of battery needed to supply that
for any length of time.

If you know the car is not going to be used for some time, disconnect
the battery. At least then you won't need to buy a new one when you
eventually want to use it.

The last Transit I owned had two lead acid batteries of equal size.
During cranking and running they were connected together. At other times
one was isolated from any gizzmos and so zero drain.

I guess that is one solution to the problem.

So effectively a larger battery. That is one solution, but an expensive
one. And some will still leave it long enough for them to go flat.


In this case only one of these batteries would be flat. As soon as the
ignition switch is turned the two batteries are connected. I dread to
think the magnitude of current flow in the first few seconds.

Any flattened lead acid battery is going to be toast, or severely damaged.