On Tue, 30 Jan 2018 20:01:37 +0000
The Natural Philosopher  wrote:

> On 30/01/18 15:54, Ahem A Rivet's Shot wrote:
> > On Mon, 29 Jan 2018 19:43:02 +1200
> > nospam.Richard.Miles@f24.n3634.z1.binkp.net (Richard Miles) wrote:
> >
> >> Probably going to see if I can get hold of a UPS hat over here pretty
> >> soon. I am getting ready to start a car pi project and I have been
> >> concerned about how to elegantly shut down when I power down the car.
> >
> >  There are permanently on rails in all cars, you'll find one
> > feeding the radio (as well as a switched rail that only comes on with
> > the instruments). Keeping a pi running won't matter to a car battery.
> > That depends. I had an alarm destroy the battery in a car after 2
> > months
> off road.
>
> 12V, 20Ah. say 5V 140Ah. 2 months is 60 x 24 hours = 1440 hours

 That's a very small car battery, the one in my car has nearly three
times that capacity.

> So 100mA draw at  5V is enough to flatten a car battery in 2 months

 Unless of course the car battery gets charged in that 2 months,
like by driving a mile or two.

> Pi's draw beween 100 and 500 mA whgen idle  depending on model
>
> Its amazing what the Abilitry To Do Simple Sums can tell you when faced
> with handwavey statements like 'Keeping a pi running won't matter to a
> car battery.'

 It shows you that I assume the car is driven from time to time,
seems a reasonable assumption to make.

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