On Wed, 13 Jan 2021 23:37:18 +0000, Theo wrote:

> As mentioned 6V lead acid doesn't work for a starting battery - it might
> be OK for a 'leisure' battery that is fine with deep discharge, but
> again we're on a part of the curve where the battery is absolutely flat
> and declining fast.
>
In the soaring world we use 12v SLA (sealed lead-acid) batteries to power
our radios, flight recorders FLARM and and various navigation systems.
Most instrument panels draw 400-800 mA when fully powered up, so a 7AH
battery is good for flights of over 7 hours.

I use Yuasa NP7-12 batteries. This is a 12v 7.2Ah sealed battery, so can
be installed any way up and is also sold for use in small business UPSs.

In my glider I use a 12v->5v 3A DC converter (under 6 quid from eBay,
where they are sold for blinging up cars with festoons of LEDs) for
powering instruments which want a 5v supply. Mains chargers which shut
off or switch to float mode at full charge are available for these
batteries.

If you go this way, and want to implement low-voltage shutdown for the
Pi, connect your low-voltage detector inputs across the battery and set
the shut-down point to 10.5v.

If the low-voltage detector is a Pi hat, make a voltage divider from a
68K and a 27K resistor, put that across the battery and connect leads
from each side of the 27K resistor to the low-voltage detector: when the
battery is drawn down to 10.5 volts, there will be 3 volts at the low
voltage detector. Or use a 10K linear potentiometer and set it to output
approximately 3 volts.


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Martin    | martin at
Gregorie  | gregorie dot org

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