Project: power manager

This week revolved around batteries, generators and load shedding. The project turns it into the chip every bigger base needs at some point: a power manager.

The plant#

The charge level comes as Ratio from 0 to 1, averaged over both batteries.

The rules#

The generator is wired the other way round from the loads: it runs when the battery runs low. The loads leave the grid by priority – comfort first, the workshop last of all. All three get a hysteresis, otherwise they flutter around the threshold.

You already know the generator pattern from the heater. For a load that switches off below a threshold, you flip the comparisons:

sge tmp level C_OFF   # still above the shedding limit?
and comfort comfort tmp
sge tmp level C_ON    # already above the reconnect limit?
or comfort comfort tmp

When the batteries disappear#

Without batteries Average returns NaN. Then: generator on, all loads off, the display shows −1. snanz ok level gives a clean 1 for that as long as there is a reading.

Milestones#

1. Generator with hysteresis (on below 30 %, off from 90 %)
2. Shed comfort below 25 %, back on from 40 %
3. Workshop last: off below 10 %, back on from 25 %
4. Reserve in percent on the display
5. Batteries gone: generator on, loads off, display −1