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Solar charged lead acid battery, how do I have automatic shut off and turn on so it does not discharge completely? Answered

I have a battery with a charge controller between it and the solar panel. But if  I connect something low power to it, (like an aquarium air pump for a windowfarm or to power a small water feature),  it needs to shut off automatically before the battery discharges too much (if it is night time or cloudy).  Otherwise I have a dead battery. I don't have a deep cycle battery. Too expensive!  So any ideas how to have an automatic on off switch for this? Thanks,   Brian.

2 Replies

seandogue (author)NachoMahma2011-03-17

If you're a diy guy with a bit of electronics ability...The idea is to use threshold detectors to control the charging and discharge cycles. There are a variety of ways it can be accomplished.

In addition to NachoMama's suggestion, I'd consider searching for "threshold detection circuit"

A simple threshold detector uses a cheap opamp, a few resistors and caps, and adjustable pot(s) for setting the detection voltage(s).

The output of the threshold detector (a variant of a comparator circuit) is used to switch a relay (or relays).

Unfortunately, I don't have time to provide a circuit to add to the post, but they're pretty simple to build..

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