# Curious about operation of charge controller

Discussion in 'General Electronics Discussion' started by kong, Jan 20, 2014.

1. ### kong

122
2
Sep 26, 2010
I found this popular circuit online which was built by Michael Davis for a wind turbine he built. He made his circuit open-source and many people have used it.

I have no trouble building it but I'm curious about how it works.

Can someone explain it to me?

http://mdpub.com/555Controller/images/555ChargeController2.jpg

Specifically about how the circuit is calibrated to charge/dump.

Thanks!

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
It's a very simple circuit that charges the batteries until they hit a certain voltage, then it dumps the power from the solar panels/turbine until the battery voltage falls below another voltage.

R1 needs to be adjusted so that TP1 is at 1/3*5V (1.67V) when the battery voltage is low (say 12V)

R2 needs to be adjusted so that TP2 is at 2/3*5V (3.33V) when the battery is fully charged (say 14V)

Note that this circuit doesn't have any control of the charge current, nor does it take into account the temperature (which causes a change in cell voltage)

To understand further how it operates, look for circuits using the 555 as a schmitt trigger. The difference in this case is that the 2 inputs are not tied together. This allows control over the switching points and thus also the hysteresis.

3. ### kong

122
2
Sep 26, 2010
Thanks Steve! That answered my question.

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
Excellent, thanks. I wasn't sure if I was going to an appropriate level of detail or not.