Low-Power Control Systems

The charge controllers used here are dump/diverter types built from G Hurd's excellent kits. These can be built to run in 12V or 24V circuits and the 12V builds can be configured to run in charge controller or low-voltage disconnect (LVD) mode.

They are very flexible and - anecdotally - very resilient against lighting strikes. To get an idea of how easy it is to build these dump controllers, have a look at Potential Power's website, where he describes how he built his in some detail.

The 'dump-trigger' voltage for these dump controllers is configurable (using the blue, multi-turn, trim-pot visible in the photos in the links above. This feature allows you to hang two or more charge controllers off a battery bank, with one charge controller set to a slightly higher dump voltage than the other. This allows you to prioritise the order in which the dump controllers power on the dump loads. There's a great description of a real set-up using this technique at this link.

If you do cascade dump controllers like this, you must first accurately set up the voltages at which the dump controllers switch. To provide a variable but precisely 'settable' trigger voltage with which to do this initial calibration, I built the to-the-right-of-the-rectifier part of this circuit, although I substituted a low power LM317L. I also added in a second potentiometer just to make the final voltage tuning easier for us fat-fingered types.

Incidentally, just to nudge credit in the right direction, I think the original inspiration for this circuit was probably this circuit here.

Boxed up, that circuit looks like this:

You can extend the on-time for dump controllers with a timer. You'd do this if you want to use surplus power to drive a motor, pump or other useful appliance for which the micro-second on-off times of a dump controller are inappropriate or damaging. I've described how to do that here.