Sentry Charger Settings

We repaired the bad capacitor in the Sentry battery charger a few months ago. But it never turned itself off at the high voltage setting and we were concerned about overcharging the AGM batteries. The charger has set points for turning on (a low voltage) and turning off (a high voltage). The high voltage setting was over 14 volts. We noticed that when anything was pulling much current the charger would never turn off. This could result in cooking (overcharging) the batteries.

So we decided to set the high cutoff threshold at 13.6 v, which corresponds to the float voltage for AGMs. This voltage doesn't get the batteries quite to full charge but is safer than setting a higher voltage. We turned on lights and fans to drain the batteries down to the point where the charger came on, then turned off the fans and lights to let it charge the batteries back up. This allowed us to set both the low and high points. There didn't seem to be much battery capacity between 13.6 and 14.3v, so the 13.6 setting seems like a good value for us. A small video camera was used to record the voltmeter reading when the switch-on and switch-off occurred, just in case we were looking at something else when it happened. We set the switch-on low voltage threshold to 12.6 v, which provides a reasonable amount of power between the switch-on and switch-off points.

This will allow the Sentry to continue to work for us until we eventually replace it with a combination charger/inverter.