Automatic gen startup - battery voltage value

KD4UPL wrote:
The right voltage will vary depending on your batteries and your loads. It's also a trade off between gen. run time and battery life. The deeper you cycle your batteries the less time the gen. will run but the shorter their life will be. Batteries not cycled as deeply will provide a longer life but you'll need to run the gen. more to do it.
If you have only small loads (no microwave or toaster thru an inverter) I would let the batteries drop to 12.0. This is a fairly deep discharge but I would rather do that then burn the propane (or whatever your gen. runs on). If you want to treat your batteries very well you could choose 12.3 or 12.4. If you have very large loads that may cycle on and pull the voltage down I might even set it to 11.8 or so.
Also, does your gen. start logic include a time delay? That is, how long does the voltage have to meet the set point before it will start? A longer time delay would make me use a higher voltage.

The start logic makes sense. If you have a 120 volt refrigerator run by inverter, the voltage might drop from 12.6 volts to 11.6 volts for a few seconds while the compressor starts, then return to 12.3 or 12.5 volts while it is running. You don't want the voltage so high that each time the refrigerator starts, then the generator comes on as well. Especially at midnight with a diesel generator.

My suggestion is to play with the voltage setting. If the inverter is turning on the generator within 6 hours of the last run time, then either the battery bank is to small, or the voltage setting is a little to high. Also recall that you might have the generator set to have a "quiet hours" from say 9 pm until 9 am, so if it starts at 8 pm triggered by a 12.0 volt setting, it can only recharge for 1 hour, bringing the battery to about 12.6 volts before quiet time setting shuts it off for the night. If you have aqua hot and a residential refrigerator, that might not be enough juice to get through the night - unless you have 6 batteries.

Of course if it is a cold night, and you see the voltage hovering around 12.3 or 12.4 volts - meaning about 60% full, you can always start the generator around dinner time and let it run a couple of hours, bringing the voltage up to 14.4 volts while charging, and leaving it around 12.7 after you are back on inverter power.

Good luck,

Fred.