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electrical:12v:battery_monitor

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Battery monitors

We want battery monitors be “gas gauges” but they are not. The monitor is more like the Range information on the dash that uses historical and present conditions to make an educated guess about how far you might get.

Battery monitors typically show:

  • battery voltage (Vbatt), more helpful with lead than lithium1); and
  • Amps or Watts in (charging) / out (discharging)

how they work

Broadly speaking the monitors work like this:

  1. you tell the monitor

In general, the monitor will watch for your system to hit a configured 100% state of charge voltage and starts subtracting amps (and percentage of capacity) when the system drops below that voltage. This is an imperfect science with lead batteries because 100% SoC is only reliable after a complete charge, and because different discharge rates will change the effective capacity. Think of the monitor as general guidance rather than gospel.

Note: Watching amps trail off at the end of lead Absorption (endAmps) will also tell you when the bank is fully charged. The battery manufacturer will specify something like C/200 or C/100 as a sign Absorption is complete.

Another note: one benefit of having a shunt-based monitor over a charge controller monitor is the shunt can discern between [dis]charging vs [dis]charging+loads.

configuration

Meters typically need a few settings defined:

  • battery capacity - remember that lead batteries are typically only used to about 50% of their rated capacity. You'll either be making that mental adjustment when you configure the meter or when you read it later. Battery capacity will also degrade over time.
  • You may also need to tell the meter what your battery manufacturer's 100% state of charge (“full”) voltage is

Bogart Trimetric

images-na.ssl-images-amazon.com_images_i_41vczv0vvml.jpg The most famous battery monitor is the Bogart Tri-Metric TM-2030 series.

This monitor will interface and operate their SX-2030 solar charge controller. The monitor will still provide amp-counting and other metrics when used on it's own.

inexpensive shunts

images-na.ssl-images-amazon.com_images_i_41zuqefexvl._sy90_.jpgFor folks who are [dis]charging at 50A/75A, a cheaper shunt is available for 1/5th the price of a Bogart.

Heavier-duty shunts are available (up to at least 350A).

1)
due to Li's very flat voltage curve
electrical/12v/battery_monitor.1587008343.txt.gz · Last modified: 2020/10/11 19:48 (external edit)