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--- electrical:12v:battery_monitor [2024/02/11 15:20]
frater_secessus [drift and reset]
+++ electrical:12v:battery_monitor [2024/10/21 10:43] (current)
frater_secessus [TL;DR]
@@ Line 7: / Line 7: @@
 [[https://amzn.to/4bxDjw8|{{ https://m.media-amazon.com/images/I/71g0M+mQjIL._AC_UL320_.jpg?100}}]]
   * Battery monitors start from a known State of Charge then count every Amp going into or out of the battery bank
+  * the shunt can be internal to the battery (lithium batts with BMS comms) or external to the bank
+  * the current acceptance of the battery bank in Absorption can tell you how close to fully charged a lead battery is((applies to Li also but the numbers are much smaller and we are not chasing 100% necessarily))
   * these measurements can go astray ("drift") over time and require recalibration
   * drift will be more noticeable with lead chemistries than lithium
@@ Line 25: / Line 27: @@
 Heads up:  there are //uni//directional monitors sold for purposes other than battery monitoring; read the specs and reviews to make sure what you are getting.
+===== sizing =====
+The shunt should be sized to handle your highest expected demand comfortably. For example, a system designed for 80A of current would work well with a 100A shunt.
+A shunt that is **too small** a shunt will fail if exposed to current that exceeds its rating.
+A shunt that is **too large** presents different problems.  Firstly, it will usually be more $$$ than a correctly-sized shunt.  Secondly, each shunt is designed to measure a certain range of currents accurately.  A 1000A shunt designed to measure many hundreds of amps accurately will not do a good job measuring much smaller currents like our 80A scenario above.
 ===== how they work =====
@@ Line 39: / Line 51: @@
 Small problems accrue over time, reducing the monitor's usefulness:
-  * the **measurement can be inaccurate** because current is very low (<1A) or very high (the monitor's upper limit).  To reduce these errors the shunt should be big enough to handle your largest expected loads comfortably without being grossly oversized.
+  * the **measurement can be inaccurate** because current is very high or low relative to the shunt's working range.  To reduce these errors the shunt should be big enough to handle your largest expected simultaneous currents comfortably without being grossly oversized.
   * the measurement and counting is **accurate but is not reliable for estimating changes in state of charge**.  This isn't a significant issue with lithium, but lead chemistries have substantial charging inefficiencies((10-20% in Absorption and 100% in Float since that stage is just offsetting self-discharge)) and consume more capacity than the count would suggest at higher currents (Peukert effect).
   * or a combination of the above
-For those reasons the monitor is regularly reset ("zeroed", "calibrated") when the bank is at a known state of charge.  This can be done at 0% or 100%; for practical reasons most owners will reset them when the bank is known to be at 100%.
+For those reasons **the monitor needs to be reset regularly** ("zeroed", "calibrated") when the bank is at a known state of charge.  This can be done at 0% or 100%:
+  - automatically by the monitor when a certain voltage setpoint is achieved.((14.0v = 100%, for example))
+  - manually by the user.  For practical reasons this reset is usually performed when the user observes the bank to be 100% SoC.
 One rule of thumb is to reset the monitor 1x/week.  There is no harm in doing a reset more often if you happen to notice it's sitting at 100%.  [Hopefully you won't regularly be encountering 0% - secessus]
@@ Line 67: / Line 82: @@
 [[https://amzn.to/4bxDjw8|{{ https://m.media-amazon.com/images/I/71g0M+mQjIL._AC_UL320_.jpg?100}}]]
-The 500A SmartShunt is available in [[https://amzn.to/3IfWai1|as the bare bluetooth-enabled shunt]] or [[https://amzn.to/4bxDjw8|bundled with a display]].
+The 500A SmartShunt is available in [[https://amzn.to/3IfWai1|as the bare bluetooth-enabled shunt]] or [[https://amzn.to/4bxDjw8|the BMV package which includes a display]]. The BMV also adds programmable visual and audible alarm and programmable relay.((https://www.victronenergy.com/upload/documents/Datasheet-SmartShunt-EN.pdf))
 Both setups can provide voltage, current, and temperature information to the app or directly to other Victron gear like solar charge controllers.((the Orion-TR is a notable and much-lamented exception))
+  * YT:  [[https://www.youtube.com/watch?v=yMJ_vzB2avE|Sync settings for Lithium battteries - BMV-712 Smart]]
 ==== Bogart Trimetric ====
@@ Line 107: / Line 122: @@
 By default the backlight is ON when  discharging and FLASHING((slow pulsing)) when charging.  The backlight can be toggled OFF/ON by holding the LEFT+RIGHT buttons at the same time. With the backlight disable charge vs discharge is still displayed by small icons on the left side of the display.
+== quirks ==
+The decimal point is small and moves as numbers increase.  Examples:
+  * 1**.**234A (also 0.123A)
+  * 12**.**34A
+  * 123**.**4A
 === Renogy ===
@@ Line 117: / Line 141: @@
 === other examples ===
-[[https://amzn.to/2BO0Eto|{{https://images-na.ssl-images-amazon.com/images/I/41ZuQEfExvL._SY90_.jpg }}]]For folks who are [dis]charging at 50A/75A, a cheaper shunt is available for 1/5th the price of a Bogart.
+[[https://amzn.to/2BO0Eto|{{https://images-na.ssl-images-amazon.com/images/I/41ZuQEfExvL._SY90_.jpg }}]]For folks who are [dis]charging at lower currents like 50A/75A, even cheaper shunts are available.
 Heavier-duty shunts are available (up to [[https://amzn.to/2XBeDiN|at least 350A]]).

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