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--- electrical:12v:voltage_sag [2024/03/10 17:58]
frater_secessus [voltage sense wire] fixed link
+++ electrical:12v:voltage_sag [2025/11/08 16:32] (current)
frater_secessus [TL;DR]
@@ Line 1: / Line 1: @@
 ====== Voltage sag ======
+===== TL;DR =====
+  * resistance in the circuit causes apparent voltage to **sag when discharging**
+  * likewise, resistance causes apparent voltage to **rise when charging**
+  * some sag/rise is normal. Circuits with excess resistance (undersized wiring, iffy connections) can cause apparent voltage to deviate enough to affect system performance
+  * voltage sensing can correct for sag/rise (within limits)
+  * [[https://www.bluesea.com/resources/1437|Blue Sea's documentation]] provides guidance on designing circuits with acceptable levels of voltage sag.
+  * sag is a function of [[https://en.wikipedia.org/wiki/Ohm%27s_law|Ohm's Law]]((in ''V=IxR'' form))
+[[opinion:frater_secessus:pareto|about these summaries]]
+===== overview =====
 [Note:  this article is written from the standpoint of the [[electrical:solar:charge_controller|solar charge controller]].  It affects all circuits to some degree and is not limited to solar. -- secessus]
@@ Line 47: / Line 63: @@
 A voltage sense wire is a separate wiring circuit running from the battery bank to the controller's voltage sense terminals (if so equipped).
-Since the circuit isn't carrying any real current there will be very little sag and even quite thin wires can be used to get an accurate voltage reading.  The controller will then adjust output voltage to put the desired setpoint voltage into the bank.
+Since the circuit isn't carrying any real current there will be very little sag and even quite thin wires can be used to get an accurate voltage reading.  The controller will then adjust output voltage((up to some max, like +1v or +2v)) to put the desired setpoint voltage into the bank.
 Example:  The absorption setpoint (Vabs) is 14.0.  The sensed battery voltage is only 13.8v, so the controller actually puts out 14.2v.((or whatever it takes to get 14.0v at the battery))
@@ Line 59: / Line 75: @@
 Some controllers use networked [[electrical:12v:battery_monitor|battery monitors]] to report back what the battery voltage is in reality.
-Example:  [[https://amzn.to/3tiqlhu|Victron Lynx shunt]].  [[https://amzn.to/3qbfcNJ|Victron VEbus smart dongle]].  [[https://amzn.to/3ijF6u9|Victron BMV-712]].
+Examples:
+  * [[https://amzn.to/3tiqlhu|Victron Lynx shunt]]
+  * [[https://amzn.to/3qbfcNJ|Victron VEbus smart dongle]]
+  * [[https://amzn.to/3ijF6u9|Victron BMV-712]].
@@ Line 72: / Line 92: @@
+===== voltage rise =====
+Voltage "rise" is the flipside of voltage sag;  it happens while charging rather than discharging.  The mechanism is the same.

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