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--- electrical:solar:pwm_tweaking [2019/05/09 21:09]
frater_secessus [battery: maintain a higher state of charge]
+++ electrical:solar:pwm_tweaking [2022/10/12 13:30]
frater_secessus [PWM's achilles heel]
@@ Line 7: / Line 7: @@
-===== the controller's achilles heel =====
+===== PWM's achilles heel =====
-During charging with a PWM controller **the solar panel will be running at the voltage of the battery bank**.  Unfortunately, this is almost never the voltage at which the panel makes its rated power (Vmp).  The panel will make less and less power when battery voltage is low.
+During charging with a PWM controller **the solar panel will be running at the voltage of the battery bank**.((or close enough for the purposes of this discussion.  Specifically, the panel will be ~Vbatt when the controller is pulsing ON.  Vpanel will be closer to Voc when the pulse is OFF because the panel is Open Circuit (unloaded) at that time.))  Unfortunately, this is almost never the voltage at which the panel makes its rated power (Vmp).  The panel will make less and less power when battery voltage is low.
 This affects charging in all three [[electrical:12v:charging|charging stages]] but it is devastating in [[electrical:12v:charging#bulk_stage|Bulk]].  Let's do some math to see why.((temperature derating is not considered))
@@ Line 46: / Line 46: @@
 Since the panels make more power at higher voltages((up to Vmp)) cranking up Vabs and Vfloat to higher-but-still-sane levels will result in more power being harvested.
+Using the above panel as an example, Vabs of 14.7v will yield 3.5% more power than a Vabs of 14.1v.  Vfloat of 13.8v will yield 4.5% more power than a Vfloat of 13.2v. \\
+Note:  consult the battery manufacturer's recommendations for the actual maximum voltages.  Controller presets often are set too low by the factory since they don't know what battery you will use it with. Better safe than sorry, say their lawyers.
+DO invest in the $10 temperature probe option.
 ==== battery: maintain a higher state of charge ====

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