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--- opinion:solar:sizing.walkthrough [2022/04/20 14:17]
frater_secessus [where and when we are camping]
+++ opinion:solar:sizing.walkthrough [2022/04/20 14:51]
frater_secessus [minimum charging current]
@@ Line 96: / Line 96: @@
 ,168Wh / 12.0v nominal voltage = **347Ah** of lead-chemistry required.
+Also see the [[opinion:solar:sizing.walkthrough#minimum_charging_current|section on minimum charging current]] below.
 ==== lithium ====
@@ Line 144: / Line 144: @@
   * **Kansas in December** - 2,316Wh((daily charging requirement)) / 1.75 FSE / 0.85 system efficiency = **1,557w of panel** (!!)
-==== minimum charging current ====
-Lead-chemistry batteries have minimum and maximum charging current specifications.  Going over the max is rarely a concernt with solar-only charging but failure to meet minimums is a real issue.
-Lead acid typically require a minimum of [[electrical:12v:battery_capacity|C/10]] charging current to stay healthy. This would be
+===== charge controllers =====
+PWM controllers are often sized thusly:  rated panel wattage / 10 = charge controller rating in Amps. \\
+Example:  400w / 10 = **40A PWM controller**.  They are inexpensive enough that a bit of oversize is no big deal.
+MPPT controllers are more expensive so they often sized to the average solar harvest wattage rather than rated panel wattage.  A rule of thumb might be rated panel wattage x system efficiency / nominal battery bank voltage.  \\
+Example:  423w((Montana figure)) x 0.85 / 12.0v lead battery = **29.96A controller, rounded to 30A**.
+==== minimum charging current ====
+Note:  if your offgrid system will use lead-chemistry batteries and needs to last for years then read this section.  If you are a [[https://mouse.mousetrap.net/blog/2020/07/04/agm-for-weekenders/|weekend camper]], use lithium, or only plan to keep the rig a couple years this section will not apply.
+Lead-chemistry batteries have minimum and maximum charging current specifications.  Going over the max is rarely a concern with solar-only charging but failure to meet minimums is [[electrical:batterycide|a real issue]].
-Lithium batteries do not require any minimum charging
+Lead acid battteries typically require a minimum of [[electrical:12v:battery_capacity|C/10]] charging current regularly to stay healthy. This would be **34.7A** for a 347Ah AGM bank (347 / 10 = 34.7).((some high-end AGM like Odyssey require C/2, or 174A for a 347Ah bank!  Not practical from solar alone.))  Note that even our strong Montana numbers above only hit **~30A**.  We could:
-===== charge controllers =====
-PWM controllers are often sized thusly:  rated panel wattage / 10 = charge controller rating in Amps. \\
-Example:  400w / 10 = **40A PWM controller**.  They are inexpensive enough that a bit of oversize is no big deal.
-MPPT controllers are more expensive so they often sized to the average solar harvest wattage rather than rated panel wattage.  A rule of thumb might be rated panel wattage x system efficiency / nominal battery bank voltage.  \\
-Example:  400w x 0.85 / 12.0v lead battery = **28.3A controller, rounded to 30A** because no one makes a 28.3A controller.
+  * increase our panel and controller to cover it.  34.7A x 12v nominal / 0.85 system efficiency = 490w and a 40A controller.((this is //only// about charging current, not the panel required to charge the batteries fully over time)) A pleasant side effect is the system would make more power (+16%) than we strictly need for charging, so we might be a little looser with power use.  Or might do a little better under adverse solar conditions. and/or,
+  * add alternator charging or other high-current source (see below) and let that system vigorously massage the batteries from time to time.
+Lithium batteries do not have a minimum charging current spec in the normal sense.

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