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electrical:solar:charge_controller [2023/08/31 01:08] princess_fluffypants [TLDR] |
electrical:solar:charge_controller [2024/06/01 21:58] frater_secessus [sensors] |
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Cautionary example: | Cautionary example: | ||
+ | ==== sensors ==== | ||
+ | |||
+ | To charge correctly the controller needs to know the precise voltage and temperature of the battery bank. | ||
+ | In the best case scenario these measurements are done with an external **temp sensor** and **voltage sense**((not a typo, it's called voltage sense)) that plug into the controller or talk to the controller via bluetooth. | ||
+ | |||
+ | In the absence of external sensors the controller tries to use any internal sensors it might have. The values will be inaccurate: | ||
+ | |||
+ | * battery voltage will read [[electrical: | ||
+ | * temperature will read high because of the controller' | ||
+ | |||
+ | With lead-chemistry batteries both conditions cause [[electrical: | ||
+ | |||
+ | |||
+ | |||
+ | |||
===== specs ===== | ===== specs ===== | ||
Regardless of type, controllers will have several specifications in common. | Regardless of type, controllers will have several specifications in common. | ||
- | * **rating (or " | + | * **rating (or " |
* **12v/ | * **12v/ | ||
* **Maximum input voltage** - the highest voltage the controller should //ever// see from the solar array.((it is common to leave ~20% margin)) | * **Maximum input voltage** - the highest voltage the controller should //ever// see from the solar array.((it is common to leave ~20% margin)) | ||
+ | * **Minimum input voltage** - a PWM controller will requires panel voltage ≥ battery voltage to charge. | ||
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[[https:// | [[https:// | ||
+ | |||
+ | === panel selection for PWM === | ||
+ | |||
+ | PWM makes the most power when coupled with panels whose operating [[electrical: | ||
+ | |||
+ | Examples: | ||
+ | |||
+ | * 16.28v Vmp panel spec would be optimal for 14.8v Absorption, as we might use for flooded lead acid. 14.8v x 1.1 = 16.28v. | ||
+ | * 15.62v Vmp panel spec would be optimal for 14.2v Absorption, as we might use for Gel or LiFePO4. | ||
+ | |||
+ | |||
+ | Some [[electrical: | ||
==== MPPT ==== | ==== MPPT ==== | ||
[[http:// | [[http:// | ||
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This ability to decouple panel and bank voltage can result in 10%-30% more power harvested from 12v nominal panels than with a PWM controller, depending on conditions. | This ability to decouple panel and bank voltage can result in 10%-30% more power harvested from 12v nominal panels than with a PWM controller, depending on conditions. | ||
+ | |||
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There are some considerations when [[electrical: | There are some considerations when [[electrical: | ||
+ | |||
+ | == panel selection for MPPT == | ||
+ | |||
+ | MPPT thrives on voltage. | ||
+ | |||
+ | Note that [[electrical: | ||
+ | |||
+ | |||
+ | == when PWM beats MPPT == | ||
+ | |||
+ | There are edge cases where an optimal PWM setup can make //more// power than MPPT for a time. This can happen because MPPT has DC-DC losses that PWM does not, typically ~5%. Since MPPT harvest from the panel is typically 10-30% greater than PWM the DC-DC losses are hidden. | ||
+ | |||
+ | But when PWM controllers and panels are optimally matched (difference between panel Vmp((actual, | ||
+ | |||
+ | |||
+ | |||
+ | |||
+ | |||
+ | |||
==== shunt ==== | ==== shunt ==== | ||
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[note: | [note: | ||
There are //DC-DC converting charge controllers// | There are //DC-DC converting charge controllers// | ||
+ | |||
+ | |||
+ | ==== boosting ==== | ||
+ | |||
+ | Most charge controllers that convert voltage do it by //bucking// (reducing) panel voltage down to the appropriate charging voltages.((normal PWM don't reduce/ | ||
+ | |||
+ | // | ||
==== how to choose ==== | ==== how to choose ==== | ||
**PWM is a reasonable default choice** in typical scenarios((12v house power, 12v panels)); they work well enough and are inexpensive. PWM controllers can cost half or a third of their MPPT workmates for any given rated output.((10A, | **PWM is a reasonable default choice** in typical scenarios((12v house power, 12v panels)); they work well enough and are inexpensive. PWM controllers can cost half or a third of their MPPT workmates for any given rated output.((10A, | ||
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**MPPT is effectively required** when: | **MPPT is effectively required** when: | ||
* when one needs to squeeze every watt out of the panel | * when one needs to squeeze every watt out of the panel | ||
- | * using panels with nominal voltages higher than the battery bank voltage, like 24v panels with a 12v bank. To be fair, [[http:// | + | * using panels with nominal voltages higher than the battery bank voltage, like 24v panels with a 12v bank. To be fair, [[http:// |
* space available for panels is limited, as on a sailboat or small vehicle | * space available for panels is limited, as on a sailboat or small vehicle | ||
* daytime loads are hampered by [[electrical: | * daytime loads are hampered by [[electrical: | ||
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See also [[electrical: | See also [[electrical: | ||
+ | |||
+ | ==== should I upgrade my PWM to MPPT? ==== | ||
+ | |||
+ | If the system has changed and now MPPT is required for one of the reason above, then yes. | ||
+ | |||
+ | But most people consider this switch to make "more power", | ||
+ | |||
+ | So the questions are: | ||
+ | |||
+ | - do you need more power than you are getting now? | ||
+ | - would +15% be enough to meet your needs | ||
+ | - if so, would you pay [whatever the MPPT costs] to get that +15%? | ||
+ | |||
+ | There is a saying in solar circles that " | ||
===== multiple charge controllers | ===== multiple charge controllers | ||
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==== present use ==== | ==== present use ==== | ||
- | In practice the LOAD terminals typically are either ignored((some well-respected controllers don't have them anymore)) or used as [[electrical: | + | In practice the LOAD terminals typically are either ignored((some well-respected controllers don't have them anymore)) or used as [[electrical: |
- | + | ||
- | One benefit to doing this is you can define | + | |
==== why loads aren't powered from LOAD terminals ==== | ==== why loads aren't powered from LOAD terminals ==== |