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electrical:solar:charge_controller [2023/09/06 12:05] frater_secessus [MPPT] |
electrical:solar:charge_controller [2023/09/10 13:50] frater_secessus [present use] |
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[[https://diysolarforum.com/threads/why-is-mppt-better-than-pwm.24892/post-295861|For technical reasons]] PWM can deliver more current than the panels' Imp, even nearing Isc. | [[https://diysolarforum.com/threads/why-is-mppt-better-than-pwm.24892/post-295861|For technical reasons]] PWM can deliver more current than the panels' Imp, even nearing Isc. |
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| === panel selection for PWM === |
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| PWM makes the most power when coupled with panels whose operating [[electrical:solar:panels#specifications|Vmp]] is very close to the controller's Absorption ("boost") voltage [[electrical:solar:charge_controller_setpoints|setpoint]]. Since [[electrical:solar:output#panel_temperature|ambient temperatures affect operating Vmp]] the panel's Vmp spec on the label should be about 10% higher than Absorption voltage. |
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| Examples: |
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| * 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. |
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| Some [[electrical:solar:panels#thin_film|thin-film]] panels have Vmp in that range but most panels are much higher. So we find the lowest Vmp practical. 17Vmp panels would perform better on PWM than 18v or 19v. |
==== MPPT ==== | ==== MPPT ==== |
[[http://amzn.to/2iD3WKf|{{ https://images-na.ssl-images-amazon.com/images/I/51bi9IjcsRL._AC_US160_.jpg}}]] | [[http://amzn.to/2iD3WKf|{{ https://images-na.ssl-images-amazon.com/images/I/51bi9IjcsRL._AC_US160_.jpg}}]] |
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There are some considerations when [[electrical:solar:mppt design|designing a system around an MPPT controller]]. | There are some considerations when [[electrical:solar:mppt design|designing a system around an MPPT controller]]. |
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| == panel selection for MPPT == |
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| MPPT thrives on voltage. In general, we should select panels that have the highest-practical Vmp while staying safely under the controller's voltage input limit. MPPT efficiency tends to be greatest when panel voltage is ~twice the charging voltage. The exact ratio varies by controller so read the docs for specifics. |
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| Note that [[electrical:solar:series_vs_parallel|panels can be run in series]] to increase their voltage. |
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== when PWM beats MPPT == | == when PWM beats MPPT == |
==== present use ==== | ==== present use ==== |
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In practice the LOAD terminals typically are either ignored((some well-respected controllers don't have them anymore)) or used as [[electrical:12v:lvd|low voltage disconnects]] power relays (see below). | In practice the LOAD terminals typically are either ignored((some well-respected controllers don't have them anymore)) or used as [[electrical:12v:lvd|low voltage disconnects]] power relays. You can define Low Voltage Disconnect (LVD) and Low Voltage Reconnect (LVR) [[electrical:solar:charge_controller_setpoints|setpoints]] to protect the battery from excessive discharge. |
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One benefit to doing this is you can define a [[electrical:12v:lvd|Low Voltage Disconnect]] (LVD) setpoint and Low Voltage Reconnect to protect the battery from excessive discharge: | |
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==== why loads aren't powered from LOAD terminals ==== | ==== why loads aren't powered from LOAD terminals ==== |