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electrical:solar:charge_controller [2023/09/06 12:05] frater_secessus [MPPT] |
electrical:solar:charge_controller [2024/04/16 20:28] frater_secessus [specs] |
Regardless of type, controllers will have several specifications in common. | Regardless of type, controllers will have several specifications in common. |
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* **rating (or "size")** - this is usually the maximum output the controller can produce (charging + loads).((for technical reasons with PWM this will also be the *input* current limit)) | * **rating (or "size")** - this is usually the maximum output in A (amps) the controller can produce (charging + loads).((for technical reasons with PWM this will also be the *input* current limit)) |
* **12v/24v/48v** - this refers to the nominal voltage of the battery bank it will be charging. | * **12v/24v/48v** - this refers to the nominal voltage of the battery bank it will be charging. |
* **Maximum input voltage** - the highest voltage the controller should //ever// see from the solar array.((it is common to leave ~20% margin)) NOTE: a 50v input max does //not// mean a PWM controller can make efficient use of mismatched panel/battery voltages; that requires MPPT. See [[#how_to_choose|how to choose]] below. | * **Maximum input voltage** - the highest voltage the controller should //ever// see from the solar array.((it is common to leave ~20% margin)) NOTE: a 50v input max does //not// mean a PWM controller can make efficient use of mismatched panel/battery voltages; that requires MPPT. See [[#how_to_choose|how to choose]] below. |
| * **Minimum input voltage** - a PWM controller will requires panel voltage ≥ battery voltage to charge. MPPT controllers will usually require a bit more voltage headroom to start/run the MPPT algorithm.((although less common, //boosting// MPPT do exist that can increase incoming voltage in order to charge a higher-voltage battery bank)) |
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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 == |
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* | |
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The PWM advantage is | |
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[note: this is a placeholder for a possible new entry.] | [note: this is a placeholder for a possible new entry.] |
There are //DC-DC converting charge controllers// (DDCCC) appearing on the market that claim to be MPPT but do not actually track power points (maximum or otherwise). They do downconvert some excess voltage into amperage. See [[https://boondockplan.wordpress.com/2017/12/15/backchannel-dc-dc-converting-charge-controllers/|this blog post]]. | There are //DC-DC converting charge controllers// (DDCCC) appearing on the market that claim to be MPPT but do not actually track power points (maximum or otherwise). They do downconvert some excess voltage into amperage. See [[https://boondockplan.wordpress.com/2017/12/15/backchannel-dc-dc-converting-charge-controllers/|this blog post]]. |
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| ==== boosting ==== |
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| Most charge controllers that convert voltage do it by //bucking// (reducing) panel voltage down to the appropriate charging voltages.((normal PWM don't reduce/convert voltage in the normal sense; they run the panels ~at bank voltage)) |
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| //Boosting// (voltage-increasing) controllers do exist ([[https://amzn.to/3Rh6QSu|example]]) but they are niche products. In most cases it makes more sense to increase panel voltage with serial wiring. |
==== 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, 20A, 40A, etc)) | **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, 20A, 40A, etc)) |
**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://mouse.mousetrap.net/blog/2021-07-09-solar-back-online-.html#pwm-spare-saved-my-bacon|one really can use higher-voltage panels with PWM and 12v banks]] -- they just end up running at about half power. | * using panels with nominal voltages higher than the battery bank voltage, like 24v panels with a 12v bank. To be fair, [[http://mouse.mousetrap.net/blog/2021-07-09-solar-back-online-.html#pwm-spare-saved-my-bacon|one really can use higher-voltage panels with PWM and 12v banks]] -- they just end up running at about half power. [[https://www.youtube.com/watch?v=V2b7z2eTb5o|Demonstration video from AltE]]. |
* 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:solar:pwm_tweaking|PWM Vbatt hobbling]] | * daytime loads are hampered by [[electrical:solar:pwm_tweaking|PWM Vbatt hobbling]] |
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See also [[electrical:solar:shunt_tweaking|shunt tweaking]]. | See also [[electrical:solar:shunt_tweaking|shunt tweaking]]. |
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| ==== should I upgrade my PWM to MPPT? ==== |
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| If the system has changed and now MPPT is required for one of the reason above, then yes. |
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| But most people consider this switch to make "more power", forgetting that **solar only makes power when it is demanded**.((for loads or charging)) //If you are presently consuming every watt the system can make// then, yes, replacing PWM with MPPT will likely increase your harvest by ~15%. If you aren't hammering the system then +15% is immaterial; there is no difference in the performance of a 150mph car and a 165mph car in a school zone. |
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| So the questions are: |
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| - 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%? |
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| There is a saying in solar circles that "adding another panel is a better deal than upgrading from PWM to MPPT." This may or may not be true in your particular use case. |
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===== multiple charge controllers ===== | ===== multiple charge controllers ===== |
==== 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 disconnect]] 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 ==== |