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electrical:solar:charge_controller [2019/09/28 17:23] frater_secessus [sizing your charge controller] |
electrical:solar:charge_controller [2020/05/25 11:53] frater_secessus [how to choose] |
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]]. |
==== how to choose ==== | ==== how to choose ==== |
**PWM is the default choice** in most situations because they get the job done in most scenarios 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 the default choice** in most situations((12v house power, 12v panels)) because 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)) |
If more power is needed (and there is physical space) additional PV can be added to match the charging output of an MPPT charger, often at a lower cost. [There are no prizes for fanciest or most expensive charge controller! Do what is best for you -- frater secessus] | If more power is needed (and there is physical space) additional PV can be added to match the charging output of an MPPT charger, often at a lower cost. [There are no prizes for fanciest or most expensive charge controller! Do what is best for you -- frater secessus] |
MPPT controllers also tend to consume more power to run themselves than PWM models due to additional processing and electronic components. | |
| |
**MPPT may be a better fit** when: | There are also edge cases((low altitude, high temperature, Absorption)) where PWM can actually make more power than MPPT on poly [[electrical:solar:panels|panels]] during Absorption stage in very hot weather, due to MPPT DC-DC conversion losses and [[electrical:solar:output#panel_temperature|temperature derating]]. |
* battery banks are cycled deeply on a regular basis so more time is spent in Bulk | |
* nominal 12v panels have a relatively high Vmp (>=18v) for [[https://www.reddit.com/r/vandwellers/comments/bmlosu/is_vandwelling_a_frugal_lifestyle/emz5lsf/?context=1|reasons discussed here]]. | |
* [[https://www.wholesalesolar.com/solar-information/sun-hours-us-map|areas of low insolation]] | |
* high latitudes | |
* overcast or rainy weather | |
* if the camper will be used in areas of partial shade((http://forum.solar-electric.com/discussion/comment/250936#Comment_250936)) | |
* canyon or "urban canyon" areas | |
* forested areas | |
* if temperatures are very low (greater harvest) | |
* the increase in cost is not an undue burden | |
**MPPT is effectively required** when: | **MPPT is effectively required** when: |
* using panels with nominal voltages higher than 12v | * using panels with nominal voltages higher than 12v ((more prescisely, when panel nominal voltage exceeds house bank nominal voltage)) |
* 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 |
* [[#overpaneling|overpaneling]] | * [[#overpaneling|overpaneling]] |
We say "effectively required" because one //can// use 24v panels with PWM and 12v banks -- it just doesn't work very well. The 24v panels will be run at 12v voltages, yielding about half the power you would get with MPPT. | We say "effectively required" because one //can// use 24v panels with PWM and 12v banks -- it just doesn't work very well. The 24v panels will be run at 12v voltages, yielding about half the power you would get with MPPT. |
**Shunt controllers are useful for [[electrical:solar:shallow_cycling|shallow-cycling configurations]]** or for battery chemistries that are not damaged by [[electrical:depth_of_discharge|partial state of charge (PSoC)]]. Their relative inexpense makes them useful for even very small systems and test configurations. | **Shunt controllers are useful for [[electrical:solar:shallow_cycling|shallow-cycling configurations]]** or for battery chemistries that are not damaged by [[electrical:depth_of_discharge|partial state of charge (PSoC)]]. Their relative inexpense makes them useful for even very small systems and test configurations. |
Their simple ON and OFF setpoints may also make them useful for charging [[electrical:12v:lifepo4_batteries_thread|lithium]] chemistries. | Their simple ON and OFF setpoints may also make them useful for charging [[electrical:12v:deep_cycle_battery#lithium_chemistries|lithium]] chemistries. |
Further reading: | Further reading: |
[[https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf|an excellent and readable whitepaper by Victron]] (PDF). | [[https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf|an excellent and readable whitepaper by Victron]] (PDF). |
| |
| **MPPT may be a better fit** when: |
| |
| * the existing PWM system is not providing enough output |
| * battery banks are cycled deeply on a regular basis so more time is spent at low Vbatt where PWM struggles. |
| * nominal 12v panels have a relatively high Vmp (>=18v) for [[https://www.reddit.com/r/vandwellers/comments/bmlosu/is_vandwelling_a_frugal_lifestyle/emz5lsf/?context=1|reasons discussed here]]. |
| * if multiple panels will be used in areas of [[electrical:solar:shading|partial shade]] |
| * if temperatures are very low (rising Vmp means increasing output which PWM could not capture) |
| * the increase in cost is not an undue burden |
| |
===== multiple charge controllers ===== | ===== multiple charge controllers ===== |
[[electrical:12v:multipoint_charging|Multiple controllers (with separate arrays) can be used to charge a common bank]]. The controllers should be configured with similar charging setpoints for the greatest efficiency.((http://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/)) | [[electrical:12v:multipoint_charging|Multiple controllers (with separate arrays) can be used to charge a common bank]]. The controllers should be configured with similar charging setpoints for the greatest efficiency.((http://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/)) |