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electrical:solar:status [2022/02/27 13:38]
frater_secessus [evening]
electrical:solar:status [2024/01/14 15:32] (current)
frater_secessus [setups with no float]
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-This page is to help solar beginners tell what their system is doing without special equipment.  The info here is oriented to typical 12v systems with lead-acid battery banks.  Folks running other battery chemistries or nominal voltages are assumed to already know what they're doing.  :-)+This page is to help solar beginners tell what their system is doing without special equipment.  A [[electrical:12v:battery_monitor|battery monitor]] can be extremely useful but we can tell a great deal without it.  The info here is oriented to typical 12v systems with lead-acid battery banks.  Folks running other battery chemistries or nominal voltages are assumed to already know what they're doing.  :-)
  
 ===== numbers rather than icons or lights ===== ===== numbers rather than icons or lights =====
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 ===== first collect a few numbers ===== ===== first collect a few numbers =====
 To tell at a glance what your system is doing you need to find a couple pieces of info about your system.  You will only have to look them up once;  it might be worthwhile to write them down on a sticky note near your solar gear. To tell at a glance what your system is doing you need to find a couple pieces of info about your system.  You will only have to look them up once;  it might be worthwhile to write them down on a sticky note near your solar gear.
 +
 +
 +{{ https://www.researchgate.net/profile/Kanaga-Gnana/publication/237049790/figure/fig3/AS:299465748566018@1448409606696/Characteristic-Curve-of-The-Solar-Panel.png?125}}
 +
 +==== panel specs ====
 +
 +The [[electrical:solar:panels#specifications|specs]] we are interested in are:
 +
 +  * **Vmp**, the voltage at which the panel makes max power under laboratory conditions((likely lower in reality))
 +  * **Voc**, the highest voltage the panel will put out under normal cirumstances.  At Voc the panel produces no current and therefore no power (Voc x 0A = 0W)
 +  * when in use, **Vpanel** is the panel voltage reported by the controller.  PWM controllers might not report this value.    
 +
 +On the curve pictured at the right Vmp is at the peak of the red voltage line, and Voc is on the far right where output crashes to 0W.  
 +
 +
 +==== controller ====
 + 
  
   * **Vabs** - the charge controller's Absorption [[electrical:solar:charge_controller_setpoints|setpoint]], hopefully tweaked to your battery manufacturer's [[electrical:12v:charging|charging]] recommendation.  Note:  EpEver and Renogy controllers often refer to Absorption as //Boost//.   * **Vabs** - the charge controller's Absorption [[electrical:solar:charge_controller_setpoints|setpoint]], hopefully tweaked to your battery manufacturer's [[electrical:12v:charging|charging]] recommendation.  Note:  EpEver and Renogy controllers often refer to Absorption as //Boost//.
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-**During [[electrical:12v:charging#absorption#absorption_stage|Absorption]] charging** lead-acid batteries will need less and less current.+**During [[electrical:12v:charging#absorption#absorption_stage|Absorption]] charging** batteries will need less and less current.
  
 **with MPPT controllers** **with MPPT controllers**
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 **with PWM controllers** **with PWM controllers**
-  * Vpanel & Vbattery == Vabs until the controller'criteria for ending absorption is met+  * Vpanel starts to creep up from Vbatt toward Voc (the more OFF((open circuit)) switching the closer to Voc) criteria for ending absorption is met
   * Controller output decreasing as current demand drops.   * Controller output decreasing as current demand drops.
   * the controller may get warmer as current demand drops((percentage of time the PWM circuit is turned OFF increases))   * the controller may get warmer as current demand drops((percentage of time the PWM circuit is turned OFF increases))
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 ==== transitioning to float ==== ==== transitioning to float ====
  
-When transitioning from Absorption to Float the voltage needs to drop about a volt.  The system will "free-fall" (make little or no power) to allow the voltage to fall.((with MPPT controllers you may see Vpanel go quite close to Voc))   The transition may take seconds or minutes, depending on how/if the system is loaded.+When transitioning from Absorption to Float the voltage needs to drop about a volt.  The system will "free-fall" (make little or no power) to allow the voltage to fall.((with MPPT controllers you may see Vpanel go quite close to Voc))   The transition may take seconds or minutes, depending battery chemistry and  how/if the system is loaded.
  
   * Vbatt starts at Vabs   * Vbatt starts at Vabs
-  * power harvest is cut off or greatly curtailed +  * power harvest is cut off or greatly curtailed (Vpanel spikes toward Voc) 
-  * vbatt drops to Vfloat  +  * Vbatt drops to Vfloat  
-  * when voltage reaches Vfloat the system will start making power to hold //that// setpoint.+  * when Vbatt reaches Vfloat the system will start making power to hold //that// setpoint. 
 + 
 +==== setups with no float ==== 
 + 
 +Configurations with no float ("charge and stop", found on some Lithium profiles) will  
 + 
 +  - charge to the Absorption ("boost") setpoint((with or without some amount of Absorption duration)) 
 +  - **stop charging** 
 +  - until voltage falls to the rebulk ("reboost", "boost return voltage") setpoint 
 +  - repeat 
 + 
 +The fall to reBulk looks like the transition to Vfloat [[electrical:solar:status#transitioning_to_float|described above]]. In both cases the controller makes no (or practically no) power until the lower setpoint is reached.  
 + 
 +A constant cycling 14.4v->13.2v->14.4v might seem extreme but in practice there is little actual cycling occurring.  A fully-charged 4S LFP with no loads will rest somewhere around **13.6v**. So for actual SoC changes we are talking about the difference between 13.6v and 13.2v.  With significant loads applied 13.2v observed could mean SoC as high as 90% and with trivial loads as low as 70%.((with trivial loads there might be only 1 cycle a day since voltage would not fall to reBoost))  In normal use the real cycling might be 100%->85%-100% and the solar is helping carry the loads during charging periods.   
 + 
 + 
 +=== Renogy confusion === 
 + 
 +By default Renogy Li profiles work this way, and cause much concern for Renogy users who have not read their manuals and/or who are not familiar with how solar charge controllers / chargers work. [The required information is present [[https://www.renogy.com/support/downloads|in the manuals]] but Renogy really should spell it out for first-timers. -- secessus] 
 + 
 +  * **Rover series** - the table on page 37 of [[https://www.renogy.com/content/RNG-CTRL-RVR40/RVR203040-Manual.pdf|the manual]] shows there is no boost duration and no float in the Li profile.  The "boost return voltage" field shows **13.2v**.  
 +  * **DC-DC/MPPT combo charger** - the table on page 2 of [[https://www.renogy.com/content/RBC3050D1S-G1/RBC3050D1S-Manual.pdf|the manual]] shows there is no boost duration and no float in the Li profile.  The "boost return voltage" field shows **13.2v**.  
 +  * **DC-DC charger** (20A/40A/60A)  
 +    * page 18 says "lithium batteries will only have an absorption charge and no float charge" 
 +    * there is no setting for Float charge, as shown in the table on page 17 of [[https://www.renogy.com/content/RNG-DCC1212-60-BC/DCC1212-204060-Manual.pdf|the manual]] and it says "for lithium... there will not be a float voltage" 
 +    * page 18 says that Float is for lead only 
 +    * the manual does not state the 13.2v boost return setpoint [an egregious error - secessus] 
 + 
 +Users uncomfortable with this behavior can set up the USER profile to meet their needs, including defining [[electrical:12v:drop-in_lifepo4#mythyou_shouldn_t_float_lithium|a quasi-Float setpoint]].((low temp charging cutoff, when available, may only be available in canned Li profiles))
  
  
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 **During Float with PWM**  **During Float with PWM** 
-  * Vpanel & Vbatt == Vfloat+  * Vpanel closer to Voc (PWM switching panel OFF((open circuit)) most of the time) 
   * controller output minimal((assuming no loads))   * controller output minimal((assuming no loads))
   * **Example:**  Panel and battery voltage holding at Vfloat == 13.8v, controller output < 1A.   * **Example:**  Panel and battery voltage holding at Vfloat == 13.8v, controller output < 1A.
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 +===== sudden voltage spikes =====
 +
 +If you are seeing sudden voltage spikes and have lithium batteries, you may be seeing [[opinion:frater_secessus:lifepo4_charging_voltage|the BMS disconnect the charging circuit]].  When this happens the controller suddenly finds itself making too much power (the charging demand suddenly disappeared);  voltage on the rest of the circuit will spike while the controller reacts to the new demand level. 
 +
 +The fix, described in the link above, is to **charge at a lower voltage** that does not antagonize the cells and trip the BMS. 
 +
 +
 +===== MPPT tracking sweeps =====
  
 +{{ https://img.mousetrap.net/2023/Screenshot_20230208-095220.jpg?150}}
 +An **MPPT** controller must sweep the **P**ower **P**oints along the array voltage curve in order to **T**rack the **M**aximum (and non-maxiumum) power points.  Basically the controller is asking "How much power does it make //here// on the curve?  And //here//?  And over //here//?"  It tracks (remembers) these power points and can return to them as needed.  But solar conditions are always changing so the power point data can get stale quickly and the controller has look again from time to time. 
  
 +Depending on the algorithm the sweep may a small one near presentVpanel, it may be a full sweep from 0v-[[electrical:solar:panels#specifications|Voc]], or anything in between.  It may happen often or seldom.  Victron famously makes a sweep every 10 minutes, resulting in visible dips in the app's graphs (see orange line on image at right). 
  
 +The sweep will interfere with power production so the mfg attempts to find a balance between
  
 +  * constant production, and
 +  * learning whether or not one is operating at the optimal power point for present conditions
  
  
electrical/solar/status.1645987118.txt.gz · Last modified: 2022/02/27 13:38 by frater_secessus