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electrical:12v:multipoint_charging [2017/10/07 11:21]
frater_secessus [why one sources wins]
electrical:12v:multipoint_charging [2022/08/21 13:53] (current)
frater_secessus [gotchas]
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 +[[lifestyle:words_of_wisdom|Words of Wisdom]]:  "Think of the batteries as a bucket of electricity. It's possible to pour water from multiple sources into a bucket at the same time, and also to do that while water is leaking out of the bucket." -- MarkSF((https://www.cruisersforum.com/forums/f14/multiple-sources-of-dc-voltage-being-fed-to-battery-bank-246008.html#post3335865))
 +
 ====== Charging from multiple sources ====== ====== Charging from multiple sources ======
  
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 ===== concurrent charging ===== ===== concurrent charging =====
  
-So what happens when multiple chargers are running at the same time?  Nothing dramatic, as it turns out.  +So what happens when multiple chargers are running at the same time?  Nothing dramatic, as it turns out.((The only caveat, for advanced users, is if one of your controller uses end-amps to signal the end of Absorption, it may [[http://forum.solar-electric.com/discussion/comment/389634#Comment_389634|get confused and drop out early]].  Also see these potential [[electrical:12v:alternator#gotchas|isolator gotchas]].))  In general, **the charging source with the highest voltage [[electrical:solar:charge_controller_setpoints|setpoint]] will "win"**.
  
-In general, **the charging source with the highest voltage will win**.  +Exception:  some commercial products integrate charging from multiple sources into a single unit so there is no "competition" See [[electrical:12v:b2b#examples_-_combo_with_solar_charge_controller|Combination DC-DC chargers]]. 
 +==== why one source wins ==== 
 +Most charging involves holding((or trying to reach)) a particular voltage [[electrical:12v:electrical_notation|setpoint]].((current-terminated Absorption excepted for purposes of this discussion))  If a charging source sees the bank voltage is above its own setpoint it thinks the job is done;  it sits quietly.
  
-==== why one sources wins ==== +Example.  Pretend you have a bank in a van with [[electrical:12v:alternator|alternator charging]] and 400w of [[electrical:solar:panels|solar panel]] (2x200w) on the roof.  Each panel has a dedicated [[electrical:solar:charge_controller|charge controller]] because the panels are of wildly different specs.  This gives us three charging sources if you are driving down the road at dawn.
-Most charging involves holding((or trying to reach)) a particular voltage [[electrical:12v:electrical_notation|setpoint]].((current-terminated Absorption excepted for purposes of this discussion))  If a charging sources sees the bank voltage is above its own setpoint it thinks the job is done. +
- +
-Example.  Pretend you have a bank in a van with [[electrical:12v:alternator|alternator charging]] and a large and small [[electrical:solar:panels|solar panel]] on the roof.  Each panel has a dedicated [[electrical:solar:charge_controller|charge controller]] because the panels are of wildly different specs.  This gives us three charging sources if you are driving down the road at dawn.+
  
 The alternator is just a plain alternator and puts out 14.0v all the time. The alternator is just a plain alternator and puts out 14.0v all the time.
 The Morningstar charge controller is factory set to start Absorption at 14.4v.((i.e. Vabs == 14.4v)) The Morningstar charge controller is factory set to start Absorption at 14.4v.((i.e. Vabs == 14.4v))
-The Xantrex charge controller has been configured by you to start Absorption at 14.7v.((i.e. Vabs == 14.7v))+The Xantrex charge controller has been configured by you to start Absorption at 14.7v.((i.e. Vabs == 14.7v)) Normally the controllers would be set to the same voltage but we will make them different to illustrate how it works. 
  
-Let's charge that battery.  Here is the battery voltage along the way:+Let's charge that battery.  Here is the battery voltage along the way:((oversimplified, but this is the Big Idea))
  
-  * **12.2v** at daybreak, approximately 50% [[electrical:depth_of_discharge|Depth of Discharge]].  Charging is in the Bulk stage and **all three sources are charging**; the battery bank voltage is lower than what they all want to provide.  The alternator is contributing the most because it can produce the most current. +  * **12.2v** at daybreak, approximately 50% [[electrical:depth_of_discharge|Depth of Discharge]].  Charging is in the Bulk stage and **all three sources are contributing**; the battery bank voltage is lower than what they all want to provide.  The alternator is contributing the most because it can produce the most current and the panels aren't getting much light yet.  
-  * **13.9v** a few miles down the road. Voltage is climbing but all three sources are still charging. +  * **13.9v** a few miles down the road. Voltage is climbing but all three sources are still charging.  The sun is higher in the sky so the panels are making more power now.  
-  * **14.1v** by the you get to a neighboring town.  **Alternator charging ceased at 14.0v**; it has plenty of current but no voltage "pressure" to force that current into the battery.  Your battery bank is now being charging only by solar. +  * **14.1v** by then you get to a neighboring town.  **Alternator charging ceased at 14.0v**; it has plenty of current but no voltage "pressure" to force that current into the battery.  Your battery bank is now being charging only by solar (the two separate controllers).((exception:  see [[opinion:frater_secessus:alternatorsolarstall|this gotcha]])) 
-  * **14.6v** in the parking lot as you stop at an Oasis [[:water|water kiosk]].  **The Morningstar stopped contributing at 14.4v**((Absorption is the stage where the controller provides as much current as it takes to hold Vabs, 14.4 in the Morningstar's case.  **It takes zero current to hold 14.4v when the bank is 14.6v**, so the Morningstar just sits there.  It might drop into Float.)) so we are down to just the Xantrex.   +  * **14.6v** in the parking lot as you stop at an Oasis [[water:drinking|water kiosk]].  **The Morningstar stopped contributing at 14.4v**((Absorption is the stage where the controller provides as much current as it takes to hold Vabs, 14.4 in the Morningstar's case.  **It takes zero current to hold 14.4v when the bank is 14.6v**, so the Morningstar just sits there.  It will drop into Float when Absorption duration is complete.)) so we are down to just the Xantrex.   
-  * **14.7v** on your way back to camp.  This is Absorption setpoint (Vabs) of the Xantrex, the highest setpoint of all three.  The Xantrex will continue the Absorption stage by itself until that stage is complete, then drop back to Float voltage (Vfloat).((where the Morningstar has probably been waiting, twiddling its thumbs))+  * **14.7v** on your way back to camp.  This is Absorption setpoint (Vabs) of the Xantrex, the highest setpoint of all three.  The Xantrex will continue the Absorption stage by itself until that stage is complete((duration or endAmps)), then drop back to Float voltage (Vfloat).((where the Morningstar has probably been waiting, twiddling its thumbs))
  
  
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 ==== how to make them cooperate ==== ==== how to make them cooperate ====
  
-So how do we make them all charge all the time?+So how do we make them all charge all the time?((and this even a thing you want?)) 
 + 
 +Barring heroic measures((exotic alternators/regulators, [[electrical:12v:b2b|DC-DC chargers]])) the alternator is going to stop contributing at some point during Bulk charging.  That is ok, the alternator provided a ton of current while it was charging. 
 + 
 +But if you want to the charge controllers (and some [[electrical:converter|converters]]) can be convinced to stay //roughly// in sync and keep charging together.  This is done by **configuring the Absorption and Float setpoints on the controllers to be the same**.((including Absorption termination setpoints like time or current))  There will be short periods where one controller makes a change before the other, but for most of the time both will be contributing at the same time.  Even if they contribute unequally it is a non-issue because the voltage setpoint is being held.  If a big load is added or conditions deteriorate it will be "all hands on deck" as in the Bulk stage scenario above.  
 + 
 +Note:  there are high-end controllers/chargers which communicate with each other to coordinate charging.  That feature is beyond the scope of this article.  
 +===== serial charging ===== 
 + 
 +Serial in this case means "one after another" Sometimes the charging is done in a particular order for best results.   
 + 
 +  - a **high current** (but fuel expensive) source handles Bulk stage that takes the battery to about 80% SoC. 
 +  - a **low current** (but free to run) source handles the much longer Absorption and Float stages. 
 + 
 +In most scenarios the **high current source** is either [[electrical:12v:alternator|alternator charging]] or [[electrical:generator|generator]] charging.  A huge influx of power gets the battery off that deeply discharged point early in the morning.  You will know when you have finished Bulk stage when the battery starts accepting less and less current.  Since running the alternator or generator uses fuel and causes wear and tear, it's time to shut them down and use the next source.  
 + 
 +The **low current source** is almost always solar.  Solar is free to run and is not subject to wear and tear;  it is perfect for the //hours// it will take to finish Absorption. 
 + 
 +===== gotchas ===== 
 + 
 +Some of these are observed, and some are theoretical. 
 + 
 +  * the vagaries of voltage sag across the system may result in the various charging sources seeing slightly different voltages and therefore contributing in unpredictable ways.((probably a non-issue as long as the bank is getting properly charged))  Voltage Sense wires can help with this issue.   
 +  * Multiple non-communicating controllers set up to trigger Float from endAmps((trailing amps)) may enter float early since they are providing only some of the charging current. 
 +  * Multiple sources may inadvertently exceed the bank's recommended charging current, or your preferred current.  Example:  a lithium battery wants 50A max but each charging source can make 30A.  This might result in overcurrent (60A) during Bulk.   
 +  * theoretical:  low-frequency PWM controllers in parallel with MPPT controllers may confuse the latter with an unstable reference voltage.  
  
-Barring heroic measures((exotic alternators/regulators, DC-DC chargers)) the alternator is going to stop contributing at some point during Bulk charging.  That is ok, the alternator provided a ton of current while it was charging. 
  
-But if you want to the charge controllers (and some [[electrical:converter|converters]]) can be convinced to stay roughly in sync and keep charging together.  This is done by **configuring the Absorption and Float setpoints on the controllers to be the same**.((including Absorption termination setpoints like time or current))  There will be short periods where one controller makes a change before the other, but for most of the time both will be contributing at the same time. 
electrical/12v/multipoint_charging.1507389689.txt.gz · Last modified: 2020/10/11 19:48 (external edit)