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Solar Charge Controllers


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There have been several solar topics on the forum lately.  We have discussed batteries, inverters, and solar panels, but solar charge controllers haven't really been discussed in detail.  This topic is intended to discuss solar charge controllers and how they work.  I cover this topic and other solar, battery and inverter related topics on my website for those who are interested.  Here are the basics:

  • Solar charging is no different than any other charging source
  • Solar panels convert sunlight into usable power through a solar charge controller to charge your batteries
  • This is no different than a charger converting shore or generator power to charge your batteries
  • Make sure your solar charge controller is a "smart" controller with temperature compensation (for lead acid or AGM charging)
  • Three stage charging is best for Lead Acid or AGM batteries
  • Lithium battery charge characteristics are different than Lead Acid or AGM, so if you have lithium batteries make sure the charge controller is capable of charging them properly

The primary types of controllers used in the RV world are PWM and MPPT

     Pulse Width Modulation or PWM are the simplest and usually the lowest priced

  • PWM controllers operate by regulating a pulsed, direct connection from the solar array to the battery bank
  • As the battery bank approaches a full charge, the length of the connection pulses decrease to gradually taper off the charging current from the solar array
  • On a 12V battery bank, PWM charge controllers can only be used with a solar array that has an open circuit voltage of 24.0 Volts or less
  • This excludes large 60 cell or 72 cell residential panels from use with a PWM controller
  • In systems with multiple solar panels of different voltages (e.g. 32 cell panels mixed with 36 cell or 40 cell panels), PWM charge controllers are preferable to MPPT controllers because their operation algorithms are less finicky

     Maximum Power Point Tracking or MPPT type charge controllers use a much more efficient method of feeding power from the solar array to the battery bank

  • Instead of a regulated direct connection, MPPT type controllers transform the optimum balance of current and voltage from the solar array into something that can safely be fed into a battery bank
  • This means that excess voltage from the solar array is transformed into more charging current (amperage)
  • For example, with a PWM charge controller you may have a solar panel operating at 19.0 volts and 6.0 amps, feeding 6.0 amps into your battery bank (ideal conditions)
  • If your battery bank is at 13.0 volts you are only getting 78 watts (13.0V x 6.0A = 78W) from the panel
  • With an MPPT charge controller on that same panel you will be able to use the extra 6 volts (19.0V – 13.0V = 6.0V) and turn it into more current (amperage)
  • 6 volts is approximately 46.2% of 13 volts (6 / 13 = .462)
  • That remaining percentage of power is converted to amps by the MPPT controller
  • 6 amps plus another 46.2% is approximately 8.8 amps (6 x 1.462 = 8.772)
  • Your charging current will be about 8.8 amps and you will be getting about 114 watts (13V x 8.772A = 114.036 watts) from the same panel with an MPPT controller vs. a PWM controller

Selecting a solar charge controller

     Performance vs. Price

  • MPPT charge controllers cost more but can harvest more power out of an array
  • If roof space is at a premium, use higher voltage panels and an MPPT charge controller to harvest more power
  • If you are on a limited budget or have modest power needs, a PWM controller can work well for you

Array Voltage vs. Battery Voltage

  • The solar array needs to have a higher voltage than your battery bank in order to push a charge into the bank
  • Some charge controllers require X number of volts above the battery bank voltage before they will even begin trying to charge the battery bank

Voltage Limits

  • Don’t let your array voltage exceed your controllers capabilities
  • PWM controllers are limited to 24 volts on a 12 volt system
  • MPPT controllers can be rated for as much as 250 volts or more depending on the model selected
  • To avoid damaging your charge controller, make sure the Voc (Voltage open circuit) for each panel or series of panels does not exceed your charge controller’s limit
  • The Voc is usually printed on the label on the back of the solar panel

Current Limits

  • Charge controllers are rated on their output current (from the controller to the battery)
  • As long as your panels are connected in parallel you can determine the maximum output current by summing the operating current, or Imp (Current maximum power point) for each panel
  • The Imp is usually printed on the panel label
  • If the panels are in series, then the output current remains the same
  • Series/parallel configurations add both the voltage and the current.  The voltage adds for the panels in series and the amperage adds for the series strings wired in parallel

Multiple Charge Controllers

  • If your desired solar array has a charging current that exceeds the current rating of your preferred charge controller, you can use multiple charge controllers
  • These charge controllers would be connected in parallel to each other across the battery bank
  • Not all charge controllers have this capability

Charge Controller Setup

  • It is very important to set up your charge controller properly
  • Set the correct system parameters within the controller such as maximum charge current, charge voltage, total battery bank capacity, etc.
  • Some controllers allow for a myriad of customized settings (often through remote controls) while others have only simple options available to them (often through dip switches)

Battery Temperature Compensation

  • It is important to incorporate battery temperature compensation on any charging system for Lead Acid or AGM batteries
  • Avoid charge controllers that do not allow for battery temperature compensation if you have a Lead Acid or AGM battery bank
  • Temperature compensation is not needed for Lithium battery banks

Monitoring

  • It is very important to incorporate some type of monitoring system
  • Whether this is through an integrated monitor or a stand alone system, you need to know what is going into and coming out of your batteries to properly maintain their life and longevity

 

 

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Chad, Nice write up. Are you bringing any extra controllers and or monitors to the rally next week? It looks like I need to replace a small one that has 200 watts of solar and recharges one 12V deep cycle battery. The one I have does not have temp sensing and I think it cooked my battery. 

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Chad, EXCELLENT summation of Solar Charge Controller operation. I tell people they simply use the RAW POWER from the Panels (which varies greatly based on sunshine and other variables) and electronically converts that raw power into Smart Staged Regulated charging compatible with the chosen battery chemistry and its proper charging algorithm. They and backed up with a batteries BMS (if so equipped) charge the batteries, provide for their protection and prevent overcharging. Now all the sophisticated electronics is above my pay scale just suffice it to say the above ONLY represents the basic theory.

In a nutshell without the regulation and control the ever changing voltage and current supplied unfiltered and straight from the panels would NOT do a good job of correctly charging and protecting the batteries. 

 Some brands of Solar Charge Controllers have but two basic specifications/labeling, the maximum PV input voltage (based on panels and how multiples are configured) and the max current, easy peasey.

 My VERY FIRST controller was a cheap PWM but since I chose MPPT and am never going back.     

PS the only caveat I might add to one of your items above is DO NOT use any so called "4th Stage" or so called "Equalize" type of feature a few smart charges may be equipped with on AGM batteries, that so called 4th Stage is intended for flooded lead acid. As you indicate a regular Smart 3 Stage (Bulk, Absorption, Float) is fine for EITHER FLA or AGM.

 Related to MONITORING Id add use of a "Shunt Based" battery monitor is more accurate than some of the cheap built in units that only monitor battery voltage ...  

Thanks Chad, great information

John T   NOT any Solar expert listen to Chad or Randy over me

Edited by oldjohnt
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Thank you Chad! One thing that this information has confirmed for me that I had concluded but was never positive is that the simplest terms, each solar panel acts very much like a collection of batteries in that in series they add voltage while parallel adds current. Am I correct to also conclude that like batteries, the lowest current limits a series group and the lowest voltage is the limit for parallel panels?

All of these discussions have really brought home to me how dated the formal training on battery principles and properties is because it goes back to my submarine days where we had very large batteries physically, with a rated voltage of 250V and flooded cell.  But this all has me thinking about upgrades!  😏

Good travelin !...............Kirk

Full-time 11+ years...... Now seasonal travelers.
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UNTIL CHAD ARRIVES to answer, clarify and correct if necessary, 

I found this article provides a good explanation of Series and Parallel solar panel configurations, how similar to batteries, current is additive in parallel while voltage is additive in series. I connected my four in Series/Parallel so I didn't exceed the max PV input voltage of my MPPT Solar Charge Controller.

   https://www.alternative-energy-tutorials.com/solar-power/connecting-solar-panels-together.html

John T

Edited by oldjohnt
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11 hours ago, Star Dreamer said:

Are you bringing any extra controllers and or monitors to the rally next week? 

I do not have any with me, but I have ways of getting one.  I don't want to break any rules here, so I will just leave it at that for now.

2 hours ago, Kirk W said:

Thank you Chad! One thing that this information has confirmed for me that I had concluded but was never positive is that the simplest terms, each solar panel acts very much like a collection of batteries in that in series they add voltage while parallel adds current. Am I correct to also conclude that like batteries, the lowest current limits a series group and the lowest voltage is the limit for parallel panels?

Yes the panels act like batteries in that voltage adds in series and current adds in parallel.  John posted a good link describing this and how putting panels of different ratings together affects those connections.  I have similar information on my website.  It is not a good idea to mix panels of vastly dissimilar ratings because of the way they interact.  If the panel groups total voltage is under 24 volts and the battery bank is 12 volt nominal, then a PWM controller will handle dissimilar panel ratings better than an MPPT controller, but that is a fairly rare set of circumstances.

 

1 hour ago, oldjohnt said:

That is a good link.  I have similar information on my website as well.

2000 Kenworth T2000 w/ Cummins N14 and autoshift
2017 DRV Mobile Suite 40KSSB4 with factory mods, dealer mods and personal mods - now in the RV graveyard
2022 DRV Full House MX450 with customized floor plan
2018 Polaris RZR Turbo S (fits in the garage)
2016 Smart Car (fits in the garage or gets flat towed behind the DRV when the RZR is in the garage)
My First Solar Install Thread
My Second Solar Install Thread & Photos and Documents Related to the build
My MX450's solar, battery and inverter system - my biggest system yet!

chadheiser.com      West Coast HDT Rally Website

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  • 5 months later...

Trying to figure out what the best configuration of charge controllers and string configurations, any input is appreciated.. . Lithium 48 volt battery bank, 400AH, 20.5 KWH to be charged, so wanting a high efficient rapid charge rate., recommend is 0-63 AMP,  max continuous is 100AH per pack,

Space will allow 12 panels to be installed, looking at the 144 cut cell technology in the 425 watt range , each panel has a VOC of 81.4  , but SCC is 6.57A.

3 panels in series puts 246 volts to a single MPPT Victron Charge 250/100 controller. Does it generate 100 amps when it sees 250 volts, regardless of SCC? IHow many more amps than the 6.57 per string would the MPPT create at 250 volts?  Better to parallel the 3 panel strings onto  a single 250/100? Or use some other configuration ?

Thanks for any feedback regrading the configuration.

 

 

 

 

 

Edited by palmeris
spelling, getting the links and math correct _ I hope
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9 hours ago, palmeris said:

Trying to figure out what the best configuration of charge controllers and string configurations, any input is appreciated.. . Lithium 48 volt battery bank, 400AH, 20.5 KWH to be charged, so wanting a high efficient rapid charge rate., recommend is 0-63 AMP,  max continuous is 100AH per pack,

Space will allow 12 panels to be installed, looking at the 144 cut cell technology in the 425 watt range , each panel has a VOC of 81.4  , but SCC is 6.57A.

3 panels in series puts 246 volts to a single MPPT Victron Charge 250/100 controller. Does it generate 100 amps when it sees 250 volts, regardless of SCC? IHow many more amps than the 6.57 per string would the MPPT create at 250 volts?  Better to parallel the 3 panel strings onto  a single 250/100? Or use some other configuration ?

Thanks for any feedback regrading the configuration.

Running three of those panels in series to a Victron 250 volt charge controller is too much.  You are way too close to the 250 volt limit of the charge controller.  You should leave a minimum of 15% headroom under the 250 volt hard limit of the controller (I prefer 20%).  If you exceed the 250 volt hard limit, you will let the magic smoke out of the controller (it will fry itself).  Victron has a calculator on there website that allows you to enter your panel specifications and the panel configuration and it will recommend the proper controller.  Solar panels can actually produce higher voltage than they are rated for in cool temperatures and bright sun (which is rare, but it can happen).  If you were to run three of these panels in series, they could easily produce more than 250 volts under the right conditions.

With a 48 volt battery bank, the Victron 250/100 and 150/100 charge controllers will handle up to 5800 watts of solar panels.  You could put all 12 of your 425 watt panels (5100 watts) on a single controller.  I would run them in series pairs on the 250/100 controller and all in parallel on the 150/100 controller.  Either controller will work, but I think I would prefer the higher voltage capabilities of the 250/100 and the series pairs configuration.  It would allow for smaller gauge wire coming down from the panels and less wiring between the panels and the combiner box.  The controller output to the batteries would be running at slightly less than max capacity (100 amps) if all the panels were producing at peak ratings, which is good for the longevity of the controller.

Edited by Chad Heiser

2000 Kenworth T2000 w/ Cummins N14 and autoshift
2017 DRV Mobile Suite 40KSSB4 with factory mods, dealer mods and personal mods - now in the RV graveyard
2022 DRV Full House MX450 with customized floor plan
2018 Polaris RZR Turbo S (fits in the garage)
2016 Smart Car (fits in the garage or gets flat towed behind the DRV when the RZR is in the garage)
My First Solar Install Thread
My Second Solar Install Thread & Photos and Documents Related to the build
My MX450's solar, battery and inverter system - my biggest system yet!

chadheiser.com      West Coast HDT Rally Website

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 Chad, thank you very much for the detailed response.

I hadn’t thought about that consequence of smoke letting which is never a good thing with electronics.💥

 2 panels in series would be about 163 volts and amps would remain at 6.57-- parallel 6 strings and voltage remains same and amps become 39.42 at the MPPT.  

The Recommended Charge (Absorption) Voltage for the pack is 57.6 volts - Is there a way to calculate the additional the MPPT will create with the additional 105.4 volts above absorption that the panels can provide?

Perhaps there’s a better, more efficient panel, controller pairing that works better with my available space and I will  check out the Victron site and calculator.

Thank you

 

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3 hours ago, palmeris said:

The Recommended Charge (Absorption) Voltage for the pack is 57.6 volts - Is there a way to calculate the additional the MPPT will create with the additional 105.4 volts above absorption that the panels can provide?

Yes there is a way to calculate the amperage the charge controller will produce.  With the solar panels specified and the configuration I mentioned with the 250/100 charge controller and six series pairs of panels, you will have a maximum wattage potential of 5100 watts.  At 5800 watts, the 250/100 charge controller will put out 100 amps to your 48 volt battery bank [5800 W / 57.6 V (charge voltage) = 100.69 Amps].  Your 5100 watts (assuming your panels produce at their maximum potential, which they won't flat mounted on an RV roof), would give about 88 amps to the batteries (5100 W / 57.6 V = 88.54 Amps).  More realistic production in mid summer with cool temperatures is 85 to 90% of ratings with flat mounted panels.  With this in mind figure 4335 W (85% of rating) / 57.6 V = 75 Amps to the batteries (approximately).  In winter time, a more realistic production number with flat mounted panels is about 65% of rating.  Now you have 3315 W (65% of rating) / 57.6 V = 57.55 Amps (approximately).

2000 Kenworth T2000 w/ Cummins N14 and autoshift
2017 DRV Mobile Suite 40KSSB4 with factory mods, dealer mods and personal mods - now in the RV graveyard
2022 DRV Full House MX450 with customized floor plan
2018 Polaris RZR Turbo S (fits in the garage)
2016 Smart Car (fits in the garage or gets flat towed behind the DRV when the RZR is in the garage)
My First Solar Install Thread
My Second Solar Install Thread & Photos and Documents Related to the build
My MX450's solar, battery and inverter system - my biggest system yet!

chadheiser.com      West Coast HDT Rally Website

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On 4/18/2022 at 6:03 AM, Kirk W said:

Thank you Chad! One thing that this information has confirmed for me that I had concluded but was never positive is that the simplest terms, each solar panel acts very much like a collection of batteries in that in series they add voltage while parallel adds current. Am I correct to also conclude that like batteries, the lowest current limits a series group and the lowest voltage is the limit for parallel panels?

 

In simplest terms, in parallel solar panels act as zener diodes, clamping the voltage of all other parallel connected panels to the maximum voltage of the lowest one.  Put an 18 volt panel in parallel with one or more 36 volt panels and the output voltage of all will be clamped at 18 volts.  Since solar panel currents don't vary significantly between 0 volts and their MPPT voltage this will effectively cut the output of the 36 volt panels in half.

In series, the current of the lowest rated panel will determine the current of the entire series string unless that panel has bypass diodes which will let excess current bypass the panel.  This effectively takes that panel out of the circuit so you won't get any voltage contribution from it.

 

 

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