Solar Charge Controller | What is it and How it works in a Solar Power System


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Find out the basics of a solar charge controller, what it does, how it works, and how to select the correct size for an off grid solar power system. A charge controller is an important component in a battery based solar system and are not used in straight grid tie systems. The primary role is to manage charging the battery bank, prevent it from overcharging and many control the rate of the current and voltage at which it charges.

We’ll cover related topics such as Bulk Charging, Absorption, Equalization, Float, Low Voltage Disconnect, PWM and MPPT types of charge controllers.

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46 replies
  1. wheredidileavemycell
    wheredidileavemycell says:

    The math annotations in the video are weird at 7:15… the way it's explained is terrible. The example should read, if you want to run 1500w heater for an hour, you need to generate at least 1500w in one day. Since you only make 300w, you will need 4 more panels (totaling 1500)to generate the 1500w your heater consumed.

    the formula should be 1500w demand – 300w supply = 1200w deficit… 1200w (deficit) / 300w (generated per panel) = # of panels needed to get 1500w

    the second example is worse. 1500w x 5hrs = 7500w demand. 7500w demand / 300w supply= 25 PANELS not 2500w. 2500w is the total W generated for you system…again it's the same information but annotation doesn't match the explanation.

  2. Sánchez Boy
    Sánchez Boy says:

    You know that the charge controller prevents the battery from getting discharged, that is it prevents the current flowing from the battery to the PV panel and instead lets the battery supply current to the DC load via charge controller in the night-time or in the absence of sun. In the daytime, the charge controller allows the battery to get charged via PV panel and at the same time, powers the DC load. Now the question is: if the battery gets fully charged in the daytime, then will the battery gets discharged during the daytime? Or does the charge controller disconnects the battery from the system? Please let me know asap because I'm extremely confused about it.

  3. Str8upbrah
    Str8upbrah says:

    I have 2 300w panels. I've noticed the 40a controllers are a lot cheaper than the 50's. Not sure how to go about it.

    Also the 600watts are 24v so I wasn't sure if I should make the whole rig 24v or not.

    Any help would be much appreciated.

  4. GcoEnterprises
    GcoEnterprises says:

    Amy looks like the Stereotypical super achieving Female Nerd, but a cool nerd that we envision when we think of someone like the astronaut Sally Ride, or many other heroins in the field of Science, Medicine, Sports, etc. It wouldn't surprise me if she had a PHD in Thoeretical physics, and/or electrical engineering and graduate some ivy league college like MIT or UC Berkeley.

  5. Bob Americana
    Bob Americana says:

    i have a 48v 18ah battery bank ( 4 batteries in a series) . i power a 48volt 750 watt (max draw) motor. i want to recharge this system using solar…..i simply cannot find anyone who can or will explain this to me. can i wire the solar panels to the controller…not use the controller for output..have the batteries wired to both the solar controller and the motor controller ? do i need to turn off the solar to use the motor ? i am completely lost in this regard……
    also- my solar array would only be 50 watts…two 25 watt panels @ 12 volts….unless i can mix wattage of the panels– due to the area available for the placement of the panels…..
    i looked at a mppt converter or two on amazon and i saw a couple that accept assorted input voltages and will give the 48volt output for my battery bank…
    i simply do not wish to buy a bunch of solar related equipment just to simply watch it all go poof the 1st time i try it out.
    I am lost…need help…

  6. rushikesh tangade
    rushikesh tangade says:

    Are the 24V,100W solar panels available n market? And are they efficient to give the required voltage. I want to charge a 48V battery pack but not getting the panel of 24V 100W capacity in market. Please suggest ideas.

  7. David James
    David James says:

    If each solar panel has its own wire (which is the case with Harbor Freight amorphous panels), then it doesn't matter much if they are series or parallel connected, cuz the current flow in them should be about the same, such as 12V 1.5A (each panel) or 48V 1.5A all 4 panels in series. You mentioned higher voltages reduce the current but that is misleading. There is no current reduction in this case, especially if you have 4 separate charge controllers, one for each of the four 12V batteries.

  8. jenny bowie
    jenny bowie says:

    Hi all loved the video, clear and concise. We have an urgent problem, we have a 120 watt panel on the Land Rover, there is power going into the control panel but not going out to the battery. What would cause this please

  9. Mikey
    Mikey says:

    super cool video! Does anyone know how a charge controller handles the excess power if its not transferred to the battery. (like after the batter is full?) Does the solar panel just stop generating without a place for the excess to go? does the controller burn it all of as heat or something? I'm really curious to find out what happens to all that uncaptured energy if it can't be put to use somewhere. Could an excessive solar panel array melt a charge controller if its producing way beyond your storage capacity?

  10. Dakota R.
    Dakota R. says:


    I'm slightly confused about your two calculations when sizing the mppt controller.
    In your first example you give a 1panel 30Vmp, 9Imp, 270W. You then divide 30Vmp/14V (voltage controller outputs)= 2.14. Then multiple this by the 9Imp to find current output by the charge controller stepping up the Amps = 19.28 to the batteries, correct? so to take into consideration the 1.25 possible increase in voltage at colder temps you would do 30*1.25= 37.5 V/14V= 2.67, then multiply by 9Imp =24.1A
    In the second calculation you then simply take 4 x 270W panels / 24V battery bank x 1.25 for safety to determine rating for the controller. = 56.25
    Given the scenario of 4 X 270W panels using method one 60Vmp * 1.25= 75 /28V =2.67, mutiply by 18A = 48.21A max output by mppt.
    Can you explain why you wouldn't use the first/last calculation to determine the Amp rating for the controller?

  11. Sindre Sæther Ulfsnes
    Sindre Sæther Ulfsnes says:

    Nice explanation, I have one fundamental question. I understand that the PV power will always go from the charge controller to the battery before it goes on to the load. This means the load is always fed by the batteries.
    My question is: Let's say the load is 100 W, and produced solar power is 200 W. Would the battery still be charged or will the power just go through the battery and directly to the inverter without charging the battery. Or will the PV power first charge the battery, and then deliver the necasarry power? When the battery is fully charged I assume PV power will still provide power to the load while keeping the battery fully charged, and only start discharging the battery when the load exceeds the PV power?

  12. Haitham AlHazmy
    Haitham AlHazmy says:

    Amy,, thank you for all your videos you are really our solar queen <3

    I have simple question , I saw some MPPT charge controllers say in their specifications that for example the MPPT CC is 60 A , and max PV input (24v battery): 1600 W

    but when I calculate it 1600 W / 24V = 66.67 A > 60 A

    so is it ok to follow their recommendation about the 1600 W PV maximum input for 24 V battery???

    TriStar TS-MPPT-60 is good example

  13. coco latte
    coco latte says:

    I am working on a camper solar system. I have C60 21.8% eff, vmpp (v) 0.574 cells, i am thinking to put on as much solar as I can fit. Here is my question: I am considering volts vs. amps, is there anyone who can tell 30 cells would produce enough volts to charge 12v batteries? Thanks in advance.

  14. Graham Elder
    Graham Elder says:

    hi , please to explain to me something that confuses me .
    first i understand that ;
    (Vabs = 14.7v, Vfloat = 13.5v ):
    Bulk – full solar power until battery reaches Vabs
    Absorption – The battery is allowed to come to full state of charge at the Vabs
    Float – Vfloat low maintenance levels

    1) Is the controller discarding power during the absorption phase? I mean it can only control either I or V – and the other follows, right?

    2) Absorption confuses me a bit. Firstly because it just runs for a fixed time – not based on any sensors or anything. So how does it know it comes to a "full state of charge"? Is it that there's a typical SOC when bulk hits 14.7v and transitions to absorption? I realize it's triggered by 14.7v voltage, but is that usually 60% or 90% SOC?

  15. Ajit Kumar
    Ajit Kumar says:

    Very good. I have à confusion, I live in indian States Uttar Pradesh. The highest temperature is recorded 43 degree C. I want to use Monocrystaline solar panel or should I use polycrystline panel. I mean temperature is between 15 degree C to 43 degree C. Please suggest. Thanks

  16. Nadeem Ahmed
    Nadeem Ahmed says:

    one question.
    will mppt charge controller work if the voltage from panels are not in the mppt range what is mentioned in the mppt charge controller manual? i mean TO ask will mppt totally shut off giving Power or it will work like PWM? thank-you for your answer in advance.

  17. t0nito
    t0nito says:

    I got a free grid-tie 20V nominal 60 cell 250W panel that has a smashed glass but is still working, can I safely use it with a PWM controller to charge a 12V battery bank (even though I'm loosing efficiency?) My first thought was to use it with a 24V battery and a UPS that I have lying aroung but then I learned that the 60 cell won't top off the battery.


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