Connecting Multiple Charge Controllers to one Battery Bank

As you probably already know, you can wire solar panels either in series or parallel.

If you change the wiring you can change the way voltage or current behaves:

  • In series, the current stays the same while the voltage adds up.
  • In parallel, the voltage stays the same while the current adds up.

Here are some reasons why you might want to add another charge controller:

  • You want to add more solar panels to your system.
  • You want to add a panel with a different specification than the one you already got.
  • You want to separate panels from each other because they receive shade at different times of the day. For example on a boat.

How do charge controllers interact with each other?

Charge controllers sense the internal resistance of a battery and send their current to the battery terminals based on the resistance of the battery. If the battery is at a low state of charge, the resistance will be low and the charge controller will charge in bulk mode.

If the resistance becomes higher, the charging current will decrease because the battery is almost full.

If two or more charge controllers charge the same battery, the battery will be charged quicker. The multiple charge controllers will not compete with each other because they all sense the same internal resistance of the battery. If charge controller A puts in 100Watts, charge controller B will also put in 100Watts.

When you program your charge controller you can add the cutoff voltage in the software. That means if your battery reaches a pre-defined voltage, it will stop charging. You can tell charge controller A to charge to 12 volts and charge controller B to charge to 12.8 volts. This is not needed but is good to know because one charge controller might stop charging if it reaches that point, and you will be wondering why that is. Also, if the wires of charge controller A are a bit longer, it might enter float mode earlier than charge controller B because of the voltage drop.

If the charging current becomes too high, the internal resistance of the battery will change because of the heat generated. The charge controllers will then reduce their power input to the battery.

Wiring two strings to two charge controllers

In this example, there are two strings or arrays of solar panels that go to every charge controller. This setup is ideal if you have multiple solar panels that do not have the same rating. Refer to the article about series and parallel wiring solar panels.

You can also use this kind of setup on a boat. If one charge controller is in the shade of a sail, but the other is in full sunshine, the sunny panel will still deliver its max power. The shaded panel will deliver reduced power. This is very similar to wiring your panels in parallel.

Two strings to multiple charge controllers and one battery
Two strings to multiple charge controllers and one battery

 

Synchronizing Multiple Charge Controllers

If you are using two or more charge controllers they do not need to be able to communicate with each other.

There might be a problem with flooded lead-acid batteries where they equalize every month. If you have multiple charge controllers attached to the battery bank they equalize more frequently, Which is not good for the battery. You need to turn off the equalizing function of the other charge controllers so you only have one charge controller performing the equalize function.

Some models are able to communicate with each other like the Victron BlueSolar and SmartSolar models. The communication happens with the built-in Bluetooth module for the SmartSolar model. For larger systems, they recommend using the VE.can port.

The reason for communication between charge controllers is so that only one charge controller will balance the cells, not all of them.

Both charge controllers will deliver their maximum amount of current to the battery.

 

Display of bulk, absorption, or float current and voltage levels.

Conclusion

You can wire charge controllers in parallel to support an expanding solar system. You do not need to have charge controllers that are able to communicate with each other but you should only enable the equalizing function in one of them if you have flooded lead-acid batteries.

13 thoughts on “Connecting Multiple Charge Controllers to one Battery Bank”

  1. Solar panel array to multiple charge controllers (parallel) and one battery bank. Just about every other article I have read about this states that it is not a good idea to do this and that each PV array should be connected to each MPPT controller independtly. I was looking to use two identical solar controllers in parallel with one PV array, but I am slightly confused as to weather this will work OK?

    Regards,
    Graeme

    Reply
    • Hello Graeme.
      This is not the most effective method to wire your solar panels to the charge controller. If the whole PV array is facing the same direction, this method will work. The problem is when something happens to the array. If one solar panel gets damaged or shaded, it will influence the whole power output of the array, which will affect performance. It’s not the most efficient way, but it will work. I recommend wiring it like the second image. I have updated the article too.

      Reply
  2. Fascinating and well explained !
    I’m thinking of the following and not sure if it’s a workable idea or not.
    This would be to harvest as much daylight during winter … (summer supply/consumption should be easily met). House only has 4x250w at the moment and cannot meet very miserly use in winter. 24v system, large lead acid forklift battery.
    Planned … barn roof installation.
    South facing: 2 x 370w in series plus the same in parallel (4 panels total) with 40a MPPT
    West facing: the same as above

    Both outputs of the MPPT controllers to feed one pair of heavy duty copper cables running to the battery 16m away.

    Arrays planned for redundancy and resilience with panels being manually isolated in extreme sunlight (if needed) or switched to a separate battery bank (if the future requires it). Potentially Heath Robinson but truly modular in scope.
    Would this system seem plausible ?

    kind regards
    Duncan

    Reply
    • We have to know that light intensity affects the amperage, and temperature affects the voltage. Knowing this, we can predict that the two panels facing south would deliver a higher current than those facing west. This means that those two series strings should be placed in parallel to make a hybrid connection, just like you said. Because in parallel connections, the amps add up while voltage stays the same. Make sure the voltage drop stays under 3% for those 16-meter cables. Place your charge controller as close to the battery as possible. Check voltage drop video here: https://www.youtube.com/watch?v=d9ByUjphO6A&ab_channel=cleversolarpower

      Reply
  3. Hi Nick,
    I first want to commend you on probably the finest book (Off-Grid Solar Power Simplified) I have come across so far on the subject of Solar Power Systems. It has been extremely helpful to have a complicated subject explained probably as best as one could explain it. Thank you

    One question I have wondered and was not answered to my satisfaction (by a company tech). I will soon have 8 X 100 Watt Renogy mono panels to a 60 Amp MPPT Renogy Charge Controller and using 540 Ah Lithium battery bank (I am going to make my own Lithium battery from online community you suggested). I asked if there was some way I could add a future wind mill. I was told they didn’t have provision for multiple power inputs, therefore not possible. But reading your article above it sounds like I can add a wind mill to a second charge controller (sized for the wind mill of course, I assume it doesn’t need to be the same size as my other charge controller, but it will be an MPPT) and then wire both charge controllers in parrallel to the battery? How does that sound? And I have a creek that runs outside my window. My goal also was to have some kind of micro-hydro someday. Therefore add another charge controller for that and wire in parallel to same connections as others. I believe I read somewhere in your writtings it would be best to have all charge controller cables the same length? And since I am using Lithium I don’t have to worry about changing any settings (like turning off equalizing, or setting voltage cutoffs to different levels, etc.). Thank you for your help

    Reply
    • Hello Andy, Thank you for your compliment about the book. I really appreciate that. I’m sorry for the late reply, I was on vacation.

      Coming back to your question, it’s not a problem to have multiple charge controllers in parallel charging your battery bank. The cables from the charge controller to the battery bank can have different lengths.
      The thing you need to make sure of is the maximum charge current that your battery bank is able to absorb. Let’s say your DIY LiFePO4 battery can absorb a maximum current of 100 amps, then all your charge controllers combined shouldn’t deliver more than 100 amps, otherwise, your BMS will shut down.

      What voltage will your system be?

      Reply
  4. Dear Nick,

    First of all thank you very much for your informative and helpful writing.

    I would appreciate, if you can share your thoughts on my subject as explained below:

    I installed an Off-Grid Solar, Wind and Battery connected parallel to each other a month ago. Solar panels(3.6kWp) are connected to Growatt SPF5000 off-grid inverter. The Wind turbine(3.3kW at 14m/s) has its own Charge Controller with 48Vdc output. The battery is also from Growatt with 3300Wh capacity, LiFePO4 type, communicated via CAN with the Solar Off-Grid Inverter. The Battery, Wind Charge Controller and Off-Grid Solar Inverter outputs are connected in parallel to a 48Vdc busbar in a panelboard. But so far no loads have been connected to the system. Only the internal consumptions of the devices use energy from the battery.

    I have been monitoring the behavior of the system for a few days through the monitoring system of the inverter and observed that the Wind Charge Controller is not charging the battery. In a normal day time, when the battery goes down to %95 SOC level, It is charged back again to %100 SOC with the Solar inverter. As the PV Modules are not generating energy at night, the level of the battery is going down to around %70 SOC level (due to internal consumption of the battery). When the Solar Energy becomes available in the early morning, the battery starts being charged back to %100 SOC. I am trying to find out, why the battery is not being charged wind turbine charge controller? I might be hard for you to figure out system in detail, but incase you need further detail, I can share.

    Best regards,
    Alper

    Reply
    • Hello Alper,
      You have explained your system well, I will try to give you a few tips.
      – Can you measure the amps going from your wind charge controller to the busbar?
      – The internal consumption of the battery is very low. If you go from a 100% to 70% SOC without appliances on, there is something wrong.
      – Could it be that the charging/discharging system voltages are different on the wind turbine than the growatt hybrid?
      – it could be that the wind turbine has no chance of charging up the battery because it doesn’t reach a low enough voltage.
      – Is the wind controller suited for LiFePO4 batteries?

      Reply
  5. Hi There,

    I appreciate this so much! I’m using this set up to wire my solar panels to 2 Epever MPPT charge controllers. Since purchasing the first charge controller, I’ve changed my setup considerably and needed a second.

    Like the charge controllers in your diagram, I chose this controller because I could wire the load directly to it and control the battery discharge this way. But now I’m wondering, how do I wire the load if I have 2 charge controllers with this capability and 1 battery?

    I hope this isn’t the silliest question. Thank you so much for your time.

    Clare

    Reply
    • Hello Clare, There are no silly questions, only silly answers and I hope mine isn’t one of them 😉
      – I do not recommend connecting your load to the charge controller. Instead, I recommend connecting your loads to the main battery terminals. Especially if you have a big setup like yours. You need to use a low voltage disconnect between the battery and your load, this will work the same way as your charge controller. The difference is that you can draw more amps because the output on the charge controller is limited.
      – If you still use the load terminals on the charge controller, then using one charge controller is fine if it meets your current demand. The current on these outputs is severely limited.
      Hope this helps.

      Reply

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