Using 2 controllers for one system?

I am helping a rural woman here in Veracruz that has 2 old solar systems on her 2 buildings. One uses 3 (12 volt) panels totaling 210 watts with its Spanish made 12 amp controller. The other uses 3 (12 volt) panels totaling 180 watts with the same type controller. I want to combine them on one roof (the one with the most sunlight). I am trying to use the 2 contollers as they are connected now, but with COMMON BATTERIES to better distribute the energy. It is difficult to buy a new controller here in Mexico (and expensive) What do you think?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    Re: Using 2 controllers for one system?

    With out knowing details--that should work just fine. Wiring the controllers in parallel should present no special problems in normal operation.

    Several things... Putting old batteries (or mixed old and new batteries) together in parallel may or may not work well. Typically, the batteries in better shape will take most of the load and the batteries in poorer shape will behave mostly like "boat anchors".

    When paralleling the batteries, make sure that they all see the same resistance, voltages and currents. Generally, that means heavy gauge wire (for the load/charging current) and a good way to do it is to have all wires the same size/length connected from each battery to a central bus bar (heavy cables or copper/brass plates). The difference between a fully charged battery and one that is not is probably less than 0.10 volt.

    I think Jim (Crewzer) or somebody else here has some nice drawings for suggested ways of connecting parallel strings together to help balance the loads/voltages on the batteries.

    The two controllers should be connected to the same low resistance point bus bar too so that they see the correct battery voltages for optimum charging.

    Also, are there some gauges/LED's on the controllers so that a quick glance during the day will show that both are passing current for charging? If not, it is possible that one failed panel/controller string will not be quickly detected by the owner--leading to batteries being over discharged and leading to an early life failure.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Using 2 controllers for one system?

    Yes BB, thanks. the family have a voltmeter and led's to show the battery condition. I am checking and adding batteries to their bank.
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    Re: Using 2 controllers for one system?

    Also, I was trying to understand if they can see if both chargers are working independently... (indication of current flowing through the chargers themselves).

    A voltmeter (and charge state LED's) will only show the battery voltage.

    If one controller/panel string has died (broken wire, bad panel, etc.), it will be difficult to quickly recognize the problem. Placing a cheap amp meter (or current shunt that can be checked with the family voltmeter in the controller to solar panel connection) would allow them to monitor the current flow of each meter independently and check for component failure before they notice the batteries not charging as well as they used too.

    The "shunt" could even be just a few extra feet of wire in the solar panel to controller connection that the family can clip onto and record the voltage (or the fraction of current through the meter set to Amps/mAmps--which ever setting works best).

    One of the problems with "redundant" systems in general is the ability to quickly diagnose when one has failed and get it quickly repaired before something else happens (the mate failing, or in this case, the batteries not fully charging but nobody noticing for a few weeks or month).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Using 2 controllers for one system?

    Thankss Bill, I was thinking of putting a simple automotive ammeter in each string. That's what I have on my mountain cabin. frank
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