Using two flexmax 80s

dell
dell Registered Users Posts: 6
Need to know ..using two fm80s in one system , one to controll one row of 8 panels and one on the other row of eight panels. The controllers are programmed properly . I want them to function as separate controllers . They are programmed alike . " problem " lets say they are off, it's a sunny morning , I go turn one on and it's working alright. So I turn the other one on , what happens is this one as it starts indicating amps/volts the other ones volts amps will start going to zero. ....... As I've said, I want both to act independently of the other. ........ What I think is maybe if I program them this way devide the charge bulk, and float numbers , this will be the value that is = to one controller. Also I do have them connected to one battery switch and. Thought this may have something to do with it ....can someone tell me how to set them .. Thanks

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using two flexmax 80s

    How are you turning them "on"? As far as I know, you would let them manage their own On/Off cycling (and various other charging functions).

    Some things to check/confirm:

    First, how are the wires from the charge controllers to the battery banks connected (gauge of wiring, length of run, are they daisy changed--controller A to controller B to battery bank, or are they "home run"--Controller A to battery bus, Controller B to battery bus, etc.)?

    Next, what voltages do the LCD displays read (and, if you have a good DMM, what does it read at the battery bus and at the controllers' outputs)?... With no current flowing, they should both read about the same. With lots of current, usually you will have some "voltage rise" in the battery cabling. If the rise is "different", it will "feed back" to the controller and start to limit its output voltage at the battery bank.

    There is a "calibration" setting where you can adjust the offset voltage get two controller to read closer to the same voltage (I believe, I am not an Outback person).

    Lastly, there is temperature sensing (inside the controller), and remote battery temperature sensing at the battery bank (optional). If there are issues with the temp compensation, or the internal/external battery sensors, or even a programming issue (it has been unclear to me if two FMxx controllers can share one RBTS when connected through a Mate/Hub).

    Lastly, if the controllers are not configured/wired to synchronize their charging--They will not always be "in sync". And the higher the battery bank's state of charge (over ~80-90% SOC) and the higher the charging currents, the more "out of sync they may be. But I would be surprised if one is at 100% and the other is at 0% of output current.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using two flexmax 80s

    Two FM60's on one bank will never act independently of one another because they are connected to the same bank. Since most of the function is based on sensing the Voltage of that bank, they will react to input from each other. There's no way around it.

    I do not see why you'd be trying to make them independent either. There's no point I can fathom to doing so. Connecting them with a HUB and letting them share data (including battery temp) is the normal procedure. Nor is there any advantage to turning them off.
  • dell
    dell Registered Users Posts: 6
    Re: Using two flexmax 80s

    Ok I want both to function as one . By turning on or off that is through a battery switch. They should both monitor the battery's and both read the same , if they are both programmed the same , shouldn't they? They are both on one battery bank through the same battery switch.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using two flexmax 80s

    You should not turn of the charge controllers with a battery switch unless you are specifically trying to reboot them because of problems. Also, many charge controllers have you connect battery power first, then solar array power. Doing it backwards can confuse (or possibly even damage) them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using two flexmax 80s

    Okay, item #1; do not disconnect the batteries from the controllers when the PV is still connected. You get that "Got Batt?" message and a confused controller.

    Item #2; difference in wire distance will cause different Voltage readings by each controller, especially under higher current. You can adjust the V reading on each controller, but it should only be done when current flow is near zero.

    The Outback's don't have MidNite's "Follow Me" function, but they can behave together even without a HUB if the wire sizing/lengths, temp comp, and PV are equal. It will be close enough to work. Do not expect 100% agreement between the two.
  • dell
    dell Registered Users Posts: 6
    Re: Using two flexmax 80s

    Battery on or off with battery switch. Both are through a neg bus , and both are programmed with the same data. Can you say more on config, / wire from your reply at the last paragraph .
  • dell
    dell Registered Users Posts: 6
    Re: Using two flexmax 80s

    When opening or closing the battery switch the circuit breakers between controllers to panels are opened. It sees to me that both are the same controller they both act the same , instead one will not if needed be absorbing , the amps will start falling to zero , which means it is not working the same as the other , and being the same controller and set the same should do the same thing . Maybe the hub would synchronize them .
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using two flexmax 80s

    They will never function simultaneously; minute differences will cause one to follow the other and not always the same lead/follow.

    If you 'start' controller #1 first and it brings battery Voltage up then turn on #2 the second one will read the increased Voltage and act accordingly. If the first one can achieve Absorb on its own the second one will most likely report "Batt Full" (meaning battery is above the charge set point from another source).

    Don't expect each controller to display precisely "14.8 Volts @ 'X' Amps" (where 'X' is exactly 1/2 the total current going to the batteries). This won't happen except by coincidence.

    Even your PV's will make a difference, though they be the same in all technical specs and orientation. There are always small variations (most everything has a 10% tolerance) that can add up. If all the tolerances are in the 'right' direction two "identical" set-ups could show 30% difference in output power.

    You should just connect them and leave them on. Are you worried about the combined arrays exceeding the maximum battery current? If so you could leave one's PV off unless the extra power is needed on a cloudy day.

    HUB synchronization is better, but it still will not be 100% the same. The biggest advantage here is allowing sharing of RTS data and being able to read both controllers from a MATE.
  • dell
    dell Registered Users Posts: 6
    Re: Using two flexmax 80s

    Yea if I start # 1 it does everything right then when I turn # 2 on #1 amps/ volts will start falling to zero. When it first done this I shut dn, the other and the first one reached a charged state as shown on display . So I've turned it off and got it on the other one one and it is in an absorb mode while the first one said battery's are full floats at 26.4 and bulk at 29.6 .
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using two flexmax 80s

    It is a guess--But if you let one controller run long enough to get "hot", its internal tempurature sensor (if that is what you are using) will crank down the output voltage.

    Turn on the second controller (cold), it will output 0.1's to 0.5's of volts higher, and take over much of the charging until the two temperatures equalize.

    Not saying that everything is working correctly--Just that they could be working fine and the controllers are "confused" by the starting/running conditions.

    -Bill

    PS: Cold batteries require higher charging voltages... About 0.005 volts per C per cell... 12 cell system * 5C difference in temperature means a 0.3 volt offset between "cold" and "hot".
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using two flexmax 80s

    To me it sounds like they're behaving exactly as we might expect. I don't see any issue here. If you want to switch extra PV power in/out turn the PV on/off; leave both controllers connected to the battery bank at all times. I don't see any point in disconnecting one or the other.
  • dell
    dell Registered Users Posts: 6
    Re: Using two flexmax 80s

    Thanks for the reply
  • unicornio
    unicornio Solar Expert Posts: 217 ✭✭
    Re: Using two flexmax 80s

    I find no reason to turn regulators on and off, unless for maintenance and testing functions.

    regulators, as has been said here, are designed to be connected and working all day as part of the whole system, continuously ...

    and certainly have them both connected through a hub and controlled by the mate (and even better with the help of Flexnet DC) provides many improvements and possibilities beyond something as basic as sharing information about the temperature of the battery, saving us from buying multiple sensors ...

    to have several controllers running in parallel with a battery, all must be configured in the parameters of time, voltage and amperage exactly the same, but if there is a possibility that they are connected intelligently and act jointly, it is worth having it ...and under normal conditions, all have to be always working ...
  • tittiger
    tittiger Registered Users Posts: 2
    edited November 2020 #15
    When you think about it  Outback adding the ability  to slave one unit off of the other would in engineering terms be child's play and would cost next to nothing to add to the Flex 80.  It's hard for me to wrap my head around why this company is so asleep at the switch.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    In reality--Stuff like this is not always "simple"... In general engineering hardware/software projects, about 20% of the project (time/work) gets you 80% of the functionality--However when you add corner cases (what about 3 controllers, what about adding a remote battery AH monitor, what happens if one controller is misprogrammed, what happens if one controller fails--what does the 2nd "good controller" do, how to keep the two different controllers, AC inverters, etc. programs properly in sync and communicating, etc.).... That last 20% of the project (error handling, corner cases, etc.) tends to be 80% of the work on the project.

    I have seen project managers say--If we can get 80% of the product function with 20% of the work--Lets call that done and move on. Many times, that ends up really causing big messes down the road.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • LewisFertig
    LewisFertig Registered Users Posts: 5 ✭✭
    I have an off grid system that uses two flexmax 60 charge controllers. One is for an older set of solar panels charging at 24v ,the other is for newer 75v array. They are both wired into a 24v bus. Both have the same setpoints. I haven't seen any problems except that one controller may finish an absorb or equalization cycle before the other. I can usually tell this by the charge amps on a remote AH meter.If this happens I will manually restart the absorb or equalization cycle on that controller if necessary.