Can you use two separate MPPT charge-controllers?

Organic Farmer
Organic Farmer Solar Expert Posts: 128 ✭✭
If I were to have a system with solar-panels, MPPT charge-controller, invertor, battery-bank, load; and a year later I wanted to combine more solar-panels. But let us assume that the new solar panels are different amperage [technology marches on].

I see the math problems of combining panels with different amperage ratings.

Can a separate MPPT charge-controller be used just for the second group of solar panels?

Can two MPPT charge-controllers co-exist feeding a single battery bank?

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Can you use two separate MPPT charge-controllers?
    If I were to have a system with solar-panels, MPPT charge-controller, invertor, battery-bank, load; and a year later I wanted to combine more solar-panels. But let us assume that the new solar panels are different amperage [technology marches on].

    I see the math problems of combining panels with different amperage ratings.

    Can a separate MPPT charge-controller be used just for the second group of solar panels?

    Can two MPPT charge-controllers co-exist feeding a single battery bank?

    It is not a problem to use two arrays with two controllers on one battery bank.

    If you use two that can talk to each other, like the Outback series, they can share data through the com system (including battery temp) and match completely.

    If you use two different controllers you'll have to pick one as the 'primary' controller and then program the other to follow it. This may not be as simple as it seems because not all charge controllers have the same functionality or degree of programmability. For instance the Morningstar uses pre-set time on Absorb whereas the Outback adjusts Absorb time according to the length of the Bulk stage. In that case use the less programmable unit (the Morningstar) as the 'primary' controller and adjust the more programmable one to follow it.

    Clear as mud?

    You can use MPPT and PWM controllers in combination too.
  • silvertop
    silvertop Solar Expert Posts: 155 ✭✭✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    Yes, I run three Xantrex XW-MPPT60-150 controllers on one 24v battery bank. I only needed to connect them together with a cat5e jumper cable very simple plug and play no system panel needed. They all play as ONE controller as far as Bulk / Absorb /Float but are for separate arrays chargeing on there own.:D
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    This feature will be coming soon to the Midnite classic as well...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • alyaz
    alyaz Solar Expert Posts: 114 ✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    FWIW, our Rogue controller and Apollo HV Turbo controller have been best of friends since installation...
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    I use an MX-60 on PV, and a TS-MPPT-60 on micro hydro, both feeding into the same battery bank. No problems.
  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    Re: Can you use two separate MPPT charge-controllers?

    Something to mention...

    If you put connect more than one CC in parallel like this, be sure to make sure that each one has it's own fuse or circuit breaker, and they are properly sized. I once saw a case where someone had added a second CC to the same existing breaker as the first one, and it was tripping under good sun. This was on an old Trace setup. We replaced it with an Outback Flex-Power-One setup, but had to add a second PV breaker for the second charge controller.

    I think the NEC technically requires dedicated overcurrent protection for each CC, but if you're not going to follow that with two CCs then at least use the same size wires for both CCs, even if one requires a larger ampacity than the other. If you should happen to have more than two CCs, then fuse them all. Same principles here as with PV source circuits (at least if you leave GDFI out of it).
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Can you use two separate MPPT charge-controllers?
    It is not a problem to use two arrays with two controllers on one battery bank.

    And just to make it completely clear, since the question has come up elsewhere:

    1. You cannot combine two CCs running either to the same or different battery banks off the same panel array.
    2. You cannot run both a CC and a GTI inverter off the same panel array at the same time unless it is a combined system designed for that purpose like the SunnyBoy / SunnyIsland combination.
    SMA SB 3000, old BP panels.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    Good points "jaggedben" and "inetdog", sometimes we assume others would automatically know these things, when in reality they don't. Good reminders.
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    Inetdog its been done thousands of times two controlllers in parallel sometimes three controllers and same panels and same batteries.
    Or how you going to charge batteries with a 10kw panel system ?The highest power chargers I know have a max capacity of about 80a.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Can you use two separate MPPT charge-controllers?
    john p wrote: »
    Inetdog its been done thousands of times two controlllers in parallel sometimes three controllers and same panels and same batteries.
    Or how you going to charge batteries with a 10kw panel system ?The highest power chargers I know have a max capacity of about 80a.

    ???
    John, If you have a 10KW array, it's really broken down into several smaller arrays each hooked up to a single controller, the whole 10 KW array doesn't hook up to each... I'll have a 4KW array, but it will be hooked up 2 KW to each CC, both CC feeding the same 24V battery bank. (and 3 CC feeding the same bank next summer)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    Photowit I know that is the accepted way but have seen and know of many that have had more problems doing it that way than simply just paralleling everything. We also did many experiments about this at work and found less problems happened if the panels were broken up into smaller groups then ALL joined together at a junction box and from there to two or more CC. The outlets from the Charge controllers then fed to one battery pack of course.
    The thing that causes the problems is passing clouds. If one panel in a group gets cloud cover for more than a few seconds and that group is connected to the master controller it alters the charge stage.
    I cant off the top of my head now remember all about this as it was done mabe 2 or 3 yrs ago,, But I certainly remember it all worked better if everything just paralleled.I remember we told some of the manufacturers of the controllers this ,some said its not good but had not tried it them selves others agreed that it could be better but had not tried it either.

    What I previously asked people that said it isnt the way to do it just putting everything in parallel. Have you tried it? and if yes ?what happened. Always same answer never tried it ,as its not how they do it.
    I will try to find all the test results that were done in next few days and put on here the most interesting parts..

    If anyone reading this has done comparison testing (on the one system) can you put it here and give us the results .
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    One caution for anyone who wants to "try this at home":

    Manufacturer says "don't do it" = void warranty.

    Not an absolute and I can't say they'd ever know unless you told them but ... caveat experimentor.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    John, I don't intend on doing that in my setup and since your "2 years ago", I think Outback's master and slave is more mature, and "boB" who is a frequent contributer here is also the engineer working on setting up the Midnite classic for similar functioning.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    Photowit you may be right about controllers having different characteristics now in how they work together. It was as I said at least two years ago and mabe three years ago we did that. And I have not had anything to do with that size system since.

    Has anyone actually seen in a charge controller manual not to parallel inputs from same panels? Its got me interested in this again now. Mabe time to investigate the whole idea again.

    I now dont get to see many really new design charge controllers for lead acid batteries any more . They seem to have reached now about the end of the line for new advances. New advanced GT inverters are where it seems to be happening now. I find them from a testing point boring.

    If anyone out there now has any ideas for interesting inverter ,battery or charge controller setups. Tell me as im retiring soon ,so can do them now before my end of use date.
  • Organic Farmer
    Organic Farmer Solar Expert Posts: 128 ✭✭
    Re: Can you use two separate MPPT charge-controllers?
    inetdog wrote: »
    And just to make it completely clear, since the question has come up elsewhere:

    1. You cannot combine two CCs running either to the same or different battery banks off the same panel array.
    2. You cannot run both a CC and a GTI inverter off the same panel array at the same time unless it is a combined system designed for that purpose like the SunnyBoy / SunnyIsland combination.

    It would have never occurred to try and parallel two CCs. I do not see what purpose that would serve.

    I keep seeing folks talk about having two different sets of panels, with different specs, and the issues that come from wiring them.

    To connect each set of like panels into separate CCs makes more sense to me.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Can you use two separate MPPT charge-controllers?

    I am getting a little confused...

    Is this a question of making a "large array" (many kWatts), and series/parallel connections to one +/- bus point (Voc-array/Vmp-array compatible with MPPT controller inputs)? Then connecting multiple MPPT charge controllers in parallel (on the solar panel side) to the common solar panel bus and on the output (common battery bus) side?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Organic Farmer
    Organic Farmer Solar Expert Posts: 128 ✭✭
    Re: Can you use two separate MPPT charge-controllers?
    BB. wrote: »
    I am getting a little confused...

    Is this a question of making a "large array" (many kWatts), and series/parallel connections to one +/- bus point (Voc-array/Vmp-array compatible with MPPT controller inputs)? Then connecting multiple MPPT charge controllers in parallel (on the solar panel side) to the common solar panel bus and on the output (common battery bus) side?

    -Bill

    I am seeing folks who have one set of panels. Then years later maybe they get a newer generation of panels with completely different specs. Combining panels of different amperages includes other issues.

    So having one CC for each different generation of panels seems to make sense.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Can you use two separate MPPT charge-controllers?

    I agree--That is the 'standard' way of addressing the issue (second MPPT controller with Vmp-array configured differently than the first array).

    But I was trying to understand John P's comment about paralleling MPPT controllers (on the input side too?).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: Can you use two separate MPPT charge-controllers?
    BB. wrote: »
    I agree--That is the 'standard' way of addressing the issue (second MPPT controller with Vmp-array configured differently than the first array).

    But I was trying to understand John P's comment about paralleling MPPT controllers (on the input side too?).

    -Bill

    One reason you would want to parallel the input and output together is for an existing system where the array is hundreds of feet away from the batteries and they initial installation used something like 4/0 cable because they were using a PWM controller and now they want to use a larger PV array with MPPT but don't want to spend the money needlessly on more wire.

    I have talked to more than one customer that had this issue before. Not very often but once in a while.

    boB
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Can you use two separate MPPT charge-controllers?

    I believe the XW MPPT controller (at least the standard voltage one) measures the array current in the negative leg--So it cannot be paralleled without confusing the MPPT function.

    boB, with your designs--Can the negative/return leg to the array bypass the MPPT controller completely? That would address a concern I would have with proper current sharing with the paralleled negative connections (assuming there is no "current steering" in the negative side of the controller).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Can you use two separate MPPT charge-controllers?

    On the Outback MX60 the negative in and negative out are a pass-through; two wire connections side by side that are the same terminal block.

    I can see advantages/disadvantages to this 'all inputs together' wiring. The advantage being if one controller's array is clouded (as John mentioned) it can draw any "extra" power it needs from the whole. This is assuming there's any to draw; I suspect it would not be of any use where you have, say, 1kW of array trying to feed two different controllers; there simply isn't enough PV to power them both to full capacity. But with a very large array and multiple controllers going to the same battery bank it could have potential.

    On that issue we have the usual questions that get asked around here such as one array feeding two different battery banks or one battery bank and one GTI. There's where the two or more MPPT's are going to disagree on settings because their output would have different requirements.

    Another part of it has to be the particular controller. Bill mentioned Xantrex's using the negative side to measure current, so it probably would have issues in a parallel set-up. Then again you have the 'old style' like the MX60 that does an occasional sweep to set its V & I vs. the 'new style' that continuously readjust. I should think the new style would be better in a parallel arrangement because they would never be 'out of sync' in their settings whereas the kind that sweep would not pick their power point simultaneously and might chose a V & I followed by change in another controller which would unbalance the panel load for the first's selections.

    Aside from all that there is the issue of wiring. Trying to send the whole current from a lot of panels down one set of wires is difficult as the wire size would get unwieldy. So it is normal to divide the array up into smaller segments on smaller wires each to its own controller. To that end, you'd look for any current potential between positive inputs on the controllers. If the array is very large there's bound to be some as the panels, even if all aimed identically, with different insolation.

    There probably isn't any danger to doing this; merely a question of which way would work better and that is, as always, going to be site dependent.

    The technical explanations I'll leave to the guys here who actually design charge controllers.