Tristar 45 MPPT and oversizing of array

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newl
newl Solar Expert Posts: 53 ✭✭✭✭
I'm not really clear on running an over sized array on this charge controller. Their string calculator suggests what I'm already running is the optimum configuration (two panels in series) and that running anything larger is indicated as a no-no. However, their product documentation indicates that it will handle an over sized array with no worries. What I'd like to do is really get the most out of the controller with the four panels that I have by running them in series (Voc is still under the 150 rating of the controller).

Looking for thoughts and advise on this. I have 1kw of panels sitting in standby that I'll end up using once I swap out the MC3 connectors for MC4 but that's just as an aside (and another charge controller).

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,442 admin
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    Re: Tristar 45 MPPT and oversizing of array

    You will have to read through section 8 of user manual:

    http://www.morningstarcorp.com/wp-content/uploads/2014/02/MS-ZMAN-TSMPPT-304560A_v05.11.pdf

    A quick read shows that ~115 volts is the maximum Vinput voltage from the array... Above that, the maximum output current is derated down to 0 amps at 145 VDC.

    And, the controller is most efficient with the Vinput voltage closest to Vbatt... With a 12 volt battery bank the differences are quite large (efficiency drops as Vinput rises . On a 48 volt battery bank, the Vinput:Voutput efficiency changes are not as large (as Vinput rises).

    So--Whatever you plan, make sure you don't run the controller at some point in its specifications where it will actually perform quite poorly.

    The typical derating number we use is 0.77 to derate panels+controller losses... In warm to hot climates, the controller will rarely "clip" the output current (solar panel Vmp falls as panel cell temperature rises). Don't know your battery bank voltage, but assuming 12 volts:

    45 amps * 14.5 volts charging * 1/0.77 derating of panel+controller = 847 Watt array "cost effective" maximum for 12 volt battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
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    Re: Tristar 45 MPPT and oversizing of array
    newl wrote: »
    What I'd like to do is really get the most out of the controller with the four panels that I have by running them in series (Voc is still under the 150 rating of the controller).

    Those panels have
    Voc = 22
    Vmp=18
    Imp = 11

    As Bill explained, your controller will be happier down converting 36 volts (2 panels in series) than 72 volts (4 panels in series).

    How about making two parallel strings with each string being two panels in series? That will keep the voltage lower, but will double the input current to 22 amps.

    How long, and what gauge, is the cable from the panels to the controller? That may affect your decision because the higher current (22 amps) may have more voltage drop. You must weigh the increased loss in the cable from higher current and lower voltage against the increased loss in the controller from higher voltage and lower current. It's better to have the loss in the cable than in the controller since the extra heat in the controller will shorten its life.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • newl
    newl Solar Expert Posts: 53 ✭✭✭✭
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    Re: Tristar 45 MPPT and oversizing of array
    BB. wrote: »
    You will have to read through section 8 of user manual:

    http://www.morningstarcorp.com/wp-content/uploads/2014/02/MS-ZMAN-TSMPPT-304560A_v05.11.pdf

    A quick read shows that ~115 volts is the maximum Vinput voltage from the array

    Section 2.2 states that 150VDC is the maximum. Section 8 reflects that. Yep, okay, I do see the chart in section 8 that indicates that 115VDC is the sweet spot before the derating that you mention.
    BB. wrote: »
    And, the controller is most efficient with the Vinput voltage closest to Vbatt... With a 12 volt battery bank the differences are quite large (efficiency drops as Vinput rises . On a 48 volt battery bank, the Vinput:Voutput efficiency changes are not as large (as Vinput rises).

    Yes, still running a 12V bank at the moment. Still intending on changing that yet without a certainty as to when.
    BB. wrote: »
    45 amps * 14.5 volts charging * 1/0.77 derating of panel+controller = 847 Watt array "cost effective" maximum for 12 volt battery bank.
    -Bill

    Yes, saw you mention this in the beginners forum and it got me to thinking on this topic, knowing that over sizing and/or multiple orientations of an array is quite common in grid tie and that some charge controllers that we use off grid are capable of clipping/load shaving.
    vtmaps wrote: »
    How about making two parallel strings with each string being two panels in series? That will keep the voltage lower, but will double the input current to 22 amps.

    That is easily workable. The second pair of panels are on a PWM controller at the moment and wouldn't take much to rework the cabling, breakers, etc.
    vtmaps wrote: »
    How long, and what gauge, is the cable from the panels to the controller?
    --vtMaps

    There is a 2m run of 4mm2 cable from the panels to the breakers, then another .5m from the breakers to the charge controller. Quite short distances really.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Tristar 45 MPPT and oversizing of array

    you do know the mppt 45 does NOT have a web server, or LCD meter display. (shown with optional meter front) and the web interface is quite handy on the mppt60.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • newl
    newl Solar Expert Posts: 53 ✭✭✭✭
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    Re: Tristar 45 MPPT and oversizing of array

    Yes, am aware of that. I typically use MSView for quick stuff with the intention of eventually getting a Raspberry PI running a software system that we've developed and collecting data via Modbus. Still don't have a remote display for the 45 yet either which is also on the list of things to purchase.
  • WillBkool
    WillBkool Solar Expert Posts: 35 ✭✭
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    Re: Tristar 45 MPPT and oversizing of array

    They make MC3 to MC4 adapters, my Evergreen 120's have the MC3 connectors(that's why they were such a good deal I think), and I bought the adapters for them. It's better than cutting them off and voiding the warranty, unless you don't have a warranty, and then it's no big deal.;)
    1220 Watts, 4 Evergreen 120 watt, 1 Eoplly 190 watt; 1 Sungold 200 watt; 2 175 Watt; M-Star 15A MPPT; C40 PWM; 6 105 AH AGM Configured to 315@24V
    Cotek 1500 watt/24v
  • newl
    newl Solar Expert Posts: 53 ✭✭✭✭
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    Re: Tristar 45 MPPT and oversizing of array

    Yup, second hand panels tested good, no warranty, no worries. :)