PV to Flexmax80 question

System Posts: 2,511 admin
I am upgrading my system with an Flexmax80 MPPT charge controller and new bigger panels. My budget allows for 5x180 watt Imp 6.95, 25.9 Vp panels (cheap ones.) I already have the charge controller but haven't purchased the pv yet.

I'm trying to figure out the parallel/serial thing. I want to use serial to save wire size. But do I need 6 panels for that? 2 strings of 3? Does that require 2 charge controllers. I'm not really sure I understand what the charge controller can handle. How would you guys suggest I connect them?

Oh and is a 275 AMP DC breaker big enough for my battery disconnect?

I have a 12 volt battery setup. 8 golf cart batteries. A 12 volt Xantrex Prosine 2000 watt inverter/charger. Honda eu2000 for backup.
My current panels are a hodgepodge of 60watt up to 120 watt panels (approx. 750 watts worth) connected in parallel to a Xantrex 60 amp charge controller. I will be moving some of the old panels to a grundfos solar pump.



  • BB.
    BB. Super Moderators, Administrators Posts: 33,404 admin
    Re: PV to Flexmax80 question

    Really need to know the brand and model number of your solar panels. And the temperature range of your location (southern California?).

    Basically, a MPPT solar charger will work from ~max bank voltage + 2 volts up to its maximum voltage (around 145 volt max operational for most Outbacks, and less than 150 volts never exceed)... So anywhere in between will work just fine. The higher the input voltage, the lower the current--so smaller wires. But, as the voltage goes up, the switching losses go up slightly to in the solar charge controller (a couple percent).

    In the end, you need to figure out the range of Vmp (cold to hot) to ensure the charge can always charge the batteries an Voc (open circuit)--typically highest on cold days--to make sure you don't damage the solar charge controller's input...

    Read through the Outback manual for details/recommendations. And give us a little more information (min/max temperature for your area, brand/model of solar panels/how much power you want--issues of series/parallel panels--even numbers and such).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: PV to Flexmax80 question

    the higher voltages provided by the each pv will be fine for you. just parallel them. being there's 5 you couldn't do it any other way unless you seriesed them all and that will push the voc possibly higher than the max input to the controller(didn't check), but that in and of itself is redundant as the controller would be more inefficient with going from 100+v down to 12v. a string of 2 of those pvs could be used if the losses at 25v isn't good enough for you and that makes the pvs a 48v system down to a 12v battery system or roughly a 4:1 ratio. that would mean 6 pvs though.
    you did not go into specifics on what the run length would be or what wire gauge you are using for a more specific comment on that.
  • System2
    System2 Posts: 6,290 admin
    Re: PV to Flexmax80 question

    I am located in Southern Baja. It not really as hot as you might think. I'm on the Pacific. In the winter it is around 55/75 low/high, in the summer I don't really think it gets above 90. It's always comfortable in the shade, just the humidity makes it uncomfortable.

    Using a sizing calculator on the web I calculated that I use 4000 watts a day. 121 Kwh a month. With my current system I need to run the generator on nights when we have music performances.

    The Panels are Sun-180's (Evergreen rebadge?)
    Test specifications:
    Ptolerance -2%
    Pmp, max 186.1
    Pmp, min 176.4
    Pptc3 159.7
    Vmp 25.9
    Imp 6.95
    Voc 32.6
    Isc 7.78

    With that many panels in parallel for my 30' run, I would need #2 wire. Is that correct?

    I could consider buying 6 170 watts panels. If I series them into 3x48v panels I would only need #4 wire. The extra panel puts me over budget. I still don't understand if the controller can handle that. (my head is starting to spin)

    It would be cheaper just to stick with the generator, but we need to buy panels for a new Grundfos water pump anyway. So I figured I would upgrade the house and use the older 100 watt panels for the pump.

    .....and if it will get me brownie points.....I purchased the charge controller from Wind and Sun and will probably get the pump from them as well.

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: PV to Flexmax80 question
    ravemind wrote: »
    The extra panel puts me over budget. I still don't understand if the controller can handle that.

    What charge controller are you looking at?

    With the panels about 25V (32Voc) you could put 3 in series, for about 75V (96Voc) and let a MPPT controller down-convert to 12V for you. 2 in series (50V) would work too, but you have more amps and fatter wire requirement. That has to be weighed against the suggested efficiency loss with MPPT controller running farther from the target battery voltage. (anyone have any specs on that ??)

    An MPPT controller, generally, safely throttles itself back if it does start to approach it's output amps limit.
    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 ,

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: PV to Flexmax80 question

    the 5 180w pvs in parallel will be fine with the flexmax. here are the ratings as listed by our host. note that the voltage is the battery system voltage being used:
    Maximum Solar Array: 12 VDC systems 1250 Watts / 24 VDC systems 2500 Watts / 48 VDC systems 5000 Watts / 60 VDC Systems 7500 Watts

    5x180w=900w. so you have room to expand to 6 of those pvs with no problem. if you ever wish to go more than 6 of them then you may wish to consider going to a 24v battery system or add another controller although 7 of them would be borderline over at 7x180w=1260w.
    imho you are good to go with the 5 pvs and the flexmax and you can add pvs later if you wish to up to 2 for a 12v battery bank.
    i did not check on the charge percentage you are presenting to the battery bank and the pv output should lie within 5-13% of the battery capacity. the disconnect i think is overkill, but will be fine as 2000w/12v=167a assuming this is between the batteries and your inverter. actually it's overkill no matter where you have it.
  • quid_non
    quid_non Solar Expert Posts: 48
    Re: PV to Flexmax80 question

    I'm also looking at those Sun panels mentioned in the post. Seems to be a great price for the performance (< $3/watt). The supplier says that they are not UL listed - - is this a serious issue for off grid use? Also - these are available in "A" or "B" panels - Anyone know what are the differences?

    Is the price too good to be true - the specs are listed in the post above.

  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: PV to Flexmax80 question

    UL is just a sticker, the panels are all the same, well except for the blemishes, regardless if they are Sun Branded, or Evergreen "A" or "B" grades

    If you are not required to have a permit or you local code doesn't require UL listed stuff, save the $$ and get the Sun Branded panels

    The Only reason they don't have UL stiecker is so the lower priced Sun panels don't takes martket share from Evergreen directly
  • System2
    System2 Posts: 6,290 admin
    Re: PV to Flexmax80 question

    The price for these panels saves me huge amounts of money. I live in mexico and the added cost of shipping and import taxes adds at least 40% to the cost. I would be paying $1200+ a panel if I bought a big name brand. These will cost me $800.
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: PV to Flexmax80 question


    You have only one option with a 12 V battery bank, five of the 180 W modules and an FM80 controller: You’ll have to wire the five modules in parallel. The controller will operate very efficiently in this configuration, but you’ll need large AWG wire between the array and the controller.

    If you decide to purchase six of the Evergreen 170 W or 180 W modules, you’ll then have three wiring options for a 12 V battery bank, all using a single FM80 charge controller:

    1) All six modules in parallel
    2) Three parallel strings of modules, with two modules wired in series in each string.
    3) Two parallel strings of modules, with three modules wired in series in each string.

    Option #3 will allow you to use the smallest AWG wire.

    The size of the DC breaker between the battery bank and the inverter will depend on the inverter specs. Please provide us with the intended make and model.

    Jim Goodnight
    Eastern Regional Sales Manager
    OutBack Power Systems
  • System2
    System2 Posts: 6,290 admin
    Re: PV to Flexmax80 question

    Thanks for all your great help.
    I flew back to US this weekend to pick up my new Flexmax80. It's a big!

    I am using a Xantrex Prosine 2.0, 2000 watt 12volt inverter.

    What would you guys recommend as a DC breaker?

    My budget allows me to buy a Midnite Solar Mini DC disconnect for all my breakers, but i'm not sure if I need an extra large breaker between the charge controller to the batteries.
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: PV to Flexmax80 question


    Interesting shopping trip! ;)

    You'll need a DC rated circuit breaker sized for 80 A continuous duty between the charge controller and the battery bank. An example is the OBB-80-150VDC-PNL from OutBack.

    Xantrex' nominal full power DC input current spec is 200 A. You'll need one of those BIG DC-rated circuit breakers rated at 250 A. An example is the OBB-250-125VDC-PNL from OutBack.

    More breaker info: http://store.solar-electric.com/oudcbr.html

    Jim / crewzer