Should I upgrade from a PWM to an MPPT with only 170 watts of Panels?

Bass-O-MaticBass-O-Matic Registered Users Posts: 45 ✭✭
edited October 2020 in Solar Beginners Corner #1
Hiya!

Hope all are well. I have 

2 x 85 watt 12v cheap-o poly panels @ 5 amps each for a total of 170 watts and 10 amps.
Mounted flat. With the glue mounts so they have some breathing room under them.
16 feet from panels to PWM 30 watt charge controller. 6 gauge copper welding cable.
2 x 6volt Costco Gold cart batts.

That's all the room I have on my wee RV. There is a PWM controller on them which works fine. Out of pure boredom -- I was wondering if upgrading to an MPPT would squeeze out more charging?

Well, I did notice on our last trip that the panels mostly kept up but we had to turn off the mini fridge. I was right at 12.1 volts for the trip. We were under some trees.

I hear you have to match your MPPT well... so 20 amp? Which one? I'm not too concerned about the cost. Reliability would matter. I hear MPPTs can be more dodgy? Or is that not true anymore?

Thanks!



Comments

  • 706jim706jim Solar Expert Posts: 484 ✭✭✭✭
    I don't think it would be worth the bother.
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 29th year.
  • andtimeandtime Registered Users Posts: 8 ✭✭
    If your panels are truly 12v, I think 706 is right--maybe not worth spending money needed for a decent mppt. Mine are 18v, so my pwm was wasting power--and living in N MN, I have less sunlight so wanted to maximize and use the voltage that was being wasted. When my pwm fried, it seemed best to go mppt.
  • InCogKneeToeInCogKneeToe Registered Users Posts: 73 ✭✭

    I used a Sunforce 30A CC at m Cabin, (until I was gifted a Trace C40) both PWM. The Sunforce worked great, gave an "Volt" readout as well as an "Amp" Harvest readout. I was running 4, 100w panels. I ran 2 12awg strings, I can't imagine 6AWG Cable for 185 watts.

    Running any "Fridge" is tricky with such a Small System. I run a small 5cu/ft Bar Fridge, for a few weeks while my Wife is on Vacation. I top off my 650AH bank every night with a Gen Set and 30A Bench Charger, while watching a movie. Some mornings, I have to fire up the Gen Set to climb above 12.3v showing.

  • spacebassspacebass Registered Users Posts: 86 ✭✭
    Definitley upgrade to Epever has temperature facility have to buy plug in separately.
  • Bass-O-MaticBass-O-Matic Registered Users Posts: 45 ✭✭
    Hiya! Long time no chat. I've upgraded. See Schematic. And I can say that this will run my mini fridge fine. It ran for a week in the Utah desert... so. full sun. Of course now I"ve discovered 12v coolers with compressors which use half the power and rock! 

    But anyway... lately... my batts died and in the process of replacement I killed my PWM charge controller. I have a 40 Amp MPPT Epever coming in the mail. Just wanted to run my schematic by the gang and see if you see anything you would change. Specifically, I have a 40amp fuse on the batts and I assume that covers the controller, the inverter and everything else down the line... it's been good so far... cheers


  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Gong !!!

    2 PV panels in parallel = OK
    3 and more in parallel, requires overcurrent protection on each panel, using the series fuse spec, a couple % higher than SSC 6.25A
     ( I can barely read the label: max fuse 15A )  so a 12A fuse or breaker would be needed on each panel.

    The PV panel's 17V may not be enough to activate the MPPT circuit in your new controller.


    Things are always good, until they aren't !!
    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 ,

  • Bass-O-MaticBass-O-Matic Registered Users Posts: 45 ✭✭
    edited September 2021 #9
    Thanks!

    1. "12A fuse or breaker would be needed on each panel."

    I do have an inline fuse on each panel just before the branch connector. 15amps each. It's those glass fuses. Do they sell 12 amps? I could go down to 10 amps?

    2. "PV panel's 17V may not be enough to activate the MPPT circuit in your new controller..."

    Oh no... Now I'm lost for sure. Can you recommend a controller? Or at least the specs for a controller for this setup?

    3. One more... i have a disconnect on the + Lead from my PV.... that's OK right? I see somethat cut the negative and positive together.

    Thanks again!



  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    OK, good you have 10A fuses.  They should be OK.  

     Look in the manual/specs for your charge controller, it should state the effective window for MPPT for a 12v battery.  

    The disconnect in the + lead is fine.
    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 ,

  • IntheswampIntheswamp Registered Users Posts: 16 ✭✭
    Hiya! Long time no chat. I've upgraded. See Schematic. And I can say that this will run my mini fridge fine. It ran for a week in the Utah desert... so. full sun. Of course now I"ve discovered 12v coolers with compressors which use half the power and rock! 

    But anyway... lately... my batts died and in the process of replacement I killed my PWM charge controller. I have a 40 Amp MPPT Epever coming in the mail. Just wanted to run my schematic by the gang and see if you see anything you would change. Specifically, I have a 40amp fuse on the batts and I assume that covers the controller, the inverter and everything else down the line... it's been good so far... cheers
    An old thread, but....  If you're still around I'm curious about what you ended up doing in regards to a SCC and how it has worked out....???
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