Looking for a switch to go between my combiner box and the charge controller

jmiller968
jmiller968 Registered Users Posts: 11 ✭✭
Ran into a bit of a problem this weekend and am looking for the best fix.

My panels (4x 100Watt Renogy) are about 150' from my charge controller in my off-grid system.  I have them in series going to my Tristar MPPT 45 controller.  When I put the system in 5 years ago, I put an AC switch in the line coming from my combiner box so that I could disconnect the solar panels from inside the cabin (for startup, troubleshooting, etc).  This weekend I added 2 more panels for a total of 6. This is where the fun starts...

I was doing some troubleshooting with the charge controller...possibly related...and i turned off the AC switch in order to reset the charge controller.  The switch started to glow, which I'm guessing is bad?  I shut everything down, pulled the disconnect out of the combiner box, and am now home looking for a better option. 

 I did some looking and discovered that the AC switch was a bad idea. Not sure if it failed today because I added the extra panels, or if it was just its time.  But I need to replace it, and want it to not fail.  If I'm doing the math correctly, 6 panels in series will be about 130 volts and 6 amps. Is there a simple switch out there that will work for this?  All the DC switches I'm finding seem to be 12v/50 or 100 amp.

Thanks!

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    How are your panels wired ?   all 6 in series ?  3S2P ?  all in parallel ?

    If you have more than 2 strings or panels in parallel, you really should be using a PV Combiner box.  With a 7A DC breaker ($15 ea) on each string, it prevents a bad panel from burning up from the power of the parallel good panels.  And then the breakers give you a very handy A-B-C compairson between your 2 or 3 strings of PV for troubleshooting,  And of course, they can all be turned off. Safely, since the Midnight breakers sold by the webhost, are DC rated to 150V
    https://www.solar-electric.com/mnpv6.html
    https://www.solar-electric.com/midnite-solar-mnepv-7-amps-circuit-breaker.html
     The right size breaker will be listed on the sticker on the back of the PV panel, Max Series Fuse/breaker  __ Amps
    so that would be the proper size to get.

    Additionally, any MPPT controller should have battery power present before PV array is connected to it,  so you could use spare slots in the combiner panel to wire that breaker (50A ballpark ? )  Here's how I did mine: 







    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 ,

  • jmiller968
    jmiller968 Registered Users Posts: 11 ✭✭
    All 6 panels are in series. they then go into a junction box with a serviceman disconnect similar to this:
    https://www.homedepot.com/p/GE-30-Amp-120-240-Volt-240-Watt-Fused-AC-Disconnect-TF30RCP/100576894

    From there I have 12 gauge wiring running to the cabin where my charge controller is.  I did this to keep the amps low so I wouldn't go broke buying 150' of heavy gauge wire. that circuit breaker you showed would certainly work...but I don't really need the combiner box, do I? Is there a small box that that breaker could go in.? I don't really want to have another large box on the wall. Thanks for the input!
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    When dealing with DC, all overcurrent protection devices, or disconnects should be rated for DC, the use of AC equipment will result in arcing of contacts in the case of a switch, particularly when opened under load, or jumping the air gap in the case of a fuse.

    The current rating of an AC fuse will generally be derated to 50% if permitted for use with DC, however it's best to choose the correct equipment if in doubt. With DC breakers it should be noted that some are polarity sensitive, being marked with a + symbol on one terminal, it is actually more accurate to describe it as a potential sensitive device, the + marked terminal should be connected to the side with the greatest energy potential, usually the battery in the case of solar.

    So with regards to the 30A disconnect, it needs to be replaced because although it may work in the closed position, it has the potential to fail when opened under load, much like the AC switch failure you described.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • jmiller968
    jmiller968 Registered Users Posts: 11 ✭✭
    Ok, so does this make sense...buy the midnight solar combiner box along with the 7 amp DC circuit breaker. Install it down at the solar array in place of the AC disconnect that I currently have. Then buy another 7 amp circuit  DC circuit breaker and install it in the cabin before the charge controller?
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Mostly, yes.    Please verify what size breaker you need, 7A is my guess.  The sticker on the panel is right.
     You need some sort of box to hold the wires and breaker,  and there are 2 styles of breakers, DIN mount and panel mount


    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 ,

  • jmiller968
    jmiller968 Registered Users Posts: 11 ✭✭
    Just as an update. I went ahead and ordered 2 of the breakers Mike recommended from the mothership.  The panels said 15 amps, so that is what i went with. I put the one on the beach by the panels in a midnight solar combiner box, and used a baby box in the camp before the charge controller.  Wired them both to the positive wire.  Everything seems to be working correctly, and I'm sleeping better at night now! Thanks for the help everyone!