MT50 Controller on my RV not putting a charge on the battery

MenindorfMenindorf Registered Users Posts: 2


Brand new to this forum, but it seems there are friendly and knowledgeable people here! 

I had this MT50 working with an outdoor off-grid system before, and it was pretty much plug-and-play.  Now on my RV, it is acting strange.  Can anyone tell by these images what's going on?  It seems like the battery is not full, but it still won't put any amps into the battery.  It switches automatically to the load setting (even though I don't have anything connected.)  I manually turn off the load, and it still won't place a charge over the battery.  My best guess is that the controller gets confused when the motor charges the battery. . . .  ?  But it seems like many have had success with the MT50 in an RV application, so I am not sure what I am doing wrong. . . .  The panel is not getting ideal sun at the moment. . .  but it seems it's still producing some voltage?  help!?  ps ~ forgive the dark/fuzzy photos


  • littleharbor2littleharbor2 Solar Expert Posts: 1,377 ✭✭✭✭
    First of all, the MT-50 isn't a charge controller. Where is and what is your charge controller? If you do, in fact, have a charge controller Tell us what it is and what you have for solar panels. If an MPPT controller you want higher voltage into the controller.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Your solar array and/or solar array wiring appears to be having problems.

    Your array should be around 21-22 volts with zero current (Voc--voltage open circuit). Assuming that the panels are getting full sun (no shade) and it is something like 10am-2pm local time (i.e., full/direct sun on panels), and with a PWM type charge controller, the current should be Varray will be something near or ~1 volt or so over the battery voltage (i.e., if full sun, battery charging with X amps from panels) or >~12.7 volts (battery typically needs ~13.6 to 14.8 volts to charge--Assuming flooded cell lead acid) with ~13.6 volts the "float voltage" (battery fully charged, just enough current to keep the battery full) and ~14.8 volts Absorb Set point (maximum charging voltage, held for roughly 2-6 hours for full charge).

    I would go through the solar array connections (in j-box if wired there), the connectors if using those, and the wiring to the charge controller. And from the controller to the battery bank.

    It would be handy if you have a volt meter of some sort, and can measure the voltage at different points in the system.

    Ideally, more information as Littleharbor2 asks... The brand/model/type of charge controller. The solar panels Vmp/Imp ratings. And how they are wired (2x panels in parallel, 2x2 panels in series/parallel, etc.).

    Given that it "used to work", I am guessing it is poor/corroded/lose electrical connections somewhere in PV array -> charge controller -> battery bank (connections near the battery bank can get corroded from venting gasses+electrolyte).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MenindorfMenindorf Registered Users Posts: 2
    Thank you Little Harbor, and BB~ I am traveling and thus don't get a lot of Internet time.  But I have received your comments, and I will experiment a bit more and get back to you!  I know the sun exposure is quite inadequate where we are currently parked. . . plus the panel is mounted flat on the roof, and also shaded by a roof vent.  This all combined with low-angled Sun in Winter. . .  I think this may simply be the issue.  But I am going to observe the system in different sun-conditions and see if the problem remains.  The "used to work fine" system had 900 watts with panels wired in parallel.  But now I have only one 170W panel. . .  Also, I have an MPPT Tracer4215B.
  • littleharbor2littleharbor2 Solar Expert Posts: 1,377 ✭✭✭✭
    I'd look into getting at least one more 170 watt panel. I'm basing this on the assumption that the 170 watt panel is a 36 cell (12 volt) panel. You need to series wire two panels together to get the input voltage higher. Also do whatever you can to prevent shadowing on either panel. That controller is a 150 Voc. max controller, btw.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

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