TS-MPPT-60A Absorption @ 0.1A?

owen_aowen_a Registered Users Posts: 20 ✭✭

I decided to register here since I needed help quite a bit with my MorningStar Tristar MPPT 60A which I've just recently bought, and I thought you people are the ones to ask!

I have it installed and connected to my 100W solar panel (I'm going to be upgrading to a 1kW array soon) and to my 12V 100Ah Numax Deep Cycle battery. On a sunny/cloudy day like it is today, I looked at my controller and saw that it's absorbing at 0.1A @ 14.15V (showing 1W being generated). This is incredibly low. Surely it shouldn't be this low? When I disconnect the battery, the battery voltage drops to 12.8, sometimes 12.69 volts, showing that it isn't charged. I've noticed my controller change to the Float stage a couple of times too.

Any ideas on what is going on?


EDIT: Just decided to check on the Web Interface again and now It's reading this;

Attachment not found.


  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    Welcome to the forum Owen.

    Your battery is some sort of sealed battery (don't know if AGM/GEL or just a flooded cell that is sealed)--14.15 volts is a bit on the low side for charging a flooded cell lead acid, but close to what you would use for a sealed battery (typically 14.2 for GEL, and 14.4 for AGM). And these numbers need to be temperature corrected. If the batter is warmer than 25C, charging voltage would be slightly lower, and if colder, charging voltage would be increased. Have you used a "known good" volt meter to confirm your 14.15 volts at the battery terminals?

    In general, a lead acid battery is ~100% full if it is 12.7 to 12.8 volts after "resting" for 3+ hours at room temperature.

    If the battery is fully charged, then you would expect to see the charging current to fall to 1% (old flooded cell battery) to 0.1% or less for a healthy sealed battery (100 AH * 0.001 rate of charge = 0.1 amps).

    All indications you have given seem to indicate that the battery is fully charged at this time. I notice that it may have a "magic eye" type state of charge indicator? You might be able to pop off the caps (if not welded/glued in place) and use a hydrometer to measure your specific gravity of the battery--The "gold standard" to use with flooded cell batteries.

    Do you have any indication that the battery is not fully charged (i.e., you have just put a 10 amp load on for 2 hours and the charger is still only outputting 0.1 amps)?

    Also, the diameter and length of the copper wire from the charge controller to the battery can make a difference too... You want pretty heavy copper wire so that you have somewhere around 0.05 to 0.10 volt maximum drop when you have heavy charging current so the charge controller can measure the "actual" charging voltage of the battery (not wire drop+battery voltage).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • owen_aowen_a Registered Users Posts: 20 ✭✭
    Hi Bill,

    Thank you very much for clearing those things up for me. I used to have a leisure battery that held a voltage at 13.1Volts and presumed these types of batteries are meant to do the same.

    The battery I have is a Sealed Lead Acid battery, and I chose to have it charging at 14.1V (originally had it set to 14.3 via the dip switches). I presumed that the battery was not fully charged when it showed 12.7-12.8 volts - this was when I disconnected the controller and looked at the controllers web interface during the night to see the battery voltage.

    Until I order my four solar panels, I'm keeping the system wired pretty rough (not neat) at the moment and using 13A cables (for wiring mains sockets), to connect to the battery and the controller.

    I have some 30A cable ready to connect to my battery bank when these panels are ordered since I'm going for a series parallel configuration on both the solar and battery bank to get my ~24VDC.

    I disconnected the RTS thinking it was causing an issue that clearly wasn't there.

    Thanks once again,
  • BB.BB. Super Moderators, Administrators Posts: 31,680 admin
    In general, connecting the RTS is a good thing.

    Keeping the battery charged while waiting to get the rest of the system installed--Also very good. Flooded cell batteries will "start to go bad" after 1 month of no charging... Sealed/AGM/GEL can go 3-6 months between charging.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.