Morningstar Sunsaver Duo Question

Mello MikeMello Mike Registered Users Posts: 15
Hello everyone. New member here. Just installed a Morningstar Sunsaver Duo in my truck camper and was wondering about the efficiency of the unit. I have a single 120 watt panel (6.5 amp max) on the roof but I've yet to ever see a 14.4v (I have 2 Group 24 wet cell batteries in my camper) reading on my Morningstar Remote Meter. Is this normal? The highest I've ever seen it go is about 13.4. Before connecting the panel to the controller I was pulling 18v regularly. I used 10-gauge wire to make all connections.



  • BB.BB. Super Moderators, Administrators Posts: 33,313 admin
    Re: Morningstar Sunsaver Duo Question

    A Group 24 battery is around 70-85 AH hours. A pair of 12 volt batteries in parallel would be twice that amount.

    A 120 watt panel and PWM controller should produce around:
    • 120 watts / 17.5 volts Vmp = ~6.9 amps in full sun
    Your battery bank is around 140 to 170 AH... And with an average of 0.77*6.9 amps = 5.3 amps average current:
    • 5.3 amps / 140 AH = 0.034 = 3.4% average rate of charge
    • 5.3 amps / 180 AH = 0.029 = 2.9% average rate of charge
    Roughly, a battery with a ~1% rate of charge is "float charging" or suitable for long term storage.

    And ~5% to ~13% is the rough rule of thumb for actually recharging a battery bank... So, in your case, you would need almost 2x the amount of panels you currently have to really properly recharge your battery bank.

    At this point, it will take a very long time to fully recharge a bank after use... For example, assuming summer weather of ~5 hours of full sun per day and a 50% discharge of a 2x 80 AH pair of batteries:
    • 50% * 2 * 80 AH = 80 AH
    • 80 AH * 1/0.80 typical flooded cell efficiency = 100 AH from charger to recharge
    • 100 AH * 1/5.3 average charging current * 1/5 hours of sun per day = 3.8 days of full sun to fully recharge the bank from 50% discharge
    At this point, it simply sounds like your batteries need more time/energy recharging. They will not reach ~14.5 volts until the batteries (in this case with low charging current) until the batteries are ~90% (guesstimate) charged.

    Do you have a hydrometer you can check the specific gravity with--Or after the batteries have rested for ~2-3 hours, you can check the resting voltage and compare it to a charge (~12.7 volts being fully charged and 11.7 or so being 20% charged--already very deeply discharged).

    Some reading:
    Deep Cycle Battery FAQ

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Morningstar Sunsaver Duo Question

    also if you are using loads during the time of the recharge the loads will take away from the charging current and could take it too low to properly charge the batteries. try it during 2 sunny days with no loads to the batteries and see if they come to full charge. if they do you need to add more in pv and possibly lower you loads to the batteries.
  • Mello MikeMello Mike Registered Users Posts: 15
    Re: Morningstar Sunsaver Duo Question

    Thanks guys. Yeah, I was thinking that I probably wouldn't reach 14.4v until I added another panel on the roof. The highest amperage I've ever seen during the day was 6.5 amps. I have SDM24 Interstate Deep Cycle batteries with each battery rated for 82 amp hours.

    As an experiment I'm going to remove all loads in the camper over the next two days and see what happens. I'll turn off the Fantastic Vent fan and pull the fuse for the LP and CO detectors.

    This is a great site. Thanx again for the replies.
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Morningstar Sunsaver Duo Question

    The LP and CO detectors are such a small load, it is hardly with the effort. Remember, a smoke detctor 9 vt battery lasts years. (though it should be change twice a year)

    Your current PV configuration is fine for long term storage, but is way too small to recoup daily draws. Just as a comparison, we live off grid, with 400 watts of PV, consume 5-800 WH of power out of 450 ah of battery, and we are fairly well balanced.

  • Mello MikeMello Mike Registered Users Posts: 15
    Re: Morningstar Sunsaver Duo Question

    An interesting thing happened today during Day 1 of my experiment. I totally removed all 12v loads and my Morningstar Sunsaver RM registered 14.4v as the max voltage for the day. Cool! Thanks Neil for the tip.

    I'll definitely be adding another 120 watt panel, but this proves there's nothing wrong with my system as it's now configured (besides that lack of panel wattage on the roof). :D
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