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Batteries not charging much in full sun

descott12
descott12 Member Posts: 46
in Battery/Electrical & Solar
Hello all,
I have a new 2025 Tab320S with 390 watt panels on the roof and the victron smart shunt and charge controller. I have two LiTime 100AH batteries in parallel. Yesterday, in full sun, with the batteries at 80%, the charge controller was only showing 36 watts when it should have been closer to the full 390. A little while later is was showing 93 watts but still far short of what it should be doing. I have attached a few screenshots of the Victron app main page. I have not measured the actual voltage coming from the panels in full sun but I plan to do that ASAP.
Any thoughts?  Does the "Smart" in SmartSolar MPPT mean it is trying to do something fancy when all I want is a fully charged battery??
Thanks in advance. I will contact Victron directly if nobody here has any ideas.
Cheers


2025 Tab320S pulled by Ford Maverick
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Comments

  • MuttonChops
    MuttonChops Member Posts: 1,934
    descott12 said:
    . . . 2025 Tab320S with 390 watt panels on the roof 
    . . . charge controller was only showing 36 watts when it should have been closer to the full 390.
    . . . later is was showing 93 watts 

    Big Picture - - - you will never see/get the solar panel 'rated' output of 390 Watts.
    Solar Industry output measurement standard testing is done under very controlled conditions that can never be achieved in the real world.  Many folks use a 60% to 75% of rated output as the realistic maximum power and you will only see that maximum output for a specific sun angle & time.

    I don't use Victron components on my aftermarket mini-solar setup so can't comment on Victron App data/usage.
    '18 320 S,  pitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    TV: '25 Canyon AT4
    Adventures:  58   Nights:  405  Towing Miles 50,180
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  • donmontalvo
    donmontalvo Member Posts: 187
    edited September 2025
    As @MuttonChops said, the numbers are under perfect lab conditions, so gotta come to terms with that.

    Curved solar panels will only ever get a fraction of the rated output even on perfectly sunny days, however they're great on overcast days, where diffused light can hit the entire solar panel.

    I have a 2024 320S BBC with 2x190 solar panels. I hang a flat 100W solar panel on the aluminum tubes at the back. I point the back of the camper South (with iPhone set to Use True North), so it can get maximum sun.

    On sunny days the 100W panel rules...on overcast days the 2x190 curved panels rule.

    I added a second 100ah LiFePO4, for 200ah total, so power lasts longer.

    Don Montalvo | Retired Veteran | Full time boondocker
    Camper: nuCamp T@B 320S BBC | 12V 2x100Ah LiFePO4 | 600W Solar
    Tow Vehicle: Jeep JLU Rubicon | 12V 100Ah LiFePO4 | 200W Solar
    https://revkit.com/donmontalvo/ | https://donmontalvo.com
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  • descott12
    descott12 Member Posts: 46
    Hey guys,
    Thanks for the comments. Yes, I understand that I will not get close to 380 watts. But 36 in full sun?  I know I have seen it producing close to 200 watts previously in full sun.
    But functionally, it should be pumping as much energy into the batteries whenever it thinks they are less than 100%. Correct?
    2025 Tab320S pulled by Ford Maverick
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  • donmontalvo
    donmontalvo Member Posts: 187
    Curious how your battery settings are set up?

    Here is what my SmartShunt and MPPT (the one used for my 2x190 roof panels).





    Don Montalvo | Retired Veteran | Full time boondocker
    Camper: nuCamp T@B 320S BBC | 12V 2x100Ah LiFePO4 | 600W Solar
    Tow Vehicle: Jeep JLU Rubicon | 12V 100Ah LiFePO4 | 200W Solar
    https://revkit.com/donmontalvo/ | https://donmontalvo.com
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  • Sharon_is_SAM
    Sharon_is_SAM Member Posts: 10,061
    Did you sync to 100%?
    Sharon / 2017 T@B CSS / 2015 Toyota Sienna Minivan / Westlake, Ohio
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  • descott12
    descott12 Member Posts: 46
    donmontalvo said:
    Curious how your battery settings are set up?

    Here is what my SmartShunt and MPPT (the one used for my 2x190 roof panels).






    Thanks for the reply.
    For the MPPT, The differences are as follows:
    Battery preset = LiFEPo4
    Expert mode is off
    Equalization voltage is disabled
    I don't have the Bulk or Absorption sections - I am guessing due to the Expert mode off.
    Equalization is disabled

    For the shunt:
    Charged voltage = 14.2V
    Tail current 2%
    Peukert 1.05
    Charge efficiency factor 99%

    Not sure what all these do but it looks like you have customized your settings quite a bit.
    2025 Tab320S pulled by Ford Maverick
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  • donmontalvo
    donmontalvo Member Posts: 187
    I'm not an expert, but I slept at a Holiday Inn...erm...I mean, I posted my settings to the Victron Energy page on Facebook. Tons and tons of feedback, after a couple weeks my solar settings hit the sweet spot and I stopped having power issues.
    Don Montalvo | Retired Veteran | Full time boondocker
    Camper: nuCamp T@B 320S BBC | 12V 2x100Ah LiFePO4 | 600W Solar
    Tow Vehicle: Jeep JLU Rubicon | 12V 100Ah LiFePO4 | 200W Solar
    https://revkit.com/donmontalvo/ | https://donmontalvo.com
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  • descott12
    descott12 Member Posts: 46
    Sharon_is_SAM said:
    Did you sync to 100%?
    Yes but now that you mentioned it, it seems like it things the batteries are topped off and it isn't trying to charge them more. Does that sound like a good theory? Maybe I need to sync them again.
    2025 Tab320S pulled by Ford Maverick
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  • descott12
    descott12 Member Posts: 46
    donmontalvo said:
    I'm not an expert, but I slept at a Holiday Inn...erm...I mean, I posted my settings to the Victron Energy page on Facebook. Tons and tons of feedback, after a couple weeks my solar settings hit the sweet spot and I stopped having power issues.
    I wish I could get on the page. I have been banned from Facebook forever. I created an account a 15 years ago, never even made a post. But I tried to reactivate it and I get denied. Even with new, completely unrelated email addresses. Go figure. I will contact Victron directly.
    2025 Tab320S pulled by Ford Maverick
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  • donmontalvo
    donmontalvo Member Posts: 187
    Create a burner email account, then use it to create a burner Facebook account. :blush:
    Don Montalvo | Retired Veteran | Full time boondocker
    Camper: nuCamp T@B 320S BBC | 12V 2x100Ah LiFePO4 | 600W Solar
    Tow Vehicle: Jeep JLU Rubicon | 12V 100Ah LiFePO4 | 200W Solar
    https://revkit.com/donmontalvo/ | https://donmontalvo.com
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  • descott12
    descott12 Member Posts: 46
    donmontalvo said:
    Create a burner email account, then use it to create a burner Facebook account. :blush:
    I did. Several times. Somehow it knows who I am. Not sure how.
    2025 Tab320S pulled by Ford Maverick
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  • ckjs
    ckjs Member Posts: 134
    donmontalvo said:
    … Here is what my SmartShunt and MPPT (settings are)…
    > MPPT 
    > Absorption 14.20 V
    > Equalization 16.4

    The 14.2V of Victron’s LiFePO4 preset is perhaps a bit low for your batteries, or, in fact, quickest charging of many brands. It will probably just take a little more time, no biggie.
    The specifications for our LiTime 100Ah’s say to charge at 14.4V.

    How did the Equalization voltage get turned on? It should be disabled for LiFePO4 batteries.

    The shunt settings don’t affect the charging rate of the batteries. It’s better to consider them as helping the shunt estimate how much charge is in the batteries.
    Charles & Judy, Santa Cruz, CA
    2018 T@B 320 CS-S; Alde 3020; 4 cyl 2020 Subaru Outback Onyx XT
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  • AnOldUR
    AnOldUR Member Posts: 1,725
    ckjs said:
    The 14.2V of Victron’s LiFePO4 preset is perhaps a bit low for your batteries, or, in fact, quickest charging of many brands. It will probably just take a little more time, no biggie.
    I had my LiFePO4's at 14.4 for absorption and 13.5 for float voltages, but recently watched a Will Prowse video that recommended 14.5V / 13.6V. The reasoning was for better cell balancing when in absorption mode. I was close enough that I'll probably not notice the change, but if you're coming from 14.2V it could make a difference.

    Stockton, New Jersey
    2020 nuCamp T@B 320S * Jeep Wrangler
    60,865 camping miles through the end of 2025

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  • donmontalvo
    donmontalvo Member Posts: 187
    ckjs said:

    ...[snip]...
    How did the Equalization voltage get turned on? It should be disabled for LiFePO4 batteries.
    ...[snip]...
    If you look closer to the screenshots I posted, I actually have automatic equalization disabled.
    Don Montalvo | Retired Veteran | Full time boondocker
    Camper: nuCamp T@B 320S BBC | 12V 2x100Ah LiFePO4 | 600W Solar
    Tow Vehicle: Jeep JLU Rubicon | 12V 100Ah LiFePO4 | 200W Solar
    https://revkit.com/donmontalvo/ | https://donmontalvo.com
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