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  1. #1
    Join Date
    May 2012
    Location
    Second Coast, Ross-shire, overlooking Gruinard Bay.
    Posts
    7,141

    Default Solar panels - can they drain/kill batteries?

    House battery kna**ered, starter battery weakened.
    For three or four seasons my two 20watt panels have maintained the starter and house battery to a good level.
    After a week "down-coast" with bags of sunshine and a lot of motoring, both batteries' "condition" dropped from the green zone, through the yellow and well into the red zone on my monitor.
    House battery (110Ahr) wouldn't even turn over the donk-lump.
    I disconnected the solar panels because their monitor showed 5%.
    I bought a new house battery and over many hours of motoring (for various reasons/conditions) both batteries are into the green zone again.

    What does the team think might be the cause; and is there a remedy for the panels?

    TIA, as usual
    Please try and keep the replies at "numpty level"
    Kay Sarah Sarah
    57°51.42' N 5°29.44' W

  2. #2
    Join Date
    Mar 2017
    Location
    mainland uk
    Posts
    264

    Default Re: Solar panels - can they drain/kill batteries?

    What type of batteries? Wet acid? Have you checked electrolyte level? What type of regulator do the solar panels go to? Do the panels give 20Volts when not connected to anything?

  3. #3
    Join Date
    Jan 2005
    Location
    Greece
    Posts
    946

    Default Re: Solar panels - can they drain/kill batteries?

    Quote Originally Posted by Robert Wilson;6790523....
    Solar panels - can they drain/kill batteries?....
    Yes if they are not connected via a solar controller - no matter how small the panels are.

  4. #4
    Join Date
    Sep 2018
    Location
    Wolverhampton, UK Boat: Gosport
    Posts
    104

    Default Re: Solar panels - can they drain/kill batteries?

    Quote Originally Posted by Robert Wilson View Post
    House battery kna**ered, starter battery weakened.
    For three or four seasons my two 20watt panels have maintained the starter and house battery to a good level.
    After a week "down-coast" with bags of sunshine and a lot of motoring, both batteries' "condition" dropped from the green zone, through the yellow and well into the red zone on my monitor.
    House battery (110Ahr) wouldn't even turn over the donk-lump.
    I disconnected the solar panels because their monitor showed 5%.
    I bought a new house battery and over many hours of motoring (for various reasons/conditions) both batteries are into the green zone again.

    What does the team think might be the cause; and is there a remedy for the panels?

    TIA, as usual
    Please try and keep the replies at "numpty level"
    Am I wrong in thinking that all solar panels have one way diodes to stop just such an experience?

  5. #5
    Join Date
    Oct 2014
    Location
    Australia
    Posts
    196

    Default Re: Solar panels - can they drain/kill batteries?

    Quote Originally Posted by Oletimer View Post
    Am I wrong in thinking that all solar panels have one way diodes to stop just such an experience?
    Yes, you are wrong ;-).

  6. #6
    Join Date
    Jul 2003
    Location
    West Australia
    Posts
    11,532

    Default Re: Solar panels - can they drain/kill batteries?

    I wonder if OP got any useful ideas from the above comments. Firstly I assume OP has a solar panel regulator (controller). He mentions the controller showing 5%. It is unlikely though possible that the controller is discharging the batteries. The solar panels can not discharge the batteries via the controller. Wisdom has it that a panel connected without a diode can discharge a battery at night. I have not been able in tests to show any reverse current. I don't believe my little 5w panel directly connected to the battery has a diode and does not discharge the battery.
    My belief is simply that your house battery died of an internal fault and or old age.
    However if OP wants to check then use a multimeter on amps range connected between the controller and the battery to check firstly for a charge current from the panel and controller. Make sure battery is not fully charged. Then cover the panels or check when dark for any current flowing form batteries to controller. Move the meter to milliamps range to check. My guess is that the solar system will be fine.
    I think Sailinglegend420 is completely wrong in suggesting solar panel without a controller will knacker a battery. It would take a small battery and largish panel to boil a battery with overcharge. Wisdom suggests panels of current capability more than 10% of battery AH rating or more than 10w should have a controller. Ok, but my experience in a very sunny location is that you can have more than that rule of thumb but best to be safe. ol'will

  7. #7
    Join Date
    May 2005
    Location
    up on the moors.
    Posts
    33,164

    Default Re: Solar panels - can they drain/kill batteries?

    Quote Originally Posted by sailinglegend420 View Post
    Yes if they are not connected via a solar controller - no matter how small the panels are.
    Errm, what is the function of a diode ?
    I think, therefore I am. I am, therefore I sail.

  8. #8
    Join Date
    May 2013
    Posts
    386

    Default Re: Solar panels - can they drain/kill batteries?

    Quote Originally Posted by Robert Wilson View Post
    House battery kna**ered, starter battery weakened.
    For three or four seasons my two 20watt panels have maintained the starter and house battery to a good level.
    After a week "down-coast" with bags of sunshine and a lot of motoring, both batteries' "condition" dropped from the green zone, through the yellow and well into the red zone on my monitor.
    House battery (110Ahr) wouldn't even turn over the donk-lump.
    I disconnected the solar panels because their monitor showed 5%.
    I bought a new house battery and over many hours of motoring (for various reasons/conditions) both batteries are into the green zone again.

    What does the team think might be the cause; and is there a remedy for the panels?

    TIA, as usual
    Please try and keep the replies at "numpty level"
    silly question maybe... but are you consuming more than you're generating during your sailing? our 40W panel only lasts us about 4/5 days of sailing (i.e very little motoring) before the house bank starts to suffer unless we turn the fridge off, or start motoring significant distances .

  9. #9
    Join Date
    Apr 2018
    Location
    Mooring, Faro
    Posts
    1,353

    Default Re: Solar panels - can they drain/kill batteries?

    Quote Originally Posted by William_H View Post
    Wisdom has it that a panel connected without a diode can discharge a battery at night.
    It will depend on the regulator being used. Some time ago, I had two regulators of different makes feeding from a common solar cable, to two separate banks. Although no flat battery problem, in the morning both banks would be balanced due to reverse current through one regulator. Problem cured by fitting split charge diode between panel and regs.

  10. #10
    Join Date
    Mar 2010
    Location
    Ammersee, Bavaria
    Posts
    4,655

    Default Re: Solar panels - can they drain/kill batteries?

    Quote Originally Posted by sarabande View Post
    Errm, what is the function of a diode ?
    A blocking diode prevents current flowing from the battery to the panels (wired in series with panels), a by-pass diode (wired in parallel with the panel) helps with shading problems on one panel allowing the current from the other panel to by-pass the dead shaded panel and still charge the battery - applicable for panels wired in series.




    A blocking diode is not needed if the panels go through a charge controller.

    There is a danger if the panels are connected directly to the battery (without a charge controller) - which I would personally never recommend, that they will overcharge the battery and destroy it, or if connected directly to the battery without a blocking diode that they will drain the battery when not charging - and destroy it.
    The best argument against democracy is a five-minute conversation with the average voter.

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