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  1. #1
    Join Date
    Aug 2018
    Posts
    114

    Default solar panel newbie still confused

    Ok so i am a numpty but having read all the stuff in the forum i still cant find an answer basic enough for my needs . I dont really understand battery charging physics and so i have gone initially for a very simple 20 watt panel with a cheap pwm charge controller to cut my teeth on . All i really want to know is at what voltage should i disconnect at the high end and the same at the low end . i dont intend to ' load' the solar panel as such just using it to top up the battery on anchorage . the batteries are sealed lead acid .

  2. #2
    Join Date
    Mar 2003
    Location
    falmouth
    Posts
    16,177

    Default Re: solar panel newbie still confused

    The controller usually has settings fixed in it. But if it hasnt I suggest something around 13.7 v which is where the maintenance voltage of your alternator usually is. There is no need to set a minimum - do you really want the solar panel to switch off when the voltage in the battery gets low?
    this post is a personal opinion, and you should not base your actions on it.

  3. #3
    Join Date
    Aug 2018
    Posts
    114

    Default Re: solar panel newbie still confused

    i think i meant when the solar panel voltage was low but im not really sure what i do mean , hence the very confused . i thought they were capable of discharging batteries when the sun went down and needed to be stopped or does that happen automatically

  4. #4
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    7,562

    Default Re: solar panel newbie still confused

    Quote Originally Posted by dunkelly View Post
    i think i meant when the solar panel voltage was low but im not really sure what i do mean , hence the very confused . i thought they were capable of discharging batteries when the sun went down and needed to be stopped or does that happen automatically
    f you have a controller, the most you need to do is set the charging voltages, if that with only 20w. What make/model of controller ? What settings does it have ?
    Rainbow Marine.
    www.rainbowmarine.co.uk

  5. #5
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,177

    Default Re: solar panel newbie still confused

    Quote Originally Posted by dunkelly View Post
    Ok so i am a numpty but having read all the stuff in the forum i still cant find an answer basic enough for my needs . I dont really understand battery charging physics and so i have gone initially for a very simple 20 watt panel with a cheap pwm charge controller to cut my teeth on . All i really want to know is at what voltage should i disconnect at the high end and the same at the low end . i dont intend to ' load' the solar panel as such just using it to top up the battery on anchorage . the batteries are sealed lead acid .
    Tell us what controller you have !

    Does it have "load" terminals in addition to the battery and solar panel connections? If so are you confusing the settings for the "load" disconnect and reconnect voltages with settings for the actual battery charging parameters
    The fact that you are talking about "the low end" suggest you may be

    If the above is the case you can ignore the load terminals and the disconnect and reconnect settings for them.
    Last edited by VicS; 17-04-19 at 20:05.

  6. #6
    Join Date
    Aug 2018
    Posts
    114

    Default Re: solar panel newbie still confused

    thankyou i think that is exactly what is confusing me . its just one of the cheap blue ones on e bay ( its on the boat unfortunately) , until i get to grips with what i am doing i thought i would experiment with that before going bigger and better . so is it that i can just leave it as it was factory set and the internal electronics or diodes or whatever look after the battery charging ?

  7. #7
    Join Date
    Sep 2001
    Location
    Me - Zumerzet Boat - Wareham
    Posts
    11,949

    Default Re: solar panel newbie still confused

    With just a 20w panel some might not bother with a controller at all, with a controller it's fit and forget as the controller will block any possible overnight discharge.
    MontyMariner.co.uk
    Facilitated by AWESEM WP Agency

  8. #8
    Join Date
    Dec 2016
    Posts
    135

    Default Re: solar panel newbie still confused

    Quote Originally Posted by LadyInBed View Post
    With just a 20w panel some might not bother with a controller at all
    In my experience a controller is almost always a good idea even with a small panel. I had an ancient 5W panel connected to my start battery without a controller for a while until I noticed it had got over 16V. That was in the middle of winter. Not good for the battery.
    Last edited by Elbows; 17-04-19 at 22:09.

  9. #9
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,177

    Default Re: solar panel newbie still confused

    Quote Originally Posted by LadyInBed View Post
    With just a 20w panel some might not bother with a controller at all, with a controller it's fit and forget as the controller will block any possible overnight discharge.
    A frequently quoted rule of thumb is to fit a controller if the ratio of watts to Ah capacity exceeds 1 watt per 10Ah and to fit a controller to all panels over 10 watts

  10. #10
    Join Date
    Sep 2001
    Location
    Me - Zumerzet Boat - Wareham
    Posts
    11,949

    Default Re: solar panel newbie still confused

    Quote Originally Posted by Elbows View Post
    In my experience a controller is almost always a good idea even with a small panel. I had an ancient 5W panel connected to my start battery without a controller for a while until I noticed it had got over 16V. That was in the middle of winter. Not good for the battery.
    Yes. I suggest that SOME might not use a controller as the OP said "i dont intend to ' load' the solar panel as such just using it to top up the battery on anchorage". Inferring occasional use.
    MontyMariner.co.uk
    Facilitated by AWESEM WP Agency

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