Simple solar charge design question

Discussion in 'OnBoard Electronics & Controls' started by L'eau.Life, Aug 13, 2016.

  1. L'eau.Life
    Joined: Jan 2008
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    Location: Bay of Islands, New Zealand

    L'eau.Life Junior Member

    Hi all,
    Firstly; what I know about electrics can be written on a postage stamp so please bear with me . . . .
    I went to check on our boat (a 3hr drive to the Bay of Islands) as winter is slowly drawing to close "down under" in NZ and understandably, found the batteries quite low on charge so over summer I plan to put in a SIMPLE, LOW COST solar charging system to keep them topped up and if possible, run an inverter during summer to give 220V to the dometic fridge so that is ready for use when arrive to use the boat.
    She is a small 30ft powercat with one engine in each hull started by and replenishing a dedicated 650CCA start battery and providing charge to individual house units.
    My initial thoughts are to install a single 100W panel (seems to be the best RoI) atop the cabin with split feeds to 10A individual charge controllers in each hull.
    Questions:
    1. Is it OK to simply split the feed or is it better to install the more expensive option of 2x60W panels?
    2. There is an existing cross link to connect both start batteries so another option to use that and just have one controller dedicated to the start system?
    3. Assuming split feed as Q1, is there a simple way to then charge both start and house batteries off the same controller without bridging the circuits?
    4. As an alternative to Q3, am I better to split the feed and have one controller for the combined start circuits and a second for the house (with a new cross link between those batteries)?
    5. Is 100/120W a realistic capacity to maintain the batteries? Too small? Too big? Is there such a thing as overkill?
    Many thanks in advance!
     
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Solar regulators are usually using the shunt principle. That means they short the solar panel input as soon as the battery voltage reaches the "fully charged" threshold.
    With more than one regulator on a single panel all charging is interrupted as soon as one battery is fully charged.

    If you intend to use one battery for the fridge, keep it isolated from the starter battery and give it its own panel.
     
  3. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Solar does a fine job of maintaing an batt set over time.

    Refrigeration is usually the highest DC load on the vessel.

    A solar setup to run much in the way of refrigeration will not be low cost or simple .

    A VERY small and very very good reefer will have the lowest power requirements.

    But they aint cheap!!!

    An inverter just adds another expense and power loss. Most house units have no where near enough insulation.
     
  4. Chuck Losness
    Joined: Apr 2008
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    Chuck Losness Senior Member

    I think that you may be making this too complex. How do you currently charge your batteries? How are your batteries separated from each other? If the batteries are separate from each other then the simplest solution to is to put a small solar trickle charger on each battery. This will keep both engine batteries charged but you will not have the capacity to run anything else.
    Once you go beyond simple engine starter battery charging you have to determine what your daily amp hour draw is and then size your system for the anticipated loads. On my sailboat I typically use 80 to 100 amp hours per day. My house bank is 4 golf cart 6 volt batteries wired to provide 12 volts. This has a total capacity of 400 amp hours. I have four 65 watt solar panels. The solar panels charge the house bank. My engine starting battery is charged via a battery combiner off the house bank. Because you have two separate engine starting batteries you would need a battery combiner for each engine battery. The solar charge controller is sized based on the output of your solar panels. But the battery combiner has to be sized based upon the output of your alternators. I hope this helps.
    Good luck with your project.
     
  5. L'eau.Life
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    Location: Bay of Islands, New Zealand

    L'eau.Life Junior Member

    Thanks Chuck, it does help.
    My system has a single 12V 630CCA start battery charged by a 75A alternator. The 120AH house battery is then charged via a relay energised by the alternator. Each "hull" is independent and the house batteries power only their dedicated systems.
    The two engine batteries can be cross fed should one fail and until now, there have been no issues over the past 12 years.
    What has changed though is that I moved the boat from a local rented marina berth to our swing mooring about 3hrs drive from here and over winter we've been traveling overseas so she hasn't been run in around 6 months. Hence, as we plan to make winter travel an annual event, I need to put solar on to maintain the new batteries in good health.
    I like the idea of keeping it simple and I'll again look at a couple of solar trickle chargers but when I checked before these are almost as expensive as going with 100W or twin 60W panels.
    Thanks to all for your inputs.
     
  6. BertKu
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    BertKu Senior Member

    Why do you want to buy a 100 Watt solar panel? I would just do it with a 10 watt, 1 Ampere panel. Then with a, like CDK mentioned solar panel shortening system when the battery is full, is all you need to keep the battery from compensating the leakage current which is in anyway only maybe 20 mA. Just make sure that you have the batteries fully charged before you go overseas. Or do you have items all the time on, which consume electricity?
    Bert
     
  7. BertKu
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    BertKu Senior Member

    Even a 5 watt solar panel is ample. Bert

    p.s. the cost is by us, for a 10 watt panel 18Volt/12 volt battery is +/- 12 dollar for each of your battery. Actual searching the internet, I'm paid less for the 10 watt then I see is asked for the 5 watt panels. Just the 5 watt is smaller and easier to mount out of the way.
     
    Last edited: Aug 16, 2016
  8. groper
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    groper Senior Member

    When you say the house battery is charged via a relay from the alt, are you referring to a voltage sensing battery combiner solenoid/relay? If so, then all you need to do is connect the solar reg output to the start battery. The voltage sensing solenoid will then combine the 2 batteries and the solar will be charging both batteries at once as soon as the start battery is above the voltage threshold for it to close the relay. If you don't have one of these then I'd recommend getting one as they quite convenient.

    If not, then simply parallel the start and house batteries together via a manual switch when you leave the boat and then feed the solar in to either- they will both be electrically the same and stay fully charged the entire time your away.

    You have 2 separate systems, 1 in each hull... if you bring a pair of wires from each hull battery system to a single solar reg, then you have effectively parralelled the batteries at the terminals of the regulator and it will again charge all batteries at once. However you will have permanently parralellel them at this point and so they will all discharge together as well. If you wish to keep each hulls system separate, then you will need 2 regulators.

    Lastly, I have no idea if you can run 2 regulators off 1 solar panel, I doubt many people have ever even considered it...
     
  9. L'eau.Life
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    L'eau.Life Junior Member

    Many thanks. I've decided to go this route for the engine batteries and will forego the fridge idea which was never really a priority.
    Cheers!
     
  10. BertKu
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    BertKu Senior Member

    Groper, that means that he could have 2 blown up batteries when he comes back from overseas after 3 months. If he does not correctly check this system, that the solar panels are really switched off, when batteries are full. Except if he has 2 controllers and 2 solar panels which charges the batteries separately and short circuit the solar panel. I did not have the impression, from what he stated in No1 thread, that he wants to use the panels also for charging while sailing, but only to ensure that his batteries are full when he comes back after 3 or 6 months out of the country.
    But a 100 watt solar panel or 80 watt panel is an overkill. For his purpose a 5 or 10 watt panel and 2 circuits as attached diagram will do the job beautiful, inexpensive. He just have to ask a hobbyist to make it for him. He could also do it with a 2 x 7815 regulators + 4 diodes 1N4007, that is all. This is all what is required to stay below the gassing voltage and compensate for the leakage currents. If he wants to do it fancy, he can put a few electrolytic caps also in the circuit. Bert
     

    Attached Files:

  11. BertKu
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    BertKu Senior Member

    Indeed you can't . Most of the regulators short the panel if the one battery is full and then the other battery will not be fully charged. Bert
     
  12. BertKu
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    BertKu Senior Member

    My apology, I over looked this point. Fair enough then a 100 watt or 80 watt panel could do the job. However, when you are out of the country for 3 months or more, I assume you switch the fridge off. In that case the 80 or100 watt panel is a total overkill for keeping the batteries topped up. My suggestion is to keep the fridge going during the summer as a different issue from keeping the batteries topped up while away for long periods of time. Bert
     
  13. L'eau.Life
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    L'eau.Life Junior Member

    Wow! Thanks Bert - that's awesome
     
  14. L'eau.Life
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    L'eau.Life Junior Member

    I have found a simple low cost solution on Aliexpress.com in the form of an EP Solar 10A duo battery controller for <$30. It seems you nominate the charge priority and the controller switches between battery 1 & 2 to keep both charged. As I already have a 20W panel, I hope that should sort the start batteries nicely.
    For the fridge; I'm heading up to the boat today and will look for a data plate to get the 220V load info for what inverter supply I need to keep it idling. Although it is a gas/12V/220V model, I understand only the 220V option has thermost control so 220V seems to be the best option for maintained running.
    Thanks again to all who offered their thoughts and advice.
     

  15. BertKu
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    BertKu Senior Member

    Hi L'eau. My apology, I should have read your thread properly and had it let sink in that you were eager also to let your fridge running day in day out during the summer month. I don't know whether it is a good thing to keep a solar panel for 3 to 6 months shortened while you are away. A 100 watt panel produces 6 Ampere and I have no idea what sort of wiring you have to allow this to be shortened day in day out, bright sunshine for 8 hours every day. The ones I use are MPPT (Maximum Power Point Tracking) and they switch the panel not short, but reroute the connection from the battery to a dummy load. I will speak to some friends at a solar cell manufacturer and see what they have to say. I have many times shortened a solar panel, also in demonstrations while part of the solar energy society. But I have never kept a panel shortened for days and weeks and months. The leakage current for a large battery is at the most 20mA = 0.02Ampere x 24 hours and consume only 0.5 watt per battery per day. I will try to find out whether there is a internal panel consequence for shortening for so long. Maybe I am concerned for nothing. But better finding it out than to be sorrow. Bert
     
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