12v solar system problems

Discussion in 'Electrical Systems' started by Tod24, Aug 2, 2014.

  1. Tod24
    Joined: Aug 2014
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    Location: newquay

    Tod24 Junior Member

    first of all hi

    ive joined these forums as i am stuck with the electrical system on my yacht.
    just want a simple set up for use through the day or when i sleep on the boat at weekends. Its a bit of all over at the min

    this is a rough guide of my power consumption i will note down the exact values tomorow.


    Power = 2 x 20w 12v Solar panels = 40w
    3 x 120 ah 12v leisure batteries = 360 ah


    load = 3 x 4w led 1m strip lights = 12w
    12v iPod speakers 25w


    not used daily

    start for engine
    navigation lights
    vhf radio

    the engine battery was already pre wired so i added an extra 2 leisure batteries under the port and starboard lockers in the front cabin /bedroom

    then put in 2 20w solar panels which i wired to the furthest battery. i take the feed for the fuze db unit from the center battery and the first battery that is wired directly to the engine. i have put in links to all the batteries live to lives neutral to neutrals.

    I have a voltmeter that comes on when i switch the fuze box feed on so i can watch the load stress.

    i have been trying to power up my laptop and bought a car convertor but when i power it on they is a big surge and the meter goes right down and it shuts off.

    just don't know where i am going wrong?
     
  2. AndySGray
    Joined: Jun 2014
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    AndySGray Senior Member

    A common issue with batteries is dirty terminals

    they will work for smaller loads but the resistance causes too much voltage drop when a larger load is applied.

    If not - test things one at a time - does the inverter work if you hitch it up to the car?

    Swap a battery with the motor battery - will it start the engine? will the engine battery boot the laptop...
     
  3. AndySGray
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    AndySGray Senior Member

    The rule is P=IV

    Watts = Amps x Volts

    Gives Amps = Watts divided by Voltage

    your 25W ipod load is a little over 2 amps

    a laptop could be drawing 7 (mine requires 19v @ 4 amps - so 6.3 at 12v assuming no loss)

    if the terminal is loose and dirty things heat up and you lose contact - terminals should be bright and silvery, inside of clamp needs to be clean too.

    when clean and properly tightened THEN apply battery grease.
     
  4. AndySGray
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    AndySGray Senior Member

    Final thing that is oft overlooked is DC loads require much thicker cables than AC loads - is your wiring of sufficient gauge?
     
  5. AndySGray
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    AndySGray Senior Member

    Re-read;-

    So - have you actually got 3 batteries wired in parallel?

    Usual to seperate house and starting battery

    Do you have any sort of charge splitting device?
     
  6. Tod24
    Joined: Aug 2014
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    Tod24 Junior Member


    yes there wired in parallel i will split and separate the engine battery today, the cables to connect the two house batteries is is the big thick cable you get on terminals. i did link the engine battery with 2.5 as i wanted the solar panels to keep it charged. And the feed from the second battery to the fuzes is 2.5? I don't have any other charging device for the engine battery as the voltage remains the same with engine running, so im assuming the brushes need replacing in the alternator but i cannot find one could it be integrated into the starter motor?

    i haven't installed a solar charger controller yet' not sure where i would put it.

    today when i go to the boat i will separate the engine battery from the two house batteries check the cables and terminals write down the correct values for load and supply, i will also eliminate the laptop inverter by checking it works in the car. ;)
     
  7. Tod24
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    Tod24 Junior Member

    il swap the batteries around today check they all start the engine cheers


     
  8. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Two remarks to think about:

    1. If the solar panel(s) supply less than 5% of the battery capacity no regulator is necessary. In your case the panels charge less than 1%, in fact just enough to maintain the batteries.

    2. With proper wiring, clean contacts and charged batteries the load from an iPod or laptop cannot be seen on the volt meter except for one small dip when the load is connected for the first time.
     
  9. AndySGray
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    AndySGray Senior Member

    Longer term I would have a heavy duty switch to link the house and motor banks - something goes wrong and you have a flat motor battey but healthy house bank - then you can start the motor. At the moment you could leave something on for a couple of days and all batteries would be dead - I had something jam a bilge pump float switch in the on position which drained one battery and a flick of the switch and I was back in business.

    Splitting out the House may be better for the alternator. Don't worry too much about the voltmeter staying at 12 with the motor running - modern regulators seem to do it that way if the battery isn't too low - I wouldnt be worrying about it's function yet.
     
  10. gonzo
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    gonzo Senior Member

    If a voltmeter shows 12V when the engine is running, there is a problem in the charging system. It should be showing 14.4V minimum.
     
  11. AndySGray
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    AndySGray Senior Member

    Thanks Gonzo for the correction - I oversimplified that one a bit (helluva lot actually) - very much correct in that there must be a higher potential than 12v across the terminals for charging to occur.

    However, it has become a lot more common recently on computer controlled charging systems to supply a 'clean' accessory feed through the loom, which becomes live on ignition on - this used to be the ideal feed for the Vm as there was no drain with the ignition off. On a ECU, ECM or any other computer related TLA (Three Letter Acronym) a standard analog voltmeter will show much less variation in normal operating state - we have three legacy VDO guages which all show 12 (ish) but the 'smart' gauges which are linked to the engine data bus show 14.75 at the same time (after about 8 button pushes). (So I don't really need to correct the wiring)This was where I was going with it not neccessarily being time to panic about a so called 12v reading. A multimeter across the terminals will put that one to rest in a moment.

    I must remember not to post in a morning until at least 2 cups of coffee have been downed. :eek: Mia Culpa :D
     
  12. gonzo
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    gonzo Senior Member

    Coffee keeps millions of brains functioning
     
  13. AndySGray
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    AndySGray Senior Member

    Too True

    ...and Beer returns them back to normal ;)
     
  14. Tod24
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    Tod24 Junior Member

    yeh thanks i think i said that already gonzo prob the brushes but i cannot find an alternator? i was thinking is it possibly combined into the starter motor? thats my next job anyway :)


     

  15. Tod24
    Joined: Aug 2014
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    Tod24 Junior Member

    Right guys here's an update (Problems Fixed ) :)
    past 2 days ive re-wired my boat ive used new battery terminal connections, The feed cable to the fuze box is 8mm, distance 5 meters. The charge supply via 2 solar panels is 2.5 as its such a low current. distance 7 meters.

    I split the battery feed and wired the 19v laptop inverter directly with a 20A inline fuze
    which i still need to install a switch to isolate the inverter.

    Then ran another feed to the fuze box for lights radio & 12v socket with usb
    all working perfectly


    I realized the problem must have been with the fuze box after i connected each battery directly to the inverter and all worked fine.

    So in the end the problem i was having was down to the fuzes

    I was and still unsure what size main fuze i should have i did have a 10A one in there and then a 8A for the inverter.
    It must have needed more power and strained the supply trying to pull it all through a 8A fed by a 10A

    3 x 1m led lights ive now put on a 5A
    ipad sound dock = 5A
    12v socket with usb = 10A

    Still unsure of main fuze size just have 10A in at the min going to try buy some bigger ones today but for some reason i thought small glass fuzes only went up to 10A ?

    thanks
     
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