Solar charger 12 or 24 Volt HELP WANTED

Discussion in 'Motorhome Chat' started by Malcolm Bolt, Jun 25, 2013.

  1. Malcolm Bolt

    Malcolm Bolt Funster Life Member

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    At the beginning of the year I got extra solar panels and now have two new batteries to store all that lovely sunshine I've been experiencing lately - Not. Tomorrow they will be fitted.

    The batteries are both Banner 115/135AmpHrs and will be connected in Parallel They will be fed via a Victron Energy blue solar MPPT charge controller. I had assumed that this charger would be connected in parallel :Cool:but the guy at the service centre says it is better to connect to the positive of one battery and the negative of the other. He says this is much better way as it ensures the charge in each battery is maintained at the same level. That does not sound right to me.

    By now you will have all gathered that electronics and I have never been good buddies. What he says sounds convincing when he is talking but as soon as he turns away I get that horrible feeling my lovely pristine pair of Banners and those sunshine harvesters on the roof are about to shrivel and die.

    I know some of you will enjoy taking the p*ss at Malcolm's expense :thumb: but the job is scheduled for tomorrow and if anyone who really does know about this sort of thing please let me know ASAP.
     
    Last edited: Jun 25, 2013
  2. Snowbird

    Snowbird Funster Life Member

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    Hi pal, Your man is right. That is the right way. Stop worrying.
     
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  3. Geo

    Geo Trader - Funster

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    2nd,d:thumb:
     
  4. lunarman

    lunarman Funster

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    Why will the batteries be connected in series? Is the Hymer a 24v system?

    Lunarman
     
  5. Malcolm Bolt

    Malcolm Bolt Funster Life Member

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    OOPS:Blush::Blush:

    OK so I know nothing. I meant parallel I just put series - a mistake. Sorry.

    I have edited above does it make sense now?

    Van is 12 volt. Batteries will be in parallel but controller will be connected to positive of one battery and to the negative of the other.

    Is that OK?

    In fact as both battery positives are connected and both negatives are connected does it matter anyway?

    (Still worrying)
     
    Last edited: Jun 25, 2013
  6. TheBig1

    TheBig1 Funster Life Member

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    if the 2 batteries are side by side and connected with high amperage thick cable, theres no difference. however if the batteries are any distance apart, the resistance of the joining wire comes into play so you put +ve to +ve on 1 battery and -ve to -ve on the other. this spreads the charge evenly between the 2.

    its the same when coupling up a larger bank of 3 or more batteries, where you connect to the first and last batteries.
     
  7. SomeoneElse

    SomeoneElse Funster

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    This is an urban myth of motorhomers, its totally fertilizer from the male cow:Laughing:
    Once the two batteries are connected in parallel they become one. What is important is the the interconnecting cable is of a suitable size. Nice and chunky in engineering speak, it must be suitable for both the charging and load currents
    What are you going to use "all that lovely sunshine" for? Its likely that the discharge current will exceed the charging current, connect an inverter and it may well be an order of magnitude higher. This is the current that should be used to size the cable between the batteries.

    In short make sure the cable between the two batteries is the sort of thing used to connect your vehicle battery to the starter and then where you connect the 15Amps from your Victron controller is of no importants.

    Now you mentioned solar panels in the plural, are they identical?
    If so you can make saving on power loss on the PV side on the Victron controller by connecting the panels in series. The Victron can take an input of 70V, panel produce a max of 23V. So connecting two in series doubles the voltage rather than the current. Its the current that causes the losses. But don't connect two different panels in series as the currents must match.

    Gordon
     
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  8. jenny and mitch

    jenny and mitch Funster

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    An Autotrail with a 325 Sargent PSU is pre wired to take a 100 Watt solar panel... Does the info in the last post mean that you could connect 2 x 100 Watt panels in series ???? Very interested..... Mitch and jenny...
     
  9. SomeoneElse

    SomeoneElse Funster

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    I don't know the Autotrail or the Sargent PSU, but if its specified to take 100W I would not expect it to take 200W.

    I made the point about connecting panel in series because the OP mentioned a Victron MPPT controller.

    The "old" Pulse Width Modulation (PWM) controllers usually specified a maximum PV voltage of 30V, a typical solar panel has an open circuit voltage of 22.9V so when two are used there must be connected in parallel. The new generation of MPPT (Maximum Power Point Tracking) controllers have higher PV voltage specifications. The Victron 70/15 unit has 70V most Chinese units have 100 or 150V limits. Therefore with these two or more panels can be connected in series. However be aware that the amount of panel wattage is still limited by the output (ie charging) current of the controller. In the case of the Victron unit this is 15Amps and Victron say its 70/15 controller is good for 200W of panels.

    The other advantage of connecting panels in series is that charging starts when the panel voltage reaches battery voltage plus 5 volts, this will occur earlier with two panels in series.

    Gordon
     
  10. Malcolm Bolt

    Malcolm Bolt Funster Life Member

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    Thanks all round. Job Done

    Thanks for all the input guys. The batteries are close although not side by side. The cables are a bit heavier than both the starter and the inverter cables and are less than 1 meter long. :Smile:

    I've got to do a bit of making good eg plastic conduit over a short length of visible cable and a cover for the additional battery compartment but all is looking well. :thumb::thumb:

    Today the original battery - now removed - was tested and found to be in good order so I'm thinking of taking up a suggestion of yours Snowbird. ie Connect the inverter to the spare battery, instead of the two fitted today and charge it using a battery to battery charger - - - - - - still thinking about that one :Eeek:
     
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