Solar/Battery Help Needed

Discussion in 'Solar Power' started by maddy1, Aug 5, 2015.

  1. maddy1

    maddy1 Read Only Funster

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    I need help with my solar install, I have an old motorhome and I want to install 6X 100W 12V panels that I've already bought, I'm thinking of 6X Trojan T105, Volt 6, AH 225 I've read lots and lots but, some say this and some say that, (I am gathering as much info as possible in written form) i now have brain overload, I would like to know whats the best way to hook all these up, please? (keep them at 12v in parallel? Or 24v in series?) I know i need a MPPT controller, which one? i looked at a Morningstar Tristar MPPT 45 amp 12/24/48V, but its a lot of money is there a good alternative? Just to add I want to run a fridge freezer, lowest energy that i can find, so i will need an inverter, maybe 12v to 240 2000w pure sine wave? any suggestions? also looking at a Durite B2B 24v to 12v charger. Many Thanks.
     
  2. DavidG58

    DavidG58 Funster

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    Morning, I can see you are fairly new to the forum, or at least do not post much

    But I am sure I saw exactly this same post from you yesterday

    We are easily confused, but equally easily frustrated if we think we are duplicating our efforts

    It would be better to add another line to the original thread to bump it back up if needed, but I think you were still getting replies this morning to the original thread

    Maybe @Jim could remove this one to reduce confusion

    Best of luck with the question though, far too deep for me :)


    EDIT - just read your last comment in the original thread, see what you are up to now, sorry for interfering (trying to help) (y)
     
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  3. funflair

    funflair Funster Life Member

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    Hi Maddy1

    Certainly a hell of a good Solar/battery installation, if you fit the 6xT105 you will total 675 ah, when you say digital inverter fridge I think you are looking at a domestic fridge to run on 240 volts. I have looked at the spec of a couple of these domestic fridge/freezers and they would seem to consume around around 60 amps per day at 12volts, I would round that up for the safety plus the inverter running and call it 100 amps which your batteries are not going to miss too badly as even on a poor sun day the solar should put this back.

    To install the batteries you just treat each pair as one battery by connecting the + terminal to the - terminal of its mate.

    As far as inverter is concerned I would be tempted to go 4000 watts as you have lots of battery capacity and good potential to recharge so a larger inverter will allow you to run a couple of 240 volt appliances together without worrying about overloading. Personally I would consider running a dedicated inverter to the fridge and it would only need to be a few hundred watts and then another one to the 240volt sockets, then if one inverter whent down you would still have a way of running your fridge.

    Martin
     
    Last edited: Aug 5, 2015
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  4. LaMB

    LaMB Funster

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    Err, I think you need to rethink the red text, at least! A bank of batteries have all their positives connected together and all their negatives together normally, so they are in parallel and not series.
     
  5. ThePeltonian

    ThePeltonian

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    I concur with @LaMB

    Parallel will increase the AMPS ie 2 12v 105 amp batteries will create 12v 210amps
    Series increases the voltage ie 2 12v batteries in series will create 24v
     
  6. vwalan

    vwalan Funster

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    the batteries in question are 6v so would need to be connected in pairs as op says .
    just pos to pos /neg to neg in this case would only end up with a bank of 6v batteries .
    given the price of trojan batteries and their expected life . i prefer 12v truck batteries .
    these also have the advantage that in emergency you can if you get the right ones . use them as the vehicle engine batteries .
     
  7. ThePeltonian

    ThePeltonian

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    ahh i see that ... (should really read it all)

    So series would work.. for banks of 2 then parallel banks together if your using 12v or series x4 of them for 24v if your going down that route
     
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  8. LaMB

    LaMB Funster

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    I see too, Trojan are batteries. lol
     
  9. Wildman

    Wildman Read Only Funster

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    you have 6 x 6V batteries so the first thing to do is connect them in ( pos-neg) that will give you 3 x 12v batteries (12v 225amp/hr) then connect the 12v units in parellel outside poss to poss and outside neg to neg) giving you a 12v 675 amp/hr bank.
    600W of solar will give you a theoretical 50 amp/hr in the summer it will average out at a quarter of that and in winter a tenth just to give you some idea of the charge available. Given the number of batteries you cannot connect as 24v so 12 or 36v are your only choices, many more things run off 12v so I would stick with that. The 45 amp controller may at times be overloaded (given max output midday/midsummer when the sun is directly overhead and producing 50 amp/hr)and given the price would not recommend it.
     
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  10. maddy1

    maddy1 Read Only Funster

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    Hello all and thanks for all the good replies.

    Hello vwalan hows things?
    I was thinking about the 12v truck batteries, but what i've read about the way batteries dont like being drained i was worried that it would kill them, unlike the trojan being deep cycle ?
    I was thinking putting the solar in series for 24v (not the batteries) and letting the controller convert it back to 12v, wont this let the controller take more watts? 1200w instead of 600w or have i got it wrong?
     
  11. maddy1

    maddy1 Read Only Funster

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    Just to add I could have a 24v battery set up (not with the 6 trojan) as well and use a 24v to 12v dc converter for the 12v stuff, I could some how charge my truck batteries from the solar as they are 24v ? is this an option? I know they do 24v inverters, so its all possible, whats your thoughts anyone?
     
  12. funflair

    funflair Funster Life Member

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    Are you going to be parked long enough to need solar on the truck batteries, if so possibly a smaller 36volt panel with its own 24volt regulator.

    You won't be able to feed more power through the controller by going 24 volts so I would stick with 12 volts and possibly a slightly larger controller or split the panels between two slightly smaller controllers and then again you have a built in spare. I have two controllers feeding the same batteries and they work fine.

    Martin
     
  13. vwalan

    vwalan Funster

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    i can only say what i have used and seen others do over the last 15 years .
    if its really not sunny then switch off the inverter. the fridge can be turned off at night if need be .
    i use 2x180amp batteries and 2x110amp batteries . the smaller ones will fit the truck. only had to use them once . that was last winter one of the engine batteries went down .
    as another person has said i do the same . 3x80wt panels through a 30amp reg . twice .
    if a reg goes down or a panel is damaged etc i still get some power .
    only need a kid to drop a stone off a m,way bridge or something like it .
    i do carry spare regs but if need be all 6 of my panels could go through one of the regs .
    unless its really sunny , fingers crossed it will be ,ha ha . i seem to be averaging 4-5 years on truck batteries . simplicity works for me .
    i also use pwm regs , they work good and are alot cheaper than mppt . i,m almost sure there is such a small difference between the two sorts . its abit like mono or poly panels . not worth worrying about.
     
  14. TheCaller

    TheCaller Funster

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    It won't make any more watts when it's working, but it might the panels work for more of the time.

    To properly charge a 12v battery, you need somewhere between 13 & 14.8 volts, depending on battery type. A nominal 12v solar panel does this with no problem, producing anything up to 21v in bright sunshine - it's the job of the controller to keep this down to the 13 - 14.8 range at the battery. But in very weak sunshine, the panel will be producing less than 12v & so no charging takes place.

    The advantage of wiring the panels in series (so now a nominal 24v for two panels) is that in weak sun, when each panel is maybe producing 10v, the two together will now present 20v to the controller & charging can take place. There won't be a lot of current, because the sun is still weak, so it won't make the panels twice as powerful or anything like that, but it will extract a bit more useful charging time early morning, late evening or on cloudy days.

    How useful this will be depends a lot on where you plan to be. If you are going to spend most of your time on the Med., I wouldn't bother. But in Northern Europe & the UK, it could extract a little more usable power on days when a 12v system struggles to do anything.

    I did this with two 100w panels in series & I've never had a day when the panels failed to produce a charging voltage during daylight hours, however overcast. But I have no easy way of checking the individual panel voltages, so I don't know if they were too low to work on their own or not. Nor do I have anything measuring the current produced, so I don't know how much useful charging was happening. I do know that I've never run out of power since they went on. Next winter will be the real test!
     
  15. Techno

    Techno Funster Life Member

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  16. funflair

    funflair Funster Life Member

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    @vwalan My experience comparing PWM vs MPPT is that the later will give an extra 25%, I ran PWM and MPPT side by side and then switched the PWM to MPPT also to come to my conclusion.

    The PWM was an old Morningstar sunsaver and the MPPT were both Votronic.

    Martin
     
  17. Techno

    Techno Funster Life Member

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    Absolutely
    100 watt panels are generally rated at circa 5.66amps max output.
    I have 3 fitted which should total 16.8amps but my mppt has produced 21.5 as I've witnessed and photographed.
    A PWM simply is incapable of doing that.
     
  18. vwalan

    vwalan Funster

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    but in winter in spain or what ever theres lots of sun. even here i can still power lots of things .
    i also consider the difference in the costs of the regs . these days you may be able to add another panel with the difference by using a pwm. the 30 amp reg s i use are only cheap. ww.ebay.co.uk/itm/231080174562?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
    fitted loads never had one go wrong yet. or give any trouble .
    how accurate are the figures . i only know my batteries are either filling or not . its acually a very small percentage over a day. only that figure at the very best time .
     
  19. Techno

    Techno Funster Life Member

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    The mppt is not tied to delivering at a fixed voltage and when in mppt charging mode it will push down the voltage to just slightly over the voltage at the battery terminals. This allows it to convert the excess voltage into higher current.
    Here at close to my maximum the regulator is pushing current in at 12.9 volts whilst the batteries are at about 12.4 having just used the inverter.
    21.6 amps is simply impossible from a PWM regulator as it will charge at 13.6 volts or higher.
    [​IMG]
     
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  20. vwalan

    vwalan Funster

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    well i cant quote figures but i do know that if your batteries get full quicker the reg will switch off so over a day is there really alot of difference if pwm takes a little bit longer to fill up. by dinner time most batteries are full . might not be here in uk in winter . hee hee .
    so long as the batteries get full who cares .
     
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