Just finished solar install...interesting figures

Discussion in 'Solar Power' started by stevec, Jul 26, 2014.

  1. stevec

    stevec Funster

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    Hi All,

    I've just finished wiring up the 120W MPPT system in my Starfire. I've mounted the controller in an overhead locker and have a 4 metre run to the battery. It meant I could use existing trunking and void spaces to run the cables. At 11.30 full sun I am getting 5.5 amps at 14.48 volts. This is on a new battery which has had only one trip away. It has had little charge taken from it . At the battery I am getting14.12 volts. Ahh ha I hear you say. You shouldn't have used such long cable runs! I've used 4.5mm2 cable from an auto shop and fused all the lines including one at the battery positive. The interesting thing is that I am losing as much volts in the fuses as I am in the cables. Using my (expensive) multimeter I am losing 0.18V in the cables and 0.18V in the fuses. With 14.48 volts at the controller I am getting 14.35V at the output of the fusebox (-ve and +ve both fused as I've seen done on here). So I've lost 0.13 volts before I've gone 12 inches. All spade connectors have been soldered (I don't trust crimps). The fuse at the battery is dropping the other 0.05V. I've heard a lot about using correct sized cables to avoid volts drop but nothing about what losses the fuses will introduce.

    Has anyone else done any tests like these? I'm tempted to remove the fuse in the battery negative line and gain myself 0.06V or so.
     
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  2. PP Bear

    PP Bear Funster Life Member

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    Wobble, fish, bananas :drunk:

    I'd say at it's a perfectly acceptable drop. It's plenty of charge for the batteries :)

    Have a cold beer and a pat on the back. Job well done I'd say :)
     
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  3. callumwa

    callumwa Read Only Funster

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    You don't mention the capacity of your battery.

    For the sake of 0.06V I would leave the fuse in place, The additional piece of mind would be worth more than 0.06V to me.

    As the sun is now passing over the yard arm I too would suggest a cold beer is in order...(y)(y)
     
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  4. stevec

    stevec Funster

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    Battery capacity 110AHr.
    Just got to wire a network cable in for the remote display then tidy up, then a beer. On second thoughts the wife can tidy up...hoovering is domestic....straight to the beer then!

    I'll leave the fuses in. After all the Sargent charger was only giving 13.8 volts and the wiring is far longer and thinner so goodness knows what the battery was seeing.
     
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  5. jonandshell

    jonandshell Funster

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    Whether or not to fuse a circuit depends on an assessment of fire risk and the consequences of a short circuit on that circuit.

    I have read many posts on here where installers put fuses every bloody where, mainly due to peer pressure on this very forum.

    Ask yourself this question-

    How likely is your circuit to meet the vehicles negative chassis earth return?

    If the cable run is through wooden lockers, not very likely! I'm not saying don't fuse the circuit, just saying you don't need them at both ends of a cable run. At the positive end, closest the battery, is just fine!

    How many fuses do you see on the main positive at the starter battery on most vehicles? None, zero, zilch!
    The fuse is, in most cases, remote from the battery. The car manufacturers don't loose much sleep over that couple of feet of unfused positive cable!

    In a nutshell, if low voltage drop is a major consideration in the function your circuit, then limit the uses of fuses (and connections) to where they are REALLY required.
     
  6. JJ

    JJ Funster

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    I fitted 4 solar panels (over time) and three 110 batteries to my live in van and used to spend hours of joy looking at read out figures...

    Soon I got to the stage when I just accepted life was too short...

    Now I switch a switch on and the item it is connected to starts working...

    When I am done I switch off.

    That's it.

    Solar power just keeps on giving...



    JJ :cool:
     
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  7. pappajohn

    pappajohn Funster Life Member

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    Up to 3% volt drop is expected and accepted as normal so it appears you are within accepted limits.
     
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  8. stevec

    stevec Funster

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    Thanks for the comments everyone.

    JJ.,,,,I like to look at numbers as well. When I know that everything is working as I expect it to, generally over a few months or so, then tend not to pay too much attention, But it's nice to check every now and then.

    I recon I was getting 80 watts at midday with the panel horizontal. Would that be about right for a 120W panel which is not perpendicular to the sun's rays (sun is about 60 degrees I think).
     
  9. BwB

    BwB Funster Life Member

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    If you have a remote display you could move the controller nearer to (next to) the battery(s) being charged. That would give you minimal loss from the regulated voltage out of the controller - moving the loss to pre-controller (where there is more room (voltage) for losses). Then stick the display wherever you need it.

    Just a thought. :)

    (and, if the battery is nearly full the controller won't be putting in the full wattage it's capable of. Turn the pump on at the same time and you'll probably see the current input go up too)
     
  10. tonyidle

    tonyidle Funster

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    Pretty damned good I'd say :):)
     
  11. tonyidle

    tonyidle Funster

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    If convenient that's where it should be.
     
  12. stevec

    stevec Funster

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    I was going to mount the controller in the locker that houses the battery, so less than half a metre run. But it would be exposed to all the stuff in the locker (chairs, cables, hoses) that needs to be accessed regularly. I then considered mounting on the other side of the locker wall just behind the passenger seat. again cabling exposed to things being store there and not very visible (things get put behind seats without looking generally). In the end I used a thicker cable and went for an eyelevel locker where it is easily seen and cables cannot be dislodged so easily. there was some trunking down the other side of the overhead locker wall that led behind the fridge which is next to the locker with the battery. Apart from in the overhead locker there are no cables visible anywhere so I looked for neatness over efficiency. I did consider several options. I also considered that the solar cable was far too inflexible to route the way I put the more flexible battery cable. All in all I'm happy with the installation, and more importantly so is SWMBO who is far more critical of the look of the thing and who doesn't care where the electricity comes from just as long as it's there when she wants it!!
     
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