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Thread: What Cable size to run from a 160w Panel to a MPPT Solar Regulator?

  1. #1
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    Question What Cable size to run from a 160w Panel to a MPPT Solar Regulator?

    Guys... for those Electrical gurus...


    I currently have an MPPT solar regulator mounted under the centre Console & a 160w Solar panel mounted on the roof. This car doesn't get driven too often and is parked under a Carport making the roof solar useless.


    To solve this, I'm thinking of buying a separate Solar Panel to leave out in the sun to charge the batteries in the car during the day. To do this I was thinking of installing an Anderson plug at the rear of the car where the cable would also run up into the Solar inputs of MPPT Solar Reg under the Centre Console and plug the Solar panel into the Anderson Plug to keep the batteries charged.





    Now, my question is what size cable should I run from a 160w Panel up to the MPPT Solar Reg mounted under the centre Console?




    I'm assuming as long as the cable is rated to carry the current of the panel it should be sufficient? Voltage drop shouldn't really be an issue due to the high volts output of the Solar Panel - Would this be correct?

  2. #2
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    Whats the 'high' voltage output of the panel? Assuming its around 18-20v?
    At a guess, I'd use 6mm2 tinned copper solar cable, only because i have heaps of itWhat Cable size to run from a 160w Panel to a MPPT Solar Regulator?. I only work with pv in the 240-1500v range so not 100% sure.
    Damien
    ------------------------------------------------

  3. #3
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    Hey Robmacca If itís just to keep the batteries topped up a bit of 2.5mm2 would be fine
    If your planning to keep a fridge running go the 6mm2

    I use this web volt drop calculator

    AC and DC Voltage Drop Calculator AS/NZS 3008 | jCalc.net

    Itís quick easy and accurate, does ac and dc and has the Australian standards based cable selection for 240/415 volt ac

    The higher the volt drop the less power (wattage) youíll get at your battery
    You can use the panels rated current as a guide to work out your wattage after working out your voltage

    What Cable size to run from a 160w Panel to a MPPT Solar Regulator?What Cable size to run from a 160w Panel to a MPPT Solar Regulator?

    Gav
    1985 110 Dual Cab 4.6 R380 ARB Lockers (currently NIS due to roof kissing road)
    1985 110 Station Wagon 3.5 LT85 (unmolested blank canvas)

  4. #4
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    I'm no expert ... but isn't is about system efficiency?

    If there is significant draw on the batteries when the car is parked up, then you want to maximise your efficiency and minimise voltage drop. Use the calculator - but I too would use 6mm2 solar cable as I have a supply on hand.

    But if its just to keep you batteries topped up, then with a big panel like that it really doesn't matter if the system is inefficient, and a cable rated to carry the max amps of the panel will do - the voltage drop will not be important.

  5. #5
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    When selecting the panel for a fixed mounting position, you need to take into account environmental factors such as orientation and shading.
    160watts sounds like a lot but that is in optimum mounting position, right angles at all times to the sun, temperature at 25 degrees C, sun producing 1000 watts per square meter of solar irradiance
    If your not within these specifications you wonít be producing 160watts
    Shading can drastically reduce the out put of the panel, even one cell can reduce the panel by 30-90% depending on the cell configuration

    Facing NE-NW and around 20-30 degrees is about the best you can achieve

    Lots more too it but themes the basics

    What Cable size to run from a 160w Panel to a MPPT Solar Regulator?What Cable size to run from a 160w Panel to a MPPT Solar Regulator?What Cable size to run from a 160w Panel to a MPPT Solar Regulator?

    Gav
    1985 110 Dual Cab 4.6 R380 ARB Lockers (currently NIS due to roof kissing road)
    1985 110 Station Wagon 3.5 LT85 (unmolested blank canvas)

  6. #6
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    i use 6mm auto (4.59sqmm) which is good for up to 50amp.
    MY08 TDV6 SE D3- permagrin ooh yeah !
    98 TDI AUTO SE DISCO - gone and will be missed.
    2003 Dingo offroad camper trailer
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    1974 VW Kombi bus
    1958 Holden FC special sedan

  7. #7
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    Hi Rob and this is just a suggestion but may not suit your needs.

    If it was me, I would be making up a LONG lead using either 6mm2 marine twin or even 8B&S ( 7.5mm2 ) twin and fitting Anderson plugs to both ends.

    This way you would have a heavy duty extension cable, which will cause very little voltage drop while being used on the solar panel and can be used for medium current drawing situations, like running a compressor and the likes.

    Overkill on solar wiring is never a drawback, but this would give you other uses as well.

  8. #8
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    The system will mainly be for keeping the batteries topped up while the vehicle is parked. Currently when the vehicle is parked up for 3-5days, the battery volts drop to around 12.3>12.4v (2010 Puma Defender), so I need a way to keep the batteries topped up to maximise the battery's life. I'm thinking this is what contributed to me killing my good AGM AmpTech Aux battery only after 2.5>3yrs of service. The VSR that I'm currently using keeps both batteries connected down to 12.4v before disconnecting and I'm sure that even though the current draw of the VSR is minimal, over time it all adds up to discharging the batteries.

    To solve this, I plan to do something similar that I did on my old Defender and install a Solar panel on the roof for travelling with a MPPT Reg mounted under the Cubby Box. When not travelling I'll use a spare 160w panel plugged into a anderson plug at the rear of the vehicle which runs up and also taps into the MPPT reg under the cubby box. Because of the trees around our place, etc the solar panel might only get about 5>6hrs of full sunlight which I hope will be sufficient when using a 160w panel...

    Well, that's my thoughts atm...

    (The specs of my VSR attached)
    Attached Images Attached Images

  9. #9
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    You need to perform math. Find the amperage of the panel at rating power and the length of the cables. Then look at voltage loss. You want to aim for below 3% of the panelís voltage at rated power.

  10. #10
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    Question

    Quote Originally Posted by Red90 View Post
    You need to perform math. Find the amperage of the panel at rating power and the length of the cables. Then look at voltage loss. You want to aim for below 3% of the panelís voltage at rated power.
    I realise that, but with the Regulator being mounted under the cubby box near the batteries under the seat, so the voltage drop is not a huge factor as the voltage output of the solar panel is a lot higher than 12v so if there is a small voltage drop from panel to MPPT, I don't think will make a big difference, as long as the cable can carry the required current... or unless I'm looking at this in the wrong way...

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