cable wiring thickness when connect gauge in cable





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  1. #1
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    Default cable wiring thickness when connect gauge in cable

    I'm fitting a Volt/Ammeter gauge in the cable running from the solar panel to the solar controller. The cable is thick enough for its length to carry the current efficiently. But the gauge came with two plugs and thin cables (maybe 40% of the thickness of the original cable). I had to cut the thick solar cable to wire this gauge to measure amps. The thin cable needs to be soldered to the thick cable in this interruption. I'm worried that there will be an energy loss when current has to travel through this thin cable.

    An engineer-friend helps with the installation. He suggests that we install a switch in the thick cable and then do a bypass of the thin cable which enters and exits the gauge. So the switch will direct energy to the gauge for a reading only when activated. Otherwise it will flow through the thick cable and switch alone - to maximize efficiency.

    Any comments or other ideas?
    He also suggested that when in full sunlight I should feel if the thin wire (which is how we connected it temporarily at the moment) becomes hot - which would indicate that it is too thin.
    Am I over-cautious?
    Custom-built expedition platform: Land Rover Series III 109 Pop-up roof Camper, 110 2.5l petrol engine with extensive self-recovery gear and extra fuel and water tanks awnings all round, solar setup etc

  2. #2
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    Default Re: cable wiring thickness when connect gauge in cable

    What your friend suggested would be the best solution for the current meter you have. The thin wires you are mentioning would be thick enough to measure the 10A which I take is the meter you have. If you solar panels have a Isc < 10A which once again I think would be the case then it is fine.

    If you use the 2 leads to the meter (1.5 sq mm) about 100mm in length each at 10A you will only be having a about 25mVolt drop due to the cable being thinner. Not a train smash. The about 4 sq mm cable from the solar panels will have a drop of about 0.825V at 10A if the panels and controller are 10m apart. Thus the total drop only goes up to 0.85V when the meter is connected without the bypass switch. Keep the 2 wires to the meter as short as is practical.

    I hope my calcs are correct.
    Last edited by ekkekan; 2020/03/14 at 10:07 PM.

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  4. #3
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    Default Re: cable wiring thickness when connect gauge in cable

    Quote Originally Posted by ekkekan View Post
    What your friend suggested would be the best solution for the current meter you have. The thin wires you are mentioning would be thick enough to measure the 10A which I take is the meter you have. If you solar panels have a Isc < 10A which once again I think would be the case then it is fine.

    If you use the 2 leads to the meter (1.5 sq mm) about 100mm in length each at 10A you will only be having a about 25mVolt drop due to the cable being thinner. Not a train smash. The about 4 sq mm cable from the solar panels will have a drop of about 0.825V at 10A if the panels and controller are 10m apart. Thus the total drop only goes up to 0.85V when the meter is connected without the bypass switch. Keep the 2 wires to the meter as short as is practical.

    I hope my calcs are correct.
    Thanks for a thorough reply, Ekkekan . Yes the gauge is 10A and panel 85W. Just to be sure: So you say I don't need the bypass because the voltage drop is minute? BTW, the cable is about 4m long I think. I thought it is not a matter of voltage drop caused by the bottleneck, but actually a matter of Amps squeezing through (is water a correct analogy? ) Excuse my awkward terminology

    So you say the current temporary setup is fine and will not restrict the number of Amps delivered to the solar controller? Then that's good news.

    Thanks again!
    Custom-built expedition platform: Land Rover Series III 109 Pop-up roof Camper, 110 2.5l petrol engine with extensive self-recovery gear and extra fuel and water tanks awnings all round, solar setup etc

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    Default Re: cable wiring thickness when connect gauge in cable

    The voltage drop is like walking uphill. The longer the hill the more you tire. Keep the thin wires as short as possible.

  6. #5
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    Default Re: cable wiring thickness when connect gauge in cable

    Quote Originally Posted by desdrake View Post
    The voltage drop is like walking uphill. The longer the hill the more you tire. Keep the thin wires as short as possible.

    Thanks. The gauge shows 17-19V received from panel - so that's fine. It's the amps I worry about. Whether the thin wires will cause a bottleneck.
    Custom-built expedition platform: Land Rover Series III 109 Pop-up roof Camper, 110 2.5l petrol engine with extensive self-recovery gear and extra fuel and water tanks awnings all round, solar setup etc

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    Default Re: cable wiring thickness when connect gauge in cable

    Quote Originally Posted by corlius View Post
    Thanks. The gauge shows 17-19V received from panel - so that's fine. It's the amps I worry about. Whether the thin wires will cause a bottleneck.
    No electrics don't cause a permanent bottleneck due to a short piece of wire. Water in a pipe is affected for the whole length due to a bottleneck. It is but only a little bit of resistance but once passed the resistance all flows normal. As long as that thin piece does not get too hot and melt the insulation you are fine. This is the reason why I indicated you have more losses over the 4m than with the short thin piece to the meter. These meters use a thin wire but of acceptable size. We were used to over engineering over decades and the new young engineers have calculated things to work on the safe limit without all the fat.

    If you had the thin wire for 4m then you had a serious problem as the resistance adds up the longer the wire is.
    Last edited by ekkekan; 2020/03/15 at 05:49 PM.

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    Default Re: cable wiring thickness when connect gauge in cable

    I have the same problem as I want to install a NL combo volt/amp meter in a NL battery box! I do not have the wire sizes at hand, but the difference in thickness/gauge between the wire in the box and the one on the meter is HUGE, to such an extent that there is no off the shelf fitting to join them.

    The intention was to do a permanent install, but I was so sh*#t scared of burning my vehicle down that I made up a separate "meter box" that I can just plug in as and when required (I had to find some use for the meter that I have bought blindly )



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    Default Re: cable wiring thickness when connect gauge in cable

    Quote Originally Posted by hatjohan View Post
    I have the same problem as I want to install a NL combo volt/amp meter in a NL battery box! I do not have the wire sizes at hand, but the difference in thickness/gauge between the wire in the box and the one on the meter is HUGE, to such an extent that there is no off the shelf fitting to join them.

    )
    I might be shot down by most but the idea when you join is to get a tight crimp. Next time you have this problem just take some house wire loose copper strands and fill up the air gap with these until you cannot get more in. Then do the crimp and it would last as well as if both wires were of the correct size. If you can solder then you don't need the of the shelf fitting to join them.

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