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Battery cables

  • 28-03-2022 11:09am
    Registered Users Posts: 2,260 ✭✭✭

    Looking for some details on how to correctly wire my batteries to the inverter.

    This will be the setup:

    The +/- cable pack comes with 2 x 2m red/black cables and as you can see above, there are two sets of 2 cables needed, one from the batteries to the breaker and one from the breaker to the inverter.

    Questions on the cable lengths:

    1. I can purchase 2 cable packs, 2m cables from battery to breaker, 2m cables from breaker to inverter. Is 4m not too long?
    2. I can purchase 2 cable packs, 2m cables from battery to breaker, cut the second cables short, from breaker to inverter?
    3. I can always use one cable pack, cut the cables in half and use each half in the setup above, making the cable run only 2m long.

    What's the best option here?


  • Registered Users Posts: 793 ✭✭✭reklamos

    From physics point of view the shorter the cable the better. Just get them long enough to stack/connect everything and that is it.

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    I'll see what slack I have left once the batteries are in place, I think I might go for 3. and cut them in two then stick the breaker in between.

    Either way I will need to cut the cables since they come with the round plug connections on each end.

  • Registered Users Posts: 1,534 ✭✭✭Pataman

    Where did you get the DC breaker?

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    Guys does anyone have one of these I could borrow that does 25mm2 cables/ferrules?

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  • Registered Users Posts: 3,171 ✭✭✭irishchris

    If you source one anywhere reasonable will you pm me the link. Assume you are using it for cables in DC breaker too?

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    Just ordered this like 5 mins ago:

    If it's crap I'll just borrow my neighbor's and send it back.

    Yes for the DC breaker since 25mm2 lugs won't fit in it so will go for ferrules instead.

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    Anyone know if it's ok to have the ferrule sticking out about 5 mm from the breaker, cannot find the right size anywhere.

    Any danger of arcing between the +/- cables?

    Could always grind 5 mm off it but it is tinned by the looks of things and wouldn't want to mess with that.

    Or just put electrical tape or heat shrink around the insulation bit and the 5mm sticking out? Or put some of that flexible conduit over it?

    Or I'm way overthinking this?

  • Registered Users Posts: 1,704 ✭✭✭Deagol

    No harm in having it poke out a little but be sure no one can accidentaly make contact with the metal bit. No harm in cutting it shorter after you crimp it all. But with large cable like that you'll need a clamp and hacksaw I'd think!

    No chance of it arcing that distance, you'll have max 50V in there. Arc distance is <0.05mm at that voltage.

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    It's inside a tiny consumer unit with just the breaker in it, no easy access once it's screwed in.

    How about some shrink tubing over the red part and a little over the pin itself?

    It only has 50v going through it but also 100a and it will be a 35mm2 cable so it shouldn't get too warm right?

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  • Registered Users Posts: 1,704 ✭✭✭Deagol

    If it makes you feel better you can.... but 35mm2 cable won't be affected much by 100A as long as it's not constrained with anything insulating.

  • Registered Users Posts: 3,171 ✭✭✭irishchris

    Just be careful with it as had the unfortunate experience of seeing dc arc first hand when testing a DC breaker for surge protector at my panels last year and it arcing between both tester probes. Bright flash, sparks and burnt out breaker within seconds.

    Is there no other ferrule type that would be more constrained within the breaker itself?

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    I will look for a shorter one, but right now I have about 200 of the wrong size.

    I'll get my electrician to sort it out, maybe take off that extra 5mm or just plug the cable in directly, 35mm2 is about the max that breaker can take and fill it nicely anyway.

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    A lot of inverters connect their battery cables like this

    So if that doesn't arc there I find it hard to believe it can arc at the breaker.

  • Moderators, Motoring & Transport Moderators Posts: 6,521 Mod ✭✭✭✭Irish Steve

    The issue with breakers arcing is that if they are carrying significant load when opened, there is a period of time, dependent on the speed the operator opens it at where the contacts are close enough to be able to arc very easily, so the separation when open has to be large enough to ensure that the arc cannot be sustained when the contacts are fully open. Different situation to bus bars where they don't move.

    Shore, if it was easy, everybody would be doin it.😁

  • Registered Users Posts: 3,171 ✭✭✭irishchris

    Mightn't look too bad there now but at the time there was large flash and arcing flame between both positive and negative

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    Those aren't battery cables though, is that DC from panels?

    Mine will look like this with just one cable going to each of the poles.

    And to be extra safe will sleeve them in 20mm corrugated conduit.

    Surely it won't arc through the conduit haha

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    Also it looks like I will have a 35mm cable going from the batteries to the breaker and then 25mm cable from the breaker to the Solis since that's the max those surlok plugs will take on the inverter.

    Don't see an issue as it will draw max 100a and 25mm can do 120a.

    Is that a problem?

  • Registered Users Posts: 3,171 ✭✭✭irishchris

    Just to follow up on this with you. Did you get shorter ferrules or how did the breaker install go in the end?

    In same situation myself now as once my battery pack is balanced will be joining them to my 125a projoy DC breaker. Will be going with 25mm cables to breaker from battery and breaker to inverter. Max load 100a

  • Registered Users Posts: 2,260 ✭✭✭SD_DRACULA

    Yeah he cut a bit off the top, I think the breaker can take around 10mm pin length so he snipped off the extra 5-6mm since 25/35mm ferules seem to come with a min 16mm pin length.

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