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Old 15 October 2019, 01:58   #1
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Battery Switch +tive or -tive

Seems to be a far bit out the but its all for bigger boats with starting and ship/leisure batteries, discussing corrosion of skin fittings etc.

I can't find any advice on a more simple system idea for a rib.

Leaning against +to be myself.

Anyone here with views either way.

Many thanks.
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Old 15 October 2019, 04:29   #2
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Quote:
Originally Posted by Ribtecer View Post
Seems to be a far bit out the but its all for bigger boats with starting and ship/leisure batteries, discussing corrosion of skin fittings etc.

I can't find any advice on a more simple system idea for a rib.

Leaning against +to be myself.

Anyone here with views either way.

Many thanks.
Battery switch is always on the positive side, if its a small boat you can get post mounted isolstors to save having to mount the switch somewhere
https://rover.ebay.com/rover/0/0/0?m...2F153628692665
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Old 15 October 2019, 04:39   #3
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as said +ve plus i always put an inline fuse rated to just above maximum current before it
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Old 15 October 2019, 04:46   #4
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as said +ve plus i always put an inline fuse rated to just above maximum current before it


+1 I always fit these to my boats

https://kojaycat.co.uk/fuse-boxes/-h...amic-cube-fuse
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Old 15 October 2019, 05:04   #5
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If you are installing a battery isolator, then as others have said, it goes in the +ve side of the circuit.

https://www.bluesea.com/products/600...king_Key_-_Red

If possible, try to make it relatively easy to access.

The only thing I'd modify / add to what has been said above would be that the fuse should go as close to the battery as possible and can be sized to protect the cable rather than being just above the maximum current. You can get neat cube fuses that fit directly on the battery terminal which will help if you are short of space.

https://www.12voltplanet.co.uk/batte...s-50-300a.html

Now almost a double post and cheaper at Kojaycat!
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Old 15 October 2019, 05:09   #6
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cable size should be rated well above fuse & maximum current used otherwise it gets hot leading to insulation breakdown over time.
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Old 15 October 2019, 11:26   #7
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Originally Posted by Ribtecer View Post
Seems to be a far bit out the but its all for bigger boats with starting and ship/leisure batteries, discussing corrosion of skin fittings etc.

I can't find any advice on a more simple system idea for a rib.

Leaning against +to be myself.

Anyone here with views either way.

Many thanks.
It's common to put a switch into the positive side but negative side is fine too. After all, if you want to isolate power from a system while work is done on it, it's common to remove the negative battery connection. And, electrons flow from negative to positive. So it's kinda your choice really.
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Old 15 October 2019, 13:07   #8
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If it's in the negative side it means everything's live to that point
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Old 15 October 2019, 15:25   #9
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If it's in the negative side it means everything's live to that point
Hehe, does it?
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Old 15 October 2019, 16:45   #10
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I don't think it actually matters for simple boat electrics.

If you isolate the -ve, you could then touch the +ve on anything, bar the -ve on the battery side of the isolator and there will be no reaction because the circuit isn't there.

However I think there is a lot to be said for following the standard procedure and isolating the +ve even if it is just to avoid confusion.
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Old 15 October 2019, 16:55   #11
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Hands up anyone with the isolation on the negative side?
I've never seen one in 40 years of playing with boats, plant & vehicles.
I doubt there will be many & I bet most would find it odd.
Personally if I bought a boat with the isolator on the neg I would change it over no matter how little it matters
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Old 15 October 2019, 17:20   #12
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Hands up anyone with the isolation on the negative side?
I've never seen one in 40 years of playing with boats, plant & vehicles.
What, you've never seen a screw down negative battery terminal isolator?

If the positive is isolated, any electrical work that is connected before the switch will be live to ground, any ground, engine, drive, throttle cables etc. If the ground is isolated the only connection which will conduct is live directly to the battery negative. No biggy I agree, but just that little bit more secure.

Not so relevant to a small rib but breaking the ground can also break ground loops.
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Old 15 October 2019, 17:49   #13
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An outboard in the water has a route to earth as does underwater lights etc standard practise to be in the +ve leg that's why fuses are in the +ve side you can weld with a dead short on a 12 v battery
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Old 15 October 2019, 18:09   #14
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Back in the day ,when building control systems for larger boats as an apprentice ,(for James and stone quite often) systems were always 24vdc and from memory always had black fuseholders in the positive line ,and white fuseholders with neutral links in them in the negative loops ,that was pretty standard procedure as it was fairly easy to pop a few modern electonic items (in the 80,s ) when the welder man arrived !!
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Old 16 October 2019, 06:01   #15
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Many thanks for all the advice.

I asked the question because I know that army land rovers that are fitted with cut off switches have them fitted on the negative side but still the fuses etc are on the positive side. Presumably this is because everything is grounded to the body of the vehicle?

Why can I not click on the links above that you guys have provided for fuses? The screen just goes blank.

A battery switched to the positive with a fuse is the way I will go.

Thanks again.
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Old 16 October 2019, 06:29   #16
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i might be wrong but from memory in the old days some vehicles were fitted +ve earth
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Old 16 October 2019, 10:19   #17
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i might be wrong but from memory in the old days some vehicles were fitted +ve earth
Correct. Some aftermarket radios came with a switch to select either when installing.
Replacement dynamos also needed to be flashed to suit the vehicle's polarity.
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Old 16 October 2019, 10:26   #18
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Hands up anyone with the isolation on the negative side?
I've never seen one in 40 years of playing with boats, plant & vehicles.
I doubt there will be many & I bet most would find it odd.
Personally if I bought a boat with the isolator on the neg I would change it over no matter how little it matters
That'll be me then. On my Range Rover Classic. Lot of aftermarket electrics & it was just easier that way.
Never had an issue.
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Old 16 October 2019, 11:22   #19
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That'll be me then. On my Range Rover Classic. Lot of aftermarket electrics & it was just easier that way.
Never had an issue.
+1

I've fitted a few battery master cut-outs on the neg side on my off-roaders, sometimes the live terminals can get quite 'busy' with ancillary outputs, winch wiring etc so its easiest just to have a switchable neg which will isolate the battery, obviously the majority of earth connections are and can be picked up on the rest of the vehicles chassis / bodywork so consequently less demand on the neg terminal of the batt
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