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Old 12 June 2014, 16:59   #1
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Correct battery cables

Hi
I'm putting in a dual battery system using a blue sea 7650 system to provide the switch and charging relay.
I need to wire up from the battery to the switch. It's less than a couple of feet. Any idea what cable I should be using.
The engine is a mercury EFI 115 which has a 50 amp alternator charging current. Not sure the starting current.
I was thinking of either 110 amp cable or 170 amp cable. The cables will be protected by a 75 amp fuse. The only info I could find seemed to suggest 6 awg but not sure how this converts to amps.

The house circuits are to drive some simple electronics and are already protected by a 30 amp fuse so this circuit isn't an issue. Really just the circuit for starting the engine.

Anyone got any ideas.

Thanks
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Old 13 June 2014, 02:16   #2
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Long time since I talked AWG... We all talk sq mm this side of the Atlantic.

6AWG is way too small. It's about 6mm which is less than 50 A off the top of my head.

What you want for starting is 25 or 35 sw mm cable.

I'd also say your 75A fuse won't last long. It's unusual to fuse starter wiring as there is a huge "inrush" with a starter motor which typically causes them to blow. Does the blue sea instructions specifiy one?
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Old 13 June 2014, 02:22   #3
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I'm slightly out with the AWG, I just looked it up.

http://www.technick.net/public/code/..._awg_to_metric

6AWG is 13 sq mm , an unusual size in the UK. We tend to use 10, 16, 25.

It will be Ok at 75A over a short distance but still isn't right for your application.
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Old 13 June 2014, 13:44   #4
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thanks

thanks,
25 sq mm equates to 170 amp and 35 sq mm equates to 240 amp. I'll probably go for 240 amp to be safe.

(The fuse is to protect the charging circuit. it's not in the starting circuit so no worries.)

i'll get the parts ordered up.

Regards
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Old 10 September 2014, 04:18   #5
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If your talking about battery to motor starting circuit, there should be a Solenoid mounted on the motor case. If there is, use a standard crimped 6-8 awg (short as possible) direct from the battery to the solenoid threaded end labelled battery. Be sure to keep the cable isolated from sharp engine components (stationary and/or throttle cables or levers. But it is not fused. The solenoid has two or three other leads; one will go directly to the starter (another 6-8 awg lead. The other one 24 awg is to the ignition switch and will be fused somewhere close to the ignition switch. Once the ignition switch is energized, it will connect the two large terminals on the solenoid switch (battery lead/Starter motor lead) together which will provide all the required amperage to the starter motor. Release the switch and it, in turn cuts the connection between the battery and starter motor.
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Old 10 September 2014, 07:57   #6
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http://assets.bluesea.com/files/reso.../990310020.pdf

I think this helps, there's a list of recommended wire on the fitting instructions on the Blue Sea site.
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Old 10 September 2014, 08:41   #7
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You'll have to keep us posted on how easy the job was, costs and any problems - as I'm toying with the idea of adding a second battery too!
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