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Car 12 volt alternator cable size

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Car 12 volt alternator cable size Empty Car 12 volt alternator cable size

Post by workyticket on Thu Feb 28 2019, 19:35

Am looking at driving a 12 volt car alternator from one of my engines, at the moment was just going to run an amber flashing beacon from it, I know there will be a small light and switch needed in the lines but can someone give me advice on what size cable/wire will be needed, for example will the 2 inner covered wires, not the bare earth one, from a 35 w household cooker wire be adequate, or is this too large or too thin sorry not much good at lecky things
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Post by Robotstar5 on Thu Feb 28 2019, 23:52

Household cable is not really suitable for the application as it is designed for a fixed installation with no vibration, movement etc.

If you plan to have a battery on charge, it will need something like 6mm² cable (the size stated is the CSA (cross sectional area) not the physical size of the cable) going from the alternator to the battery and the same from the battery back to the alternator ground/earth.

To power lights, beacons etc. you can use a smaller size cable such as 1.5mm² and even smaller for the switch and charge lamp.

Don't forget to include fuses for protection.

Have you worked out I'm a sparky yet? Very Happy

If possible, scribble a block drawing showing what you want to connect and post it up, I can probably work out what you need to do from that. On the beacon/lamps body or the bulbs inside, there should be some of the following, a number followed by W (Watts), A (Amps) and probably V(Volts) from that we can work out the loading then cable sizes.

I think that's enough to be going on with, feel free to ask any questions and I'm sure we can get it working.

Stuart.
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Post by chiefy on Fri Mar 01 2019, 10:38

Hi Robotstar,
A sparky thats good it is a mystery to me.
Regards,
Chiefy.

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Post by Robotstar5 on Fri Mar 01 2019, 12:32

chiefy wrote:Hi Robotstar,
A sparky thats good it is a mystery to me.
Regards,
Chiefy.

"Sparkies are gods amongst mere mortals" Laughing no idea where the phrase came from, but I always smile when I see it.

Stuart.
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Post by woody on Sat Mar 02 2019, 09:44

At the risk of being shot down by a sparky .....

An ordinary alternator might deliver 45 amps when working flat out, so yes, that might warrant 6mm cable.

Now your rig will need a car battery in it (to energise the alternator), but I assume the battery won't be used for starting the engine. Therefore the alt. will only be topping up the battery to run the lights.  So it will probably not need deliver more than 10-15 amps max.  You could put an ammeter in the circuit as part of your display.

In that case, I'd say domestic 3 core 15 amp cable will cope easily with that current so thats worth a try.

By the way, the alt. may need to have the "ign" warning light connected to work correctly - without that it may not excite properly.


Last edited by woody on Sat Mar 02 2019, 10:06; edited 2 times in total

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Post by Robotstar5 on Sat Mar 02 2019, 10:00

woody wrote:At the risk of being shot down by a sparky .....

An ordinary alternator might deliver 45 amps when working flat out.

Your rig will need a car battery in it (to energise the alternator), therefore all the alt. will be doing is topping up the battery as well as running the lights.  So it will probably not need deliver more than 10-15 amps max.  You could put an ammeter in the circuit as part of your display.

Now house wiring 2.5mm cable will cope easily with that current so thats worth a try.

By the way, the alt. may need to have the "ign" warning light connected to work correctly - without that it may not excite properly.

The reason household wiring is unsuitable for stationary engine use is it's construction, it is designed for fixed installations with no movement/vibration.

6242Y (household 2.5mm² twin & earth) has single solid copper cores which will soon work harden and fracture when exposed to movement/vibration whereas automotive 2.5mm² cable is made up of 35 very fine strands which allows it to cope with movement/vibration without breaking. They can both carry the same current, just designed for different applications.

Stuart.
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Post by woody on Sat Mar 02 2019, 10:07

Yes I realise that now Stuart, and have modified my post.

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