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Topic Title: 60 Amp electric outboard motor connections.
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Created On: 21 April 2017 03:14 PM
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 21 April 2017 03:14 PM
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Zoomup

Posts: 3266
Joined: 20 February 2014

What would you buy from an electrical wholesalers to connect a 24 Volt d.c. electric outboard motor to your 24 Volt batteries in the boat? The outboard already has a flexible cable attached that runs into the boat over the transom. The max. load is 60 Amps d.c.

Z.
 21 April 2017 03:39 PM
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davezawadi

Posts: 3845
Joined: 26 June 2002

I suggest some welding cable, well oversized as you really need to minimise volt drop, perhaps 35mm2, a common size. You may need a welding supplies shop.

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 21 April 2017 10:17 PM
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mapj1

Posts: 9348
Joined: 22 July 2004

I'd start by looking at the cable and terminal sizes already on the motor - to be waterproof at the junction gland may require a particular cable diameter.
Then estimate the total cable length - I assume it goes via some sort of speed controller.

There are waterproof boxes and glands of various sizes. As a sanity check the absolute thinnest that you should ever consider for 60A is probably around 10mm sq, but realistically to avoid problems of voltage loss, if the cable run is more than a couple of feet, then larger is better.
More than a volt or so of drop at full load is probably undersizing it, so you need 1/60th of an ohm or less, lets say 16 milli-ohms or less.
for copper, that resistance is a round run length of roughly 10m of 10mmq, or 25m of 25mm sq etc.

-------------------------
regards Mike
 22 April 2017 11:29 AM
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broadgage

Posts: 2380
Joined: 07 August 2007

Another alternative would be tri-rated switchgear cable in a suitably large size. Short lengths are often available cheaply on fleabay.

Do not forget a fuse close to the battery, a short circuit from a large battery would spoil your whole day !
In the absence of anything more sophisticated, a house service cutout fuse and holder are useful for this sort of thing, probably with an 80 amp fuse.
Various types of purpose made fuses and holders exist for this sort of current at ELV, but most are IMHO of very poor quality and liable to failure.
A DNO cutout is a proven design and available on fleabay if you don't have one lying around.
 23 April 2017 07:42 PM
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davidwalker2

Posts: 299
Joined: 29 April 2009

.....and make sure the fuses are rated for breaking d.c.

David
 23 April 2017 08:12 PM
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broadgage

Posts: 2380
Joined: 07 August 2007

In practice, fuses rated for AC will be fine for DC provided that the voltage is much reduced.
A useful rule of thumb is that fuses, switches, contactors and the like intended for AC may be used for DC provided that the voltage is limited to about 10% of the AC value.

So a fuse intended for AC at up to 415 volts will be fine for a DC system up to about 42 volts.
 23 April 2017 09:33 PM
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iie63674

Posts: 108
Joined: 17 May 2006

I'd go to a boat chandler...
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