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Old 12-01-2013, 06:27 PM   #1
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Fuse advice needed

As mentioned in another thread, I have bought the Bluesea Automatic Charging Relay and am trying to plan the install. I am going to add a fuse to each battery post to run all leads from. But I can't figure out what size fuse is the right one for each battery. The ACR instructions provide a chart for wire and fuse sizes but the calculation is based on "charging amps." Don't know what that could mean except maybe the amps put out by the alternator. Unfortunately I don't know what that is since there is no record of that from the PO.

I am going to run AWG 2 wires from the battery. The engine is a 36 hp diesel and the draw from the house batt is pretty minimal - lights, electronics and a couple of small fans, that's about it.

Any thoughts? The instructions:

http://assets.bluesea.com/files/reso.../990310020.pdf
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Old 12-01-2013, 06:39 PM   #2
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The fuse should be sized to protect the wire or the consuming device whichever is less. In the case of the ACR main fuses, it could see the full charging amperage of your alternator (not a consumer) so the wires should be sized in excess of the max. alternator output off the 2% drop chart and the fuses should be in excess of the max. alternator output also.
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Old 12-01-2013, 07:26 PM   #3
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Right. But how to discover the amp output of the alternator?
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Old 12-01-2013, 07:33 PM   #4
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Two suggestions. Find the model of the alternator and look up on line. You should have the model info for other reasons. Or set your multimeter to amps and read the output underway. This will likely be different. If you have a SOC you may get the output reading. I have separate ammeters for each output device so I can tell what is happening (and strange things happen).

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Old 12-02-2013, 06:49 AM   #5
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Their specks list 1000A as cranking feed ability (10 seconds max), so it sounds like a std $17.00 RV solenoid is used.. and a bunch of electronics , instead of a key switch .

I would NOT fuse the battery leads in any way .

I would not fuse the ALT in any way as the fuse blowing will cause most alt diodes to depart.

Using the field cut off terminals in the back of a better quality rotary switch is all the Alt protection most need.
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Old 12-02-2013, 07:07 AM   #6
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Quote:
Originally Posted by Brooksie View Post
The fuse should be sized to protect the wire or the consuming device whichever is less.
The consumer should be protected by the branch circuit breaker or its own fuse.

The wire serving the branch should be fused as close to the source (switchboard) as possible.

Fusing a circuit at the consumer (as in fusing the alternator output at the battery) does nothing to protect the wire. If that wire shorted to some part of the engine "upstream" of the battery, the wire would burn.

The only fuse you should put on the battery is something like the MRBF type sized to protect the wire between the battery and the switchboard. Do not fuse the starter. Install a battery switch or continuous duty relay if you are concerned about a hung starter or wish to have start isolation.
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