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Old 07-20-2011, 11:55 PM   #1
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Fuse on startermotor

Hi Forum,

Got a 30 ft clipper with 80 Hp Ford Lehman.

There are 2 battery banks, 1 dual 12 V 775 CCa for starting

1 200 Ahr as house battery.

The 200 Ah has a 250 A fuse on it, should I put a fuse between the starter battery and starter motor? and what fuse size should I go for ... There are no specs on the starter motor, I guess I can measure it with an AMP meter ....

There is also a 1/2/Both switch than can switch the house consumers to the starter battery, or starter to the house battery, or put both banks in parallel , if that makes sense

Tanks for your input.

Erik
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Old 07-21-2011, 04:29 AM   #2
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RE: Fuse on startermotor

Fuses are not ordinarily used for disconnecting a starter , a good rotary switch , out side the engine room is a better bet.

Also disconnecting the starter frequently will disconnect the alternator from the batts , a big NO NO on a running engine.

Rotary switches with field (break before break) cut offs only cost a bot of wire to install.
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Old 07-21-2011, 04:44 PM   #3
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Fuse on startermotor

Quote:
shipshape wrote:
Hi Forum,

Got a 30 ft clipper with 80 Hp Ford Lehman.

There are 2 battery banks, 1 dual 12 V 775 CCa for starting

1 200 Ahr as house battery.

The 200 Ah has a 250 A fuse on it, should I put a fuse between the starter battery and starter motor? and what fuse size should I go for ... There are no specs on the starter motor, I guess I can measure it with an AMP meter ....

There is also a 1/2/Both switch than can switch the house consumers to the starter battery, or starter to the house battery, or put both banks in parallel , if that makes sense

Tanks for your input.

Erik
You cannot protect a starter circuit with a fuse.* Starter motor circuits are the only circuitsd not required to have overcurrent protection by the ABYC.

*

If you plan on doing any electrical bork on your boat, I strongly recommend that you buy and study a couple books on the subject.* There are a lot of things you could do wrong.


-- Edited by rwidman on Thursday 21st of July 2011 04:46:08 PM
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Old 07-21-2011, 05:18 PM   #4
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RE: Fuse on startermotor

You cannot protect a starter circuit with a fuse.* Starter motor circuits are the only circuitsd not required to have overcurrent protection by the ABYC.

Yep, that's right. I tried. The fuse blew right away.
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Old 07-23-2011, 06:57 AM   #5
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Fuse on startermotor

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Fotoman wrote:
You cannot protect a starter circuit with a fuse.* Starter motor circuits are the only circuitsd not required to have overcurrent protection by the ABYC.

Yep, that's right. I tried. The fuse blew right away.

*

The reason is, the current normally drawn by the starter is so high, that a fuse sized to accomodate that current would not protect anything.* The battery is actually what limits the current in this case.

It pays though, to make it very unlikely that the starter cable can short to anything that's connected to ground or negative.* Don't bundle the positive and negative cables together for instance.
*


-- Edited by rwidman on Saturday 23rd of July 2011 06:59:47 AM
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