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Old 28-11-2017, 06:37   #1
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Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

Hello Cruisers:
I have a (new to me) 2009 Honda outboard, four stroke, x-long shaft, power tilt.

I installed a 75 amp fuse between the battery and the engine. The first time I tried to start the engine, it started and ran for a minute and died. I waited a minute or so before trying to start it again, and when I restarted it, the fuse blew.

I've left voice mail with Honda Customer Support, but thought I'd ask the experts here: what size fuse does Honda recommend between the battery and the engine?

I've looked online and read my manual, but no love there, either.

Thanks in advance for any input.
Blue skies,
--c
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Old 28-11-2017, 07:54   #2
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Re: Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

Greetings and welcome aboard the CF, chasm.
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Old 28-11-2017, 07:57   #3
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Re: Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

How many watts is the starter motor?
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Old 29-11-2017, 01:58   #4
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Re: Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

Are you talking about the Relay Circuit or the Starter Circuit.
- If it's the relay circuit, there is something seriously wrong if it's blowing a 75amp fuse.
- Starter Circuits are not typically fused

Assuming you fused the starter circuit for some reason, 75amp fuse is probably marginal. With losses, that works out to around 1hp which sounds about right for a 15hp motor but electric motors typically have a startup amperage 2-3 times the operating amperage, so even if it only draws 30-40amps once spinning, startup could easily push 90-120amps.

Another consideration where where was the engine in the compression cycle:
- The first time, the exhaust valve could have been open, so it didn't take much to get spinning and by the time the engine went into compression, it already had momentum on it's side.
- The second time, if it was just going into compression, it could be fighting startup load and compression resulting in much higher amp surge to get started.
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Old 29-11-2017, 02:59   #5
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Re: Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

AFAIK, the battery leads on a Honda 15 connect straight to the battery.
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Old 29-11-2017, 03:48   #6
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Re: Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

Hello Chasm

As indicated upthread, typically the battery leads are kept short and are not fused. The difficulty with this is that it leads to a stern-heavy boat with attendant risks in following seas and has probably contributed to the countless sinkings of small fishing boats when an anchor line is run to the stern. Better to put the battery further forward, and yes, that begs the question of fusing.

Typical small outboard starters are going to draw roughly 50-100 amps.

If it were me I'd use a fusible link. Essentially a 6" piece of wire spliced into the battery lead that is 2 or 3 sizes smaller than the battery cables and covered with a fire resistant sleeve. They provide a reasonable degree of short circuit protection in higher amperage circuits, because they'll fail before the insulation catches on fire on the battery cable. (I've seen that and it's not pretty)

Otherwise, you can measure the actual draw of the starter using a magnetic ammeter and fuse to 150% of that, or just switch to a substantially larger fuse than the 75a one you just blew. I would try 150a if it will fit in your existing fuseholder.

Engine starting circuits are intermittent in use and often involve higher amperages for the cable size than would be considered safe in other applications.
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Old 29-11-2017, 03:56   #7
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Re: Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

Quote:
Originally Posted by Jammer View Post
Hello Chasm

As indicated upthread, typically the battery leads are kept short and are not fused. The difficulty with this is that it leads to a stern-heavy boat with attendant risks in following seas and has probably contributed to the countless sinkings of small fishing boats when an anchor line is run to the stern. Better to put the battery further forward, and yes, that begs the question of fusing. A 60lb battery doesn't make a 32' boat stern heavy or lead to sinking.

If it were me I'd use a fusible link. Essentially a 6" piece of wire spliced into the battery lead that is 2 or 3 sizes smaller than the battery cables and covered with a fire resistant sleeve. They provide a reasonable degree of short circuit protection in higher amperage circuits, because they'll fail before the insulation catches on fire on the battery cable. (I've seen that and it's not pretty)
An undersized wire is asking for problems. Also if it does fail,
your starter is out of commission.
If this is just a home brew idea, return it to a standard setup as recommended by the manufacturer.
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Old 29-11-2017, 04:42   #8
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Re: Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

Thanks for the replies and thoughtful responses. Good stuff.

I was attempting to fuse the starter circuit but will likely go straight to the battery with short leads as recommended.

Very helpful and much appreciated!
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Old 29-11-2017, 11:03   #9
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Re: Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

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Originally Posted by valhalla360 View Post
A 60lb battery doesn't make a 32' boat stern heavy or lead to sinking.
I thought it was for a dink.

If it's an auxiliary then my questions would be where the motor and the battery are going to go. If the battery cable penetrates the deck then I would fuse it because the consequences of fire are so much greater than in an open dink. If the cable shorts inside the motor for whatever reason you could end up with fire that is very hard to put out.
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Old 29-11-2017, 23:08   #10
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Re: Honda 15HP Outboard -- Fuse Size Between Battery and Engine?

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Originally Posted by Jammer View Post
I thought it was for a dink.

If it's an auxiliary then my questions would be where the motor and the battery are going to go. If the battery cable penetrates the deck then I would fuse it because the consequences of fire are so much greater than in an open dink. If the cable shorts inside the motor for whatever reason you could end up with fire that is very hard to put out.
Even on a dingy it's not going to sink the boat.

Home brewing your own electrical specifications is not a good idea. Follow the manufacturers recommendations and that doesn't include fuses.
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