Can electrical power be pulled from a 25hp Merc outboard?

Crazy_Pilot

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We bought my father in law a new fish finder this summer, a Garmin Striker 9SV. It's a big upgrade from his previous little Hummingbird. Problem is, the little 7 amp hour battery he used for that one will only run the Garmin for a few hours. It might have lost some capacity already but he'll still need an upgrade for long days on the lake. His boat is a simple one, a SmokerCraft with a ~2016 manual start/tilt Merc 25 EFI (model F25MLH), so it doesn't have an onboard battery. He takes the battery out every night to charge it but once he gets a bigger one that'll become more inconvenient.

I'm wondering if there is a way to pull power off the motor to keep the battery charged. The motor has electronics so it obviously has a source of electrical power, I just don't know if there are any provisions to tap into that to keep a small 12V battery topped up. It would save him worrying about charging it at night and keep it from dying on a long day.

A picture of the model label is attached.

Thanks!
 

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Scott Danforth

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it has EFI, so it has a charge stator. look at the wiring. bet you could add electric start easy as well.
 

Crazy_Pilot

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Oh for sure, electric start is an option and you can see where the starter would go. I think the harness would need to be added for it though. The stator is easy to see and there are a few blanked off connectors but without a diagram I don't know which would be power out. I think there's a diagram on the backside of a plastic panel but it's bolted on and one of the rules of my marriage is thou shalt not tinker with the in-laws machines without being asked. I haven't been able to find anything online that would give it away.
 

roscoe

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Easiest would be to buy him a couple or three new batteries so he could switch them out during the long fishing days.

Or buy a service manual with wiring diagrams for the motor.

Or buy him the upgrade at the dealer. Might as well add the electric start while its there. Great Christmas present for him.
 

sam am I

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I'm wondering if there is a way to pull power off the motor to keep the battery charged.
Does your motor on this side look anything like the same side of the motor below? Three yellow wires leading into vertical finned rec/reg? Red wire coming out of rec/reg with a inline fuse? Can you snap a pic of this side of your motor?
 

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dingbat

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The Striker draws 0.75 amps. To keep it running for 8 hours your looking at a small, 6AH rechargeable battery.

The 12v, 8AH battery (8x3x2) used in the solar fencer outback is 8AH for $19.

Going to a “2 day” ~14AH battery would run roughly $40.

Using the motor to charge battery brings up the question of output and run time.

Most outboards don’t charge until your above 1,500 to 2,000 rpm. How many hours a day does he spend above those speeds?

Outboards have relative low output. My 200 has a 35 amp output. Can’t see a 25 being anywhere near that.
 

sam am I

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My Honda 9.9HP w 12A alt (rated @ 3K) at a whooping trolling speed 1-2MPH (guessing 1000 RPM) puts out around 2-3 amps............Would/DOES run a 0.75A FF easily and leaves any AH battery topped off indefinitely. Guessing a MERC 25HP would be close/similar
 
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dingbat

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My Honda 9.9HP w 12A alt (rated @ 3K) at a whooping trolling speed 1-2MPH (guessing 1000 RPM) puts out around 2-3 amps............Would/DOES run a 0.75A FF easily and leaves any AH battery topped off indefinitely. Guessing a MERC 25HP would be close/similar
So it comes down to run time.

Using your model your looking at roughly 4:1 run time to maintain.

Assuming a long day of fishing is 4 to 5 hours. Runtime would need to be 1 to 1.2 hours to maintain. Possible, but not likely running a 16’ boat with 25 hp on a lake

Something to think about
 

sam am I

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So it comes down to run time.

Using your model your looking at roughly 4:1 run time to maintain.

Assuming a long day of fishing is 4 to 5 hours. Runtime would need to be 1 to 1.2 hours to maintain. Possible, but not likely running a 16’ boat with 25 hp on a lake

Something to think about
Actually, if your alternator is able to provide 2 amps @ 1000RPM or greater for example, which then is of course more current then the example load is consuming (0.75 amp), then any excess current will be made available for charging the battery, this is in perpetuity.

This is the case because if there is no dis-charge that is occurring while running, then run time or "maintaining" times calculations are not needed/involved, the battery is always charging as the load can't present a dis-charge as long as the motor runs @ 1000RPM or greater. This all assumes he (I) start (t=0) with a freshly charged battery of course.
 
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sam am I

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@Crazy_Pilot

D.B. makes a good point, is Dads fishing stop and go bass type fishing? What type of runtime while on water are we talking? I'm 99% trolling/motor running these days seems so my perspective is more in that area.
 
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