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

[Crazy_Pilot]

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!

 

[Scott Danforth]

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

 

[Crazy_Pilot]

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]

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]

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?

 

[dingbat]

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]

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

 

[dingbat]

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]

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.

 

[sam am I]

@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.

 

[Crazy_Pilot]

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?

His is missing everything past the grey connector - regulator, fuse, red wire. I saw the mounting points on the intake manifold and figured they might be for the power out components but wanted to confirm. Thanks for the picture, it's a big help to see what's needed. I think with that in mind he's just going to stick with a new/larger battery than the one he's currently using. It would be nice to have a self-charging setup but the cost for all that is certainly going to be more than a battery, probably several times over.

He's a walleye guy so it's similar to bass fishing but he
prefers to troll back and forth along the shore he's working, so the motor is idling all day long.

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.

Thanks, I had been trying to find the amp draw for the finder. Given that it's relatively low he'll probably just stick with a 14-21 AH battery and call it a day. His current battery must really be getting long in the tooth, it only keeps the unit powered up for 2.5 hours or so.

 

[sam am I]

the cost for all that is certainly going to be more than a battery, probably several times over.

Nah, just try not to buy anything "Genuine Merc" and it becomes much more affordable. At Merc, they evidently sprinkle magic dust in their parts for the extra high cost. It's actually re-branded Chinese stuff with some shelf dust, but we let them think we don't know otherwise.......

So, your motor has is a three phase stator, probably 10'ish amps max, buy this and roll your own, easy peasy.

It's yellow's(boat) to yellow's(rec/reg) on the input, green(rec/reg) to ground(boat)and red(rec/reg) to inline fuse then to battery+ on the output........DONE, not so hard. Cut all connectors off, solder/heatshrink and hard wire the thing in place.

Or if you want to connector'ize it............(it might go bad someday)

Cut off original connectors, solder/heatshrink this in for the yellows(both sides), cut off and solder/heatshrink this for the red and green(rec/reg side). Pigtail side then has black to ground, red to inline 10 amp fuse then to battery +

$40'ish total and Dad is set. You said he trolls and idles mostly for the trips.....PERFECT!! Start him off with topped off battery for the season, it'll charge the whole time he fishes and will end the day still topped off, it'll last *all season.

Here is the critter the rec/reg came out of FWIW, a 12V stator is a 12V stator +/- current. Boat, motorcycle, it's all the same! Nothing magically about a Merc stator (shhhhh).

*The output diodes internal to the rec/reg prevent any back discharge of the battery through the rec/reg to ground when the motor isn't running, just make sure he remembers he'll have to manually shut off his FF(any loads) at the end of the day. I suspect the tiny bit if any leakage current both from the rec/reg and FF would be in the uA range and would take months and month to drop the battery any significant amount .

 

[waterinthefuel]

Cut off original connectors, solder/heatshrink this in for the yellows(both sides), cut off and solder/heatshrink this for the red and green(rec/reg side). Pigtail side then has black to ground, red to inline 10 amp fuse then to battery +

This is actually bad advice. Solder is ok for repairing electrical connections on things that don't move, but it is FORBIDDEN on things that vibrate. Solder becomes brittle over time with vibrations, so CRIMP connectors are what is recommended. If you notice on your outboard you don't see solder anywhere, you see crimp connections everywhere. There is a reason for this.

If the FAA catches you soldering anything on an airplane you will never touch an airplane again.

 

[sam am I]

Agreed, solder makes for a rigid mend and if flexed will break, butt splices would work as well however considering the solder joints here are more or less mid wire/down some distance from the replacement connectors, these are pigtails, no soldering is being done at the housed connectors and/or mounting points.

The instructions were to cut off and replace e.g., replace originals with Dorman's, thus leaving factory crimping at the replacement connectors alone. The wires at the sealed soldered joints can be securely fastened down w zip tied/taped or can float mid air and thus aren't pinned/positioned in such a way as to make or need the joints to flex.........

As far as aircraft wires and soldering?........IDK, guess you're the expert there