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Author Topic:   Older Mercury 80-HP, Boat With Increasing Electrical Load
stubbleduck posted 01-25-2007 12:17 PM ET (US)   Profile for stubbleduck   Send Email to stubbleduck  
First, thank you in advance for any suggestions, direction, or insight to my lengthy description of my boating situation as electrial is not my forte. Simply put I don't have a good understanding of electrial.

Currently I have an c.1988 four-cylinder 80-HP Mercury that runs fine. I do a considerable amount of fishing using an Minnkota bow mount 24-volt [electrical motor with] four batteries which are not connected to the engine battery. However, while I’m fishing I need to utilize my SONAR's. The operation of these SONAR's for the last couple of years appears to slowly drain the engine battery so that the old Merc 80 becomes hard to start. I’m assuming that the engine does not produce the electrical output required to recharge the engine battery significantly enough to run my two fishfinders and livewell. If I [increase the motor speed] for charging [the motor's electrical output] is still not sufficient

Existing Engine Battery connection and load on a Stowaway 160 deep cycle battery is:

--80-HP Mercury Engine
--livewell pump
--two SONAR's

Alternate Batteries on the boat (Stowaway 160 deep cycle):
Four other batteries used as two sets for a 65/Autopilot/unversial sonar.

I carry jumper cables in the boat and often jump the engine battery from one of the trolling motor sets.

Is there a different type of engine battery that could [provide better starting]?

What would happen if I connected my engine battery to a second identical to my trolling motor sets? Could I do this with some sort of voltage regulator?

Would a solar panal trickle charger provide enough maintenance during fishing to alleviate this problem?

Are there other electrical options? Or riggings?

Any idea what sort of current that Mercury motor generates while is running?

Thank you,

p.s. I’m also hesitant to add another battery on the boat for weight concerns. As it is right now, I have five batteries (about 250-lbs), motor (guessing 250-lbs), two people (400-lbs), full livewell (100-lbs). This totals 1,000-lbs and the boats rated for 1,100. Assuming tackle, caught fish, anchors, and miscellaneous this max's me out.

Chuck Tribolet posted 01-25-2007 03:30 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
You shouldn't use a deep cycle battery for a starting battery.

I'd look at the livewell pump, not the fishfinders, as the
source of the drain.


Buckda posted 01-25-2007 04:09 PM ET (US)     Profile for Buckda  Send Email to Buckda     
A solar charger certainly wouldn't hurt, and I'd also plug the boat into a charger/maintainer when not in use to keep the battery in top condition.

Your charging circuit on that motor (are you sure it has one?!) is likely strong enough to bring the battery up to full charge while running your other electronics, when operating above 3,000 rpm, but it may take up to a half hour of running to fully re-charge the battery between fishing holes - less than that and you may be net discharging the battery when fishing hard across many spots on a smaller lake/bay.

You can always carry an extra, but it sounds like you've got lots of juice aboard anyway.

As Chuck says - your livewell is probably the culprit here. Pumps are notoriously piggy on electricity. Consider swapping for a more efficient pump, if it can be found, and also consider running the pump off a different, non-critical battery (such as the one for the trolling motor).

Good luck.

What kind of Whaler is this on, and where are you keeping all of those batteries!?


Bulldog posted 01-25-2007 08:04 PM ET (US)     Profile for Bulldog  Send Email to Bulldog     
Do you have a timer on your livewell, you can cut your load drastically if you run the livewell the whole time....Jack
jimh posted 01-26-2007 09:36 AM ET (US)     Profile for jimh  Send Email to jimh     
There is no way to increase the electrical output of the motor except by refitting a better charging system to the motor. This may not be possible. Older outboard often only have a modest charing system, and at idle speeds there may not be much charging current available, even if the system can produce 10 amperes when running at speed.

You should isolate the motor load from all of the other loads so that you do not run down the starting battery with pumps and other non-starting loads. With FIVE batteries on board, this ought to be a simple matter of doing a bit of re-wiring. It would be much more convenient to have the battery running a pump go flat than to have the engine starting battery go flat.

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