Trolling with 90hp outboard not charging enough!!! Help

[mainejohn]

Last year during the fishing season while trolling with my 2005 Johnson 90hp 2 stroke, I would seem to be slightly discharging when running my fishfinder and radio. I troll at about 2mph and after a while my fish finder would flash that its getting less then 12 volts. Is this Normal or is my alternator getting bad?

 

[jhebert]

Re: Trolling with 90hp outboard not charging enough!!! Help

What is normal:

--the output of an alternator in an outboard engine increases with engine speed

--the voltage of a battery increases with its charge level

If the electrical load of your radio and fishfinder is greater than the output of the outboard engine alternator charging the battery, the battery will lose charge over time.

The best way to assess the condition of your alternator is to monitor the terminal voltage of the battery when there is no external load on it. If the alternator is charging the battery, the battery terminal voltage will tend to increase.

To have an alternator go bad on an outboard engine is not unusual. I'd check your alternator as the first step.

 

[NYBo]

Re: Trolling with 90hp outboard not charging enough!!! Help

Your motor uses a stator, not a traditional alternator. If you have the manual for the motor, it will list the maximum current output. It may also list another important piece of information: the cut-in motor speed. The stator may not put out any charging current until the motor is brought up to this speed, after which you can drop it down to trolling speed. It will then continue to charge the battery albeit at a level greatly below the maximum output.

Do you have a voltmeter in the instrument panel?

 

[mainejohn]

Re: Trolling with 90hp outboard not charging enough!!! Help

No it does not have a voltmeter.

 

[UncleWillie]

Re: Trolling with 90hp outboard not charging enough!!! Help

No it does not have a voltmeter.

Take a portable voltmeter with you the next time.
The magic lucky number to remember is 13!

If the voltage is above 13, (typically above 13.8) it is charging.
If it is below 13, (typically below 12.6) it is not charging.
It is highly unlikely you will see any voltage between 12.6 and 13.8. :joyous:

 

[foodfisher]

Re: Trolling with 90hp outboard not charging enough!!! Help

Your manual should tell you how many rpms are needed for the system to put out a charge.

 

[ondarvr]

Re: Trolling with 90hp outboard not charging enough!!! Help

Even at just above an idle that motor should put out enough power to keep the system charged.

Unless you have a very old fishfinder it should be able to display the voltage on the screen.

 

[jhebert]

Re: Trolling with 90hp outboard not charging enough!!! Help

Your motor uses a stator, not a traditional alternator.

All alternators have stators or stationary coils. You probably mean to distinguish between a permanent magnet alternator and a field-excited alternator. Field-exicted alternator are only "traditional" in the sense that they're often used on cars. Permanent magnet alternators are more traditional on outboard engines.

 

[NYBo]

Re: Trolling with 90hp outboard not charging enough!!! Help

All alternators have stators or stationary coils. You probably mean to distinguish between a permanent magnet alternator and a field-excited alternator. Field-exicted alternator are only "traditional" in the sense that they're often used on cars. Permanent magnet alternators are more traditional on outboard engines.

Correct, but mainly I wouldn't want the OP getting frustrated poking around under the cowl looking for an automotive-style alternator for troubleshooting.

 

[midcarolina]

Re: Trolling with 90hp outboard not charging enough!!! Help

How old is the battery? have you checked and made sure the connections for the fish finder are all clean and tight? seems to me if you actually had less than 12 volts your motor would of been acting up.....

As UncleWillie said checking your output voltage is easy....... pick up a cheap DMM at any home supply or wally world, check your battery static voltage, then put muffs on motor start motor see if voltage is higher if not go to a little hi idle and see if voltage increases..

I'm betting its a connection issue for the fish finder.

 

[mainejohn]

Re: Trolling with 90hp outboard not charging enough!!! Help

I just troll at idle so the rpms are probably 800. The battery is new and the fish finder is a new hummingbird 587. so where do I check the voltage while running? On the battery?

 

[ondarvr]

Re: Trolling with 90hp outboard not charging enough!!! Help

In the menu there should be an option for onscreen displays, this will be where you find the place to display the voltage on the screen at all times. Check the Humminbird manual if you can't find the correct menu.


Update;
Page 31 in the manual explains how to show the voltage on the screen.

 

[dingbat]

Re: Trolling with 90hp outboard not charging enough!!! Help

What your seeing is pretty typical when trolling. Most outboards don't put out much of anything until they're over 1500 rpm. I jumped up to a grp 27 deep cycle and get most of a day out of it. Your typical starting battery will not get it

 

[ondarvr]

Re: Trolling with 90hp outboard not charging enough!!! Help

I had a 90hp Evinrude 2st, at an idle the voltage was in the 13.5 to 14.5 range. My current 90 Merc holds at 14.2 all the time right from an idle. Yes they will produce more juice at higher RPM's, but at those levels running a FF and radio the battery shouldn't be discharging.