Results 1 to 5 of 5
  1. #1
    Member
    Join Date
    Jan 2015
    Location
    Tampa
    Posts
    651

    150 4S Charging Question

    Mercury 150 4S Serial Number 2B043673

    I am relatively new to boating and have a question about the charging systems on my motor. My boat/battery is connected to the charger 100% of the time except when on the water. I have a three year old main wet cell battery that came with my boat when I bought it new three years ago (Interstate 27M-XHD). And I check the battery water levels at least every three months.

    Jump forward a couple years and I have noticed that when I spend about 8 hours on the water my main cranking battery voltage is real low according to the smartcraft and my HDS units. Of those 8 hours on the water, my motor will run maybe 1 hours (I only have 70 hrs on my three year old motor). When I get home and plug in the charger I get only two red lights meaning it is only 40% charged. I only have 2 each HDS7 Gen 3 plotters, 8' power pole (barely gets used) and a small Jensen radio (MS30BT), and a NMEA with a point 1. 99% of the time I do not keep fish so live wells are empty and not running.

    I assumed that when running the motor, the alternator charges the main battery much like an automobile does, so I try to find a stretch where I can run my motor about 4,500 rpm for a good 5-10 minutes to charge the battery. I will see a slight increase in voltage on my smartcraft (maybe .3v), but nothing like I would expect it to display if being charged like an automobile charging system.


    My question:

    Does the alternator on the 150 4S charge the main battery when the engine is running and if so, does it need to be a high rpm for a prolonged period of time to make any noticeable change in indicated voltage?


    I realize my main battery may also be due replacement and this may not be a charging issue, at all but I wanted clarification on the alternator charging while the engine is running.

    Thanks in advance.
    2013 Z118 w/Merc 150 4S

  2. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #2
    The alternator on your 150 is designed to MAINTAIN the fully-charged state of:

    One Good, Properly Rated, Fully-Charged Cranking Battery.

    The first step is to determine that you have "One Good, Properly Rated, Fully-Charged Cranking Battery". A load test will help to confirm that.

    Once that is confirmed, note voltage BEFORE starting.

    Then engine AT IDLE after starting

    Then, after a 5 minute run (engine at 3000+ RPM).

    Then finally, at idle (before shutdown).

    Voltage in the last 3 should be in the 12.9 - 14.4 VDC Range, and will normally be .5 VDC (or more) above the original/stationary battery voltage.

    More "technical" testing is available, but the above will cover most common situations.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  3. Member
    Join Date
    Jan 2015
    Location
    Tampa
    Posts
    651
    #3
    Quote Originally Posted by EuropeanAM View Post
    The alternator on your 150 is designed to MAINTAIN the fully-charged state of:

    One Good, Properly Rated, Fully-Charged Cranking Battery.

    The first step is to determine that you have "One Good, Properly Rated, Fully-Charged Cranking Battery". A load test will help to confirm that.

    Once that is confirmed, note voltage BEFORE starting.

    Then engine AT IDLE after starting

    Then, after a 5 minute run (engine at 3000+ RPM).

    Then finally, at idle (before shutdown).

    Voltage in the last 3 should be in the 12.9 - 14.4 VDC Range, and will normally be .5 VDC (or more) above the original/stationary battery voltage.

    More "technical" testing is available, but the above will cover most common situations.
    Thank you Don and next time on the water I will check it out.

    Smartcraft reading good enough or recommend a multimeter directly off the battery?
    2013 Z118 w/Merc 150 4S

  4. Member
    Join Date
    May 2011
    Location
    Spangle, WA
    Posts
    6,181
    #4
    Smartcraft should be fine for the test Don recommended. If you need to do more technical testing then a DMM at the battery works best.
    _______

    Phil
    '09 Hewescraft ProV
    '09 150 Optimax


  5. Member berudd's Avatar
    Join Date
    Apr 2013
    Location
    Morrisville, NC
    Posts
    7,071
    #5
    All of Don's technical recommendations are, as always, detailed, useful and highly reliable. But, I'd guess your 3 year old battery is ready to be replaced. They do wear out. I've never had an Interstate but by and large BBC posters don't have much good to say about them. Don't do what I did and chase 100 different things when it was ultimately the battery. That said, how low is real low? Also, don't take the voltage reading on your HDS as gospel. Not only will some say they are unreliable, they can also read lower due to bad connection, wire that is to small and extended leads to the battery. One of my bow units reads almost a half volt lower than what I have on the console. SmartCraft can be trusted though.
    Bruce
    2019 20 TRX Patriot
    Mercury 250 ProXS Fourstroke
    HDS 12 Live - Console
    HDS 9 Live - Bow