help with 75hp merc

[squidkid]

after eliminating potential battery problems(had them load tested) i am at a standstill on my motor problem. i tested my battery voltage and it read 12.3 after hooking up to the engine and starting it, it still registered 12.3 i then unhooked the battery(my engine continues to run) and tested the return cables and they registered 0. i know very little about engines but was told to do this to see if the problem exists in my batteries or my engine. i was told if they don't read in the 14 range while the engine is running, that the problem lies in the motor.<br />is this true?<br />any suggestions?<br />and if so, what is the next step to take to diagnose my problem? thanks

 

[roscoe]

Re: help with 75hp merc

You don't state what the initial problem was, so am assuming your batteries were not being kept charged. (Maybe you had this in a different post?)<br />(you also should state the model and year of your engine)<br /><br />The problem is probably a bad voltage rectifier, which converts AC to DC, which charges the batteries.<br /><br />If the rectifier wasn't bad before, it probably is now. You can blame who ever told you to disconnect the battery from a running outboard. A running outboard has to stay connected to a ground (battery). An outboard with a stator and rectifier, is very different from an automobile charging system. If disconnected, the current has nowhere to go, and the rectifier will fry.<br /><br />The correct way to test charging voltage, is to use a meter, across the battery terminals, while engine is running.

 

[Trent]

Re: help with 75hp merc

Roscoe is right! Thank your friend! Never unhook the battery on a running outboard OR hook up backwards or its fried electronics.

 

[squidkid]

Re: help with 75hp merc

sorry guys, the motor is a 1996 75hp mercury outboard.<br />i originally thought that my charging problem was due to the batteries but after fully charging my batteries and having them load tested i determined that my batteries are not the problem.<br />i was told that they should read in the 12-13 range when the motor is not running and a few points highr when the motor is running. mine read the same regardless of the motor being ran. the volt meter that i borrowed doesn't read in the 10ths.<br />i can only assume then that the problem lies within my motor now, but i have no clue what to check next to narrow down the culprit.<br /> <br />can running the motor without a battery hooked to it for a ground ruin a rectifier in just a few short moments(a minute or two)? the reason i ask is because i think that i have had this problem for awhile now. i just assumed that when i lost power to my electronics(graph, gps radios) but my motor kept running was that i had a bad battery or severely drained one.i would then hook up my spre battery and finished out the day. i would go home and throw the chargers on and they would be ready to go the following week. i guess what was happening was that all my electrical use was coming straight out of my batteries with no help from my motor. <br /><br />is the rectifier something that can be replaced with relative ease?<br /><br />can i still use my boat knowing that my batteries are going to be seriously drained BUT without causing any further damage?<br /><br />thanks for the help guys. i think i will cut and paste this to a new topic something like 75 hp merc outbboard charging help......