Yes I searched. A different alternator and 90 amp starter fuse problem

Joined
Sep 7, 2016
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6
I tried the best I could to find an answer without starting a new thread, but I could not find what I was looking for.

I just picked up my first boat. 1983 Sea Ray 225 Cuddy Cruiser. 260 Merc with the "pre" Alpha outdrive ....S/N 627XXXX. The boat had newer batteries in it, but they were dead. I replaced them with brand new batteries. Took it out for my first cruise, and my voltmeter wasn't looking good (soon to replace with one with actual NUMBERS rather than green/red). I noticed it was this way before takeoff. Checked batteries with a multimeter, showed 12.2volts or so on both. Everything ran OK electrical wise ( but I found out that I have the dreaded shift interrupt - cable issue). During the cruise, we used battery #1 (I have a battery selector switch)

​Anyways, after we got back home, I put my multimeter on the back of the in dash voltmeter to see what my actual numbers were. Battery #1 was 12.00 volts. Battery #2 was 12.2 volts. I started the engine (on muffs) and the voltage did not change. I turned the engine off. Tested voltage right at the batteries. Voltage was around the same as pre-cruise numbers but #2 was higher than #1 now. I didn't write them down this time but #2 was higher again...... Started the engine....no change.

Since it looks to be an aftermarket cheapie alternator, I figured it was bad, so I disconnected the orange wire at the alternator. Started engine.....put the + lead of my multimeter on the alternator positive terminal and grounded the - lead on a battery negative terminal. It showed 121 volts DC...NOT 12.1, it was 121. Kinda freaked out at that. Turned off the engine. Put the + lead of the multimeter back on the alternator positive terminal and I could watch the voltage bleed back down to zero.

Then I checked for continuity from the alternator end of the orange wire to the other end of the orange wire where it is also connected directly to the red/purple wire at the 90 amp fuse and I had continuity so I knew the alternator cable was good. Then I checked for continuity from the alternator end of the orange wire to the main battery cable connection at the starter (which is the other side of the 90 amp fuse) and I didn't have continuity. To me that means there's no continuity through the fuse.

So, my thinking.....alternator went bad and threw out an overvoltage and also fried the fuse. But my question is, if the fuse was bad, why does everything in my dash work, the engine runs, etc etc?

Am I wrong in my assumption? If the 90 amp fuse is bad, could you still have power at the dash and the rest of the boat? I ran out of time but tomorrow I hope to completely remove the fuse to test it for continuity sitting by itself.

THANKS IN ADVANCE!!
 
Last edited:

Grandad

Lieutenant Commander
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Jun 7, 2011
Messages
1,504
Welcome to Iboats Chester. I'm no authority on alternators but I believe you won't see any appreciable voltage output until it's running at a threshold RPM that may be higher than what you should run the engine while on muffs. And yes, if you're confirming a fuse is OK, a continuity test should be done with the fuse isolated from the circuit. You might be well advised to confirm that the "cheapie" alternator is a marine design, not an automotive type with potential arcing and sparking that could ignite fumes. - Grandad
 
Joined
Sep 7, 2016
Messages
6
Thanks for the replies guys. I did find the fuse was bad for sure. Also, someone in the past had put the big red wire from the battery and the red wire that feeds the 50 amp circuit breaker on the same side of the fuse as each other. That is why the boat never lost power even though the fuse was bad. The Orange wire coming from the alternator was by itself on the other side of the bad fuse which is one reason why it was not charging.

So....if the alternator was never connected to a load since who knows when, would that fry it like stated in an earlier reply from Bruce?
 

bruceb58

Supreme Mariner
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Mar 5, 2006
Messages
30,620
All those people that think they can remove a battery cable to see if their alternators are good are frying their alternators and they don't even know it.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
Messages
51,344
in many cases, the alternator goes out with a really beautiful blue glow that can melt the case when you disconnect the load and sense wires
 
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