Voltage drop while using the power trim

[rwcobalt]

I've looked all over the forum for answers on voltage drop while using the trim and have found nothing. Several topics on the trim not working, but not just voltage drop. Sorry if I missed it.

boat: 1999 Cobalt 25ls, 7.4 gi pwtr (4110178868)

My problem: trim up or down, the voltage drops at battery immediately from 13.8 ~ 13.9 (engine running) to 11 ish then continues to fall as the trim button is up or down until eventually (within seconds) the 50 amp breaker on the breaker box starboard side above exhaust trips. Happens at idle or revving or for that matter 50 mph. also note that all of the low amp items (blower, cockpit lights, nav lights, etc) have zero affect on the voltage when running, however when I turn my docking lights on I do get a .5 to 1 volt drop with engine running.

What I've done: new batteries fully charged (13.4 each), tested battery cables, removed & cleaned grounds on enigine block, tested grounds on a ground pole mounted to transom, tested alternator voltage key off (same as battery), tested voltage at alternator and battery engine running (both 14.0).

My skills are limited to say the least. I have not tested anything on the trim motor itself simply because I get the impression if their is a problem there the trim simply will not work up, down or both not to mention the voltage drop when using my docking lights lingers in the back of my head.

Is it possible that the alternator will show a good voltage output to battery at idle as mine does (14.0 even) yet not be able to absorb a load from a high amp draw item such as the trim motor or docking lights? I have not taken it off to bench test simply b/c it read 14.0 output. What else do I need to look at from a ground standpoint?

Thanks

 

[tpenfield]

Re: Voltage drop while using the power trim

My docking lights really show a sharp drop in voltage, similar to what you are seeing with the trim motor. The engine hatch motor is also a voltage killer on my boat. I have not noticed as much with the trim motor, but every motor that draws a fair amount of current will show voltage drop when it is running.

One thing to try is have the ingition 'on' but do not 'start' the engine. Do the trim motor thing and see it the voltage drop is similar. The voltage may not be as high than with the engine running, but see if it drops down to about the same voltage, etc.

It could be that the connection to the alternator is corroded or wearing thin, and you are getting a big voltage drop accross the bad connection.

I have been chasing electrical gremlins around my boat now and then, and it usually ends up being a connection that has aged a bit or something like that.

 

[Maclin]

Re: Voltage drop while using the power trim

In my opinion you have isolated the problem and it is with the trim motor. Failing brushes, some corrosion on the armature shaft, etc. Any of that can give the symptoms you describe, while at the same time providing enough drive to do what it is supposed to do. Until the breaker goes anyway.

Is the trim motor is getting hot? Are any of the wires feeding it getting hot right at that motor? Do any of the trim motor feed wires "move" as the current draw goes higher?

 

[bruceb58]

Re: Voltage drop while using the power trim

Are you actually measuring the voltage on the battery with a meter when you observe this or the gauge on the dash?

 

[rwcobalt]

Re: Voltage drop while using the power trim

i am using a meter, although the gauge does drop in conjunction with it. I will go ahead and pull the alternator and have it tested while I check the connections. Good suggestion on inspection of the trim motor/wires for heat. We will see. Dropping voltage is like finger nails on a chalk board to me.