Low Voltage

[tlcausey]

Hello, I've got a 1996 Mercruiser 5.7 noticed the voltage gauge was reading about 11 volts when I cranked the engine. I checked the battery with a multimeter with the engine off it reads 12.2 volts, when I crank the engine it drops to 11.2 volts. I've checked the connections and the alternator and the battery all is good. I'm thinking I need a new alternator just wanting to get second thoughts before I buy one. Is there anything else that would cause this problem. Thanks very much.

 

[Bondo]

I checked the battery with a multimeter with the engine off it reads 12.2 volts, when I crank the engine it drops to 11.2 volts.

Ayuh,..... What's the voltage at 1500/ 2000 rpms when runnin',.....

 

[H20Rat]

Alternators don't do anything during starting, and in most marine GM engines, don't actually do anything for a couple seconds after starting, or at least until rpm's hit 1500 or so.

12.2 volts is low for a battery that is just sitting there, should be 12.8. Cranking voltage could easily be 11 volts, or even lower sometimes.

 

[Alumarine]

When you say crank or cranking do you mean when you are trying to start it or when it is running?
Cranking means the starter is turning it over trying to start it.

 

[tlcausey]

The voltage doesn't change when I increase the rpm's on the engine. No difference at 700 or 2000. Thanks

 

[Bondo]

I'm thinking I need a new alternator just wanting to get second thoughts before I buy one. Is there anything else that would cause this problem.

Ayuh,..... If the charge wire from the alternator to the starter's solenoid lug is Good, then ya, it sounds like the alternator has died,....