Testing Charging System on 98 Force 120 HP

[Jefro573]

Hopefully I am posting this in the correct spot, so I apologize if its not.

Is there is a simple test I can do on the charging system to see if its working properly? I have a 1998 Force 120 HP OB. I just put in two batteries with a switch (1/2/Both/All). One is a deep cycle and the other is a starting battery. I have the deep cycle running just the radio, horn and bilge pump (if its ever used) and then the starting is of course for the engine. I started the engine up and the starting battery runs about 12.71 V while engine is idling. I have heard that if the charging system is functioning correctly that it would read more in the 13.5 V range. Is there truth to that at all?

 

[roscoe]

Output voltage will vary according to rpm of the motor.
The faster the motor runs, the more voltage it puts out.

What was the voltage on the the battery with the engine off ?
If it was less than 12.7, then went up to 12.7 after starting the motor, then it is likely working fine.


You might want to put the bilge and horn on the same battery as the engine.
That way you can use them while underway, without worrying about which battery the switch is set on.
I guess if you leave the switch set to "both" all the time, it would be ok, but defeats the purpose IMO.

 

[Jefro573]

Both batteries were about 12.5-12.7 with engine off too. So that mean it's not working?

Good point about the bilge and horn. Fortunately I haven't had to run the bilge but you never know. I'll just separate those from the others and run them to the battery that the engine is on. Thanks for that idea.

 

[roscoe]

A lot of these motors just don't generate enough juice until the engine rpm get over 2000.


Run the engine up to 2000 and test the voltage.

 

[Jefro573]

OK will do. I'll try that out tomorrow and will check the voltage. I'll let you know.Thanks for the tip.

 

[Jiggz]

Your charging system is equipped with a voltage regulator. Hence the voltage output will vary according to the charge state of the battery. The best way to test is to make sure the engine is at least at fast idle around 2000 rpm, measure voltage at the battery at regular idle and at fast idle. If there is no difference try running accessories like radio and bilge pump to see if the voltage will go up. And yes, at 2000 rpm the output voltage should be around 13.5V~16.0V depending on the charge state of the battery being charged.

 

[Jefro573]

I ran it at about 2000 rpm and the starter battery was about 14.4-14.6V. It was about 12.7V at idle. So I should be good, right?

 

[Jiggz]

Yup, you are good to go! Enjoy boating!