Voltage while running

[San Chan]

So couple of questions for battery experts.

1) running at 4000rpm or so, why sometimes I see 13.5v and sometimes between 12.2v-12.7v?

2) I understand there will be a voltage drop from my battery to the Lowrance unit but ......how low is too low voltage meter showing before the battery couldn’t crank my 90hp-4Stroke? 10.5v? 10.8v?

[Ozark Bob]

Are you having problems? It may be charging the battery when you see lower voltage. If the battery is charged up it may be higher. Your alternator generates over 14 volts with a well charged battery. As a battery gets older it looses power . I have seen motors crank slowly at 10 volts but if it doesn't start quick it wont start at all. Only one battery and over 4 years is a bit of a risk. If your motor cranks slow you may need a new or even larger battery. Larger fishfinder screens pull a lot of AMPS! Bob

[San Chan]

Maybe I should have mentioned. I remembered I used to have 13.6v while running on plane. Is it possible as the rpm goes higher, the Voltage will gets higher. This is a new battery so I couldn’t get my eyes off, watching it all day. Maybe I am overthinking, is the alternator too old if it’s doing 12.3-12.7 while running 4000 rpm?

[DW]

The voltage regulator is the primary control of alternator output.

[San Chan]

So DW, replacing it you think?

[cyber16]

Keep in mind many alternator stators produce 3-phase AC
which is rectified by a diode bridge creating sort of DC waveform
So before I would be replacing the voltage regulator
I would double check the output of the alternator prior to voltage regulator.

I am NOT positive that the alternator stator of your motor is 3 coil 3-phase AC
I'm sure someone that knows more about it will chime in
Point I'm getting to is don't just start throwing parts at it until you know what is does need.

[DW]

Before spending money on new parts, I suggest several tests. Can you rotate another good battery into position to see if you get different results. Could be a battery problem and it is conceivable that a bad battery would cause the results you describe possibly

You didn’t mention the type of voltage indicator instrument you are using. Many are not accurate. Perhaps temporarily rig a multimeter to your battery to validate your voltage during operation.

Possibly a bad, shorted cell, and maybe intermittent.

Loose wiring connection?

[San Chan]

Thank you guys so guide me what I am trying to do now is “Correct”.

I am thinking at the battery;
1) using Voltmeter and see what number?
~~if more than 12.5v I am good.
2) fire up engine and test again @ idling?
~~if more than 12.5v I am good.
3) neutral running 5000 rpm test again?
~~if more than 13.5v I am good.

Am I in the right direction testing with limited tools?

[DW]

12.6v is fully charged. 12.5 is about 85%. Delay measuring for hours after charging or voltage will be higher. When running the voltage should be mid 13 to mid 14v.

[San Chan]

Thank you Members!! Problem solved .....should say I was looking a problem that I didn’t have. Voltmeter shows 12.6 (30mins after charged) and climbing slowly towards 13.5 after I fired engine up. Lowrance unit was showing 1.0-1.2v lower than the voltmeter (average). I guess I worried too much. Guess my alternator and/or rectifier working like it supposed to.