Low charging voltage while running at idle/trolling speed

prowlersfish · Post by **prowlersfish** » Tue Jun 14, 2011 12:05 pm

Its not a regulator , most likely slipping belt or weak alternator

bernietech · Post by **bernietech** » Mon Jun 20, 2011 8:40 am

hi, just a thought, Is there any corrosion on the field connections or the alt output stud. I have seen similar problem on older cars. A high resistance at the field may cause your problem. The best test would be to bench test alternator. I know Auto zone will test, but it will be a go or no go test with the newer duratest station. I think Advance still uses the older style testers which will give you hard numbers, not a go-no go. If you do get numbers , compare to your readouts. If the same it is an alternator problem, if different it is a boat wiring issue.

How are you measuring your on boat voltages? A digital meter is not the best as it is a high resistance meter. An older analog (pointer neddle) is more accurate because of its lower internal resistance.

keep us posted

bernie

prowlersfish · Post by **prowlersfish** » Mon Jun 20, 2011 7:45 pm

I will have to disagree on the volt meters

Big D · Post by **Big D** » Mon Jun 20, 2011 9:34 pm

Personally, digital is the way to go unless you're monitoring fast changing readings ie you wouldn't want a digital tach as I once had on my bridge. My understanding and experience is that it's a requirement for testing sensitive electronic circuits, certainly not a detriment to accuracy. Not that I've ever heard anyway. A perfect example in a marine application is to try and measure the voltage drop across isolator diodes. No problem with a digital meter, not so much with an analog.

By the way, does anyone know if my didgital tachs were original? They certainly were old tech; looked like idividual small vacuum tubes for each number (3 per gauge). They were wired to two boxes at the bridge that were wired to the coils. Most likely aftermarket, never seen any since.

Codger · Post by **Codger** » Mon Jun 20, 2011 9:42 pm

I'm using a digital meter.

I loosened and retightened the belt just to be sure. Same volt readings. I've been using the boat all summer (but not trolling because i am worried about this issue), and have not had any low battery issues, even with the low reading. The boat does not have a charger to replenish on shore power. I might try an Arco replacement alternator just to be safe. They come internally regulated so I would not need the existing external voltage regulator. Still thinking it over before maybe ordering the new alt.

bernietech · Post by **bernietech** » Tue Jun 21, 2011 9:07 am

Hi again,

If I am reading this correctly, you have an external regulator on the alternator. Is it solid state or an older mechanical regulator?

I would first start by cleaning all connections.

My comments on the meters was mis-interpreted. Both styles of meters are useful. Digital meters are high resistance (like the old VTVM's) and do not load the circuit they are measuring. A traditional analog meter does load the circuit, which does change the circuit. DMM usally will give a higher voltage reading when compared to a analog VOM. try testing a weak, but not dead flashlight battery with both meters. the DMM will show about 1.5 vdc and a low resistance analog meter will show a much lower voltage because it loads the battery. When testing a marine or automotive battery it is tested under load, not no load. Many times when testing circuits the low resistance analog will help you find the problem faster. Typically, VTVM's and DMM's are 10-11 megohms /volt. Analog VOM's ar 5k/volt.

later,

Bernie

Codger · Post by **Codger** » Sat Jul 09, 2011 1:22 pm

OK, here's the final outcome.

Bought a new Arco alternator that has the regulator built in.

Installed the new alternator and removed the existing voltage regulator from the boat.

Hits 14.3 volts and stays there when RPMs are over 800. Looks like its charging right now.

Thanks for all the help.

MTP · Post by **MTP** » Sat Jul 09, 2011 10:11 pm

prowlersfish wrote:Its not a regulator , most likely slipping belt or weak alternator

what on earth would a professional wrench know about this subject?

prowlersfish · Post by **prowlersfish** » Sat Jul 09, 2011 10:58 pm

MTP wrote:
prowlersfish wrote:Its not a regulator , most likely slipping belt or weak alternator
what on earth would a professional wrench know about this subject?

Not much