Alternator questions 14.8V output

[CheapboatKev]

Hello guys..
Have a question on my old (1968) 2.5L 4 banger mercruiser alternator.
My battery doesnt seem to hold a charge (although fairly new)
I had the alternator tested (but at a auto chain)
Showed 14.8V output, but didnt have a way to test amperage.
Just by the voltage level, can we call this alternator good?

Thanks as always..

 

[Don S]

Re: Alternator questions 14.8V output

Sounds like a normal charge voltage, get your battery load tested. I've run into to many brand new batteries that were junk.
If the battery does load test ok, then get your alternator checked at your local starter/alternator/electric motor shop. They have the tools to check them under load.

 

[Boatist]

Re: Alternator questions 14.8V output

Alternator has very little to do with the battery holding a charge.
All the alternator does is supply a proper voltage to charge the battery. 14.8 Volts is great. Do you have a Volt meter on the boat or in your GPS or Fish Finder.
If you do then with the engine running check the voltage, if it is 14.8 volts then the alternator is not the problem.

What is this battery used for on the boat?
Does it run a electic trolling motor or big Stereo?
A deeply discharged battery can takes 12 hours to charge?
Batteries used for starter motors and run every day would have no problem charging up.
Batteries running heavy loads like a trolling motor or big Stereo can have big discharges that take a long time to recharge. They will not recharge in the 10 minute run back to the launch site.
Also all Batteries self discharge so need recharged weather used or not. Must recharge once a month in summer and every 2 months in winter to keep the battery in good shape.
A good Automatic or Smart charger or on board charger to fully charge the battery at the end of each trip is best. I like charger in the 10 to 15 amp range so charge can complete in less than 20 hours.
Leave the battery discharged a few times at the end of the day and you will need a new battery. Any time a battery is left discharged damage is done.

 

[fishrdan]

Re: Alternator questions 14.8V output

My battery doesnt seem to hold a charge (although fairly new)

Explain, how does it discharge, sitting for a long time, short run out at the lake and it's dead? Do you have and use a battery switch, IE: disconnect the battery while the boat is stored?

You could have something on the boat draining the battery, stereo left on, some item drawing a bit of current, enough to drain the battery over time. I had this with my old boat (73) I always had to flip the batt switch when I parked it, or the battery would be dead in a month or 2 of just sitting.

 

[CheapboatKev]

Re: Alternator questions 14.8V output

Explain, how does it discharge, sitting for a long time, short run out at the lake and it's dead? Do you have and use a battery switch, IE: disconnect the battery while the boat is stored?

You could have something on the boat draining the battery, stereo left on, some item drawing a bit of current, enough to drain the battery over time. I had this with my old boat (73) I always had to flip the batt switch when I parked it, or the battery would be dead in a month or 2 of just sitting.

The battery's sole purpose is to start the engine. I have all running lights, bilge & gps/fishfinder on a seperate large deep cycle battery.
I also have a "kill switch" that kills all power from the starting battery. No way anything is draining the batery.
I'll get 10 to 15 (guessing) starts outta it then zippo....

 

[Boatist]

Re: Alternator questions 14.8V output

Do you have a volt meter so you can mesure the voltage while running?
Is it the alternator that came with the Boat or has it been replaced?
A 1968 I think would be a 3 wire alternator.
Are all three wires hooked to it?
One large wire that runs to the battery or starter solenoid.
A small field wire and a Small relay wire.
On that old of a alternator I think you would also have an external voltage regulator.

Your are going to need a voltmeter to trouble shoot it.
If you do not have one you should get one, there cheap.
Harbor Freight has them usually around $4.

 

[j_martin]

Re: Alternator questions 14.8V output

Could be as simple as a bad belt or pully. I've seen alternator pulleys that were worn so the belt bottoms out in it. The result is no traction.

Tension the belt normally, then try to turn the alternator pully by the fan blade on it with your fingers. If it slides in the belt, the pulley, belt, or both are bad.

My father in law, for instance, paid for 3 new batteries and 2 new alternators, along with labor. The real problem was a $3.00 pulley.

Also, 15 starts, if they are hard ones, could drain a battery.

hope it helps
John

 

[CheapboatKev]

Re: Alternator questions 14.8V output

Thanks John...
But the belt is tight. I was holding the flashlight for dad when I was alittle guy,and learned how to use a big arse screwdriver to put leverage on the alt to keep the belt tight.
Thanks dad...lol

 

[drewpster]

Re: Alternator questions 14.8V output

A shadetree way to check for a component drawing current would be to turn everything off, disconnect the cable to battery ground, use a multi meter set to DC volts, touch one test lead to the battery negative post, touch the other test lead to the end of the removed ground cable. If you see voltage, something is drawing power. If you see voltage leave the meter in place and start removing fuses until the voltage on the gauge goes away. If it goes away, then the last fuse removed has the voltage sucking culprit in its circuit.

If you have a DC amp gauge that reads below 1 amp you can do the same thing described above without removing any cables. Or if you have a good meter that will read amps below 10A you can also do the same thing, but you still have to remove the battery ground cable.

enjoy
drewp