Why Won't Battery Charge While Engine Runs

[stb100]

I have an '84 Wellcraft 200 elite w/a 260HP merc. Symptoms are as follows:
- Battery never charges while under way after a day on water. Has died sometimes but I take a spare. Still, no fun.
- Dash voltmeter never reads more than 11V --usually less. I recharge bttys before each trip. 11V or less even w/new battery.
- Have to retighten alternator belt often. Rubber dust on engine hood says it's getting ground down. Running out of room on adjustable bar for Alt.

Here's what I've done so far:
- Brand new marine battery, new Alt and Starter last year.
- Brush corrosion from posts, cables, wires.

While idling, Alt reads 40A on back w/ multimeter. No juice getting to btty, tho. Someone said maybe Alt pulley is wrong size (tho I gave old one to match at Alt shop). Said maybe a '9 series' pulley to match belt #9440. Alt shop guy never heard of it tho. How crucial is belt brand? Have matched size of new one from auto parts store to old one.

Any ideas much appreciated! THANKS.
-- STB

 

[Don S]

Re: Why Won't Battery Charge While Engine Runs

Rusty pulleys will destroy the belts just like sand paper.
Loose belts on alternators = no charging.
You also need a good clean tight connections and wiring to and from the alternator.
Pulley size is the same will work if everything else is in good shape.

 

[tommays]

Re: Why Won't Battery Charge While Engine Runs

It sounds like you have very rusty pulleys the belt should not be shreading at all

You need to use a real DVM (electric meter ) and measure the voltage at the battery when the motors running
.
A good battery will hold a charge around 12.6 to 12.8 volts ? how old are they

At a high idle 1500 RPM you should see it reading bettwen 13.5 and 14.4 you might need run in the water at speed to see the full 14.4 volts

Tommays

 

[stb100]

Re: Why Won't Battery Charge While Engine Runs

Thanks for your input
Battery is brand new (2 days!) Do have some rust on main pulley - not alt pulley. Thought I had belt tight but does keep loosening tho I've stretched and tightened hard.

Ran engine in driveway sunday...Ran RPMs up to 2 then 3000. Voltmeter dropped to 10.5. At low idle hovered at 11 and would 'twitch' a bit downward... I agree it oughta sit steady at 13 plus...but won't !!?!

2 questions:
- Can rusty pulley be saved -- worth it or not? Or buy new one?
- Does belt brand matter? - last one was Gates (automotive)

Thanks again!

 

[tommays]

Re: Why Won't Battery Charge While Engine Runs


The dash meter is useless for repiar purposes

It does not sound like your chargeing BUT you need real numbers to find the problem

The pulleys can be sanded or wire wheeled and repainted with rustolem unless there really torn up and that would be my first step as if the alt is slipping you will not be able to charge the battery

Tommays

 

[Bt Doctur]

Re: Why Won't Battery Charge While Engine Runs

Check to see if you have a square plastic block mounted to the main starter lug. supposed to be a fuse type arrangement for the alt. but with some corrosion it wont pass it to the battery

 

[stb100]

Re: Why Won't Battery Charge While Engine Runs

Thanks. Will do

 

[bruceb58]

Re: Why Won't Battery Charge While Engine Runs

Curious how you read 40A with a mutimeter. Are you using a current clamp probe?

 

[Boatist]

Re: Why Won't Battery Charge While Engine Runs

I have many questions as to your set up.
First what type alternator do you have? Is it a one wire with an internal regulator or is it a 3 wire with a external regulator?

Belt problem can be rusty pulleys wearing belt but also often just the wrong belt. Many buy the belt at an auto store and that is fine but make sure you get the right width and length. V belts wear on the sides so when worn out they appear to be narrow. When you get a new belt it should ride at the top of the pulley not down near the bottom. If a new belt rides near the bottom then you got too narrow a width.

If the alternator is turning and it is a good alternator then should put out at least 13.8 volts even at idle. If it is 12.6 or lower and not riseing while the alternator pulley is turning then likely bad alternator or regulator.
Even a brand new alternator can be blown if you have a loose or coroded battery cable for even a part of a second. Also if you have a battery switch and it is turned while the motor is running.

 

[whywhyzed]

Re: Why Won't Battery Charge While Engine Runs

Curious how you read 40A with a mutimeter. Are you using a current clamp probe?

I was thinking the exact same thing....

Not to many multimeters go more than 10A without an amp clamp.
Using an amp clamp right near the alternator is sometimes not reliable because of the magenetism of the field.

There's often a fuse or resetting circuit breaker in the alternator line to the batt. - could be a blown fuse or failed or tripped breaker

 

[stb100]

Re: Why Won't Battery Charge While Engine Runs

THANKS to all for the great advice!

Works fine now, after:
-- had Alt Shop bench test alternator. Rins fine.
-- replacing fuse block on back of starter (white plastic thing)
-- wire brushing and repainting pulleys
-- finding/replacing a badly corroded inline 10A fuse/fuseholder that was on thin wire to bilge pump
-- wire brushing corrosion off of battposts and as many wires/fittings as I coul reach
-- new merc belts

Also everyone who caught my mistake about 40A on back of Alt...You were right.

Ran all day yesterday on prettiest day of the summer. THANKS again!

STB