Quick Alternator Question

[dearmosd]

Can a 55amp alternator be string enough to keep up with 2 batteries. One for the engine and a 29series battery for decent size stereo? Asking cause turnover efforts seems to slow and sluggish. I question if the batteries are charged enough to crank it over. Even after 20min run on the lake sitting for 30min with no accessories running the boat was hard to start and had a jumper pack for extra help.

Can you go up in size alternator if i were to replace the OE alternator.

No auto parts shop said they could test marine alternator. Plus i went out and go a cheap voltmeter and the numbers dont support that the alt is charging right away as it takes X amount of time for the volts numbers to increase with reving to 1000-1200 RPMs. The gauge will sit at 10-11amps and after several minutes of running the gauge jumps to 13amps. The alternator is 14 years old and i would feel better having one anyway.

___Can I and would it benefit me any to get a slightly larger alternator or is 55 amps for two batteries enough?

 

[Don S]

Re: Quick Alternator Question

Can a 55amp alternator be string enough to keep up with 2 batteries.

Yes, a 55a alternator should keep up fine. You need to have the belt tight, all the connections tight to the batteries, and the alternator has to work.

Take your alternator to a alternator/starter/electric motor shop. Your auto parts stores just done't have a clue, the alternators a basically automotive alternatators spark protected for use in an enclosed bilge so it won't ignite any gas fumes should you develop a leak.

The gauge will sit at 10-11amps and after several minutes of running the gauge jumps to 13amps

What engine and year do you have? SN would be better, and what alternator.
I doubt you have an ammeter. More likely a volt meter.

 

[dearmosd]

Re: Quick Alternator Question

Mercruiser K276772 is on the block

Engine is a 5.7L alpha one

yes only volt meter and it reads only 0-500volts so no fine number just whole numbers. Ya i figured family safety first so i didnt bother going to parts store for auto part for marine application.

I figured 55amps would be okay but i have seen newer 5.7L with higher amp alternator so i thought i would ask before getting new one.

Same with starter, going to stop by local place and ask to test before looking into marine applications. Try the alt first since its the source for all power

 

[Don S]

Re: Quick Alternator Question

Forget about throwing parts at it until you have a reason to. If your batteries are low, it's going to crank slow, but it sure isn't a starter problem.
Loose or corroded battery cables or faulty cable can be the cause of all your problems.

yes only volt meter and it reads only 0-500volts so no fine number just whole numbers.

You have me confused, never seen a voltmeter on the dash that goes to 500v.
Are you referring to a multimeter you are using for testing?

Have a look at this service bulletin.

View attachment Testing alternators.pdf

 

[airshot]

Re: Quick Alternator Question

Don is absolutely correct, helped me a few years back with a similiar problem. I was using hand tightened wing nuts on my battery connections. Cleaned everything thoroughly and replaced with nuts that require a tool to tighten, coated everything with grease to stop corrosion and had no more problems. Also test your batteries, not just volts, get a good load test.

 

[dearmosd]

Re: Quick Alternator Question

Sounds good i will try the new test that you posted.

I did test starter off the motor and seemed to perform fine. At least without load applied to the starter.

I must have the tool mixed up. the multimeter reads 0-1000 only wholes numbers so when people talk 12.5-13.3 (example) i thought the decimals would add up when dealing with small differences.