Is my alternator dead? Where can I buy 5424 spares?

[MarkSF]

I suspected my alternator is dead, so today I tried this :

Check voltage when A/C charger is on : 13V
Disconnect charger : drops to 12.7V
Turned on all lights, radio, etc. for 10 minutes - dropped to 12.4V.

So far so good, I think. A/C charger is doing it's job, batteries can store some charge.

Then I started the engine, and the voltage stayed the same. 12.4 on both sets, regardless of whether the switch is set to 1,2, or both. Shouldn't it go up to 13.5-14V on the batteries connected to the engine?

So I think the alternator is dead. Where can I buy one for my Universal 5424? I'd like to get some other spares too like an impellor.

[capttb]

Did you only run the engine at idle ? Most alternators have a "turn on speed" they don't produce till they reach a set minimum RPM, sometimes 1200-1500 rpm. They can/will have a "cut-in" speed also which is the minimum speed at which power is produced once turn-on speed has been reached. Anyway, try running the engine faster before buying a new alternator.

[MarkSF]

Thanks, think I'll try my DVM directly on the batteries too, rather than trust the old gauge in the boat.

[CalebD]

Keep in mind that your alternator could have fried diodes on the output side. The alt. makes an alternating current (AC) that uses diodes to create a DC charge and if the diodes fry or fail then no current at all.
It is easy enough to remove the alt. from your engine and take it to a alternator/motor repair shop to get a check up or overhauled.
Check the numbers with your DVM first but replacing the diodes should be a good bit cheaper then buying a new unit, if the diodes are done.

[LakeSuperiorGeezer]

Originally Posted by CalebD

Keep in mind that your alternator could have fried diodes on the output side. The alt. makes an alternating current (AC) that uses diodes to create a DC charge and if the diodes fry or fail then no current at all.
It is easy enough to remove the alt. from your engine and take it to a alternator/motor repair shop to get a check up or overhauled.
Check the numbers with your DVM first but replacing the diodes should be a good bit cheaper then buying a new unit, if the diodes are done.

I agree, have it checked; some automotive parts stores will even do it for free. Have it rebuilt; they are sometimes rebuilt better than new. Maybe you can ask around about who does a good job. Many times alternators have a fuse to protect against putting the battery in backwards. Sometimes this is just a length of wire. Without a fuse, if the battery posts are switched positive to negative, the diodes are like a dead short and burn out very quickly. Put your voltmeter on the larger wire going to the alternator and the other end of the meter to ground. You should get about 12 volts. If none, check for blown fuse. If the diodes suffered reverse polarity without a fuse, you will still have 12 volts. Also see if the small wire at the alternator has 12 volts. I am not sure, but believe there is an excitation voltage needed to make it work even if there is a built in voltage regulator in the alternator. Do not disconnect alternator from battery while running the engine or it will damage the alternator.

[celenoglu]

The brushes ofthe rotor might be finished. An alternator is not easy to destroy completely. It can easily be repaired.

[capttb]

I am not sure, but believe there is an excitation voltage needed to make it work even if there is a built in voltage regulator in the alternator.

You are correct, one of the diodes is a Zenier diode which turns output on when voltage drops and off when it reaches target voltage.

[speciald]

Number of things could be bad - no exitation current - check for fuse in circuit, bad regulator, blown diodes, shorted windings. Take it to an automotive alternator repair shop for testing. I have had to replace the core on multiple Balmar alternators over the years - not cheap, but cheaper than buying a new one.

[JimsCAL]

Here's a source for a new one.

New Motorola, Leece Neville 12v 51 Amp Alternator: Alternators &amp Alternator