Alternator Light On and Tach Out

[duefocena]

Anyone have an idea why my altenator light is staying on even though the alternator is charging? Also my Tach went out. I discharged the batteries and then started diesel to see if the alternator charged and it did. Also to make sure the charging system wasn't full which I heard can cause the alternator not to read.
Any help out there?

[Hydra]

Maybe a disconnected wire between the engine and the control panel? I suggest that you test all connexions with a voltmeter.

Alain

[Vamonos]

I have no idea what alternator you have but I just had the alternator rebuilt on my Perkins 4.108. It had a strange connector that I wasn't familiar with from my automotive background. Since diesel engines don't have ignition systems, you can no longer get a tachometer signal from the ignition. There is a separate winding in some alternators (intended for diesel engines) that provides the tachometer signal.

Richard

[Svsilvergirl]

On my boat , the "ignition switch" both energizes the alternator and power to the gages . On several occasions the ignition switch got bumped off while the engine was running , and it would cause the exact scenario you just described . The motor remains running until you kill the fuel with the fuel shut off solenoid , but the tach shuts down and the alternator light comes on . The key on my boat is inconveniently located freight behind one of the lazarette doors , and can easily be bumped to the off position when you are digging four something in the bottomless pit. So maybe your ignition switch is intermittently failing or faulty

[Dennis.G]

Vamonos likely has answer. There will be a separate wire from your alternator giving a signal to the tach. Alternator will still charge without this wire, but you will see 0 RPM. Alternator warning light - not sure, but they are wired in different ways and might be same issue as tach.

[donradcliffe]

Are you SURE you are charging?? Your symptoms are the classic signs that you aren't. Unless someone's been messing around with both the ignition AND the tach wiring, your alternator is probably not putting out. Measure between ground and the output terminal of the alternator when the engine is running--should be about 14 volts, and higher than the voltage across the battery terminals.

[duefocena]

Hey Don,

Thanks for your input.

I ran batteries down to 12 volts then fired that engine ( twin engined sail boat= double trouble) and they started charging so I feel confident the alternator is working. Shows 14.5 on my guages.

[CarlF]

Did the tach work when you were charging after discharging the batteries? The most common cause of tachs dropping out is when the batteries are full and the alternator stops charging. The tach signal can go away. In this situation, the tach will work again if you turn on some load - such as several lights so the alternator starts charging again.

It sounds to me like the alternator isn't working (or working sporadically) for a different reason. It could be the alternator or the regulator. Remove and clean to shiny all screw wire connections. Most regulators have a few fuses. Check all with a multimeter. They can sometimes look OK but are blown.

Carl

[duefocena]

Thanks for the reply Carl,

I removed the alternator and had it checked. It's putting out 14.5. I am at sea right now ( heading for a haul out up the coast) and have everything on, Radar, radios, 2 chart plotters, refridge, etc. and all is charging but no tach and alternator light still on the starboard engine panel. Gotta be a short somewhere.

[Dsanduril]

What Vamonos said.

Most current marine diesel manufactures use the alternator to provide the tach signal (Volvo used to use a magnet on the flywheel with a pickup sensor, but they have switched to the alternator as well, I know that most Yanmars use the alternator, and several others I have seen, but don't know as well). Amongst other things that means that changing the pulley ratio on your alternator will affect your tach.

Anyway, in this situation there should be a minimum of three different connections to the alternator:

1. the charging connection

2. the field connection (which comes through the ignition circuit and the regulator [if external])

3. the tach signal.

Don't know if the tach signal is also used to run the charging light, but I would start with the tach signal wire, run a temporary wire straight from the alternator to the instrument panel and bypass the harness and see what happens.

(BTW, just did this yesterday on a Yanmar, and found that there was a broken wire in the harness somewhere deep in the engine. Routed a new wire with the harness and all works fine).

[duefocena]

Vamanos,
Thanks for the reply. I run one Volvo and one Perkins. They are very similar as Volvo bought the rights to the Perkins Parama M 30 and produce it as a Volvo 2030. The original engine ( Perkins) is the one I am having difficulty with. It has a larger alternator, with what appears to be external regulator.

[duefocena]

Dsanduril,
The bottom of your message didn't come through. Where you started to list something only the 1. bullet mark came through.

[clifford sloan]

The external regulator is most likely to be the culprit. Just replaced mine to the tune of $600.00 USD

[duefocena]

Holy Smokes Cliff,

Does yours make beer or something? THat seems really high. Here in Newport Beach they'll rebuild the whole thing for $200.

[donradcliffe]

Here is a pretty good description of the alternator warning light for most systems with internal regulation:

Understanding Alternators, How Alternators Work

Here is a good source for external regulator wiring--the color codes are pretty standardized.

http://www.balmar.net/PDF/Max%20Charge%20MC-612.pdf