Engine battery ligh does not go out

[Pagos]

Have a Volvo penta md2040b and the bolt broke from the altenator on passage , have now replaced however now the light on the panel stays on has anyone advise on what the problem may be, have tested usual stuff but no clue?

[cal40john]

What's the usual stuff? Voltmeter to see if alternator is actually putting out a charging voltage?

John

[Pagos]

Correct have checked output and voltage.

[colemj]

Which light stays on? The glow plug, the oil pressure, the voltage?? Does an alarm sound?

What bolt broke? Have you checked the wiring on the alternator to make sure none of the connections were broken?

Jeez, help us out here - a map of your current location doesn't help us at all.

Mark

[Pagos]

Ok sorry so little info . The voltage light stays on and the bolt that broke was the one holding the alternator to the engine it basically sheared off.
I have no wiring diagram for the alternator however I am fairly sure it is right however if you have the diagram that would be a help.
Regards Adrian

[mjwarner]

Adrian, you mention that the bolt sheared on passage. Are you still on passage? What I'm wondering is, are you anchoring each night and then raising anchor with a power windlass each morning? This would cause the alternator light on the panel to remain lit for quite some time (with the engine running) as the battery recharges. Generally, that light indicates that the alternator is actively charging something in the system, you need to figure out what is being discharged. I have found that the load from the windlass is great enough to require the alternator charge light to remain on for several hours. It should get dimmer as the hours pass, but if you have hauled a lot of chain, it can take hours for this to occur.

[colemj]

When the alternator is running, do you have 12V (nominal) output on the D+ terminal of the alternator? If not, that could explain the low voltage light and the tach not working.

What specific model of instrument gauge do you have (key/no key, alarm test/no test)?

Again, check to make sure that all the wires on the back of the alternator have good connections - particularly the ones on the small D+ and W terminals because these are small wires with weak connectors and these are the terminals where the voltage and tach are sensed. Check to make sure the small 2-wire plug hasn't fallen off the tab on the D+ terminal and also that the tab didn't break off.

Mark

[colemj]

Originally Posted by mjwarner

Adrian, you mention that the bolt sheared on passage. Are you still on passage? What I'm wondering is, are you anchoring each night and then raising anchor with a power windlass each morning? This would cause the alternator light on the panel to remain lit for quite some time (with the engine running) as the battery recharges. Generally, that light indicates that the alternator is actively charging something in the system, you need to figure out what is being discharged. I have found that the load from the windlass is great enough to require the alternator charge light to remain on for several hours. It should get dimmer as the hours pass, but if you have hauled a lot of chain, it can take hours for this to occur.

The light on that engine is a low output warning light and not a charging indicator.

Mark

[GordMay]

Volvo Penta Workshop Manual - MD20 (10, 20, 30, & 40):
➥ http://www.bluemoment.com/manuals/Vo...0-20-30-40.pdf

[cal40john]

Originally Posted by Pagos

Correct have checked output and voltage.

You're not making this easy. Where did you measure the voltage? Did you measure it at both the alternator and the battery? What was the value you measured? What was the voltage on the batteries with no charging source applied in the last couple of hours? Do you have an internal or external regulator? If an internal regulator is the voltage constant somewhere around 14.2 volts once the batteries have had a chance to charge? Does the voltage vary with rpm? Belt slipping?

Loose corroded connections can cause problems.

There are different types of regulators. Commonly on an internal regulator the alternator light is connected to the excitation wire, this provides the initial current to the field winding to start the alternator providing electricity. Once the output of the alternator increases, its voltage rises (through the trio diodes). Since this is also connected to the excitation wire, when the voltage comes up the drop across the light becomes about 0 and the light goes out. I can't think of many situations where the light can stay on and there isn't something wrong inside the alternator other than the loose connections mentioned above. Unless you have spare diodes or a spare regulator there's not much you can do yourself on the alternator.

See image 010 for one kind internally regulated alternator:
Alternator Theory v15

I have seen a failed regulator where the light stayed on and the alternator still put out some voltage, but it wasn't regulated, it went up and down with rpm.

A modern external regulator like the Balmar ARS-5 the light is an optional output. So the regulator could still be working with just a failure in the light circuit. Seems unlikely though.

John

[delmarrey]

If the alt fell, it may have jared a diode loose, which would cause a voltage drop, causing the light to come on.

[Redcoat]

The light indicates a call for power to excite the alt. After it begins charging it should go out. If your not charging you need to replace or rebuild. Remember make or brake for diodes.

[colemj]

On his alternator, the warning light is not part of the excitation circuit. The alternator is residually internally excited. The light is powered off the D+ terminal and is simply a warning light that the alternator is not working. Doesn't necessarily mean it isn't working - could mean that there is a bad connection on the D+ terminal. The tach is also powered off off that terminal, and he has a dead tach too.

Mark

[delmarrey]

Originally Posted by colemj

The tach is also powered off off that terminal, and he has a dead tach too.

Mark

Where do you see that posted?

[colemj]

The part about being powered off the D+ terminal is posted in the schematics of my service manual for the same alternator as his.

The part about the dead tach is posted in his separate thread on this forum.

Mark