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Dotterel has an alarm behind the control panel. It makes lot of noise when you switch on until the engine starts. Then it makes an annoying but less noisy noise for ever more - well until you switch off. 

 

It is the black round thing in the picture. The white wires are power. When the engine is running the alarm has about 4 volts across it. Where the purple wire comes from I don't know. 

 

The other interesting bit in the picture is the resistor wired across a warning light which has a battery symbol on it. This light also has a voltage across it when running so glows dimly - you can only see it in the dark.

 

Does anyone (Richard) know what drives the light and the alarm and why I have a voltage across them. 

 

I should say this situation had been on the boat for 11 years at least so clearly doesn't cause a problem. 

 

It is just annoying and I would like to understand what is going on.

 

Cheers Graham

 

 

IMG_20180513_172554587_HDR.jpg

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The resistor across the charge warning light is to ensure that the alternator excites at low revs. 

 

The warning buzzer is sounding because it has a voltage across it. Often these buzzers are fed with 12V and the negative connection supplied by whatever it’s warning about. It could be from the oil pressure switch, temp sensor or something else. The quickest way to discover what the culprit is would be to remove the wire from the sender and see if the buzzer stops. 

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The bulb with the resistor across it is the alternator warning light. When the ignition is switched on voltage is applied to the alternator to excite it. When the engine is running the light should go out. It sounds to me like you may have fault in the alternator regulator or a bad connection between the bulb and alternator. 

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2 hours ago, Flyboy said:

The bulb with the resistor across it is the alternator warning light. When the ignition is switched on voltage is applied to the alternator to excite it. When the engine is running the light should go out. It sounds to me like you may have fault in the alternator regulator or a bad connection between the bulb and alternator. 

I've never seen my alternator get excited, it just sits beside the engine creating electrickery. B)

 

Sorry, I'll get my coat.

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It’s reasonable to assume the dim light quiet buzzer sound are related and the wiring to, and alternator need investigating. Have you tried blipping the throttle  and does that have any effect on the light or buzzer?

 

Might be worth tracing the white wires I’d expect the buzzer to have connections via diodes to Charge, oil pressure and temperature warning lights.

 

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5 hours ago, Graham and Jo said:

 

 

IMG_20180513_172554587_HDR.jpg

Well there's your problem! (sucks teeth)

That wiring's all wrong …. it should look like this: -

 

 

o-SNAKES-facebook.jpg

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Thanks guys for all the helpful comments so far and the pictures of snakes!. I now understand the function of the resistor. So I'll check the wiring between the alternator and the light to see if any dodgy contacts are causing problems. Having said that why is there a voltage across it when the alternator is running, isn't most of the voltage supposed to be dropped in the alternator circuit leaving none to light the light? I did try increasing the engine revs but it still stays on. 

 

I have just been up at Odiham on the Basingstoke for a trip in our inflatable canoe to the end of the navigable part (that gets me a point in the IWA thingy on navigating obscure places - I just need to visit the rest by car and drop the canoe in now or am  I missing the point). I dropped in for a chat with Arthur who runs Galleon Marine and he happened to have a control panel apart and showed me the diodes connected the various warnings to the buzzer. I can't see those on mine so a little more digging is required. 

 

So the good news is my understanding of the problem has increased considerably and I can go back and have another look. So thanks to everyone again.

 

Cheers Graham

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1 hour ago, Graham and Jo said:

why is there a voltage across it when the alternator is running

That’s a very good question. The voltage on both sides of it should be virtually identical. If someone’s changed the bulb for an led (which would be a very good reason for the resistor) then they can glimmer with just a volt or so - what’s the voltage across the resistor with the engine running?

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1 hour ago, Graham and Jo said:

Thanks guys for all the helpful comments so far and the pictures of snakes!. I now understand the function of the resistor. So I'll check the wiring between the alternator and the light to see if any dodgy contacts are causing problems. Having said that why is there a voltage across it when the alternator is running, isn't most of the voltage supposed to be dropped in the alternator circuit leaving none to light the light? I did try increasing the engine revs but it still stays on. 

 

I have just been up at Odiham on the Basingstoke for a trip in our inflatable canoe to the end of the navigable part (that gets me a point in the IWA thingy on navigating obscure places - I just need to visit the rest by car and drop the canoe in now or am  I missing the point). I dropped in for a chat with Arthur who runs Galleon Marine and he happened to have a control panel apart and showed me the diodes connected the various warnings to the buzzer. I can't see those on mine so a little more digging is required. 

 

So the good news is my understanding of the problem has increased considerably and I can go back and have another look. So thanks to everyone again.

 

Cheers Graham

I agree with WotEver, you should see 12v on both sides of the bulb with the engine running and the alternator charging, therefore the bulb should be completely off. With regard to the diodes, they act as a gate to send the voltages from the various sensors to the buzzer without interfering with each other. If  one of diodes went short circuit or leaky, the buzzer may sound all the time. I've included a panel diagram for the Barrus Shire series so you can see how the diodes are configured. Most modern engines will have a similar arrangement. 

 

img020.jpg

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28 minutes ago, WotEver said:

That’s a very good question. The voltage on both sides of it should be virtually identical. If someone’s changed the bulb for an led (which would be a very good reason for the resistor) then they can glimmer with just a volt or so - what’s the voltage across the resistor with the engine running?

At this stage I'm not sure, I did measure the voltage across the buzzer. That was about 4 volts. When I was poking at it with my meter the other day I didn't understand what I was looking at. I'm up there again shortly and will have a look. 

 

3 minutes ago, Flyboy said:

I agree with WotEver, you should see 12v on both sides of the bulb with the engine running and the alternator charging, therefore the bulb should be completely off. With regard to the diodes, they act as a gate to send the voltages from the various sensors to the buzzer without interfering with each other. If  one of diodes went short circuit or leaky, the buzzer may sound all the time. I've included a panel diagram for the Barrus Shire series so you can see how the diodes are configured. Most modern engines will have a similar arrangement. 

 

 

Thanks for the diagram that helps. 

 

Cheers Graham

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When we had this issue is was the temperature sender causing the buzzer to sound faintly.

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Thanks, I'm going to check all the circuits if they are ok, test the alternator diodes. I hope to find the diodes that should be in the lines to the alarm. I just need to follow the purple wire I hope. Cheers Graham

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If the charge light is glowing there is a voltage across it, if there is voltage across the light then unless you have a very odd charging system an alternator diode has failed. What alternator is it? Picture?

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And you will may well have a reduced charging voltage AND a lower maximum charging current. If its a field diode that has failed you might have a higher charging voltage.

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3 hours ago, Sir Nibble said:

If the charge light is glowing there is a voltage across it, if there is voltage across the light then unless you have a very odd charging system an alternator diode has failed. What alternator is it? Picture?

I'm not at the boat at the moment so pics will have to wait until the weekend. 

 

1 hour ago, Tony Brooks said:

And you will may well have a reduced charging voltage AND a lower maximum charging current. If its a field diode that has failed you might have a higher charging voltage.

Thanks I will have a look and let everyone know. Looking at the wiring diagram for the Barrus engine am I right in thinking low voltage on the wire feeding the light would also cause the alarm to have volts across it? 

 

Cheers Graham

 

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Yes

 

On a car that can have much heavier loads on it that a typical boat's ignition switch when the switch got old and you put your wipers etc. on the voltdrop across the switch could make the warning lamp glow but its rare on a boat.

 

When a diode fails in an alternator you get a different voltage at the D+ (w/l) terminal and the main output B+ terminal. The D+ is in effect connected to the warning lamp on the alternator side. The B+ connects to the battery so when the switch is on is also connected to the other side of the warning lamp so any voltage difference between the two alternator terminals may make the bulb glow. But any poor connection anywhere in the charging and ign. sw. circuit, including battery terminals can do the same if it causes voltdrop.

 

A simple way to check the diodes is to set the engine running at about 1500 rpm and stick a voltmeter between D+ and B+. It should red all but zero. If it reads a volt or more then you probably have a blown diode. ( Sir N's test).

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My reasoning for not immediately jumping on the alternator as being faulty is that OP wrote that it’s been like this for 11 years. I’d have expected battery problems to manifest themselves if the alternator had a blown diode. 

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23 minutes ago, Tony Brooks said:

Yes

 

A simple way to check the diodes is to set the engine running at about 1500 rpm and stick a voltmeter between D+ and B+. It should red all but zero. If it reads a volt or more then you probably have a blown diode. ( Sir N's test).

Ok I'll do that. 

 

5 minutes ago, WotEver said:

My reasoning for not immediately jumping on the alternator as being faulty is that OP wrote that it’s been like this for 11 years. I’d have expected battery problems to manifest themselves if the alternator had a blown diode. 

I'm fairly surprised too! The batteries seem to be Ok though, I have had to change them once in the 11 year period. They ist on one of those charger systems that conditions them most of the time. 

 

Cheers Graham

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I will go further. It's a field diode. If it was a main diode then the resulting voltage difference would stop at the audible warning blocking diode. One or two alternator system?

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And that is likely to maintain the charging  current output and may increase the charging voltage. Hence batteries seem OK.

 

The reason I did not answer at first was because I felt I needed to know charging first thing in the morning, the alternator's rated output and the charging voltage before shut-down at the end of the day or with 10 amps or less of charge.

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And if it's an engine battery alternator then an alternator with a blown diode, corroded connections, an earth on the stator and a loose belt would probably keep it up.

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It is a one alternator system with a split charge relay. There is one starter battery and 3 household batteries. We don't use a lot of power with a very low current TV (less than 1 amp), led lights and a new fridge. 

 

Cheers Graham

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