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Old 16-05-2013, 06:27   #16
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Re: Electrical Problems

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Originally Posted by rwidman View Post
Often you can start in the middle. This cuts the troubleshooting in half.
Often that would work and in fact if you know your system in detail you can usually go directly to the problem and avoid all that annoying troubleshooting.

However, if you have a particularly perplexing problem, you aren't sure how the whole thing is put together and/or your skills in electrical somewhat limited then best to be as methodical as possible. Makes it harder to miss something and as a side benefit you also learn how that whole system is wired up and where all the bits are located.
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Old 16-05-2013, 06:30   #17
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Re: Electrical Problems

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Originally Posted by Dockhead View Post

But still need to figure out what's going on with my alternator
Are the field coils excited?

Generally if they are it should work / partly work

To Test...
With the ignition on but engine not running, take a screwdriver or other metallic object and put it against the front of the alternator, you should feel a magnetic effect on it.

Then do the test with the ignition off and it should go away or be greatly reduced.

Then report back here.
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Old 16-05-2013, 06:49   #18
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Re: Electrical Problems

Thanks -- I'll do that, but I'm presently 1500 miles away from the boat! I'll be back on board at the beginning of June.

My alternator is something called "Ignition excited" -- Prestolite - Leece Neville

Maybe that's the issue -- a contact at my helm is bad which is not exciting the alternator, and not switching on the control circuit for the windlass.

How is that for a theory?

I guess your test will show if there is excitement or not.

How does this work? Sorry for my electrical ignorance. A voltage is applied to one terminal of the alternator, switched by the ignition, and this "excites" the field coils?

So if there is no voltage, no excitement, no alternator output?

If I'm understanding that right, then I just need to verify that there is no voltage on the wire which is supposed to be exciting the field coil, and trace it until I find the bad connection. So?
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Old 16-05-2013, 07:28   #19
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Re: Electrical Problems

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Originally Posted by Dockhead View Post
Thanks -- I'll do that, but I'm presently 1500 miles away from the boat! I'll be back on board at the beginning of June.

My alternator is something called "Ignition excited" -- Prestolite - Leece Neville

Maybe that's the issue -- a contact at my helm is bad which is not exciting the alternator, and not switching on the control circuit for the windlass.

How is that for a theory?

I guess your test will show if there is excitement or not.

How does this work? Sorry for my electrical ignorance. A voltage is applied to one terminal of the alternator, switched by the ignition, and this "excites" the field coils?

So if there is no voltage, no excitement, no alternator output?

If I'm understanding that right, then I just need to verify that there is no voltage on the wire which is supposed to be exciting the field coil, and trace it until I find the bad connection. So?
Yes, generally what you have said is right. Ignition excited means it needs external power to work and this power excites the field coils, which on an alternator of this size will be around 3amps at 24v. The screwdriver test will not show whether the problem is internal or an external fault. However, if there is no magnetism with ignition on, then it is worth checking , the warning lamp bulb itself and warning lamp bulb circuit which I think goes to the D+.

If the warning lamp circuit is ok then maybe the alternator fault is internal but I somehow think its external.

But at this stage, I would get the electrician back involved.

Did he do the screwdriver test because this is usually stage one when diagnosing alternator faults.
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Old 16-05-2013, 07:47   #20
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Re: Electrical Problems

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Originally Posted by rwidman View Post
If your friend, the marine electrician is actually a marine electrician, he will figure out that it is much simpler to power the control circuit from an "always on" source than to install some sort of bypass switch.

This could be a simple as moving the control circuit power wire from one terminal of the ignition switch to another (yea it's not really an "ignition" switch on a diesel but we think of it as such).
Well he really is. The reason for the bypass switch is that generally using the windlass eats a lot of juice and so it makes some sort of weird sense for the engine to be running. OTOH, you want to be able to use the windlass if the engine poops out on you.

Understand now?
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Old 16-05-2013, 07:49   #21
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Re: Electrical Problems

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Originally Posted by Fuss View Post
Yes, generally what you have said is right. Ignition excited means it needs external power to work and this power excites the field coils, which on an alternator of this size will be around 3amps at 24v. The screwdriver test will not show whether the problem is internal or an external fault. However, if there is no magnetism with ignition on, then it is worth checking , the warning lamp bulb itself and warning lamp bulb circuit which I think goes to the D+.

If the warning lamp circuit is ok then maybe the alternator fault is internal but I somehow think its external.

But at this stage, I would get the electrician back involved.

Did he do the screwdriver test because this is usually stage one when diagnosing alternator faults.
I don't have an electrician involved (I think that was Carsten, not me), and am trying to avoid it. Finding and getting a good marine electrician on board will be more hassle than fixing it myself, not to mention the cost, I am thinking. I am thinking this is not rocket science, even if it is all obscure to my mind -- so far.

So the screwdriver test will tell if there is excitment or not. Likewise, I guess I should test the field wire for voltage. I am guessing I'll find no excitment, and no voltage on the field wire, and need to trace it back.

The wiring at my helm is not all that great, because it is impossible to completely weatherproof it, and I would be not the slightest bit surprised if there is a bad connection there.

I guess the field wire will be connected to the ignition switch via the alternator light, so this should not be rocket science to trace. I'll try to dig up wiring diagrams.
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Old 16-05-2013, 08:16   #22
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Re: Electrical Problems

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Originally Posted by skipmac View Post
Often that would work and in fact if you know your system in detail you can usually go directly to the problem and avoid all that annoying troubleshooting.

However, if you have a particularly perplexing problem, you aren't sure how the whole thing is put together and/or your skills in electrical somewhat limited then best to be as methodical as possible. Makes it harder to miss something and as a side benefit you also learn how that whole system is wired up and where all the bits are located.
Let's say that your electrical device is not working. You have power at the battery but not at the device. If you start troubleshooting at the battery, you may test at several points before you find the fault just before the device. If you start testing at the device, you may test at several points before you find the fault next to the battery. If you test in the middle of the circuit, you can isolate the fault to the first half or the second half.

I used to do this sort of thing for a living but on circuits that spanned several acres. Narrowing the problem down saved me a lot of work.

If you want to learn your boat's electrical system (a good idea for those so inclined), it's best to do it before you have a problem.
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Old 16-05-2013, 08:18   #23
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Re: Electrical Problems

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Originally Posted by carstenb View Post
Well he really is. The reason for the bypass switch is that generally using the windlass eats a lot of juice and so it makes some sort of weird sense for the engine to be running. OTOH, you want to be able to use the windlass if the engine poops out on you.

Understand now?
I think I understood all along. Why have a bypass switch when it can be wired to work anytime you want it to without an additional switch? You have control of the windlass. You decide when to use it.
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Old 16-05-2013, 09:53   #24
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Re: Electrical Problems

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Originally Posted by rwidman View Post
Let's say that your electrical device is not working. You have power at the battery but not at the device. If you start troubleshooting at the battery, you may test at several points before you find the fault just before the device. If you start testing at the device, you may test at several points before you find the fault next to the battery. If you test in the middle of the circuit, you can isolate the fault to the first half or the second half.
Believe me, I completely understand the process and the logic. Have a BSEE and have been fixing my own boats for 40 years and have tried just about every permutation of troubleshooting techniques possible from making educated or uneducated guesses, random stabs, hit and miss, to methodically starting at one end and working to the other. I have found that I usually end up saving time by starting at a point where I can easily verify proper function and working out from there, even in fairly simple systems where the whole thing is fairly obvious and straightforward.

Quote:
Originally Posted by rwidman View Post
I used to do this sort of thing for a living but on circuits that spanned several acres. Narrowing the problem down saved me a lot of work.
As a pro and working on large scale projects, depending on the problem and other circumstances, it could be highly inefficient to work one end to the other.

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Originally Posted by rwidman View Post
If you want to learn your boat's electrical system (a good idea for those so inclined), it's best to do it before you have a problem.
Of course but one can't always learn every system on a boat before problems arise. I based my suggestions on the situation faced by the OP and in the context of what he's trying to accomplish. Other situations, other people could certainly justify other methods.

Of course always better to know the system before it breaks but for some odd reason the systems I have figured out on my boats aren't always the ones that break first.
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