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Old 11-09-2017, 15:49   #31
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Re: Alternator good, not charging battery

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Originally Posted by redbeard1 View Post
With your multimeter set to volts, what are you getting when you place one end on the purple wire at alternator and the other end at a good ground?

With the ignition on, you should get less than 12v but more than 2V. On our set-up, we get about 3V. If you are getting 0v, it is less likely corrosion and more likely a break in the circuit (is your alternator bulb on when the ignition is on?)


I have been defeated for the day. I'll check tomorrow.
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Old 11-09-2017, 16:09   #32
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Re: Alternator good, not charging battery

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"The Flat Earth Society Has Members Around the globe"

I'm going to steal that one! It was a good job I had just put my coffee mug down when I read that.
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Old 11-09-2017, 19:16   #33
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Re: Alternator good, not charging battery

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Do NOT do this unless you want to replace your diodes.
That is something I should have known, but didn't. I guess I have been lucky the times I've done it. If the OP did any damage on my bad advice, the replacement is on me.
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Old 12-09-2017, 06:40   #34
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Re: Alternator good, not charging battery

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Originally Posted by redbeard1 View Post
With your multimeter set to volts, what are you getting when you place one end on the purple wire at alternator and the other end at a good ground?

With the ignition on, you should get less than 12v but more than 2V. On our set-up, we get about 3V. If you are getting 0v, it is less likely corrosion and more likely a break in the circuit (is your alternator bulb on when the ignition is on?)


I get .3v at the purple wire, both at the instrument panel and at the alternator.
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Old 12-09-2017, 06:44   #35
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Re: Alternator good, not charging battery

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Hi,

We chased a similar problem for three months. Finally traced it to spider webs in the socket for the light that indicates the alternator is working (most consoles have this light as is serves to provide the current to excite the alternator). The circuit is designed so that the resistance of the bulb will draw enough current to excite the alternator. If the circuit has too much resistance (spider web in our case, usually corrosion for others), the amps drop and not enough current is delivered to excite your alternator. There is often a parallel circuit with a resistor to supply the current if your bulb burns out but in our case, this extra circuit was broken).

If you have a multimeter, check for resistance at each leg of the circuit. Remember to isolate the circuit before checking for resistance.

edit: sorry took a while to type my reply, did not see the replies after 5:04


The only light I have is a small battery symbol that lights up when voltage is low. If the alternator is charging, the battery symbol isn't illuminated.Click image for larger version

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Old 12-09-2017, 06:51   #36
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Re: Alternator good, not charging battery

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Could it have something with this diode? The red/yellow wire becomes hot when the key is turned on.
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Old 12-09-2017, 07:15   #37
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Alternator good, not charging battery

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When I disconnect the wiring harness from the engine panel:

Key On position:
I now have 1.75V on the purple wire on the panel side and .2 V purple wire on the engine/alternator side.

Key off position:
0V purple wire panel side and .2V purple wire engine/alternator side.
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Old 12-09-2017, 07:42   #38
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Re: Alternator good, not charging battery

I'm no expert, but I had a similar non-charging situation with a tested good alternator. I did two things, so I'm not sure which worked.
First, my ground connection on the housing was painted after a rebuild. I cleaned it to bare metal and made a tight connection.
Second, I verified that the control wires were correctly connected, they were not good. I did a new sense wire.
It looks like the red wire coming out of your housing is the sense wire. Make sure it's good, not grounded out.
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Old 12-09-2017, 09:09   #39
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Re: Alternator good, not charging battery

Also check the ground connection - some alternators are not case grounded; there is a separate negative output which is cabled to the engine block. Mine had a poor connection at the engine said (too many things including a cable clamp piled under the same bolt) so we lost 1-2 volts there. Measuring Alternator output at the + and - of the alternator should not read different than measuring from Alternator + to engine block.
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Old 12-09-2017, 09:18   #40
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Re: Alternator good, not charging battery

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Originally Posted by Redline452 View Post
Also check the ground connection - some alternators are not case grounded; there is a separate negative output which is cabled to the engine block. Mine had a poor connection at the engine said (too many things including a cable clamp piled under the same bolt) so we lost 1-2 volts there. Measuring Alternator output at the + and - of the alternator should not read different than measuring from Alternator + to engine block.


I'm pretty sure problem is with the purple wire.
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Old 12-09-2017, 10:12   #41
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Re: Alternator good, not charging battery

The voltage drop across the diode should only be about .7 volts.

I may be way off here, but have you checked that the diode is conducting in only one direction? It seems awful small for the application of a power diode, then again the voltage is pretty low to begin with. It is not something I've had inline on anything of mine, the alternator should already have a protection diode internally.

Can you post the specs on the alternator? It would be pretty easy to look it up and find it's wiring diagram and voltage requirements.
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Old 12-09-2017, 11:02   #42
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Re: Alternator good, not charging battery

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The only light I have is a small battery symbol that lights up when voltage is low. If the alternator is charging, the battery symbol isn't illuminated.Attachment 155946

Hi,

Thanks for the picture. Your battery/alt light is lit so that means you are getting 12 volts into the light. I would treat the .3V you found at the alternator as as 0V for debugging.

I also think your problem is in a) the purple wire circuit or b) possibly in the resistance element of the alternator (b is a guess, on our boat, the lightbulb's resistance usually drew about 9V leaving 3V to enter the alternator. If there are 3V entering that part of the circuit, then there must be a resistance inside to draw those volts. I concluded there must be some resistor inside the alternator to split the voltage).

a) I would focus on tracing the purple wire from the light to the alternator. The purple wire is probably split into several sections. One section goes from your alternator to the beginning of the harness. Another section of wire runs inside the harness which goes to your console. Usually the harness connects to another section that splits into the various console areas (either the white or grey connector in your picture).

Turn off the main battery switch (even better disconnect all batteries - testing resistance on a live wire will ruin your multi-meter). Take out the lightbulb. Put your multi-meter on Ohms. Place one end of the multi-meter on the negative part of the bulb socket and the other end on the purple wire at the alternator. If you have high resistance, then you know the problem is in one of the sections and just need to repeat the test on each section to find the problem. If you have no resistance in the complete circuit, then I would conclude the problem is inside the alternator option (b).
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Old 12-09-2017, 14:22   #43
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Re: Alternator good, not charging battery

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If you have no resistance in the complete circuit, then I would conclude the problem is inside the alternator option (b).
EDIT:
If you have no resistance in the (lightbulb socket negative) to (purple wire on alternator) part of the circuit, then I would conclude the problem is inside the alternator option (b).
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Old 12-09-2017, 15:00   #44
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Re: Alternator good, not charging battery

What about the tension on your belt?
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Old 12-09-2017, 16:12   #45
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Re: Alternator good, not charging battery

I can't see where the type of install is mentioned?
My boat has the ability to be started from the engine or the helm.
Some have that as well as the fly bridge.
Mine has a relay etc at the engine to avoid 40' of heavy wire to key and back again.
Just posing questions to where there might be a connection problem.
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