batteries , diodes and poor charging problems.. - SailNet Community

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  #1  
Old 04-23-2009
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batteries , diodes and poor charging problems..

I am stuck in the Bahamas untill money comes in so I can have someone check my batteries, stuffing bow (excessive leaking) and bildge pump that will only work manually. The batteries have a diode system and it seems that thge diodes click off most the time either draining the batteries or not charging at all of sometimes they will infact charge the batteries but for only a short time but not enough to top them off. My tachometer stops reading rpm when the batteries are not charging which is kind of weird too.
I have a beneteau first38 and the engine is a perkins 4108 50hp. I single handed the boat from the Turks/Cacos to the bahamas where I gave up the voyage because of low batteries and no bildge and excessive stuffing box leaking. I originally started the voyage from the BVI Tortola with some crew which had to get off in Provo T&C islands. I am stuck here untill I can resolve these issues. Now I am trying to get some sdvice on what to do so maybe I can save some money or oversee the repairs are done correctly because I will be single handing to texas and will need my auto pilot, to run GPS and auto pilot and bildge ect. Thanks for any advise. Also can the stuffing box be fixed with out having to put the hull on the hard???
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Old 04-23-2009
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It sounds to me that you have an alternator problem, on my boat the RPM will not read if the alternator is not working. last year I had a problem with the alternator cutting in and out and it was the voltage regulator that was the problem.
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Old 04-23-2009
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proflyer... you might be right.
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Old 04-23-2009
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Hi John,

Sorry to read that your adventure is turning into an ordeal...

You mention that
Quote:
The batteries have a diode system and it seems that thge diodes click off most the time either draining the batteries or not charging at all of sometimes they will infact charge the batteries but for only a short time but not enough to top them off.
I don't want to sound difficult but there are a couple of things that need to be clarified so that I can hazard a guess; 1. batteries do not have diodes. Batteries are connected to the Alternator, which does have diodes. Batteries are sometimes connected to a battery isolation diodes, which enables you to charge seperate battery banks independently 2. Diodes do not "click." Diodes are semi-conductor devices, and have no moving parts. Did you mean to say that you have a Battery Paralleling Relay?

Assuming that you do not have a relay, your second observation
Quote:
My tachometer stops reading rpm when the batteries are not charging
helps identify the situation. The tachometer in a diesel is frequently connected to the alternator. I believe that you may have a fault in the field winding circuit of the alternator, or possibly a bad voltage regulator. Does the tachometer work when you start the engine, and then unexpectedly stop working, or does it not work at all?

I would carefully check the alternator, looking for a disconnected (ABYC Standard would be Brown) wire that sets the field in the alternator. The terminal on the alternator is probably marked "1," "F," "DF" or "FLD." This wire may either go to the voltage regulator, a pressure switch on the engine block, or to the key switch. A "quick and dirty" test would be to disconnect the negative (ground - should have a black or yellow wire) lead from a 12V cabin light and attach one end of a length of wire to it, start the engine, and touch the other end from that wire to the alternator feild winding. If the alternator starts charging, then you have narrowed down the problem to one of the switches that I mentioned above.

If you have shut off the key switch before pulling the engine stop lever, or before the engine has stopped turning, it is likely that you have blown the diodes in the alternator. These diodes convert from AC (produced in the alternator) to DC. To test them you will need a multi-meter.

HTH!

- Ed
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Last edited by eherlihy; 04-23-2009 at 05:27 PM. Reason: clarify negative = ground
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Old 04-23-2009
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Quote:
Originally Posted by john232 View Post
I am stuck in the Bahamas untill money comes in so I can have someone check my batteries, stuffing bow (excessive leaking) and bildge pump that will only work manually. The batteries have a diode system and it seems that thge diodes click off most the time either draining the batteries or not charging at all of sometimes they will infact charge the batteries but for only a short time but not enough to top them off. My tachometer stops reading rpm when the batteries are not charging which is kind of weird too.
Diodes don't click off or on...they're solid state... relays might click off and on...but diodes never will. The problem with using diodes in a battery charging system is that they create a voltage drop. The voltage drop is usually about .5-1.0 volts, depending on the make/brand and type of diode used. If your boat uses a battery charger and it hasn't been adjusted to compensate for the diode induced voltage drop, it will never charge the batteries properly...and if the batteries are never properly charged, they will sulfate and die.

For instance, the float charge on a wet cell 12 VDC system is about 13.2 VDC or so. If you have your charger set for 13.2 VDC, and you have a diode or set of diodes in the charging circuit that induce a .7 VDC drop... the batteries are being float charged at 12.5 VDC, which is lower than the actually full charge 12 VDC system voltage of 12.6-12.7 VDC... meaning that they will never be fully charged. So, while diodes are fairly reliable, they are generally not very good to have in your battery setup.

Quote:
I have a beneteau first38 and the engine is a perkins 4108 50hp. I single handed the boat from the Turks/Cacos to the bahamas where I gave up the voyage because of low batteries and no bildge and excessive stuffing box leaking. I originally started the voyage from the BVI Tortola with some crew which had to get off in Provo T&C islands. I am stuck here untill I can resolve these issues. Now I am trying to get some sdvice on what to do so maybe I can save some money or oversee the repairs are done correctly because I will be single handing to texas and will need my auto pilot, to run GPS and auto pilot and bildge ect. Thanks for any advise. Also can the stuffing box be fixed with out having to put the hull on the hard???
No, I would not recommend trying to change the stuffing box packing while you're in the water.
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Old 04-23-2009
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got a good tight belt on the alt.??
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