Electrical leak to ground

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jwwarwick

I have recently discovered that with the Main Switch on and everything else on the boat turned off, that I have a 1 amp drain on the battery. I consulted Nigel Calder's "Boatowner's Mechanical and Electrical Manuel" and went through all the tests. I have isolated the current drain to the positive cable from the Main Switch to the positive terminal of the starter motor. This was done by disconnecting one circuit at a time in the main panel until the current drain went to zero. Two small drains were the 1 watt pilot light on the panel and the CD Player which were just a few milliamps. Now taking wires off the positive starter terminal one at a time, I found .8 amps draw from the small red wire to the alternator. I have two wires to the alternator, red and orange, and this red one goes to the small terminal at the top. Had alternator checked out at shop and they said everything was fine but recommended I run a separate wire from the back case of the alternator to ground wire of battery. I did this and same results. The other .2 amp drain went away when I disconnected the (-) wire from the engine block to the main panel. I have checked and replaced cable ends on each end of suspect wires and even bypassed them with a new wire using alligator clips. VOM reads 18 ohms between (-) battery terminal and (+) terminal of starter motor. Voltage is 28 mv between (+) battery terminal and (+) terminal on starter solenoid and 12.39 volts (system voltage) between (+) battery terminal and (-) connection at engine block. What could it be??? The alternator and starter are not the insulated-return type. Should they be the insulated gd. type on a 1989 C-34? The alternator shop said the drain to ground should be no more than a few ma for the alternator which is the stock one furnished with the Universal M-25 XP Engine. Current drain is zero with main switch off. What is the normal current draw with main switch on and everything else off? Bilge pump is not the problem as I checked that first. Any suggestions to finding this ground leak?

John Warwick

Stu Jackson

John

Having seen no responses to your post, I invoked the old standby: go to the source.  A number of our members are very electrically oriented, but are not active on this Message Board.  

Try this:

There is a wire from the stock alternator which goes to the ignition switch and provides the voltage reference for the internal regulator.  The other small wire coming from the alternator goes to the tachometer and provides a variable frequency ac to determine engine speed.   If the wire that goes to the ignition switch is left connected to the battery (not through the ignition switch) and the engine is stopped, there will be around an amp drain at all times.  Of course, the only way that could be a problem is if someone moved that wire from the switched terminal of the ignition switch to the battery side - I've seen it happen more than once.  Opening the wire at the alternator with the ignition switch off should tell the tale on
that.  I think the tachometer wire is orange and the wire to the ignition switch is red but it's been some years since I changed from the stock
alternators to externally regulated alternators with "smart" regulators so I'm not sure.

A single wire, grounded system is used for the engine electricals on all Catalinas and, for that matter, virtually all  boats except for a few
European makes.  He doesn't need an isolated ground system to eliminate battery leakage current and its only advantage would be to avoid
electrolysis.  From the readings he is getting, it appears that the alternator is the most likely culprit and I would think that any shop should be able to determine if there were a leaky diode in either the main bridge or secondary bridge which feeds the internal regulator.

Many thanks to our electrical guru.

In addition:  you can check the wiring color coding on the C34 website and finding "Wiring Harness Upgrade," which has the original re-wiring diagrams posted, with the wire colors identified.  Most likely in FAQs.
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."

jwwarwick

I have finally found the problem! I was sure it was in the alternator somewhere so the second trip to the alternator store solved the problem. They replaced the rectifier and the voltage regulator and that solved the problem. I have done the wiring upgrade and added a solenoid on the starter circuit. The wire to the "Sense" terminal on the alternator and the "Output" wire on the alternator should be hot all the time from the starter terminal and not switched. The "Excite" terminal is wired to the oil pressure switch to send 12 volts to that terminal when the oil pressure rises to a preset psi. This turns the alternator on. The guy at the alternator shop said, "Yeah, some of them do leak quite a bit from defective components"

John Warwick

Stu Jackson

John

Thanks for the update and the resolution.  Much appreciated.  There is ALWAYS something to learn.

Stu
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."