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Telstar 28
992 Posts

You might want to check the boat and see if you have a 12 VDC leak. I've posted instructions on doing so previously... if you'd like me to repost them here, let me know. :)

BTW, if you're on a mooring, I seriously doubt it is a stray current problem, since the nearest boat to you is probably at least 30' away. :) Stray current doesn't travel very far, especially in salt water, since it will want to ground out.

Telstar 28
992 Posts

If you're on a mooring, chances are good that it is one of two issues. The first is that you got cheap zincs...and the material got eaten away because of the quality of the material used. If you bought "brand name" zincs, then the problem is more likely a DC ground leak on your boat.

To find a DC ground leak, use the instructions I posted a while back, which I've re-posted here.

If you want to test to see if you have a DC-based ground leak, the test for that is rather simple. The steps for seeing if you have a DC-ground leak are as follows:

First-the preliminary diagnosis test:

1) Turn off all equipment and disconnect any solar panels
2) Disconnect the positive side of the battery banks.
3) Leave the main battery isolation switch turned on for the bank in question
4) Set the meter to VDC mode, range appropriate for your battery bank
5) Connect the meter between the positive terminal and the disconnected cable

The meter should give no reading. If it reads XX volts for your XX VDC system, one of two things is happening.

1) You've left some equipment connected and turned on. This could be a bilge pump, a power feed to a stereo for the radio's memory and clock functions, or a hard-wired fume detector.

2) If you've disconnected all the "hard-wired" equipment and still get a reading, then you've most likely got a ground leak in your boat's DC system.

The Ground Leak Check:

1) Set the meter in Ohm mode and set it to the lowest range (x1).
2) Connect the leads of the Ohm-meter (or multimeter in Ohm mode) to the disconnected positive lead and the negative terminal of the battery.

The meter is now reading the resistance of any circuit to ground that exists in the boat's wiring. The reading on the Ohm meter display can help you identify the cause of the leak.

0-10 Ohms means it is most likely a piece of equipment left on
10-1k Ohms is a low-drain piece of equipment left on, or a serious ground leak
1k-10k Ohms is a minor leak
10k+ Ohms is an insignificant leak

How Big is The Leak?

The ammeter function of the multi-meter can tell you what the current leakage is. If your meter can read up to 10 Amps DC, then you can use it to measure amperage for leaks down to about 1.3 Ohms resistance on a 12 VDC system, or 2.6 Ohms for a 24 VDC system.

To see how big the leak is, put the probes on the positive battery post and the disconnected cable. The meter readings can be interpreted as shown:

<1mA - insignificant leakage
1-10mA - minor leakage
10mA-1A - major leak or some equipment left on
>1A - Usually some equipment left on.

Telstar 28
992 Posts
Dog, Thanks. I too have this problem and will find this helpful. Three questions:

1. I have a memory circuit for the stereo, which is switched so I can stop the battery drain during long periods of non-use. I'll switch it off before doing the leak test. I know this isn't a "leak", but does this minimal powered ciircuit contribute to the zinc corrosion?
If there isn't a ground leak to the water...then it shouldn't matter. BTW, I would highly recommend that you physically disconnect all the wires for the DC ground leak testing...

2. I have a bilge pump with a float switch. As long as it's not actively pumping, this shouldn't affect the leak test, should it? In your preliminary diagnosis test, I assume you are referring to bilge pumps with electronic switches that draw current as part of the sense circuitry. A float switched bilge pump shouldn't have to be disabled before the leak test, correct?
see above. :)

3. Your instructions tell how deterine if you have a leak. How do you isolate it if you determine you have one?

I don't give instructions for isolating or fixing a DC ground leak, because they're very specific to each individual case. :)
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