Current mystery

boydgatlin · #1 (**permalink**) 10-07-2008

I've trying to find the reason the boat I bought 18 months ago eats prop zincs like candy. Today I disconnected all four batteries and both shore ties, and I still measure about 40 milliamps between the chain plates and water. The potential difference is about 1 volt DC. I tried the same measurements on neighboring boats and the same meter barely deflected.

I've been keeping a zinc 'grouper' connected to the chain plates in an attempt to save the prop zinc (and my prop), but I''m not sure it's helping.

Anyone have any ideas or suggestions?

badsanta · #2 (**permalink**) 10-07-2008

sounds like alot of current. Can you connect the grouper directly to the shaft? maybe the chain plates are not inter connected (grounded) with the thru hulls. Just a thought.

boydgatlin · #3 (**permalink**) 10-07-2008

Thanks for the thought.

I measure the same thing from any grounded point on the boat that I can
reach (e.g., mast, AC receptacle plate). My thru-hulls are not bonded, but everything else on the boat (including SSB ground plate) is connected via copper strips, as far as I can tell. I suppose a capacitor in the battery charger/inverter could be supplying a sneak current even with everything else disconnected.

sailingdog · #4 (**permalink**) 10-07-2008

I would try testing the voltage and current while the boat is anchored out by itself... if the readings change, then the problem is most likely related to the marina itself, rather than the boat. If it hasn't changed, then the problem is likely on the boat itself. Once you know whether the problem is the boat or the marina slip, you can troubleshoot the issue much more easily.

Hartley18 · #5 (**permalink**) 10-07-2008

What else do you have on board that might be generating electricity?

Are you using solar panels or a wind generator to top up the batteries??

Rockter · #6 (**permalink**) 10-07-2008

boy...

That is a very aggressive leakage. It's about 250 times what would occur naturally, without the zincs. A full volt is collosal.

boydgatlin · #7 (**permalink**) 10-07-2008

No wind or solar; just a genset and Trace inverter/charger. I have four batteries (two house, two starter). With all four disconnected, the reading remain unchanged.
I did make some measurements earlier while at a remote anchorage. The readings were lower, but not insignificant.

I'm surely overlooking something.

sailingdog · #8 (**permalink**) 10-07-2008

From an earlier post of mine:

Quote:

Originally Posted by sailingdog

Zanshin-

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.

I'm not sure how to test for a ground fault in the AC side of your boat.

I hope this helps.

TillerJohn · #9 (**permalink**) 10-07-2008

Try removing the batteries from the boat and then measuring. Remove the batteries one at a time and measure after each removal.

mikehoyt · #10 (**permalink**) 10-07-2008

SD

Very nice post.

Boyd,

Simple change similar to anchorage. Move to other side of marina to ensure not a neighbouring boat.

The boat that used to be beside us (before we moved) had old OMC saildrive that was having this problem. We never found source and boat has since removed saildrive and been sold ... It would eat one zinc per year.

Mike