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Go Back   SailNet Community > On Board > Gear & Maintenance > Ground leak?
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Topic Review (Newest First)
09-24-2008 10:36 AM
SEMIJim Is it DC or AC current? Easy to tell: It's whichever measures higher on your multimeter. On most decent-quality multimeters, DC won't show up at all on AC measurements and AC will either not show up or will show up at much lower values on DC ranges.

Jim
09-23-2008 06:20 PM
sailingdog
Quote:
Originally Posted by patja View Post
Hi, me again. I've done some more troubleshooting and think you are right about the memory on the stereo. I saw this same effect on the battery charger and the inverter...they all show 20 - 50 mA current even when "off". Then I tried lifting the negative return cable from my negative bus for these individual circuits and the current stopped flowing, which I believe rules out a ground leak as the cause for their minor current draws.

I've got things cleared up now so that I am not getting any current flow more than a couple mA when measuring between the positive cables and the battery positive posts.
That's good to hear... that's what it sounded like from your description. Unfortunately, lots of equipment has parasitic current draws when off.

Quote:
I picked up Charlie Wing's Boatowner's Illustrated Electrical Handbook which suggested an additional test for current leak: measure DC current between the green bonding conductor and the through-hull or other fitting it is protecting. I did this with the easiest item to measure: the springy grounding conductor that rides on the prop shaft. It is showing 30 mA of current. Wing's book (page 88) says even 1 mA is cause for concern on this. I am seeing this current even when I completely disconnect the batteries (remove all positive and negative cables from batter posts). Is this a real cause for concern? Where could it be getting its current? It looks like it is flowing from the bonding wire to the shaft (red/+ multimeter probe is on the bonding conductor, black/common probe is on the shaft).

-Pat
How are the bonding wires for the boat connected, and to what? Without knowing more about how the boat is setup, it is hard to say what the problem is. It could be coming from outside your boat, from another boat at the marina or a fault in the marina's AC shore power system. Have you tried doing the same test when anchored out in a cove by yourself?? If it is the same there, it is likely due to something on the boat. If not, then it is likely due to something at the marina or on a nearby boat.
09-23-2008 06:00 PM
ckgreenman
Quote:
Originally Posted by sailingdog View Post
If it is something like the memory line to a stereo, it might have a capacitor on it...and that might account for the higher initial draw...while the cap is charging, and then the steady state of 2mA is what it draws after the cap is finished charging.

BTW, it might not be wired to the positive battery terminal, but to the battery switch or some other place you'd have an always hot 12 VDC connection.

If you don't have any wires that could be such a leak... then you're up to checking the Ground Leak, which is the second section of that post.
I was just gonna say that it sounds like a capacitor charging up. Check everything possible.

You might also try pulling the fuses one at a time until it stops. that would at least give you somewhere to start tracing it out.
09-23-2008 05:47 PM
patja Hi, me again. I've done some more troubleshooting and think you are right about the memory on the stereo. I saw this same effect on the battery charger and the inverter...they all show 20 - 50 mA current even when "off". Then I tried lifting the negative return cable from my negative bus for these individual circuits and the current stopped flowing, which I believe rules out a ground leak as the cause for their minor current draws.

I've got things cleared up now so that I am not getting any current flow more than a couple mA when measuring between the positive cables and the battery positive posts.

I picked up Charlie Wing's Boatowner's Illustrated Electrical Handbook which suggested an additional test for current leak: measure DC current between the green bonding conductor and the through-hull or other fitting it is protecting. I did this with the easiest item to measure: the springy grounding conductor that rides on the prop shaft. It is showing 30 mA of current. Wing's book (page 88) says even 1 mA is cause for concern on this. I am seeing this current even when I completely disconnect the batteries (remove all positive and negative cables from batter posts). Is this a real cause for concern? Where could it be getting its current? It looks like it is flowing from the bonding wire to the shaft (red/+ multimeter probe is on the bonding conductor, black/common probe is on the shaft).

-Pat
09-16-2008 12:23 AM
sailingdog If it is something like the memory line to a stereo, it might have a capacitor on it...and that might account for the higher initial draw...while the cap is charging, and then the steady state of 2mA is what it draws after the cap is finished charging.

BTW, it might not be wired to the positive battery terminal, but to the battery switch or some other place you'd have an always hot 12 VDC connection.

If you don't have any wires that could be such a leak... then you're up to checking the Ground Leak, which is the second section of that post.
09-16-2008 12:17 AM
patja Thanks sailingdog, your prior post was one of the resources I've been referring to.

I am pretty sure everything is off. There are literally zero cables connected to the positive battery terminals, other than the battery interconnects from positive terminal to positive terminal. This is true for both the house bank and the starting battery. Is that what you mean by shutting everything off?

What do you think of the declining current readings from 90 ma down to 2 ma? Is that some effect of the multimeter itself?

I think my next step is to start flipping individual breakers and seeing if current is drawn by the device on the circuit even though it has no neutral connection at the negative/grounding bus bar (hence it is completing its circuit through the ground leak). This is what Casey recommends in his book.
09-15-2008 10:14 PM
sailingdog This is from a post I wrote a year ago:

Quote:
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.
My first question is are you sure you've disconnected all the "hard wired" equipment and turned everything else off. If you haven't then you can't be properly checking for a ground leak. Things like bilge pumps, memory power for electronics, etc are all possible sources of the 12V that may not be "leaks". Did you disconnect all of them?

90 mA is a relatively large leak, and would tend to indicate to me that more likely, you've left something on. It could be as simple as an led indicator light, which you aren't aware of.
09-15-2008 09:55 PM
patja
Ground leak?

I am evaluating a potential ground leak and could use a second or third set of eyes on the situation.

I've removed all positive cables from the batteries, and the only negative connection is to the grounding system...to the engine and then grounding wires to thru-hulls, props, tanks, etc. All breakers are off, and the shorepower cord is disconnected.

My observations under the above conditions:

I am getting a 12V reading between the positive battery terminal and the disconnected positive cable. This is always cited as the primary indicator of a leak.

The resistance is fairly high, about 100,000 Ohms, between the negative battery terminal and the disconnected positive cable.

When measuring the current flow across the positive battery terminal and disconnected positive cable, my multimeter gives an initial reading of 90 milliamps for a few seconds, then it drops down to about 2 milliamps.

First question: do I really have a problem or not? Casey and Calder say ground leaks are only "serious" with a resistance of under 10,000 Ohms. But then again, they also say that all leaks greater than 5 milliamps must be eliminated.

Is my leak 2 milliamps or 90?

The boat is fairly new to me so I don't have the history, but my divers did just replace my zincs at 50% after only 3 months.

Thanks in advance for any helpful insight!

 
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