|Topic Review (Newest First)|
|09-24-2008 09:36 AM|
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.
|09-23-2008 05:20 PM|
Originally Posted by patja View Post
|09-23-2008 05:00 PM|
Originally Posted by sailingdog View Post
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 04:47 PM|
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).
|09-15-2008 11:23 PM|
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.
|09-15-2008 11:17 PM|
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 09:14 PM|
This is from a post I wrote a year ago:
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 08:55 PM|
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!