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  #1  
Old 03-25-2012
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Help with DC negative question

Hi folks,
OK, so I found something interesting today, and I'm trying to understand why it is the way it is. This might be a dumb question on my part, I don't know.

I removed the main DC negative wire that runs from my negative bus bar (by the house bank) to the main DC bus next to my DC panel (planning to upgrade the gauge). I expected this to cause everything supplied by my main DC panel/bus not to work. However, the whole boat still had 12v power. I realize that means that the system was picking up negative somewhere else. I'd like to understand where. (Note: to be clear, I had everything turned off when I did this. I subsequently realized they all still had a DC neg connection though).

I started to play with the DC neg bus immediately next to the house bank. Leaving the battery connected to the bus, I removed everything else and eventually the power went off. Either of two different cables would make a neg connection to light up the boat:

1) Case ground from the battery charger

2) Main cable to the engine block (to which the AC ground and bonding systems are also connected)

AC was disconnected from the boat, so the charger was off, and this was just the way the boat is wired.

So is it something improperly wired to the bonding system? Something funky about the AC ground? I'm just not getting how this could be.

I appreciate any suggestions on how to figure this out.
Cheers,
J
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Old 03-26-2012
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Re: Help with DC negative question

Is another electrical item connected to the bonding circuit, other than at the engine block? That is a possibility and the bonding system shouldn't be used for a negative return. I would check this.

As far as the battery charger I guess its DC negative is grounded to its chassis.
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Old 03-26-2012
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Re: Help with DC negative question

If you have a solar panel wired in it's got a ground connection ????
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Old 03-26-2012
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Re: Help with DC negative question

Quote:
Originally Posted by Capt Len View Post
If you have a solar panel wired in it's got a ground connection ????
Yes, to the battery through the negative bus. The wire from the negative bus to the main panel was removed so I do not think that is the issue.

josrulz

How is the battery charger wired as far as DC output?

What I said about the bonding circuit is possible. As far as the charger goes unless the negative output goes somewhere other than the negative bus or the batteries I don't see how that could complete the circuit.

The AC ground should only be connected to the DC negative in one location so that should have nothing to do with it.

Wish I was there - an interesting puzzle.
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Old 03-26-2012
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Re: Help with DC negative question

Bet it's the battery charger!

Now, if you remove the negative cable from the battery and your boat still lights up, then you've REALLY got a problem :-)

Bill
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Old 03-26-2012
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Re: Help with DC negative question

Hi everyone, thanks for all the replies/suggestions. Some responses below...

Quote:
Originally Posted by mitiempo View Post
Is another electrical item connected to the bonding circuit, other than at the engine block? That is a possibility and the bonding system shouldn't be used for a negative return. I would check this.

As far as the battery charger I guess its DC negative is grounded to its chassis....
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...How is the battery charger wired as far as DC output?

What I said about the bonding circuit is possible. As far as the charger goes unless the negative output goes somewhere other than the negative bus or the batteries I don't see how that could complete the circuit.

The AC ground should only be connected to the DC negative in one location so that should have nothing to do with it.

Wish I was there - an interesting puzzle.
mitempo, nothing that I KNOW of is connected to the bonding circuit. That doesn't mean it's not there though. Could be something a PO did years ago that I wasn't aware of and haven't yet discovered.

The charger is connected straight to the DC neg bus. AC side connected straight to the AC panel on its own switch. AC ground bus (on back of panel) is connected to engine block. As far as I KNOW, no breaks or weirdness there.

I do have a few theories, but I'll need to go back to the boat today to try them out.

And speaking of interesting puzzle, I'm still confused as to how the entire boat would be powered up. If something was tied into the bonding circuit for instance, it would need to also be tied into the DC negative. Possible, but I haven't seen it.

Quote:
Originally Posted by Capt Len View Post
If you have a solar panel wired in it's got a ground connection ????
No solar, but thanks for the suggestion!


Quote:
Originally Posted by btrayfors View Post
Bet it's the battery charger!

Now, if you remove the negative cable from the battery and your boat still lights up, then you've REALLY got a problem :-)

Bill
Ha ha! That's kind of how it felt when I first found the problem.


I'll head back to the boat today and disconnect a few more things in sequence to see if I can further isolate the issue. I can disconnect the bonding separately at the block, for instance. I'll report back.
Thanks!
-J
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Old 03-26-2012
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Re: Help with DC negative question

Wireless DC power with no power source required. Do you guys have any idea how many folks have been trying to make that happen for how many years? Even Tesla couldn't do it without a transmitter!
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Re: Help with DC negative question

Hi all, I have an update. It appears to center around the engine block/bonding system (or something connected to them). Here's the only way I can explain it, so I hope you can follow:

Problem 1:
I disconnected everything from the DC NEG bus, except the batteries themselves. Of course everything turned off. At the engine block, I disconnected the main cable to/from the DC NEG bus, AC ground wire, and bonding wire (they all attach to a single bolt). From here on, I'll oversimplify the connections, just to make it clear:

- When I connect the batteries to the engine block, everything turns on. That's with no AC ground or bonding wire attached.

- When I connect the batteries to the bonding wire, everything turns on. That's with no AC ground or main cable from battery to engine block attached.

- When I connect the batteries to AC ground, nothing happens.

So basically, whether I connect the batteries to the engine block OR the bonding wire, I get DC power all over the boat.

Problem 2:
This may not be a problem, but here's how the charger is involved. The charger case ground cable seems to be linked to the AC ground inside the charger. Is this normal?

The effect is this: With the charger case ground cable connected to the batteries, it's therefore connected to the AC ground cable. When I connect that AC Ground cable to either the engine block OR the bonding wire, everything turns on. So that's essentially the same problem as described above, assuming that it's normal for the case ground and AC ground to be linked under normal circumstances. Is it?

Back to problem 1:
As mentioned, whether I connect the batteries to the engine block or the bonding wire, I get DC power all over the boat. Which means that the DC NEG at the panel is connected to both the engine and the bonding system. I can see how it shares NEG connections with the engine, considering all the wiring there. But the bonding system should not be.

Is it possible that the engine block has some other connection with the bonding system besides the main wire? Perhaps from the raw water intake seacock through the steel reinforced hose, or something like that?

Or am I definitely looking for something wired incorrectly to the bonding system? I haven't seen anything like that since I've owned the boat, but that doesn't mean I haven't missed something.

I appreciate any thoughts you may have on how to proceed next.
Thanks!
-J
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Old 03-26-2012
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Re: Help with DC negative question

Another update, not much different, but a little more specific.

With the batteries completely disconnected, everything off the DC NEG bus bar at the house bank, and everything disconnected from the engine block ground post...

...I used my multimeter to check for continuity between the bonding cable and the neg connections at the DC panel. There is continuity.

I also checked continuity between the engine block and the neg connections at the DC panel. Also continuity.

Basically, that's just confirmation that if I connect the negative battery post to either the engine block or the bonding, I'm able to light up the whole boat. WHY?

I reviewed the bonding connections everywhere possible. I did not see anything wired in. However, I did see a post on the fuel tank. The bonding goes from the strut to the fuel tank post, then to the fuel fill inlet fitting on deck. ALSO, there is a wire from that same post into the wiring harness. Hmmm. It looks factory though. The problem is, I disconnected where I believe it terminated, and it didn't change anything.

Is it possible that the boat was wired this way from the factory, and that there are many overlapping ground connections between the engine wiring and the DC panel? Is it also possible that there may be multiple factory connections between the bonding system and DC neg?

So far, I can't find the link(s).

-J
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Old 03-26-2012
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Re: Help with DC negative question

The bonding circuit should be connected to the engine but should not be electrically connected. Something along the bonding circuit is connected to a negative feed that leads to a negative bus and then on to everything else that is connected to it.

Because the bonding circuit goes to the engine block either the engine or any part of the bonging completes the circuit.

If you are in a marina there are good reasons not to bond through hulls. It invites them to corrode when they would be perfectly fine isolated as they are all of one type of metal that is highly resistant to have corrosion. There is a very interesting article by Stan Honey about grounding worth reading here: Grounding
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