weird grounding issue

[airshot]

As I am not an electrician by any means, not sure I am wording this correctly, but hopefully the real electricians here can sort out my issue. Recently discovered what I call a parasitic draw on my house battery. Never noticed it before but that doesn't mean it wasn't there. Recently my battery kept dropping off quite a bit over a week or two, so I added a cut off switch. While checking things out I touched the neg battery post with neg meter lead and touched the hull with the pos meter lead and my battery voltage showed up on the meter!
Actually touched the hull by accident and saw a small spark from the pos lead. Disconnected each pos accessory lead from the battery one at a time but no change. Done a lot of aluminum boat wiring over the years but never used the hull as a ground.
Not even sure I can call it a ground as it only reads 12.8 volts when the neg lead touches neg battery post and the pos lead touches the hull. If I do the opposite it shows nothing. Just a wild guess here, is there some type of bad connection in the wiring or am I looking at something that makes no difference ??? Where to check or what to check would be very helpfull and I thanks you all for any info you can give. Been a toolmaker for the past 50 years, can make about anything, but electricity is not my expertise by any means !!

 

[flashback]

Maybe disconnect the start battery and then check it again, I've seen stray current cause similar symptoms but your boat is not in the water.

 

[airshot]

I have disconnected the battery and of course nothing shows. In my mind, how is the pos getting to the hull ? Everything works, radio, ship/ shore, lights, bilge pump, live well pumps are plugged (don't use them), fish finder, etc.

 

[flashback]

You have two batteries Right? I'm suggesting you disconnect the battery that's not draining and test again.

 

[Bondo]

Not even sure I can call it a ground as it only reads 12.8 volts when the neg lead touches neg battery post and the pos lead touches the hull. If I do the opposite it shows nothing. Just a wild guess here, is there some type of bad connection in the wiring or am I looking at something that makes no difference ???

Ayuh,.... I take it, this is an aluminum hull,..??
While you are right, in that you never ever want to use the hull as the ground path for anything, as that will lead to electrolysis corrosion,...

You still need to Bond the hull, 'n anything metal in it,....
That's why you see a heavy copper wire bonding the fuel tank, 'n it's fill fitting, 'n the fill hose's wire wrap, to the hull at the transom, or directly to the engine block, which ties to the battery's (-) terminal,....

As for yer root problem, I think, one or more of yer electrical accessories, doesn't have a good ground connection through it's wiring harness,....
Pull each fuse for each appliance, 'n yer draw will go away when you find the right one,....

 

[airshot]

You have two batteries Right? I'm suggesting you disconnect the battery that's not draining and test again.

Yes, a start only battery and a house battery. I did disconnect the start battery and no change. It appears to me the house battery is the one charging the hull, but no idea how.

 

[airshot]

Ayuh,.... I take it, this is an aluminum hull,..??
While you are right, in that you never ever want to use the hull as the ground path for anything, as that will lead to electrolysis corrosion,...

You still need to Bond the hull, 'n anything metal in it,....
That's why you see a heavy copper wire bonding the fuel tank, 'n it's fill fitting, 'n the fill hose's wire wrap, to the hull at the transom, or directly to the engine block, which ties to the battery's (-) terminal,....

As for yer root problem, I think, one or more of yer electrical accessories, doesn't have a good ground connection through it's wiring harness,....
Pull each fuse for each appliance, 'n yer draw will go away when you find the right one,....

First off of thanks for responding !! All my accessories have inline fuses and a lead going to the house battery. I think I was doing what you suggested by removing one lead at a time from the battery, then checking, no change until all were disconnected ! Then I reversed the order and added each back on and testing after each connection. No change until all were connected.......so, does this mean I might have more than one accessory with a bad connection? Just so you know, I have an outboard motor and a plastic built-in fuel tank, just replaced the fuel line and there were wires from the metal plate for the fuel gage going into a harness, can't say for sure about the bonding wire you speak of. Thanks

 

[airshot]

OK....tried some additional testing after dinner. Looks like this issue took place after installing the switch. Test now show there is no 12.8v reading when the switch is on (battery on ) , but when the switch is turned off then the meter shows 12.8v going thru the hull. Before installing the switch I had the parasitic drain, thus the reason for the switch. So...does this solve anything ? Damned if I know !! Apparently the battery positive 12.8 is transferred to the hull when neg wiring is cut off from the battery post.
Not sure if this answers any questions or solves any problems but it sure is confusing to me !! Thanks in advance for your thoughts......

 

[dubs283]

Apparently the battery positive 12.8 is transferred to the hull when neg wiring is cut off from the battery post.

If you installed the switch on the negative/ground cable from the battery then my guess is the electrical system is finding ground through the hull and getting back to the battery (-) post via that route

The battery is the main ground for the entire boat and engine 12 volt electrical system. By removing the ground path to the battery with a switch the circuit needs a way to complete the path and is using the aluminum hull. Gonna guess the switch housing itself is connecting to the hull through the fasteners used to mount it and the battery lead along with it/them

A battery switch should only be used to disconnect the (+) lead(s) from the battery(ies). Remove the switch on the (-) side of the battery

To find which circuit is draining disconnect all the leads from the (+) side of the battery thats draining. Lightly strike each lead independently to the (+) post on the battery. The one that produces a spark is the drain.

A true test would involve the use of an ammeter in line with each lead and the battery (+) but you've stated your electrical expertise is minimal so the quick and dirty method above is most likely appropriate for your situation

 

[airshot]

The switch mounts to the battery post itself then has a threaded post to attach the ring terminals from the accessories. The battery is a group 29 deep cycle with posts and threaded posts on each side. The switch is just a knob that tightens to make connection or loosen to break the connection. Used the same in my motor home for years for storage. Based on pkg instructions and recommendations for disconnect switches all over the internet including marine approved switches, say to mount on the negative side ...so now you recommend the positive side...getting two different opinions here. No problem switching them if that is the issue. Your first paragraph did make some sense to me about the ground path. I do have a digital VOM that I use in my testing. I have one at a time tried connecting each accessory then going back and disconnected one at a time testing each one and no change was made until all accessories were added or removed, no matter which order I used. Beginning to wonder if more than one accessory is causing an issue ?? Many thanks for your responses !

 

[dingbat]

The switch mounts to the battery post itself then has a threaded post to attach the ring terminals from the accessories. The battery is a group 29 deep cycle with posts and threaded posts on each side. The switch is just a knob that tightens to make connection or loosen to break the connection. Used the same in my motor home for years for storage. Based on pkg instructions and recommendations for disconnect switches all over the internet including marine approved switches, say to mount on the negative side ...so now you recommend the positive side...getting two different opinions here.

No problem switching them if that is the issue. Your first paragraph did make some sense to me about the ground path. I do have a digital VOM that I use in my testing. I have one at a time tried connecting each accessory then going back and disconnected one at a time testing each one and no change was made until all accessories were added or removed, no matter which order I used. Beginning to wonder if more than one accessory is causing an issue ?? Many thanks for your responses !

Power flows from positive to negative (ground).

Unless you’re from the British isles, you switch positive for safety reasons in DC circuit

The difference between power and ground switching lies in the location of the control devices, either closer to power, or to ground, respectively. Power switching will more likely result in the tripping of a breaker or fused device. Ground switching will more likely result in a latching of the load device in an energized state.

House and start battery grounds get tied together then connected to the engine ground.

On the power side, the positive terminal gets tied to the switch and that’s it.

Here is a good write up of why and how a grounding systems works with a 12volt system

12-Volt Electrical Systems: Grounds Explained

In this post, we will talk about your vehicle's grounding system. Now I know I’ve touched on this subject before, briefly, but I wanted to dive a little deeper to explain why we do it, and why i

blog.down4soundshop.com

 

[dubs283]

Power flows from positive to negative (ground).

This is true, hence DC (direct current) the current only flows one direction. From (+) to (-). This is why a power windlass can change direction by simply reversing polarity at the motor connections

I think your setup is a bit cobbled and the attempt to switch the ground side is wrong. I've seen this setup once before and it was an attempt to stop a battery drain in a system without a (+) battery switch. Of course it was a fishing boat with multiple leads for main engine, kicker, and accessories at each +/- battery connection

You need to start fresh with a basic understanding of dc electricity. Isolate every circuit and use an ohm meter to locate your grounding issue. It's by far the most preferred and safest method

 

[airshot]

This is true, hence DC (direct current) the current only flows one direction. From (+) to (-). This is why a power windlass can change direction by simply reversing polarity at the motor connections

I think your setup is a bit cobbled and the attempt to switch the ground side is wrong. I've seen this setup once before and it was an attempt to stop a battery drain in a system without a (+) battery switch. Of course it was a fishing boat with multiple leads for main engine, kicker, and accessories at each +/- battery connection

You need to start fresh with a basic understanding of dc electricity. Isolate every circuit and use an ohm meter to locate your grounding issue. It's by far the most preferred and safest method

This is what I am trying to understand..
50 years as a toolmaker, not an electrician.

 

[dingbat]

This is what I am trying to understand..
50 years as a toolmaker, not an electrician.

A simple analogy is to compare the flow of electrons from your battery to ground as a faucet and a drain

If you want to stop the flow of current, you turn off the faucet (battery) you don’t plug the drain (switch negative)

 

[airshot]

A simple analogy is to compare the flow of electrons from your battery to ground as a faucet and a drain

If you want to stop the flow of current, you turn off the faucet (battery) you don’t plug the drain (switch negative)

That makes sense, but I can't believe how much information is out there that states the opposite !!

 

[airshot]

Switched over to the pos post on house battery, now the hull is at battery voltage all the time whether switch is on or off ! Did some further testing and found the wire harness going to the dash for accessories might be the culprit. When that harness is disconnected completely, there is no voltage on the hull. Going to try to get up under there and see what the problem is after wife's doc appt...if there is anything else I need to look at, feel free to suggest.....thanks again.

 

[dingbat]

That makes sense, but I can't believe how much information is out there that states the opposite !!

Had to Google....... lot of the confusion comes from automotive burring the lines between power distribution and control circuits.
It works, so it must be right.......lol

Power distribution requires that you switch and fuse the Source for safety considerations.

When using a switch as a "sensor" for feedback (open or close) to a control module (most circuits in an automobile), you typically use ground switching as its easier and simpler to communicate with logic control modules.

Switched over to the pos post on house battery, now the hull is at battery voltage all the time whether switch is on or off !

Obviously you have a wire switched up or a dead short to ground somewhere.

Pull the power cable(s) off the battery.
Check for continutiy between the ground and power cable clamps one at a time. Should be no continutiy between any of the grounds and the positive cable. If there is, you've identifed the circuit with the short

Bear in mind that power can back feed through a device. Pretty common for the windings in a bilge pump to fail with power shorted to ground.