Electrical gremlins - need help figuring things out.

[calmissile]

Originally Posted by Oceanride007

Think you need to get your volt meter out and measure again, I have a aissue with Hull voltage close to Negative potential, but the leakage is quite small, its not important right now. Heres a dwg of where/how I tested and my results.


Test 1.
Resistance Neg Bus to Hull = .7 K ohm, Pos Bus to Hull = 7.7 K ohm.


Test 2. Voltage Neg Bus to Hull = .023V, Pos Bus to hull = 13.35V.


PS My boat is metal.

Not sure what your post is related to. Is your 'issue' that the negative bus is 23 mv above your hull voltage and you feel that it should be less, or are you concerned that the negative bus is not isolated from the hull?

[Captain Anthony]

Calmissile, where did you gain all of this valuable electrical knowledge?

[redwood1957]

First when you get your low voltage alarm check to see you have a true low voltage. Preferably with a volt meter. Also check your batteries with a load tester when charged to see they are good.
Make sure your batteries and terminals are clean. Also check all connection's to see they are clean.
A ground is when your power is going to ground or draining your battery. Not following it's intended path for the circuit. Do this stuff first and see if it still happens. The rest is involved and you should have somebody with experience with you.
You will need to measure amps leaving your battery. With everything off. If no load going out that's good. With everything off and you are pulling amps you then want to start pulling fused until you see amps go to zero. At that fuse you need to check that circuit. You also need to check your instruments and see they are not drawing more then rated for. Grounds are not easy to find in some cases.

[calmissile]

Originally Posted by Captain Anthony

Calmissile, where did you gain all of this valuable electrical knowledge?

University of Washington and Edison Technical School - Broadcast Engineering, 60 years as an Aerospace Engineer, a 'ham' operator since the 6th grade and always had an electronics lab at home.

The 'hands on' experience is perhaps the most valuable of all of it. A very large library of books and downloaded technical material helps too.

I would take a photo of my lab and machine shop but it is so embarrassing a mess that I will wait until I have some time to clean it up. My priorities at the moment are my full time job as an engineer and getting everything ready for my next trip to the boat.

I have tried to encourage young men to gather some real life 'hands on' skills that will be useful throughout their lives, but have not been very successful in the effort. They would rather play on their computers.

We used to have classes in our public school system such as wood shop, metal shop, machine shop, mechanical drawing, etc. but no more. When I asked the school officials why they have disappeared from the curriculum, the answer is because of the lawyers and lawsuits. I don't know if this is true or not but it is a shame that most young adults can't change the oil in their own cars let alone overhaul a simple lawn mower engine. They will have to either throw the item away and buy a new one or pay someone skilled in the trades to do their repairs.

On the bright side, when things get tough financially, those with hand skills such as construction, welders, handy-men, mechanics, electricians will have a field day soaking them for what they should have learned while growing up.

On the humorous side, when I owned an Avioncs company I used to work until late at night because it was the best time to get work done without interruptions. I would often stop at the local bar for a cocktail before going home. One night the local crop duster was in the bar and we chatted it up while having our drinks. At one point he stated "I have something you absolutely need to have and I will make you a great deal on it". He said that he bought a helicopter and it had an oil leak so his mechanic took the engine out and quit his job before he got it back together. He assured me that all of the parts were there. After he bought me a few more drinks I had agreed to the purchase the helicopter as long as he would deliver it to my shop across the field (Santa Maria, Ca.)

You can imagine the dismay of my employees when a flat bed trailer arrived at my shop the next day with what was barely recognizable as helicopter parts. Over the next few months we completely stripped, disassembled, inspected and overhauled the engine, main transmission, tail rotor transmission and completely stripped and painted the fuselage. It was beautiful and I knew every part in it. I was very lucky to have a high ranking FAA official give me all the dual instruction (free) since I only had my single engine fixed wing license at the time. This was another time when all the critics said it could not be done, would never fly, etc etc.

Also had a stroke of luck getting my multi-engine rating. I had a customer that had his twin engine plane at the shop for a major Avionics installation and he got busted for some kind of drug run (by land). I got permission from him to use his plane while he was in jail. I got my multi-engine rating with only having to pay for the instructor and fuel.

I am glad that I grew up in the era I did. I feel sorry for the present generations.

[calmissile]

Originally Posted by redwood1957

First when you get your low voltage alarm check to see you have a true low voltage. Preferably with a volt meter. Also check your batteries with a load tester when charged to see they are good.
Make sure your batteries and terminals are clean. Also check all connection's to see they are clean.
A ground is when your power is going to ground or draining your battery. Not following it's intended path for the circuit. Do this stuff first and see if it still happens. The rest is involved and you should have somebody with experience with you.
You will need to measure amps leaving your battery. With everything off. If no load going out that's good. With everything off and you are pulling amps you then want to start pulling fused until you see amps go to zero. At that fuse you need to check that circuit. You also need to check your instruments and see they are not drawing more then rated for. Grounds are not easy to find in some cases.

Just to add a quick note. I found that on my boat there are a large number of LED's that are still lit up on the Blue Sea panels even with the main switches are off. These parasitic loads can eventually drain the batteries if you should loose shore power when you are not around for extended periods of time. I will fix this problem on my boat so that when the switches are all off, the only thing connected to the 12 VDC bus is the bilge pump.

[Oceanride007]

Originally Posted by calmissile

Not sure what your post is related to. Is your 'issue' that the negative bus is 23 mv above your hull voltage and you feel that it should be less, or are you concerned that the negative bus is not isolated from the hull?

Calmissile. I would want the hull electrically separated from the Pos and Neg Cables by at least 1Megohm. I do need Neg attached to Eng for using the Engine, it is switched. All vessels in my experience as a Marine Engineer were isolated in this manner on all electrical circuits. If a Earth Lamp test indicated there was a short, it was a priority to find out where it was. Think you could say this was required for both statutory and classification rules. 2 shorts of course could lead to hull corrosion a bigger one would end with fuse or CB operating. If it happened on a smaller vessel it could well drain the batteries.

[calmissile]

Originally Posted by Oceanride007

Calmissile. I would want the hull electrically separated from the Pos and Neg Cables by at least 1Megohm. I do need Neg attached to Eng for using the Engine, it is switched. All vessels in my experience as a Marine Engineer were isolated in this manner on all electrical circuits. If a Earth Lamp test indicated there was a short, it was a priority to find out where it was. Think you could say this was required for both statutory and classification rules. 2 shorts of course could lead to hull corrosion a bigger one would end with fuse or CB operating. If it happened on a smaller vessel it could well drain the batteries.

OK, I think I understand your comments now. I did not realize you were talking about a steel hull. I have not ever worked on a steel hull, but think I understand your comments about isolating the hull (or even the through hull fittings and keel on a fiberglass boat) from the battery terminals both + and -. It makes sense to eliminate any currents between the water and components on the boat. Your more of an expert than I am on this topic.

I notice that a lot of boats connect the negative terminals of the battery banks to the keel and through hull fittings. I question whether that is a good idea when you are trying to use the keel and through hull fittings for lightning protection. In my mind, I want them isolated so that a lightning strike is less likely to propagate throughout the boats power system and electronics. What is your view on this aspect?

[Suddy]

Originally Posted by George_SD

On a few recent trips that are only 4-5 hours long, I would get a low voltage alarm. This was happening with minimal electricity use (depth and speed transducer + single display for both).

Today, I needed to look into wiring power for the autopilot and decided to test my power disconnects. I have 3 of them
- negative disconnect
- positive disconnect (engine battery - Group 29 flooded)
- positive disconnect (house battery - Group 29 flooded - brand new)

As I understand:
- negative is supposed to disconnect everything by opening the circuit on DC circuit for both - house and engine.
- positive Engine - should connect or disconnect engine battery from the DC circuit
- positive House - should connect or disconnect house battery from DC circuit.

In essence - i can run on engine, house or both.

Well, here is where the gremlins come in.

I have a volt-meter built into 12v DC panel. I've seen other boats with the same panel show that the tester switch being used to check either of the batteries (my boat's manual is silent on this).

UP - engine battery test
Center - OFF
Down - house battery test

So I've started putting all disconnects to off and looking at what the battery/volt meter shows. Shore power is OFF at the shore and on 110v panel for all these tests. Everything on 12v DC panel is OFF as well.


--- Test 1 ----
Negative - OFF (disconnected)
Engine - OFF
House - OFF

Tester
UP (engine) = no reading
Down (house) = ~4v-4.5v

--- Test 2 ----
Negative - ON (connected)
Engine - OFF
House - OFF

Tester
UP (engine) = no reading
Down (house) =~ 12.6v

--- Test 3 ----
Negative - ON
Engine - ON
House - OFF

Tester
UP (engine) = 12.5
Down (house) = 12.6

--- Test 4 ----
Negative - ON
Engine - OFF
House - ON

Tester
UP (engine) = 12.7
Down (house) = 12.6

List of 12v electrical equipment
- bilge pump
- speed/depth transducers and single display, stereo, vhf
- fridge
- nav/anchor/steaming lights
- cabin lights
- macerator
- freshwater pump
- gas valve


List of 110v/shore power
- AC main switch
- charger
- water heater
- outlets

Questions

1) With all three disconnected - negative and both positives, I think it should be giving me 0, not 4.5v. How is it even possible with everything disconnected to show me voltage and a strange low reading at that?! What could possibly feed it?

2) With negative enabled, but both battery disconnects off - it should be showing 0 for both, right?

3) does this seem to indicate that at least my house disconnect is not really disconnecting?

I believe Kelkara is correct about the "House" and "Engine" labeling; they seem reversed from the schematic you added in your next post.
Your "Test 1" indicates there is a high impedance short between your meter's negative post and the "Negative" bus on the battery side of the "Negative" disconnect switch. Your other tests indicate normal operation of the circuit.
To prove my theory, you would need a voltmeter with test leads. Set up "Test 1" again and measure the voltage across the "Negative" disconnect switch when you push the "Tester" down. If you measure the remainder of the battery voltage (12V - 4V = ~8V), that would verify the high impedance short. (If your meter measures 0 Volts, then my theory is incorrect.)
If my theory is correct, then the high impedance short is present in one of the wires attached to the "Negative" disconnect switch. Remove 1 wire at a time from the "Negative" disconnect switch and repeat "Test 1" while measuring the voltage across the "Negative" disconnect switch. Replace the wire and remove another until you measure the full battery voltage; the wire you removed has the high impedance short in it. You should also see 0 Volts on your panel meter instead of ~ 4 Volts.
You will then have to isolate the piece of equipment on that negative wire to find the high impedance short.
This problem may or may not (probably not) be related to your original low voltage alarm. That problem is probably related to a loose or corroded connection or a frayed wire. I assume the alarm is being reported by one of the instruments you are using. I would look for loose connections, corroded connections, frayed wire or wire that is partially broken on the circuit for the instrument that is causing the alarm. I had a similar problem with my Garmin Chart Plotter and my wheel driven auto pilot. I had to put the auto pilot on a separate circuit to stop the alarms, but a corroded terminal contributed to the problem.
I hope this helps
Suddy

[Oceanride007]

Originally Posted by calmissile

OK, I think I understand your comments now. I did not realize you were talking about a steel hull. I have not ever worked on a steel hull, but think I understand your comments about isolating the hull (or even the through hull fittings and keel on a fiberglass boat) from the battery terminals both + and -. It makes sense to eliminate any currents between the water and components on the boat. Your more of an expert than I am on this topic.

I notice that a lot of boats connect the negative terminals of the battery banks to the keel and through hull fittings. I question whether that is a good idea when you are trying to use the keel and through hull fittings for lightning protection. In my mind, I want them isolated so that a lightning strike is less likely to propagate throughout the boats power system and electronics. What is your view on this aspect?

Well think you know lots.



Well apparently no one is expert, with regard to lightening. But heres my take. But first off lets forget the direct hit, lets just protect ourselves from induced voltage (Due to build up up of magnetic flux that induces a voltage in parallel circuit when magnetic flux line due to lightening expand and again on its retraction) assuming my mast alone gets hit (or Solar panels), all circuits even if left open will fry most everything because air gap in a open switch is so small and voltage is way high. But I can minimize things if I have flying leads for TV, VHF antenae, pulled plug on Nmea 2000 up the mast, pulled mast light circuits, disconnected autopilot both leads, same with nmea 2000 power injection, opened battery terminals for good measure, but however closed my negative connection to hull. Think so to stop build up of voltage,otherwise it would find its own way out that could be sad.

[George_SD]

Thanks everyone! All this feedback and ideas is why I appreciate the sailing community and people willing to put their time chiming in and helping.

1) I have found at least one bad connection at the battery terminal (cable was somewhat loose in the clamp/compression terminal attached to the battery post), so I need to re-crimp it. Just need something that can put enough force on the metal as none of my home instruments are beefy enough.

2) I'll do the test suggested by members and see what I find.


Additional information:
The alarm would normally show up on Lowrance chart plotter that was set to alert when voltage dropped into 11v territory. Because I knew that I don't have much capacity or have a drain issue, I would only turn on the plotter sparingly when I needed to know the position. I've removed the plotter and replacing it with a better suited Raymarine (old one was too big and mounted improperly on the nav station).

As mentioned earlier, I'm putting a Raymarine Evolution EV100 Wheel pilot right now, so with a single engine and single house battery - i'm probably going to need additional capacity to run it.

Boat is a weekend cruiser and spends most time plugged into shore power via Xantrex 20+.