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Old 04-13-2018, 05:52 PM   #1
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puzzling electrical question

Hi all,
I have an electrical question I'm hoping someone can help me figure out. For a "house bank", the PO just had a battery that charged off shore power and then ran 12 gauge wire to the bilge pump. From the bilge pump it connected to everything else and worked the lights, water pump etc.... There is a battery selector on the DC panel and it had a cable running to the engine room. I moved the battery and hooked it up to this cable and grounded it to the engine. After doing this, the breakers on the DC panel would read 12v on the voltmeter but nothing would actually turn on. When I reattached the ground to the bilge pump, everything would work again. So to summarize, positive is always connected to the battery selector on the DC panel. With negative connected to engine, panel reads 12v but nothing works. With negative connected to bilge pump, panel reads 12v and everything works. So my question is, with the negative connected to the engine, why would the panel read 12v but nothing works?
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Old 04-13-2018, 06:22 PM   #2
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I'm assuming you have 2 batteries, one for the engine and the other one. The 12 volts you are seeing at the panel maybe the engine battery and not the house battery. When solving thiese kind of mysteries, it's best to eliminate competition. Discount the start battery (negative terminal ).

I would trace the negative wires from your accessories and determine how they reach the battery. Nothing wrong with both batteries and all accessories sharing the same negative buss. Don't think you are there yet.

This information is deemed reliable and guaranteed to the amount you paid me for this free opinion.

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Old 04-13-2018, 06:27 PM   #3
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Thanks. The start batteries actually don't go to the panel at all. They are just wired to their respective engines. I will also be addressing this in the future as well.
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Old 04-13-2018, 06:29 PM   #4
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I guess my biggest question is how could the panel be reading 12v but the stuff isn't turning on?
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Old 04-13-2018, 06:41 PM   #5
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Quote:
Originally Posted by jsplichal2 View Post
I guess my biggest question is how could the panel be reading 12v but the stuff isn't turning on?
From your original post, you said the bilge pump was connected to the negative terminal of the battery. Then everything else was tied to the bilge pump negative. If the bilge pump negative wire isn't tied to the negative of the battery in some round about way, nothing else will be either. What did you connect the bilge pump negative to?

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Old 04-13-2018, 06:49 PM   #6
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Btw, without trying to be too negative or critical, you have all the makings of a really nice boat fire. Running all the negative wires to one 12 gauge wire is asking for trouble. Boat fires start on negative wires just as easily as on positive wires. How much do you know about boat wiring? Sometimes it's better to seek professional help. I'm all about doing what I can, myself. But sometimes you have to know when to ask for help.

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Old 04-13-2018, 06:51 PM   #7
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Sorry - See if I can explain better. Normal DC system with panel and everything that the PPO disconnected all batteries from. PO put a battery under the the dinette and wired it into the bilge pump, both positive and negative. The bilge pump was already wired into the rest of the system through the DC panel, so everything would turn on via this battery being connected to the bilge pump. I disconnected the battery and moved it to its proper location in the engine room. There was a loose battery cable running to the battery selector switch on the dc panel that I connected to the positive terminal. The negative terminal I connected to the engine, through another battery cable that was already there. Once I did this, I could read 12v on the DC panel but nothing would turn on. When I would reconnect the battery to the negative side of the bilge pump, I could read 12v on the DC panel and stuff would turn on. I assume the engine is already tied into the system or I wouldn't be able to read 12v when connected only to the engine and the battery selector. So the big question is, why would I be reading 12v on the panel without anything turning on?
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Old 04-13-2018, 06:51 PM   #8
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Thanks. This is the PO setup that I am trying to correct. I had the same thought when I saw it. Boat is going in for a bottom job at the end of the month and I will ask them to look things over as well. But in the mean time I am trying to figure out how to undo what the PO has done. And I was trying not to overcomplicate everything but there is also a converter between the AC and DC panels. The DC is mainly running off this at dock and I just wouldn't turn anything on off dock. And I was turning off the converter before taking the voltmeter readings.
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Old 04-13-2018, 07:10 PM   #9
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Do you have a volt ohms meter? Disconnect all batteries negative terminals. If there is a shore power battery charger, make sure it is turned off. You will need to extend one of the meter leads with a piece of wire.

Test for continuity between the positive battery wire and the breaker panel. Then test between the negative battery wire and the negative buss. If both have continuity, your accessories should work. Btw, is either engine tied to the negative buss in the breaker panel?

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Old 04-13-2018, 07:14 PM   #10
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One thing I noticed is that you mentioned that things like you lights pump etc are connected from you bilge pump. If I am right this is a “dangerous” setup as everything is on the same circuit protection (breaker or fuse). If one connected thing blow out this circuit protection your bilge pump would be off too and your boat left without bilge pump. If this, by any bad luck, occurs when you are away and when you have a water ingress...

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Old 04-13-2018, 07:23 PM   #11
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Thanks. Getting on a plane right now so no more responding for a bit. Also won't be back on the boat until a couple days before I take it in for paint. At shore, the dc panel receives power from a converter connected to the ac panel. There are many breakers going to the various items. I was just trying to fix the "house bank" that the PO set up. Instead of connecting the battery to the DC panel, the PO just connected it to the bilge pump, which then the electric would run reverse through the breaker and power the rest of the DC panel. He wasn't using it as a house bank, just wired it to the bilge pump so if the power would go out, the bilge pump would be powered by the battery. So all the DC stuff was not being used off the battery nor was the battery regularly being used. He just put it there as a contingency. I would like to hook it up the proper way for obvious reasons. My big question is, under what condition would I be able to read 12v on the panel without anything turning on?
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Old 04-13-2018, 07:26 PM   #12
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Sounds like a mess to me but Ill try. I would start by verifying the ground and positive connections to the battery are solid. Ohm meter opposite ends of disconnected wires (one long wire with gator clips on either end works ok for this) if you cant see where they go and are not labeled. Then label and reconnect the right way. I would assume if it was my boat the PO did it all wrong, and I don't blindly rely on any of it.


To try and answer your question. The volt meter on your boat is probably wired either to your gauge panel or another source of 12v. The bilge pump could be completing your panel circuit due to a bad main ground elsewhere. Grounds as already explained by OC Diver are very important. Grounding to the engine is sometimes ok but sometimes not depending on how its setup. If you have multiple buss's grounded together to multiple spots for instance. Then you loose the main ground to the battery (because the engine ground was taken out of the house battery loop for instance), and then re-establish a ground through a little bilge wire, you are indeed asking for a melt down/fire. First thing if it were me doing the work, would be to put a high amp terminal fuse on the positive connections to the battery or a large breaker before I started reattaching things. You might already have this but I have no way of knowing.


Some ideas that come to mind: Start with +&- on the battery look at the main supply connections use a multi-meter before you connect the wires, so you know for sure you have the polarity correct. Do you have no resistance between the - battery terminal and the panel when the bilge is not connected? Unfortunately some PO could have used red for - and/or black for + so don't trust just verify.
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Old 04-13-2018, 07:35 PM   #13
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One last thought. Some panels have a selector switch for the volt meter. This allows you to check the voltage of other batteries such as the engine (s) start batteries. If the switch is set to one of the engine batteries it doesn't bring power to the accessory breaker panel. Think that might be why you saw 12 volts but had no power to accessories.

It's worth repeating. Disconnect the engine batteries when solving this problem so that you you don't see other sources of 12 volt power.

Ted
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Old 04-13-2018, 08:07 PM   #14
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Back at my new gate and on for a minute. I have to apologize, I tried to limit how much I shared of the mess that is this system so we all didn't get in the weeds and I think I just confused everyone. Also, yes I was using a multimeter, not a volt meter - brain fart on that one. I was trying to figure out if this sounded like maybe the ground cable was cut in the middle or something (as it disappears behind walls etc....) and maybe someone had a similar experience that would tell me if it were shorting out or something. From all of your responses I think it is pretty clear I need to do a better job of mapping the ground side of all of this. I was just using the gauge ground to test as it was closest and I assumed everything would be grounded together. Thanks to all who replied and sorry for the confusion.
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Old 04-13-2018, 08:22 PM   #15
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One thing I would suggest you is to draw a diagram of your finding to illustrate your issue and share it here. This would help to get a clear picture of your setup.
Just a thought.

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Old 04-14-2018, 11:25 AM   #16
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Buy and read this book for the solution to your problem. If that isn't feasible, I'd recommend hiring a professional to complete the job safely and correctly.

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Old 04-14-2018, 12:22 PM   #17
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Good luck with figuring it out. As has been mentioned, take the time to trace out what you have, and then figure out how you want it to be wired. Then develop a step by step plan to go from one to the other.

The current situation doesn’t sound good at all, but unfortunately that is not uncommon if folks like me are let loose on an electrical system.
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Old 04-14-2018, 02:22 PM   #18
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Quote:
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Buy and read this book for the solution to your problem. If that isn't feasible, I'd recommend hiring a professional to complete the job safely and correctly.

That was one of my first purchases years ago great to have around
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Old 04-14-2018, 05:08 PM   #19
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Buy and read this book for the solution to your problem. If that isn't feasible, I'd recommend hiring a professional to complete the job safely and correctly.


The OPer is providing confusing and probably inaccurate information about his electrical system. He needs to follow the advice above. I don't think that this forum can help much more.

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Old 04-21-2018, 07:57 PM   #20
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The biggest challenge is deciding when it's best to start fresh. One very important thing to keep in mind with boat wiring is that ALL parts of the circuit can develop problems. The time you spend debugging what is or isn't working may be better spent on installing brand new, known-good gear with properly done connections.

Voltage drop due to corrosion INSIDE the wire's insulation is an often overlooked problem. The wire can look fine externally and even be a large enough gauge to handle the desired load on it. But if there's corrosion in it then it won't deliver the full load and potentially overheat/catch fire. So it's important to not only find and visually inspect all the connections, but verify that the voltages are stable and consistent under load.
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