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Old 07-09-2012, 04:09 PM   #1
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No DC power, Where to Start?

I will admit that electrical systems are probably my weakest strength, and this has me stumped.
Yesterday we went out for a day of crabbing. Everything was up and running as we left the dock. Dropped the anchor after a short 30 minute cruise. When I hit the windlass deck button to raise the anchor after about an hour, nothing. Went inside to make sure the breaker was on, and it was, but the DC panel was dead. Nothing was working. Volt meter on panel was at 0. After a shor period, maybe 3-4 minutes, the voltmeter went up to 14, bounced around a little bit, then stopped at little over 12. Went back out to raise anchor, same thing. Went back in and panel was dead. After a bit came back on. Turned on bilge pump at breaker panel and voltmeter went to 0. When I turned it off, voltmeter went back up. Tried a few other things that are swithced directly at the panel, spreader lights, anchor lights, etc. same result. Voltmeter at panel went to 0, then would go back up.
Battery meters show as fully charged. Replaced 2 house 8D's 2 years ago, voltmeters at helm show both charging at 14 volts.

Any idea where I should start? Thanks
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Old 07-09-2012, 04:33 PM   #2
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Any idea where I should start? Thanks
Clean your battery terminal connections for a start and make sure they are tight.

If that doesn't cure the problem then:

Make up a test light using a 12V high wattage bulb and start tracing power until the bulb dims because of the high resistance connection.

Don't depend on a digital multimeter to tell you much about this problem, it has too high an impedance to detect the most likely fault.
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Old 07-09-2012, 05:09 PM   #3
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Greetings,
Yup, what Mr. Rick said. One other quick, dirty and easy test is to beg or borrow one of these things...



to test your batteries under load. If you choose to buy one, they're less than $50. How did you get your boat started?
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Old 07-09-2012, 05:12 PM   #4
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A dirty/poor battery connection can ruin your whole day!! Check your batteries first. Clean and tighten.
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Old 07-09-2012, 05:51 PM   #5
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I will admit that electrical systems are probably my weakest strength, and this has me stumped.
Yesterday we went out for a day of crabbing. Everything was up and running as we left the dock. Dropped the anchor after a short 30 minute cruise. When I hit the windlass deck button to raise the anchor after about an hour, nothing. Went inside to make sure the breaker was on, and it was, but the DC panel was dead. Nothing was working. Volt meter on panel was at 0. After a shor period, maybe 3-4 minutes, the voltmeter went up to 14, bounced around a little bit, then stopped at little over 12. Went back out to raise anchor, same thing. Went back in and panel was dead. After a bit came back on. Turned on bilge pump at breaker panel and voltmeter went to 0. When I turned it off, voltmeter went back up. Tried a few other things that are swithced directly at the panel, spreader lights, anchor lights, etc. same result. Voltmeter at panel went to 0, then would go back up.
Battery meters show as fully charged. Replaced 2 house 8D's 2 years ago, voltmeters at helm show both charging at 14 volts.

Any idea where I should start? Thanks
Check your batteries, check the connections, then check your wiring.
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Old 07-09-2012, 06:09 PM   #6
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And don't forget to look at the fuses and fuse holders for corrosion and connections. Obviously a blown fuse stays dead, but bad connections can come and go.

If you're huntng for dropping voltage, a DVM is more accurate than a light bulb if you know how to read it.
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Old 07-09-2012, 06:18 PM   #7
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Could he have a thermal circuit breaker that is opening then reseting itself when it cools?
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Old 07-09-2012, 09:46 PM   #8
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Don't do it!

Max,
I locate problems similar to this a lot for our customers. Like Rick suggested, a test light is the right tool. But my approach is to NOT clean any terminals OR shake any wiring. This may solve your problem, but probably short term. I suggest that you have someone ready at the breaker panel, put your test light alligator clip at the negative battery post clamp and probe the other end at the center of the positive post. Have the bilge pump breaker turned on and confirm the light does not dim or go out as the breaker is tripped. Continue the process "downstream" as far as is possible onthe positive side, and if you have not located the bad connection reverse the process. Alligator clip on the positive post battery clamp and the probe onthe center of the NEGATIVE post th start, then continue downstream. Let us know what you find!
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Old 07-09-2012, 10:10 PM   #9
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Everybody is right on here. It's probably not your batteries and is more likely an issue with your wiring connectors between the battery terminals and the main panel. Start at the batteries cleaning the terminals, cable ends all the way through the battery switches up to you DC panel,testing as you go and pay extra attention to your grounds.

It may take some time, but 12 volt systems are fickled and a dirty connection, bad battery switch or old circuit breaker or ground may look good and tight, but it may not carry a load and will give you the results that you are seeing.

Like Rick B. said, a volt-ohm meter or multimeter will tell you if there is 12 volts or if ground is present, but it won't tell you if a circuit will carry a load. So you have to put each test point under load to determine where the problem is. It may be a two man job to trace it out, so don't be afraid to ask someone to help you.

I use an old combo (two filaments) brake light/turn signal light socket and bulb with 10 inch long pigtails as a tester. It was salvaged from an old car and it is simple and works great.

Good luck
Larry B
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Old 07-10-2012, 12:38 PM   #10
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As menruoned before, start at the batteries as the windless is probable wired directly from the batteries and not through the main panel. If both the windless and main panel are dead it's at/before they junction off. I would check/clean/tight the battery terminals, the battery on/off main selector switch, and the bus bar where they junction off. There might also be fuse/breaker in the same area.

Wing nuts are not recommended as they come loose easily should be regular nuts with lock washers. Also stacking should be limited to 2 maybe 3.

So how did you get the anchor up? Your SO must be very strong!
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Old 07-10-2012, 02:46 PM   #11
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............Don't depend on a digital multimeter to tell you much about this problem, it has too high an impedance to detect the most likely fault.
If you understand electricity and know how to use it, a digital multimeter is the best tool to diagnose electrical problems. You can't accurately jusge voltage or resistance by the brightness of a test lamp.
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Old 07-10-2012, 04:09 PM   #12
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If you understand electricity and know how to use it, a digital multimeter is the best tool to diagnose electrical problems. You can't accurately jusge voltage or resistance by the brightness of a test lamp.
A digital multimeter is a fine diagnostic tool. But when you have "nuthin", accuracy to less than a tenth of a volt is unnecessary.
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Old 07-10-2012, 04:55 PM   #13
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A digital multimeter is a fine diagnostic tool. But when you have "nuthin", accuracy to less than a tenth of a volt is unnecessary.
It's hard to do good work if you don't have good tools.

Granted, one tenth of a volt accuracy is not usually needed, but judging voltage drop with a lightbulb is about as redneck as it gets.

My brother in law claims he can test nine volt batteries with his tongue. He is a redneck and proud of it.

Me, I use a meter when diagnosing electrical or electronic problems. They used to pay me quite well for my expertise and skill.
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Old 07-10-2012, 04:56 PM   #14
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I just bought a digital multi meter because everyone said I should have one. I don't even know how to use it, but a test light. I can see a light go off or on.
I at least know if I have power or not. So that is what I use

SD
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Old 07-10-2012, 05:06 PM   #15
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I use a meter routinely as well, but recently ran into a situation where the light bulb also came in handy. I was installing a new fishfinder/depth sounder on my dinghy using the terminals on the back of the "accessories" cigarette lighter outlet(needs a new name now so few smoke!!). The fishfinder worked fine but when I plugged in my handheld spotlight to the accessory outlet it would not light up. Checked the voltage -- fine at 12V+. Tore apart everything looking for the problem. Finally checked with a light bulb at the same terminals feeding the fishfinder --- no light!! Long story short, the wiring had corroded to the extent that it would only carry enough current for the FF, not enough to light the spotlight or the the test bulb. The bulb came in quite handy. Maybe next time I'll try licking the terminals!!
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Old 07-10-2012, 05:09 PM   #16
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Maybe next time I'll try licking the terminals!![/QUOTE]

Now That really cracks my ass up
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Old 07-10-2012, 05:11 PM   #17
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I use a meter routinely as well, but recently ran into a situation where the light bulb also came in handy. I was installing a new fishfinder/depth sounder on my dinghy using the terminals on the back of the "accessories" cigarette lighter outlet(needs a new name now so few smoke!!). The fishfinder worked fine but when I plugged in my handheld spotlight to the accessory outlet it would not light up. Checked the voltage -- fine at 12V+. Tore apart everything looking for the problem. Finally checked with a light bulb at the same terminals feeding the fishfinder --- no light!! Long story short, the wiring had corroded to the extent that it would only carry enough current for the FF, not enough to light the spotlight or the the test bulb. The bulb came in quite handy. Maybe next time I'll try licking the terminals!!
Being more experienced in the field, I would have clipped the meter's leads to the connections on the accessory socket, measured 12 volts, plugged in the spotlight, noted the voltage drop, and determined that there was a high resistance connection somewhere in the circuit, just as you eventually did.
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Old 07-10-2012, 05:16 PM   #18
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Thanks for the tip, rwidman.
And I did say lick the TERMINALS, Skipperdude!!!!
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Old 07-10-2012, 05:18 PM   #19
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I just bought a digital multi meter because everyone said I should have one. I don't even know how to use it, but a test light. I can see a light go off or on.
I at least know if I have power or not. So that is what I use

SD
If you don't know how to use a meter, by all means keep it in the original packaging.

You need to know two things:

1) Obviously, you need to know how the meter operates. How to turn it on, and how to set the switches and where to plug the leads in.

2) You need to know where to connect the leads in the circuit you are troubleshooting and how to read and interpret the results.

If a light bulb does what you want it to do, by all means, break out the light bulb when you have a problem. I don't own a test light. I own three or four meters. One is on the boat, the rest are at home. The meter can do everything a test light can do (except light up the area I am working in) and more.
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Old 07-10-2012, 05:19 PM   #20
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Thanks for the tip, rwidman.
They paid me well enough for my skills that I was able to retire and buy my trawler.
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