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Old 04-17-2021, 09:11 AM   #1
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Lost our 12 volt system

we bought a 1968 Navy trawler a few months ago. Last night my boyfriend discovered our 12 volt system isn't working. He is an electrician and has done everything he can think of trying to find the problem. He thinks our cat may of got into something. He has traced every wire he can.
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Old 04-17-2021, 09:20 AM   #2
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He also would like to know in a 36 volt system what makes the 36 volts? Thanks.
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Old 04-17-2021, 09:22 AM   #3
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If the whole system isn't working... sounds like a switch or a breaker somewhere... or a loose/disconnected battery cable.

So (if he hasn't already) maybe trace from batteries to panel one direction... and trace from panel to batteries the other direction.

??

I've read folks often use four 8V batteries to make 32V. Not sure if that means actual readings while charging might be closer to 36V (much like a 12V battery under bulk/absorption charge might read ~14.7V).

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Old 04-17-2021, 09:59 AM   #4
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Sounds like your engine alternator, starter and starting battery are 36 (or 32) volts. So to provide 12V DC for most common marine stuff, the boat probably has a DC to DC converter. Look for one and it may be bad.

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Old 04-17-2021, 10:00 AM   #5
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Three 12V batteries in series makes 36 volts. If you have a 36V boat with a small 12V system, likely there is a 36 -> 12V DC-DC converter somewhere, and that is worthy of investigation if the 12V isn't working.

Edit: looks like David was quicker!
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Old 04-17-2021, 10:09 AM   #6
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He is going to check that out now. Thanks for responding. We sure have a lot to learn.
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Old 04-17-2021, 10:33 AM   #7
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Greetings,
Welcome aboard. Check ALL the grounds, as well. Keep in mind there are some MAJOR differences between marine and land based electrical systems. If not sure, get a marine electrical book like:



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Old 04-17-2021, 11:30 AM   #8
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Welcome aboard. Agree on checking the grounds, they can cause a lot of problems. If not then maybe map the system out and see what points can cause the whole system to go out. Then check them.
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Old 04-17-2021, 11:59 AM   #9
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Here is where my mind went. Solution at the 15 second mark. Classic problem.
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Old 04-17-2021, 12:23 PM   #10
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Quote:
Originally Posted by MaryEllen View Post
we bought a 1968 Navy trawler a few months ago. Last night my boyfriend discovered our 12 volt system isn't working. He is an electrician and has done everything he can think of trying to find the problem. He thinks our cat may of got into something. He has traced every wire he can.
What do you mean the 12v system isn't working? There is no voltage to the 12v panel, or no voltage in the 12v battery? If no voltage in the battery is its charger working? If no voltage to the panel, the wire (probably pretty thick) connecting to the panel is either cut or its fuse is blown -- and it should have a fuse close to the battery.

If you also have a 36 volt system, you almost certainly have 3 12volt batteries in series to produce that 36 volts. One of those batteries, the one wired to ground, may also be the battery for your 12v system. Is the 36 volt system working?
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Old 04-17-2021, 01:21 PM   #11
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I’ve never seen a boat with a 36 volt system. Nobody even makes 36 volt bilge pumps.
It must be a 32 volt system. Even 32 volt systems are pretty rare today.
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Old 04-17-2021, 03:59 PM   #12
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Wow! This is proof positive that boat electronics and wiring are different than what is considered normal for land based electronics.

Here we have a competent electrician who can't get to square one on a boat problem.

All the answers seem awfully rudimentary for a qualified electrician. Come on, a switch or breaker, a bad ground, a broken feed wire?

I guess I would have to know more about the electrician. Has he overstated his qualifications?

At one time I had a similar problem with the 12 volt system on my Albin. Big problems are easy to find. I'm no electrician but I knew the answer had to be obvious, and it was.

Something kind of goofy going on here.

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Old 04-17-2021, 04:18 PM   #13
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12V, 36(2)V vs 110/220V.... pretty different animals.
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Old 04-17-2021, 06:27 PM   #14
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Maryellen, could you please expand on "we bought a NAVY trawler." Is it possibly a YP - I was a qualified operating engineer on them about a million years ago.
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Old 04-17-2021, 06:31 PM   #15
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I went to school for this stuff. A very long time ago.

As I recall, we studied DC theory and then moved to AC theory. There is not a big difference, there needs to be a complete circuit, resistance affects the circuit the same way, etc..

From my experience, these questions don't sound like they are coming from an electrician. I'm not trying to insult anyone, but surely an electrician could figure out how 36 volts is generated from simply looking at the batteries and how they are connected. He should also be able to figure out where 12 volts is coming from. And why it's not working.

There are not a lot of 36 volt boat out there, but the theory is the same for 36 volts as it is for 12 volts.

My suggestion to the OP is, if your boyfriend can't figure it out, hire an experienced marine electrician to both find and fix the problem and explain the system to him so he will be able to work on it in the future.
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Old 04-17-2021, 11:33 PM   #16
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What Hopcar says! Nobody has heard of a 36 v anything.

My bet is you have 8 volt batteries in series, making 32 nominal voltage. Probably charges at 36 v similar to 12 v charges at about 14 v.
Quote:
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I’ve never seen a boat with a 36 volt system. Nobody even makes 36 volt bilge pumps.
It must be a 32 volt system. Even 32 volt systems are pretty rare today.
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Old 04-17-2021, 11:48 PM   #17
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I think this might be a spin-up.
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Old 04-19-2021, 01:39 PM   #18
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I'd be more apt to believe there is a 24v and a 12v system and they are sharing a common ground, making one think they are looking at a 36 volt system in series rather than a 12v with a 24volt in series.
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Old 04-20-2021, 06:25 AM   #19
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I guessed 32V because it's a "1968 Navy trawler" and I'd expect that means DD's of some sort... plus other 32V stuff that was more common back then.

Counting series-wired batteries would likely solve it. 4 x 8V = 32V. 3 x 12V = 36V. Et cetera...

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Old 04-20-2021, 06:53 AM   #20
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Quote:
Originally Posted by Pete Meisinger View Post
Wow! This is proof positive that boat electronics and wiring are different than what is considered normal for land based electronics.

Here we have a competent electrician who can't get to square one on a boat problem.

All the answers seem awfully rudimentary for a qualified electrician. Come on, a switch or breaker, a bad ground, a broken feed wire?

I guess I would have to know more about the electrician. Has he overstated his qualifications?

At one time I had a similar problem with the 12 volt system on my Albin. Big problems are easy to find. I'm no electrician but I knew the answer had to be obvious, and it was.

Something kind of goofy going on here.

pete

I use to fix big printers, in the 10k to 60k range. Guys would go out and overthink the problem. Replacing P.C. boards, switches and more. For what ever reason they just could not see problem. You have to go back to basics!

As someone else pointed out, start at the batteries and work your way to the panel. Where are you loosing it?

On my new to me boat, 20 years old. I past owner put a inline fuse to the starting battery to charge it off the inverter charger. He mounter it on the side of the battery box. Where it was dark and low almost touching the floor. It took me 45 minutes to find it and discover the fuse was bad. A simple fix but hard to find.
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