Need 12V help!

[ChuckZ]

We're stranded in Melborne (if you can call that stranded in February) and our 12V system has started blowing fuses for no apparent reason. I thought it might be the lousy LED's that I put in that are now all flickering. I removed them all and then tried replacing the fuse again and it blew immediately. I'm no electrictian but I bet there's someone out there that can guide me on how to trouble shoot this thing. It's the fuse on the negative line if that means anything. See the picture. Any thoughts? Please!

[HowieE]

Need more info.

Are you saying that the one fuse kills the complete 12 volt system in the trailer? What amps rating is that fuse. Fuses are generally on the hot leg of a system not the Negative side.

The LED were most likely blinking do to low voltage and not the cause of the problem

Retry to post a picture. Use the preview post to check t the picture is there before you post.

[Al and Missy]

I'm not familiar with your trailer, so I'm mostly guessing. Do you have a fuse panel with fuses for each group of loads? If these aren't blowing, then the problem is very close, electrically speaking, to the battery. IIRC, some of the older trailers had fuses in both the positive and negative. Where does the fused wire go? IT could be toward the loads or toward the converter, or maybe to a bussbar where both the loads and converters are connected. Any circuit that has a smaller fuse in line is not involved with your problem, e.g. your LEDs. I'd look for things that are probably fused separately and follow those wires. Examples are the breakaway switch, and the tongue jack.

Where in Melbourne are you?

Al

[Ted S.]

I read somewhere the LEDs can only be installed in one direction. Otherwise they can have issues, I wouldn't think tripping breakers but you don't know.

[NavyCorpsman]

When was the last time it was trouble free, and were any modifications made? If you have a voltmeter, what is the output of the converter. Just a guess, but it sounds like you have a short to ground somewhere.

[ChuckZ]

OK. this is getting ridiculous. How do I post a picture? I know I've done it before but can't remember. I think the picture is going to help a lot.

[ChuckZ]

Here is the picture.You can see the middle connection that I have removed. That is the fuse that continues to blow.

[Al and Missy]

OK, I'm assuming that the wire you have disconnected goes to the battery negative. The other side of that fuse looks like it goes to that busbar with all the yellow wires.

The bussbar itself is mounted to the case which is probably mounted to the frame. Disconnect all the other yellow wires from the bussbar and wrap their ends with tape. Replace the fuse and wire you have disconnected and see if the fuse blows. If the fuse blows with none of the yellow wires connected, make sure the battery connections aren't reversed. If not, you must have a short to the frame on your positive circuit somewhere.

If the fuse doesn't blow, replace the yellow wires one at a time until the fuse blows. When the fuse blows, follow that wire to see where it goes. If it goes to the converter, the converter is probably bad.

Al

[mimiandrews]

Suspect something like a wire rubbing against metal. Those rubber grommets they use where the wires pass through holes in the aluminum do fail with age and let things rub.

With the battery disconnected, disconnect one wire at a time on the positive side of that fuse. Use an ohmmeter between each wire you disconnect and the metal frame of the trailer. If that circuit is OK, you'll get a reading of infinity on the meter (open circuit). When you find the bad wire, there will be a low resistance reading between that wire and the frame. Follow that wire until you find bare wire touching metal.

[Mollysdad]

I'm confused.
The white wire(?) you have disconnected goes through the blown fuse, and then appears to tie into the ground bus on the right screw. Why would there be a fuse on a ground wire?
The fact they're wrapped in e-tape makes me think someone did some back yard engineering. Everything looks old too.
You may have to use a volt/ohm meter to trace the individual wires.
Keep us posted.

[ChuckZ]

Thanks everybody. You've given me some things to do today.

[Al and Missy]

Originally Posted by mimiandrews

Suspect something like a wire rubbing against metal. Those rubber grommets they use where the wires pass through holes in the aluminum do fail with age and let things rub.

With the battery disconnected, disconnect one wire at a time on the positive side of that fuse. Use an ohmmeter between each wire you disconnect and the metal frame of the trailer. If that circuit is OK, you'll get a reading of infinity on the meter (open circuit). When you find the bad wire, there will be a low resistance reading between that wire and the frame. Follow that wire until you find bare wire touching metal.

Unless I'm not seeing the picture correctly, there is no "positive side" to that fuse. They are all grounds, connected to the ground bussbar which is mounted on the case which is probably connected to the frame. IF that is the case they will all (correctly) show a short to the frame.

The first part of the post, however, is pertinent. Somewhere, one of the positive lines is somehow shorted to ground before it is fused. It will, most likely, be a separately-fused line like the tongue jack, or maybe a bad converter.

Al

[newsgauger]

Hi ChuckZ,

This might help you through the investigation process.

Good Luck,
Chris

[newsgauger]

Opps, let's try this again...

Chris

[Mollysdad]

Originally Posted by Al and Missy

Somewhere, one of the positive lines is somehow shorted to ground before it is fused.

If it shorted before the fuse, the fuse wouldn't be blowing, or am I missing something?

I always made a long (10') wire with alligator clips on both ends. It makes testing with a VOM meter easier. The leads on a meter are never long enough to reach all over.

[Mollysdad]

Originally Posted by newsgauger

Opps, let's try this again...

Chris

That's really interesting. Both sides of the battery go through fuses before circuits, then the positive side is through a circuit breaker also.
It sure looks like the OP's circuit too!

[TG Twinkie]

Here is what I see.
The 3 fuses are to do with all of the DC POWER in the coach.
The two fuses with red wires are protecting the positive side; one on the battery lead; one on the charge line from the TV or possibly from the converter or both.
The wire connected to the center fuse is on the negative side. Many trailers of this vintage had fuses on both the positive and negative side.
The individual circuits are protected by the circuit breakers in the lower left of your pic.
It is hard to tell from the pic but it looks like the fuse is slowly cooking itself. The fuse holders look in bad shape.
My guess is these three fuses are rated at between 30 and 50 amp.
I think the problem has more to do with old equipment and poor connections than a short somewhere.
Clean up the fuse holders, make sure the fuses are tight in the holders. At your earliest convenience replace the fuse holders with the more modern style.
You could as a temporary measure pick up a 40 amp fuse of the modern style. Wire it up with two spade connectors at the fuse and eyelet connectors. Pull the old glass fuse and wire in the new fuse to the existing screws on the fuse block.

[TG Twinkie]

More questions:
Are all three fuses the same size?
Try removing both red fuses then install a new fuse in the center holder. Replace one of the red fuses at a time to see which circuit causes the center fuse to blow.

[TG Twinkie]

How old is the converter?
What shape is the battery in?
How much stuff do you have running?

[ChuckZ]

I'm not sure how old the converter is. But I don't think it's that old. It's obviously the newer style. The battery is in great shape. Only running lights and a fantastic fan on the 12 V system.