Battery 30amp Inline Fuse

[kdrickard]

This last weekend I had the inline 30 amp fuse right off the batteries go bad. I assumed it was blown after seeing what I thought was melted plastic inside the fuse holder around the fuse – but in trying to get the holder apart to get at the fuse the power was cycling on and off (ok, the fuse is good?). I could not get the fuse out, it looked like it was glued in. Curious, I scraped some of the hardened gunk that was halfway over the top fuse and the circuit was fine (Yes, it seems the fuse is good). I had to break the old fuse to get it out of the holder and scrape out the hard gunk, but after replacement everything continued to be fine. The inside of the fuse holder looked normal after scraping the gunk out, and I could not see anything that looked like the plastic had melted inside.

So, as everything is fine for now, this is mostly a curiosity question; does anyone have any ideas as to what the problem was or what the hard gunk was?

Thanks,

Kevin

[Bill]

Trail Manor uses a cylindrical glass cartridge fuse and fuse holder. This really isn't capable of handling a 30-amp circuit reliably, and meltdowns are common. After mine melted, leaving me with an uncharged battery at the beginning of a three-day dry camping trip, I went to WalMart and bought an inline automotive-type fuse holder - the kind that takes the flat fuse with the two flat blades. Since I removed the cylindrical fuse holder and wired the new one in its place, no more meltdowns!

BTW, be sure you carry a couple spares for this fuse, as well as spares for the ones in the converter.

Bill

[RockyMtnRay]

My experience with similar situations is that the gunk is probably the glue that holds the fuse's end caps to its glass tube. I've typically seen it when something caused one end of the fuse to get hot enough to melt that glue. Typically the cause was a poor, fairly high resistance connection between the fuse and the fuse holder, sometimes the result of a build up of contaminants from the air or a bit of corrosion. And yeah, the fuse usually still worked because the current wasn't high enough to melt the inner fusible link and the fusible link still remained attached to the end caps. I haven't seen this problem in cars or RVs but I have seen it in my motorcycle...the fuse box sits right above the fairly hot engine. Add in an occasional poor connection to a fuse box connector and the end cap glue tends to melt

Now that you've replaced the problematic fuse and cleaned the contacts inside the fuse holder (probably the key) , I'd personally just periodically check it (especially after you've put any sizable loads on the battery). If it recurs, I'd start fixing things by replacing the fuse holder.

[kdrickard]

Thanks all. I'd guess it was the glue in the metal fuse cap as that scenario seems consistent with what I found. The flat fuses seem like a good idea as the contact with the fuse & holder should be better. Oh yeah, a bunch of fuses, a spare fuse holder, wire, and crimping kit found their way into my TM tool kit the next day.

Thanks again,

Kevin

Bill,

Was replacing the fuse with a whole different type really difficult to do? I tried taking mine out last year, and when I finally got it out, I was so afraid I wouldn't get it back in again later (because of the hard angle to work with it,) that I put it right back in. An automotive fuse (I often refer to them as bayonet fuses for some reason) would be a lot more straight forward.

[Bill]

The cylindrical glass fuses are indeed sometimes called bayonet fuses, because the fuseholder that accepts them is sometimes called a bayonet holder. Until recently, a lot of these cylindrical fuses were used in cars. Most of them would be snapped into a fuse block containing many such fuses. Occasionally, though, a single fuse would be carried in an in-line fuseholder, which has two wires sticking out of the ends, and is wired directly into the circuit. This is what the TM factory uses for the battery fuse.

With the cylindrical fuses, both the fuse block and the inline bayonet holder were troublesome. Most cars have switched over to the flat blade type of fuse - the same fuses you find in the TM converter. The TM battery fuse is about the only place you'll still find a cylindrical fuse. You want to trash this original fuseholder, and replace it with a blade-type fuseholder. It was easy. This is what I did.

First, I removed the negative (white and bare copper) wire from the battery to prevent shorts.

The old fuseholder has two wires coming out of it. One was twist-connected onto the black battery wire, secured with a yellow wire nut. The other had a crimped-on ring lug - this is what goes under the wing nut on the battery post.

I removed the wing nut from the battery, and removed the ring lug. Then I removed the yellow wire nut and untwisted the connection. This gave me the fuseholder, free in my hand, and I gave it a nice arc about 20 feet into the trash can.

Then I went to the automotive department at WalMart and bought a couple 30-amp blade type automotive fuses, and an in-line automotive fuseholder that takes this blade-type fuse. The new fuseholder has two wires coming out of the ends, just like the original bayonet fuse holder. I crimped a ring lug onto one of the fuseholder wires, using the crimping tool and lug assortment that I had thoughtfully picked up in the same department at WalMart. Then I twisted the other wire onto the end of the TM's black battery wire, and replaced the yellow wire nut (actually, I soldered and shrink-sleeved the connection, but that's just me). Connected the ring lug to the battery, plugged in the fuse, reconnected the negative wire, and voila! Done. I am a lot more confident about the battery fuse since I did this.

Just as a note, if I were doing it again, I would probably use the self-resetting circuit breaker mentioned in another post. But the important thing is to get rid of that old fuseholder.

Bill

Without looking at my unit and the wires while reading this, I can't quite visualize it, but if there are as few wires as you say, it doesn't seem to challenging. Thanks.

[mjlaupp]

Bill,
There are actually two glass fuses in the TM. A 30A for the battery and a 5A in the Thetford Electa-Magic. Both could/should be replaced with the automotive blade type fuse & holder to reduce the on-board parts inventory. I have had to replace most of the inline holders in my vehicles. The automotive type do not hold up to higher amp loads. The one in the Thetford is an industrial type and is less prone to overheating problems but, I have had to replace this type on several occasions.

Just as a note, if I were doing it again, I would probably use the self-resetting circuit breaker mentioned in another post. But the important thing is to get rid of that old fuseholder.

I would not replace the 30A battery fuse with a self-resetting circuit breaker because there is no switch to isolate the battery. In the case of a wiring short, the breaker would cycle on and off untill you could disconnect the battery. This would not be a good thing if the TM was in storage with no one in attendance.
MJL

Lol, Mike, you're correct......especially in my case, mine's got so many glass fuses in it, they outnumber the lights almost......(my whole fuseboard is made up of ol Buss fuses.........) But thanks guys for the heads up if I should run into the glue thing.......lol, at one point, I probably will. That's one thing I really like about this place, even if I don't have a problem with such and such, if I do, I'll prolly know the answer before it happens......thanks so much guys......


Happytrails

I revived this thread because I have a question about using the Walmart ATC blade type fuse holder that I just purchased. It is for a 30 amp blade type fuse and it has #12 gauge lead wires attached. When I got home I noticed that the wire that is on the TM for the inline glass fuse is of a heavier gauge (it says 10awg). Now can I use the Walmart fuseholder safely? Or back to the store and get something more heavy duty?

Mike Anderson