HELP - Melted Main 12v Fuse

[David Tilston]

Originally Posted by John in Santa Cruz

on a 100AH battery thats fully charged, there's still an amp or so residual leakage.

That is news to me. I have this handy smart charger, that will display either voltage, current, or percent charge. I watched the current while it charged, it slowly fell, (0.1 A at a time near the end). When it was displaying zero for some time, the display changed to FUL, (in seven segment LED).

1 Amp of leakage current seems high. If the charger is always putting out 14.4 VDC, perhaps. But, once the smart charger drops to 13.4, (according to Xantrex) the leakage current should drop to a negligible value.

Even at 1 amp, the 0.1 ohm resistance in your example would represent only a 0.1 VDC drop.

[John in Santa Cruz]

yes, the current drops to nearly zero once it enters the maintenance phase.... but *before* it drops to the maintenance/trickle voltage, during the 'absorption phase' there *is* about an amp of residual current.... if the battery doesn't see the full 14.2-14.4V or so, it won't get fully charged

[John in Michigan]

Originally Posted by John in Santa Cruz

yes, the current drops to nearly zero once it enters the maintenance phase.... but *before* it drops to the maintenance/trickle voltage, during the 'absorption phase' there *is* about an amp of residual current.... if the battery doesn't see the full 14.2-14.4V or so, it won't get fully charged

John in Santa Cruz, so how does this relate to Joe's issue (melted fuse holder), possible solutions (increase wire gauge, fuse holder/fuse size, etc), and what is your recommendation?

[redbarron55]

The fuse holder was history the first time it overheated. The contacts lost tension and will not be capable of gripping tightly enough, if they ever were.
This fuse holder. Is probably not capable of handling a continuous 30 amps nor close to it.
It should be derated by at least 20% to 24 amps.
Fuses of this size in automotive applications are probably good for intermittent operation and short circuit protection.
For a main circuit a better arrangement would be a bolted in fuse and holder or a DC rated circuit breaker. (With a back up higher rated fuse to failsafe a bad breaker that failed to clear a short.

[Joe & Cherie]

I’d agree as I read more like the link above. I almost bought a MAXI fuse but couldn’t find out the manufacture. I’ll have to order a better setup off tha mothership (Amazon) soon! I think I can use this for a week or two with full batteries.

[John in Santa Cruz]

for a circuit that actually sees 30A sustained on a regular basis, I would use a fuse holder rated for TWICE that, or 60A, with a 30 or maybe 40A fuse.

[ljcs1]

Couple other things you might check

When batteries are discharged (60% +/-) check voltage of each battery, they should be nearly the same. Even at only 17 months old sometimes a battery can be faulty. If one is say 4.5 volts and the other at say 5.7 volts, the charger will be working very hard and generate lots of heat.

Another concern is battery water level, NEVER FILL your battery. The water level should be between the top to the plates and the bottom of the ring insert within the fill port.

If you are checking the current draw from the charger and some device Refrigerator or other high wattage device is ON then your current reading is a combination of battery and that device.

If you have a power distribution point other than the Batteries you might disconnect it temporarily while measuring current from charger to batteries. this also a good trouble shooting point when you have a current draw problem. disconnect one device at a time and see how it affects the current from the batteries.

I don't know what you use for a current meter, I use a wrap around type that way I can quickly check each wire without disconnecting it. I use a UNI-T model UT 203 and there are several others available.

[HVance]

I am new to the forum and currently shopping for a 13' -16' fiberglass. I am a ham radio operator and my current camp trailer, a teardrop, is modified for general ham radio and emergency communication so lots of battery, heavy gauge wire and fuses.

I think of the fuse placed near the battery as the battery fuse, it's purpose is to protect the battery from a dead short, not to protect any down stream equipment. I place it physically as close to the battery as possible. For a battery fuse I always use the largest size blade fuse called a Maxi in comparison to the regular ATO/ATC fuses. The Maxi is a good deal more robust, I often need pliers to pull the fuse from the holder.

I am suspicious of the Trojan batteries playing a role in your melted fuse. I recall they are flooded cell batteries. Flooded cell batteries must be ventilated not only because they release hydrogen, but they also cause corrosion of many kinds of metal in their immediate vicinity. I use AGM batteries for several reasons, mostly having to do with safety, but I can leave them in a closed space and they do not release chemicals that damage their immediate environment.

So, my thought is that the plastic fuse body melted because the resistance at the fuse blades increased due to corrosion caused by the battery gasses. This caused both voltage drop (frig stopped, etc) and power dissipation (heat) that melted the fuse body.

best regards, Hugh

[gordon2]

Originally Posted by HVance

...
I think of the fuse placed near the battery ....I place it physically as close to the battery as possible. ...

So, my thought is that the plastic fuse body melted because the resistance at the fuse blades increased due to corrosion caused by the battery gasses. ....

Thats an interesting theory. I dont recall where the OPs fuse was but if in the battery box, this makes sense.

As for battery fuse location, I agree.. as close to the battery post as possible is best for safety and protection. That why I use this right on the battery post:





But you bring up a good point about the corrosive environment at the battery. I'm sure that is why Scamp, among others, puts the fuse inline but about 12 inches from the battery terminal, and also outside the battery box.

Its a trade off. The post mounted one offers more protection but will need to be monitored for corrosion (with wet cell batteries). The inline version exposes a short piece of unprotected wire that can short out to the common ground if the insulation fails, but it will not be as much subjected to corrosion from the battery (although weather might still be an issue).

When using the post mounted fuse holder that I use, its another plus on the "pro" side for an AGM over a wet cell battery.

73