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30 amp fuse failure


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Now this is beginning to really piss me off. :bbblll:


My Sport used to melt its 30 amp "regulator/ charging" ATC fuse in its fuse block without "blowing the fuse." So, I added an external holder and it did the same thing. So, I modified the holder, improved the connections and it burned off one of the blades. Still without "blowing" the fuse.


So, I soldered in the MAXI fuse holder in 2008 and all has been well. Until today, looking into a failed turn signal flasher, I noticed the case of the 30 amp MAXI "Smart" fuse had opened up slightly. I couldn't pull it out by hand, so carried on with our ride until I got home.



Took some electrical cleaner, electrician's pliers, and a good deal of force to extract the fuse. All melted and burned up. Still without "blowing" the fuse.



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I know some have removed this fuse entirely.


What does it actually "protect" if it can go this bad and not open the circuit?


What is the downside of completely removing it?


*conflagration*? :o

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Yet, at this point, the holder will also be trashed.


While the bike's charging system is reliable, I wonder if it relates to the way I charge the battery (EnerSys Ultimizer designed for the Hawker Odyssey).


I remember reading somewhere in all that research about maybe removing this fuse during external charging (?)


Is the regulator also vulnerable to external charging input?

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Having fiddled with my Aprilia for a while, one of the weaknesses of the marque of a certain vintage (like mine) is that it melts loom connectors on a regular basis, especially the connectors associated with the alternator and regulator.  There are many threads on the "brown connector" on Rotax engined Aprilias.


The favorite fix is just eliminating the connectors altogether and splicing the wires right together.


Seems that the good folks building the bike never properly soldered the wires into the connectors, and the loose, not-perfect connection overheats under use and melts.


Maybe the issue with your 30 amp maxi fuse is similar: the spades don't quite mate with the holder properly, some corrosion builds up, the thing overheats, and the holder melts, all without blowing the fuse, because there is no short, just power flowing over a poor connection.


Just a thought.


Where do I find the 30 amp maxi fuse on my Sport?

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+1 on corrosion and/or contact issues playing a role. Had an issue with the charging circuit on a JD 2305 tractor. Turned out the connector between the voltage regulator and main wiring harness were so gunked up, the regulator's positive DC out wires at the connector fused open on both sides.

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Factory 30 amp fuse is an "ATC" in the factory fuse block, position 3 from the front. (I added the MAXI fuse after trouble with melting the smaller fuses.)


Agreed that the common wisdom is that heat = poor connection. But, sheesh, I really thought I had this addressed with the MAXI fuse installation (much bigger connection blades).


I am suspicious of using an external charger.  I will endeavor to remove the 30 amp charging fuse during external charging and report back in eight years . . . :huh:

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Bummer - electrical gremlins.


I have a spare regulator with a broken fin. Maybe good for testing purposes. Your for free if you want it. 


It so happens that I also have some spare maxi holders and fuses (it was about the same price to buy 10-packs as to buy 2 of each). Also yours for the asking - and In the mail tomorrow if you want 'em.

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While I thought I had this "melting/scorched"30 amp fuse issue solved by improving connections/ contact, this obviously is not so.


The question of applying external charging current has come up. Josh suggested monitoring fuse temperature during external charging.


I have a vague recollection of reading a recommendation to isolate the charging circuit (pull the 30 amp fuse) during external charging.  I have never done so and will have to try and find that reference.


Perhaps the too-common melted 30 amp fuse issue is from applying chargers? :huh2:

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Kiwi_Roy has told us about the importance of good grounding.

Grounding the regulator to it's mount, the mount to the engine, the gearbox to the battery, all should be shiny metal to metal connections assembled with a grease such as vaseline or similar to keep out moisture and oxygen. 

I think he is right.

If the regulator ground voltage is above battery ground, then the regulator output voltage could go high, meaning higher current output, resulting in heating at any high resistance connection (like a tarnished fuse holder). 

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I have added all the recommended grounds, as well as a few others. I am sure it is time to go through them all and clean /service their connections.  Something tells me the Tank Off Maintenance Checklist is going to get some updates!


Marty, can you explain this further to me (I'm not sure what you mean by "above.":


"If the regulator ground is above battery ground, . . ."

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For the ground I crimped a lug on both ends of about 6" of #12, Later on I thought that's not very smart Aluminum to Copper why not just take a piece of Aluminum sheet metal and make a strap from the alloy regulator to the alloy engine case it would hold it's shape better than a wire but add grease as well.

I think all the VIIs have a black wire all the way from the regulator to battery negative, it just has too much resistance. It's also been responsible for smoking up several bikes when the main ground has worked loose, the starter current can't get back through the regular cable so it finds it's way back through this regulator ground which gets red hot and melts itself to the rest of the loom.


I cannot stress enough the importance of cleaning the battery terminals and adding Vaseline to them, I have seen where a battery becomes completely disconnected although bolted tight by Lead Oxide creeping in between the lug and post, one application of Vaseline will protect the connection for years.


Re Maxi Fuse connection.

As you can see the fuses aren't blowing, it's just a high resistance that causes heating,

Might I suggest drilling a couple of holes in the blade and bolting the wires to it.

I would be very cautious about doing away with the fuse, the battery can easily melt any wire on the bike if you get a short


I think the Ducati Energia series type regulator might be partially to blame for the heating, once it decides the battery needs to be topped up it effectively connects the alternator directly to the battery delivering as much current as the alternator can produce as, I haven't measured the current pulses but I suspect it may be as high as 40 Amps, its a short duration of high current probably exceeding the rating of the fuse clip.

This is another reason to keep your battery terminals in good shape, as you know the alternator Voltage can go to 90 Volts open circuit, you don't want that getting into the ECU if the battery disconnects.


Our Guzzi regulators are series type that break the alternator circuit,

Most other bikes use shunt regulators that short out the alternator,

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 I have seen where a battery becomes completely disconnected although bolted tight by Lead Oxide creeping in between the lug and post, 


Me, too. I fixed a Rosso Corsa with intermittent starting problems that a lady had spent big money on at a dealer  :rolleyes: with a wire brush, some DeOxit, and vaseline. I was her hero.. :rasta:

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Thanks, gentlemen! :thumbsup:


I recently serviced my terminals by loosening them, spraying them with CRG Electronics Cleaner, applying Vaseline then using a heat gun to force the Vaseline to penetrate all the surfaces.


@Chuck - Which Caig DeOxit product do you use? (I always get confused by their broad selection of products).


@Roy - Is there a possibility that the external charging has been a "wild card" of sorts?

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