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+--- Thread: Headlight Fuse is Melting, not breaking but MELTING! (/showthread.php?tid=60820)
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Headlight Fuse is Melting, not breaking but MELTING! - willmckeand - 04-11-12
Hey everybody, the headlights fuse on my FZS600 Fazer is getting extremely hot after about 30 seconds of having the lights on. So hot that it melted the plastic off of the fuse which then ran down into the fuse box.
I've re-wired the fuse to another fuse holder but I'm still having the same problem. The ammeter showed around 10A at the fuse which explains why the 20A fuse is not breaking, just getting very hot.
Does anyone have any thoughts on what could be causing this? I have checked the majority of the wiring and the bulbs seem okay. I thought initially that water had caused it as the bike was out in the rain all day on the day the problem started, however it's been 4 days in the dry now and still no improvement.
Running out of ideas, please help!
Will
Re: Headlight Fuse is Melting, not breaking but MELTING! - andybesy - 04-11-12
What's the voltage across the wire?
And what's the resistance?
Andy
Re: Headlight Fuse is Melting, not breaking but MELTING! - willmckeand - 04-11-12
Andy, the voltage is 10.3V (engine not running and battery has been used a lot for tasting lately without charge)
The resistance is about 70 ohms although this changes as the fuse gets hotter, any ideas?
Thanks for your response
Will
Re: Headlight Fuse is Melting, not breaking but MELTING! - Motorbreath - 04-11-12
Silly question, but, have you tried another fuse?
Re: Headlight Fuse is Melting, not breaking but MELTING! - His Dudeness - 04-11-12
its probably a dodgy connection or wire causing higher resistance. try pulling the connectors in that junction box apart
Re: Headlight Fuse is Melting, not breaking but MELTING! - Motorbreath - 04-11-12
(04-11-12, 08:38 PM)His Dudeness link Wrote:its probably a dodgy connection or wire causing higher resistance. try pulling the connectors in that junction box apart
I think that is not correct. Higher resistance=less current=less power=less temperature.
Re: Headlight Fuse is Melting, not breaking but MELTING! - His Dudeness - 04-11-12
(04-11-12, 09:08 PM)Motorbreath link Wrote:[quote author=His Dudeness link=topic=5187.msg45056#msg45056 date=1352057897]
its probably a dodgy connection or wire causing higher resistance. try pulling the connectors in that junction box apart
I think that is not correct. Higher resistance=less current=less power=less temperature.
[/quote]
or the alternator is supplying more current to overcome the higher resistance of a bad connection or bad wire so you're getting more heat
Re: Headlight Fuse is Melting, not breaking but MELTING! - Motorbreath - 04-11-12
An increase of available current would make no difference, to increase the power it would have to increase the voltage too. Also, the place where the bottleneck is should be the hottest, so if ithe fuse is the hottest it should be the faulty part.
Re: Headlight Fuse is Melting, not breaking but MELTING! - His Dudeness - 04-11-12
i thought heat was proportional to current squared times resistance so how can an increase in current even at the same voltage not cause more heat? also maybe the wire has more of a heat sink around it than the fuse so the fuse can't dissipate the heat as fast as the wire?
Re: Headlight Fuse is Melting, not breaking but MELTING! - Motorbreath - 04-11-12
The current cannot be increased for a given resistance and a given voltage. (I=V/R). To increase the current yo have to increase the voltage or decrease the resistance (or both). You can increase available current (for example, having a big car battery), but the actual current that will run through the circuit will be the same.
I do not know how the fuse can melt before break. But if another fuse do the same then probably the circuit is shortend to ground, by water or a peeled wire or other reason.
I hope I explain myself, English is not my first language.
Re: Headlight Fuse is Melting, not breaking but MELTING! - His Dudeness - 04-11-12
yes i see what you mean I=V/R. but if the resistance has increased due to a dodgy wire or connection then there would have to be more current flowing through the circuit to maintain the 12V wouldn't there? and if heat is proportional to the current squared and there's a higher resistance then you've got more heat. i'm only guessing here btw you probably know more about it than me
Re: Headlight Fuse is Melting, not breaking but MELTING! - richfzs - 04-11-12
(04-11-12, 10:18 PM)His Dudeness link Wrote:you probably know more about it than me
Yeah, he does @pokefun
The 12V (nominal) is produced by the battery, that doesn't change (as the revs rise, the reg/rec keeps the voltage where it should be), so as Motorbreath says, the two variables are the current and the resistance - a dodgy/corroded connection increases the resistance, so the current drops. With a lower current, the power equation, P = I*V shows that the power also drops, with less power, you've got less potential for heat.
Re: Headlight Fuse is Melting, not breaking but MELTING! - scottyboy2203 - 04-11-12
just to put my 2p in, excess heat heat in a wire is a sign of too much current being drawn through it. Since the voltage and resistance of the wire/alternator is fixed (within a small range depending on engine revs and heat etc) it's only current that can change dramatically. This is usually caused by something drawing too much, like a faulty bulb or short-circuit. The common mistake is to think that the alternator/battery produced too much power/current but its the other way round, the bulb draws the current it wants and the alternator/battery tries to provide it. So my point is that you probably have a short circuit between the fuse and the headlight or a faulty bulb that is drawing too much current and then melting the fuse. I've probably rambled on enough though... :rollin
overheating = too much current
Re: Headlight Fuse is Melting, not breaking but MELTING! - His Dudeness - 04-11-12
(04-11-12, 10:43 PM)richfzs link Wrote:[quote author=His Dudeness link=topic=5187.msg45074#msg45074 date=1352063905]
you probably know more about it than me
Yeah, he does @pokefun
The 12V (nominal) is produced by the battery, that doesn't change (as the revs rise, the reg/rec keeps the voltage where it should be), so as Motorbreath says, the two variables are the current and the resistance - a dodgy/corroded connection increases the resistance, so the current drops. With a lower current, the power equation, P = I*V shows that the power also drops, with less power, you've got less potential for heat.
[/quote]
yeah i see what you're saying but if there's more load caused by a dodgy connection or just an increase in load like by heated grips or something like that would the alternator not produce more current to compensate for the increased resistance?
Re: Headlight Fuse is Melting, not breaking but MELTING! - richfzs - 05-11-12
Quote: there's more load caused by a dodgy connection or just an increase in load like by heated grips
these are 2 different scenarios.
The dodgy connection (assuming its corrosion) just means its an increase in resistance, so lower current - the scenario I described before.
extra load (such as heated grips) will pull more current out of the battery (and reg/rec combination) yes, but that's perfectly normal for the accessory that's being switched. And it's not what is happening in the OP scenario (I dunno what the problem is there tho!), he has a fault of most intriguing origin !!
A dodgy connection could be a fault to earth - and then there's very low resistance, and hence a very high current, with the attendant heat and melting wiring & fire risk - and that's why we use fuses, they're not really there to protect the accessory, but to protect the rest of the bike.
What the OP problem is, I dunno - the fuse should be doing its job long before the plastic melts :eek :eek
Will, is the heat definiately coming from the fuse, its not something else right next to it?!? Cant recall whats next to the fuse box, and its WAY too cold to go take a lok in hte garage
Re: Headlight Fuse is Melting, not breaking but MELTING! - His Dudeness - 05-11-12
ok
i thought that a bad wire would cause an increase in load in the same as say heated grips cause an increase in load.
Re: Headlight Fuse is Melting, not breaking but MELTING! - unfazed - 05-11-12
Have you modified the headlight?
Re: Headlight Fuse is Melting, not breaking but MELTING! - ponkster - 05-11-12
As some one said earlier in the thread heating is due to increased resistance or load if the bulbs are standard and in good order I would suspect a poor conection - Its a simple enough circuit so I would check and clean the conections and put in a new fuse.
You can never rule out the PO factor ( previous owner) - my wiring was getting real hot when on full beam - on inspection the main beam on one bulb had a wire soldered on it linking it to the un used dipped fillament - way too much load - again strangly didnt pop a fuse but the bulb connectors started to melt!
Re: Headlight Fuse is Melting, not breaking but MELTING! - willmckeand - 05-11-12
Hey everyone, thanks for all of your responses, I'll change the bulbs and then do a more thorough check of all the connectors and wires in the circuit.
@unfazed
I do have a modded headlight but the problem still occurs when I disconnect the wire, it even does it when just the side/tail lights are on so I'm not sure it's an issue.
Thanks
Re: Headlight Fuse is Melting, not breaking but MELTING! - JZS 600 - 05-11-12
http://www.aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ATM_Specs.pdf
Here you go, all you need is a multimeter set on DC amps in line with the circuit and you see what's happening.