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Discussion Starter · #1 ·
Hi guys,

I have yet more issues with my B4 750. Today while playing around with the data logger I got from Merc07 I noticed that logs showed the voltage to be only around 13.5 - 13.8 even while up at 4k rpm. So I went to test the battery with my volt meter and noted that at idle I was seeing voltages of over 14v... I then looked at the fuse on the starter relay and saw that it had melted, it had not blown, but was melted.

Now, this has all happened before, when I bought the bike back in 2015/2016 and it had a new spu fitted (it was still running the old blue one) a new generator/alternator and an ignition coil.

So does anyone know what could be causing this issue, I don't believe that an alternator that is only a few years old has failed on its own. I am guessing there must be something that is causing it to fail. Can anyone shed some light what the possible causes could be?...

The bike has always seems like it runs a little rough, it's never been as smooth as I would have expected a 4cyl to be. It just sounds a little rough and can't get quite a few vibrations above about 5k rpm.



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Heat is caused by resistance.... When a fuse or other plastic electrical bit (connectors, etc) has melted from heat there is resistance at hand.
Either the fuse holder is loose or there is corrosion/contamination present on the contact surfaces. Anything that hinders the flow of electrons in the circuit will develop heat as the voltage drops across the resistance and amperage is consumed.
If there was too much current going through the fuse, for whatever reason, the fuse will blow. So your 40 amp fuse capacity has not been exceeded...but a lot of amperage is being consumed by the electrons trying to get past the high resistance, being pushed along by the voltage.
Which also explains you low voltage in the data logger.... voltage drops as electrons go through the loads (resistances) in the circuit.
 
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Discussion Starter · #3 ·
Thank you for getting back so quickly!!

The relay assembly is pretty new as I replaced it not that long ago when I had the same issue. I looked at it today and didn't notice any corrosion but I will look again. What I don't understand is why the battery is receiving so many volts at idle, but the logger is only seeing mid to high 13s the whole time.

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The voltage the data logger sees is dependent on the location of the connections.
If the data logger is connected downstream of the high resistance (likely), then it will see lower voltage.
 

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Discussion Starter · #6 ·
I guess that would makes sense, I assume the logger is reading the voltage from the ECU rather than directly from the battery.

I am sorry I am not fully grasping that wiring diagram. Should I read from that the voltage at the battery is correct at 14v at idle??

It's doesn't rise above this when I rev to 2000rpm.

I guess I need to look for a bad earth somewhere that could be causing high resistance.

Under the faults section of the data log it says:

Current Faults
Input: none
Output:none

Stored Faults
Input: BVS
Output: Inj1

It is set to clear validated faults but the stored Faults seem to stay listed.

I am confused because it is saying there are no current Faults but won't clear stored Faults.


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Charging voltage should be around 14 vdc (13.9 - 15.1) with the bike at 2000 rpm.
Measure that voltage directly across the battery.
 

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Discussion Starter · #8 ·
I have done a little more reading and looks like I am wrong in my assumption and the voltages are actually ok.

So I am thinking a bad earth somewhere is causing the issue.

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Discussion Starter · #9 ·
Charging voltage should be around 14 vdc (13.9 - 15.1) with the bike at 2000 rpm.
Measure that voltage directly across the battery.
That's what I was getting. I was just expecting to see lower than 14v at idle, that what threw me.

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Then you are good.
 

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So I am thinking a bad earth somewhere is causing the issue.
good to clean your main ground to the engine case. Follow the negative lead to mounting point.
 

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Discussion Starter · #12 ·
That was going to be my first inspection point. Really annoyed as I have just done this last summer. I guess I did I shit job of it. Or missed something.

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IF you used dielectric grease make sure it's cleaned off as it is non-conductive. Electric component contact cleaner is helpful. Clean brightly. tighten the connection and THEN if you wish to add dielectric grease to the outside of the connection point otherwise it could prevent proper continuity (although some say that's a myth). Many use, many do not. --Environmental conditions play a part in the decision-making. (Aside from general knowledge that dielectric grease is displaced when connectors are tightened but let's NOT go there.) Be a purist first then get sloppy.

Don't beat yourself up over electrics. It's a PITA. Consistent methodologies help route out possible problems.
 

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Discussion Starter · #14 ·
I didn't use any dielectric grease. Only thing I used was copper grease . My engine is loosing a lot paint these days and the metal is showing lots of oxidation, I may well have just not cleaned the ground points properly, all the bolts are starting to oxidise as well, so that is probably not helping. I thinking I will start replacing every bolt with stainless ones.

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Show us a photo of this "melted" fuse please....
In an electrical system, when there is excess resistance causing heat, the heat is at the point of the resistance. If the fuse is in fact "melted" then that is where the resistance is.
Look at the spades and sockets for the fuse itself.
The solenoid has male terminals that plug into the females in the wiring harness connector. Those females are where I would be looking next. .
Wiring will get hot when too much current (amperage) is flowing through it, but fused circuits are supposed to protect against that. A long extension cord (longer wire equals more resistance) will get warm to the touch when connected to a high demand device.
Hence the circuit breaker for your house electric receptacle will trip when you accidentally create a short circuit by sticking a screwdriver in the box touching the bare wires and giving yourself a shock.
 

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Discussion Starter · #16 · (Edited)
Here it is. It's melted, but not charred. It's the same fuse taken from both sides.


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I'd like to see the condition of the device that came out of....
 

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Discussion Starter · #18 ·
It looks to be OK. The socket that fuse goes into is a little melted but a new fuse when in OK. It's from the started relay. I will try and get a look at the 4pin connection tomorrow, I suspect it will have signs of corrosion/oxidation.

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Discussion Starter · #19 ·
Been thinking about this on the way into work this morning, could a knackered battery be the issue?. I have noticed that despite being on charge the battery just doesn't have the punch it should have when starting the bike, it's a very weak turnover. My thinking is that with a weak battery the system would be needing to pull more current to turn the starter. 🤔
 

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Something is off...
The alternator and ignition coil were replaced not too long ago. Why? Was the rectifier/regulator replaced as well? Do you keep your battery maintained?



You double checked for oxidation and loose connections at your starter solenoid? Does your noid need replacement? I think it does. You’ve stated you have overall oxidation issues. Loose connections generally become more loose when oxidation forms and grows producing more resistance therefore generating more heat. Then BAM, a melting.
 
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