CalVin - Electrical problem

[JMVintage]

After reading about some problems with alternator output, some time ago (900Km ago) I installed a voltmeter on my Vintage. Lucky me!
From the first time I had it installed I found very weird that with engine stopped it showed a little bit below 12v (correct) but while riding it showed a load of 15v and with the fog lights ON it showed 13.5V
I asked the dealer who installed it and he said he had compared with a professional voltmeter and that the readings were accurate and normal. I didn’t find a load of 15v normal but I took his word for it.
Yesterday I was riding on the motorway and suddenly I saw the load drop to 10v, then 9v. I decided to stop and check it out. When I switched the ignition ON I noticed I only had 10v on the battery. Miraculously I managed to start the engine and immediately I called my dealer who was kind enough to pick-up the phone on a Sunday afternoon. He said that, if the engine was running I could carry on till home and load the battery later. Fortunately I didn’t take is advice because I thought that an EFI engine needs electrical power to run. I let the engine running for less than a minute and I noticed the voltage dropping. When it reached 8v (minimum readout) the engine stopped (obviously).
Next I checked the Fuse box and I found that F1=30A “Battery Recharger” was so badly burned that it even melted the plastic top.

I replaced the fuse and managed to push start the bike (alone!)
Afterwards while ridding the voltmeter showed 12.5v at any range and 12v with the fog lights ON.
When I arrived home 45 minutes later (80Km) I stopped the engine and the battery showed 11.5v. I tried and started the engine again normally.
My questions are:
- Why was the alternator previously loading at 15v (too high) and now at 12.5v (a bit low)?
- Has the battery been damaged?
- Shall I have the alternator checked?
Thanks for your help.

 

[kiwi dave]

It's a guess, but I think your main problem is with that fuse that got burnt. The current was not enough to blow the fuse, but obviously there was a lot of heat there, generated by the current through a poor connection, causing the volt drop.

Basically volts x amps = power and power x time = heat. The fuse holder and fuse should be replaced.

I suspect the voltmeter is on the alternator side of this fuse, and this is why the voltage climbed so high. I was going to suggest that the connection should be relocated on the battery side, but if the fuse holder plays up again the voltmeter will show the malfunction.

Why the voltage dropped I have no idea, perhaps the load was too much for the alternator. Replacing the fuse temporarily "fixed" the connection issue, and the voltmeter started reading the battery voltage.

 

[Brian UK]

I would agree with all dave said above, and add a little more.
You clearly had a high resistance connection on the fuse, which eventually caused enough heat to melt it.
The voltmeter must have been connected on the alternator side of the fuse, so giving the high voltage you saw. Equally when the engine was off you saw a rather low voltage, (a fully charged battery should read about 12.5 off charge). This is because the high resistance connection was reducing the voltage from the battery.
Then eventually that connection got so badly burned that it stopped working, thus stopping the battery from charging.

As Dave said, replace the fuse and fuse holder, as the spring contacts in the holder will now be useless.

But as 12.5v is correct for the battery if fully charged but off charge, it does sound as if you are no longer getting a charge from the alternator, and it is possible that this fault has killed the regulator.

 

[JMVintage]

Thank you Dave and Brian for your help.
I just had the battery fully charged and checked it.
Ignition ON: 12.5v
Engine running > 2,000RPM: 14.5v (fluctuating a bit with rpm between 14v and 15v)
Suddenly it went back to 12.5v steady regardless of rpm.
After a little while it went back to 14v/15v. I don’t know much about this but it doesn’t look very normal to me.

 

[kiwi dave]

Voltmeters, like oil pressure gauges, are not desirable IMHO. All they do is cause worry. Better not to know? :roll:

 

[JMVintage]

Voltmeters, like oil pressure gauges, are not desirable IMHO. All they do is cause worry. Better not to know? :roll:

There you have a VERY strong point, Dave

 

[Brian UK]

Do you have another voltmeter/multimeter which you can connect across the battery terminals? Then you can see if the other voltmeter is telling porkies or not.
Certainly if the voltage is fluctuating like that, it doesn't sound right. If the bike is still under warranty, get it looked at.