84 FJ1100 over charging?

[jdvorchak]

After getting my barn find running, I was doing some "pre-flight" checks and noticed the voltage at the battery terminals. Pretty normal about 13 VDC at idle but 2500 RPM and above I watched the voltage rise and finally stop at 15.02 VDC. Brand new AGM battery and all lights functioning and on.

I realize that usually an AGM will charge at a higher rate than plain old lead acid. But I'm used to seeing 14.8 tops with AGM. Other than the FSM on PDF I can't seem to find any good wiring diagrams. Are the FJ1200 similar enough to use?

[ribbert]

After getting my barn find running, I was doing some "pre-flight" checks and noticed the voltage at the battery terminals. Pretty normal about 13 VDC at idle but 2500 RPM and above I watched the voltage rise and finally stop at 15.02 VDC. Brand new AGM battery and all lights functioning and on.

I realize that usually an AGM will charge at a higher rate than plain old lead acid. But I'm used to seeing 14.8 tops with AGM. Other than the FSM on PDF I can't seem to find any good wiring diagrams. Are the FJ1200 similar enough to use?

It's technically outside the specs but if that's as high as it goes, IMO, ignore it. Or.... you can open a can of worms and "fix" it. You will more than likely find it only peaks at that and spends most of its time at a lower charge rate.

If you're worried about it, duct tape your volt meter to the tank and take it for a ride and observe the charging cycle.

IMO

Noel

[FJ_Hooligan]

Also, if you haven't already done it, check the red 2-wire connector under the left sidecover.  If it's corroded or has a bad connection that can cause over-charging.

Be sure to pull the connector apart.  Sometimes it looks fine on the outside but can be melted inside.

DavidR.

[jdvorchak]

Also, if you haven't already done it, check the red 2-wire connector under the left sidecover.  If it's corroded or has a bad connection that can cause over-charging.

Be sure to pull the connector apart.  Sometimes it looks fine on the outside but can be melted inside.

DavidR.

Connector looked good on the outside but one of the female connectors on the white side of that connector had melted a hole in it. I'll replace that connector. On Gold Wings we just cut that connector out and solder the wires directly. If that is the main charging wire. On the Gold Wings the troublesome connector is the 3 yellow wire stator output to the Rectifier/Regulator. I gather this Yamaha has the RR attached to the stator assembly and you don't have the stator output wires as problematic?

[FJ_Hooligan]

It's not the main charging wire for the alternator to battery charging.

From what I understand, this wire provides the battery feedback voltage to the field generator of the alternator to tell it how "hard" to charge the battery.  If the voltage it is carrying is lower than the actual battery voltage (due to excess resistance, like a bad connector), then it will cause the alternator to overcharge.

DavidR.

[oldktmdude]

   My FJ charged at around 15 volts for the first four years of a brand new Motobat AGM battery's life with no ill effects. When it started charging over that, I replaced the regulator with a Bosch RE55 regulator. Charges consistently around 14.5 volts ever since. Also check you multimeter against a known accurate meter, small discrepancies are not unheard of.
   Regards, Pete.

[jdvorchak]

According to the Yamaha FSM that two wire connector has the main charging wire (red) and the sense wire (brown). The red one showed evidence of getting hot. The brown sense wire goes from the regulator to the ignition switch, which connects it to the red charging wire. I'll measure the voltage on the brown wire but I suspect the voltage drop is occurring through the ignition switch or it's multi-pin connector.

Thank you for pointing out the wires/connector!

Since all of the lights and switches seem to be working, I moved cleaning the electrical connectors phase, of the revive, down the list.

I have to say, after working on this bike for a week, it is a very well made and sophisticated machine. Especially when you consider it's age. My experience is mainly with Honda, Kawasaki and Suzuki bikes of this period. This is the first Yamaha I've worked on since the 1960's with the exception of a Virago. That was a simple clean the carbs and give it back to my friend.

Thank you again for pointing me in the right direction.

[jdvorchak]

   My FJ charged at around 15 volts for the first four years of a brand new Motobat AGM battery's life with no ill effects. When it started charging over that, I replaced the regulator with a Bosch RE55 regulator. Charges consistently around 14.5 volts ever since. Also check you multimeter against a known accurate meter, small discrepancies are not unheard of.
   Regards, Pete.

I use a Fluke DVM but have no way of calibrating it. What I do instead is weed through the 3 or so DVMs I have and use only those that are within a few hundredths of a volt of the Fluke.  Usually I don't care about a 10th of a volt or so, but half a volt? I start to question what I'm seeing. Hondas seem to charge at 14.2 when they work. Suzuki 13.8 and Kawasaki 14 VDC. I know to expect a higher charge voltage with an AGM battery. So I thought I'd ask here.

[FJ_Hooligan]

According to the Yamaha FSM that two wire connector has the main charging wire (red) and the sense wire (brown). The red one showed evidence of getting hot. The brown sense wire goes from the regulator to the ignition switch, which connects it to the red charging wire. I'll measure the voltage on the brown wire but I suspect the voltage drop is occurring through the ignition switch or it's multi-pin connector.

Yes, that sounds familiar.  I was wrong.  The red wire does charge the battery and the brown wire tells the alternator how much to charge.  And it has lots of potential for voltage loss.

I've wondered if running a wire directly from the battery would be a better solution.

DavidR.