How much voltage?

[Hoser]

When riding back from IZ, in the rain,north of Des Moines.  A car drifted into my lane and I blew my airhorn to wake them up.  When I did so, the engine started to sputter and miss.  It stopped sputtering when I let off the button.  I had on the driving lights for maximum visibility.  Green light on my Kury voltage indicator also flashed yellow.  Checked my voltage accross the battery when I got home, at 2000 rpm, the reading was 14.4 volts.  How much should it be?  Is my alternator getting weak?  Hoser  ???

[fat6man]

First I would check your battery to be good with a digital multimeter - It should have a NO-LOAD Voltage of 12.6 - 12.72 volts for a good 100% charged battery.

The alternator should have an output of between 13.5 and 14.8 volts @ about 2000 rpm.

Also check your ground connection to be good.       

[Patrick]

I would think that your alternator seems just fine.. That horn must really really like electrons..

[Hoser]

Charged the battery when I got home, it has never done that before, bike turned 70k on the trip.  I think I will replace the brushes and clean it up. check ground, etc.  Hoser  ???

[Daniel Meyer]

I'd also pull the battery and do a load test and see if it's still any good...the voltage test above is one test...you also need a load test if the voltage test holds.

Or just replace it if it's very old. With lots of stuff running...yeah, you could use more than the alternator puts out...but the battery should be able to cover it for a while.

[Ricky-D]

Patrick had it right!

With the driving lights "on" you're already drawing a lot of current and then energizing the compressor for the horns simply overloaded the battery.

Why it didn't happen earlier times is because the battery was in better shape. (newer)

Good thing you have all that extra stuff on their own circuits. Without that you most surely would have fried the bikes wiring!

***

[Hoser]

Kinda like I figured, I'll load test the battery also.   hoser Update:  Problem was a faulty ground on the negative cable from the battery.  You could actually hear and see it spark when I hit the button.  Cleaned it off, reassembled, applied grease, no problems.    Hoser