I've found, and read, every thread concerning charging system I can find on the web but still....please, humor me. Noticed, out of the blue, that my 2010 Ultra's volt gauge dropped to 12ish at idle but climbed back to 14ish off idle. Brother's '15 Ultra reads 14 ALL the time. Even though I've had no problems with the battery, starts fine every time, I pulled out the multi-tester and, with a charged battery-2.8, ran the voltage regulator test and at 3000 got 13.8, the 2010 electrical diagnostic manual states;
Off Idle Voltage Test
1. With the vehicle is neutral, start engine and run at 3000
rpm.
2. Test battery voltage.
3. Is voltage above 13V?
a. Yes. Charging system working properly.
b. No. Go to Test 3.

So, apparently, I'm fine but...why would my volts not hold at 14 while others do, I've even been advised by a friend with a 15 King that there's a chance lower volts mean something else could be slowly starting to fail in the system? even the Fix-My-Hog guy says it should put out 14 volts?

 

well...that's the way mine works on my 2012.

 

confirm ALL readings with a voltmeter at the battery- always.

the meter in the dash is subject to voltage drop within the wiring...honk the horn and the meter dips...same with flashing the spots- a measurement at the battery would not show this same dip.
( and this is why we use AC power in our home, not DC- your lights would brown out everytime the air conditioning kicked on)

Newer touring models ( and many cars) now use a "canbus" electrical system where each circuit is better controlled by relays and less affected by electrical demands elsewhere on the bike- the lights are less likely to dim when you hit the horn

So:
the "nominal voltage" is 12...usual observed voltage while running will be about 13.15

MAXIMUM voltage from the charging system is 14.8 ( higher that that indicates a bad voltage regulator).

I'll try to phrase this:

the left side of the motor has the rotor attached to the crank- the rotor spins at which ever rpm the motor is turning.
The rotor has magnets glued to it, so these magnets are spinning too.
close by is the stator- which is a long piece of wire arranged into a coil - a loop.

the magnets whizzing past this coil cause electrons to move within the coil.

how fast the electrons move depends on how fast the magnets are moving

"Volts" is a measurement of speed...how fast are the electrons moving.

fast magnets ( spun by the motor) is more volts, slow magnets ( low rpm) is less volts.

usually in a Harley stator coil 16 to 20 volts will be produced for each 1000 rpms ( so at 3000 rpms that could be 48 to 60 volts).

this is AC power- which is a sine wave.

but our bikes use DC power-
the AC need to be "recitified" diodes are used to convert the AC to DC ( which causes a loss in speed= voltage of the electrons)...and then regulated so that high voltage doesn't blow up our light bulbs or overcharge the battery.

the regulator down between the frame rails has cooling fins, the recitifying creates heat as does excess power so some is shed as heat ( that is why chrome regulator covers is stoopid)
, some excess is just drained to the ground on the frame.

this shows that power produced by the charging system is dependent on motor rpms- got it?


the battery not only stores power for the next time we want to run the bike, it also serves as a reservoir to even out demand spikes in the electrical system- kind of a buffer

what you are seeing on your bike is pretty normal

mike

 

Good deal, I got 13.8 @ 3000 rpm at the battery with a voltmeter so I'm not gonna worry about the dash gauge dropping at idle, even when I'm 2000 miles from home.

thanks mike!

 

That is an impressive and very informative post. Kudos sir.

 

It is good. I was just wondering what would happen if you lost one of the legs of the 3 phases of the a/c portion of the stator? My new 45 amp stator in my wg puts out a solid 14.4 at an idle, 13.8 seems a bit low, just curious.

 

volts is speed...how FAST the electrons are moving

amps is the current used.

if the current draw goes "up" the voltage will often drop.

so go look at your meter and honk the horn...flash your lights.

most low beam lights draw 4.5 amps of current, most high beams draw 5...just flicking between low and high can show up on the in-dash meter as a wiggle of the needle ( this is amplified by the voltage drop in the wiring I mentioned in the earlier post..on earlier models. The canbus bikes are not as deeply affected.

if you do this when the motor is stopped, you'll just be on battery ( unplug a tender if you have one) and the result will be more extreme than if the motor is running and the charging system is reaction to load...the regulator will react to an imbalance and provide more power if demanded...up to the rated capacity*

* this is where a bad battery can cause problems- rather than storing power a duff battery can be a constant drain on the charging system..stressing it beyond capacity and something may burn up




plumbing is often a good analog when describing electricity.

so imagine your 1/2" garden hose in the yard with the tap on you get a certain amount of water

it comes out at a certain speed ( that'd be volts)

now if we replace the 1/2 hose with a 3/4" hose to represent more current draw ( more amps) and the same amount of water is coming down the hose, it will move slower...less "volts".

the relationship between volts ( speed) and amps ( current) is often related when we are measuring one, it gives a quick indicator, but measuring both can give better data.

for anyone finding this post charging system diagnostics are posted on the tech board electrical section...or in your service manual.
the info there will be Empirical

Mike