I titled this message "voltage observations" rather than "voltage issues" because I'm not sure I have a problem. Here's the scenario: I had a weak battery for some time that held a charge but would occasionally balk at start-up, never enough to cause a problem but got worse as the weather warmed up. Doing a stress test showed that CA was low (275A) and I replaced the battery. That solved the starting issue.

However, over the past month or so I've noticed that my voltage had been lower than normal for this bike. The voltmeter in the fairing always shows about .7-1.0V lower than the ECM and a VOM report, the latter two being very close. For reference I'll show voltage as 13.0/13.8 where the first number is the fairing gauge and the second the VOM and ECM value. Ever since the bike was new the stock gauge would show ~13.2/14.1V at all times, idling or cruising, and I never had a charge-related issue. Lately it has been showing 13.0-13.1, sometimes going down as low as 12.0/12.8 at idle when hot, but usually recovers quickly and I may not see this low voltage again for a while.

This week I pulled the VR off the bike and cleaned the connectors, and the checks for ground and stator integrity were all good. When I rode the bike yesterday voltage was higher, around 13.4/14.2 while cruising, down to maybe 13.2/14.0 at idle--but when I rode into my garage at the end of the ride my voltage dipped down to 12.0/12.8V again. Revving the engine a bit caused voltage to go back up and didn't fall down that low again.

Considering I don't watch the voltmeter that often compared to other gauges but have lately because of the battery issue, it has occurred to me that it has always behaved like this and I just didn't notice it. I am getting no fault codes and the battery warning light stays off, and the bike has never had a charging issue. Does anyone think this behavior is abnormal and suggests maybe the VR is going bad? The bike is an '07 FLHX with the usual stuff running at all times (stereo, GPS, Power Vision LCD, etc.), and I do have an Elf mini amp attached but no added lighting. Nothing except the amp should be taxing the charging system.

 

I have not bothered with detailed measurements on the 09- but will relate what I found on the 1995 FLHTC.

First off the voltmeter in the dash is more a coarse indicator of battery condition.

measurements made with a real voltmeter at the battery give a better indication of charging system function.

- one of the batteries jobs is to "filter" surges through the electrical system and stabilize voltage ( unlike the older bikes where the lights in the dash dim with the turn signals or the headlight gets brighter with rpms.)

a real voltmeter can be used to also check the alternator output in AC volts ( 16~20 VAC per 1000 rpms )

the power is then converted to DC by a diode bridge in the regulator and limited to under about 14.8 volts (DC) and sent to the battery


DC power does not travel well through wires- which is why our houses etc are all AC, and often converted to DC by wall warts for the phone, router etc. etc. most electronics use AC and DC inside the TV, stereo, guitar amps etc.

as DC travels through wire, it looses speed --- in the Electricity World we call speed "volts".

so DC voltage drops as it travels.


in a DC circuit, measurements can be made along the way which will show a "voltage drop" as the distance in wire adds up and the various connections and resistance build up, slowing the power, reducing the speed ( volts).

On my 1995 FLHTC I could measure the voltage drop at about -.7 VDC between the battery and the voltmeter in dash- WITH the lights OFF.

turning on the low beam ( 55w) would drop it by a total of -1.5 VDC...turning on the spots ( 2 x 55w) would drop it to -2.5 VDC.

this is because of the extra load being put on the stock wiring, the ign. switch ( known to be weak on those, the switch contacts could arc and burn causing failure) the ignition coil etc etc.

my "solution" was to run a 10 ga wire into the fairing from the battery ( fused)- this 10 Ga. was used to power relays for;

low beam
high beam
rt spot
lft spot
voltmeter

each of these relays received trigger input from the stock wiring

this not only gave direct battery power to each of these loads, but removed that load from the ign. switch.

the in dash voltmeter then read reliably about .3 VDC low from the battery.


watching the gauge would give quick indication of dead alternator ( low voltage reading) or dead regulator ( usually high voltage reading).


I have not bothered with all this on the 09 as the charging system is better, the ign. switch does not have the same issues as the old and the optics of the factory lighting is FAR superior to the previous stuff ( in which I had the 2 x 55w spots and a Hella headlight with a 80/115 w h4 capsule).

it can be too easy to start staring at gauges, which is why I haven't bothered with an oil temp gauge.

The old Eagle busses had all the gauges arranged so that "3 o'clock" was the normal position for everything but the speedo, tach and fuel gauge.- you could tell at a glance if 10 or so gauges were all showing normal. Nice


Mike

 

That's what I've heard and I use it as a relative indicator based on what it normally has run since new.

That's why I used a VOM to check as well as tapping into the ECM for its voltage readout. These two are in line with each other, which is about .7-1.0V above the stock gauge.

Since it is showing good output most of the time and the stator passed the continuity test I assumed it was outputting AC voltage okay. I didn't do an AC test the other day.

This might explain why the stock gauge is reading low. I did check voltage at a point under the fairing a few years ago and it was close to what the stock gauge showed. This may be why some people set up relays for headlights, which increases output considerably by boosting voltage, but also decreases bulb life.

I might not do the headlight conversion for the reason given above, but that's a great idea for the voltmeter. I have a 12-ga. wire going from the battery to my amp, so I could tap into that--but I wonder if the drag from the amp might pull voltage down by the time the voltmeter sees it.

The continual voltage drop at the gauge doesn't bother me, though, because as long as it is reading reliably low and is consistent I'm okay with it. What concerns me is the occasional voltage dip to 12.0 at the gauge and 12.8V at the battery when the engine is hot and idling. Does that indicates a potential problem with the VR or something else? This may be normal since it doesn't trip fault codes and the battery light doesn't come on.


I have a Hella E-code with 80/100W bulb and I'm very happy with the result. I use a modulator on high-beam and it results in about the same current flow as a stock headlight when on high-beam.

Well, I wish I had your resolve. I have all the gauges plus the Power Vision display which shows many ECM parameters plus gas mileage (instant and average), Lambda (from wideband O2 sensors), etc. I like info, but do practice restraint looking at it too much while riding.

I'd like your take on the occasional low-voltage readings I get while idling and only when hot.

 

well at idle ( say 1000 rpms) spec would be 16 to 20 volts AC at the alternator...and then converting to DC you loose some so your reading look normal.

and if your 80 w headlight is on, that thing is sucking close to 7 amps all by itself.

so I think you are seeing "normal".


instruments: yeah look at the road, smell the flowers, eat the bugs. My Dad flew 4 piston ( v12) engine bombers.
I asked him how he sync'd the revs and the fuel mixture while flying the aircraft...he said "oh we just did it by ear...until the vibrations stopped"
A low tech and perfect solution.

relays/ bulbs/ bulb life.

the relays give full power to the bulbs and remove the strain of the extra watts ( current draw) from the stock wiring- each 100 watts of load is 8.3 amps current draw through the wiring, switches and load on the battery- on my old evo with my spots and high beam I was drawing over 20 amps up front.

harmful to longevity of halogen bulbs is low voltage or fluctuating voltage.

In about 30,000 miles of riding the evo after the relay conversion I lost my low beam, once ( I sold the bike at about 83000 miles- no complaints from the current owner)

I have not used a modulator because I know the bulbs like a steady glow, rather than dipping down from 100%.*
I bet that if you put an ammeter on the modulator you would see that the modulator dims the light by shunting power to ground, or burning it off as heat...and that the current draw for the modulator on high beam is pretty steady to 8.5 amps.


remember watts is not a measurement of how much light the bulb produces- that would be lumens.
"watts" is more a measurement of how much current the bulb consumes for the electrical system.
It is completely possible for a "60 w" bulb to produce more useable light than a "80 w" bulb.


Mike

* i really like the idea of a modulator- but really think a physical "shutter" type device in front of the light might be better for the electrical system---- I'd thought about using a big capacitor to smooth out he spikes, but as I said earlier I am really satisfied with the stock lighting.

I may switch the LED when the cost comes down and the reliability goes up- and the optics improve.

From the excellent compaos of the trucklite 6 and 7 vs the HD LED lighting, I think the HD has been beam spread.

I'll wait.


Mike

 

I'm relieved to hear that, but why does it move from ~13.0 on the stock gauge at idle to 12.0 for no apparent reason. It's a rare occurrence but when it happens there is no more stress placed on the alternator from accessories than it was one minute before when it showed 13.0V. Remember that 13V on the gauge translates as 13.7-14.0 at the battery.

Yeah, I hear you. If I didn't have a gauge I wouldn't suspect that anything is amiss at all, as everything works fine, it's throwing no codes, the battery keeps a good charge, and the battery light never comes on. I'm just trying to understand what's happening when I get these rare low-voltage occurrences at idle when hot.

I was running 100w + 70w for the aftermarket spots (35w x 2), about 14A, and the 15A breakers on my '96 RK would often trip. I wired a relay for the spots only and ran that setup without issues for the next eight years.

These modulators (Kisan Pathblazer) don't work like that. They use a soft-switching technique that throttles the current flow through the bulb filament, so that there's no "thermal shock" due to a sudden in-rush of current which can damage the bulb filament or shorten its life considerably.

The Hella 100/80W bulb in my bike was installed when I bought the bike in Nov. '06, first in the stock headlight and later in the Hella E-code I now have, and it was in my old RK for at least several years before that. In the time I've had the modulator (eight years) I don't think I've replaced a headlight bulb even once. Remember that pulsing 20-100% 4x/sec. allows the bulb to run cooler, which is also a factor in bulb life.

Me too. I like the pattern and output of this Hella E-code with the high-output bulbs, and the price was right ($40-50 total).

BTW, thanks for all your input!

 

When your voltage dropped down to 12.0 THAT WAS THE BATTERY VOLTAGE READING AT THAT TIME. A volt reading CAN NOT go any lower than the amount of volts left in the battery. A battery with a volt reading of 12.0 volts is SEVERLY DISCHARGED!

Now given the fact that revving the engine caused the volt readings to return to normal I would guess that you have a corroded or loose cable connection some where in the system! This could show up as a low volt reading. That is why volts should be read directly from the battery cable connections! If the battery is truely at 12.0 volts, you are headed to a no start situation. I would be removing , cleaning and reconnecting the battery cables AT BOTH ENDS as well as making sure all other wires are clean and tight.

AMMENDED - to include the connections at the gauge!

 

The 12.0 reading comes from the stock gauge, which has always read .7-1.0V lower than when measured at the battery. The ECM reports 12.8-13.0 at the lowest state and when checked it always jibes with my VOM reading at the battery. The battery normally shows 12.8 with engine off after several hours of non-use, so it isn't discharging even when at its lowest point. Remember that all accessories are on including stereo (with 250W amp) and headlight, and with engine off and ignition on it shows 11V or less at the gauge, at which time it is definitely discharging.

Remember that the low-voltage situation occurs rarely and only at idle when hot, so we're not talking about a constant situation here. I've seen it happen maybe three times in three weeks, but I admittedly don't look at the gauge constantly so it may be happening more often. It might happen at one traffic light, then at the next one it is showing normal. I've checked both battery cables and their connectors are clean, as well as checked them with the VOM for abnormal resistance. I also checked the ground at the VR, all of which is well within HD specs.