voltage drop at the tail-light bulb

[DimitriT]

I'm trying to diagnose a long term issue which I think might be affecting my 82 gs550.
In the last 30K miles it has blown out two stators. I just replaced the second one and
at the same time installed a Honda 6-wire RR. The RR required that I splice the sense (black)
wire into the tail-light positive wire (brown wire on my bike). I noticed that the voltage
difference at this wire is about 2V lower that at the battery terminal.

* Is this normal or is it a sign that I have bad connectors in my wiring?

With the new stator and RR I am seeing 13.5V at idle and 15.9V while revving the motor at
the battery terminal. I wired in a voltmeter LCD display. It's usually accurate within .5 V.

* Sound good?

 

[Nessism]

15.9 volts is too high. As an experiment I'd put the sense wire on the positive battery terminal and retest the voltage.

Did you bypass the factory harness and wire the stator directly into your R/R? Did you add extra grounds to the R/R circuit?

 

[DimitriT]

Yea I figure 15.9 might be too much.

The sense wire is reading 14.0 when the motor is revving
so my guess is the RR is outputting too much in response
to the voltage drop.

My question is why is there a voltage drop? Could the contacts
be bad in the key switch? I guess I can go poking around with
my ohm meter.

The stator goes directly into the RR even with the factory
wiring. The RR ground goes directly to the battery.

I think my problem is I have a bad switch or connector somewhere.

 

[posplayr]

Although Duange steadfastly disagrees(he thinks everyone should just keep their contacts clean), using the brake light as a sense point location just opens up the charging system to charging voltage sensitivities do to any of the voltage drops the brake lights might see.

Adding a coil relay modification and using the relay output as a sense point is the only good answer.

I'm pretty sure this has been reiterated about 100 times by now.

 

[DimitriT]

Although Duange steadfastly disagrees(he thinks everyone should just keep their contacts clean), using the brake light as a sense point location just opens up the charging system to charging voltage sensitivities do to any of the voltage drops the brake lights might see.

Adding a coil relay modification and using the relay output as a sense point is the only good answer.

I'm pretty sure this has been reiterated about 100 times by now.

How would you wire the relay?

[edit] never mind I did a search

 

[Redman]

Dimitri,

Good that you have a multimeter.

Good that you noticed that the tail light circuit was less than battery voltage. Must be a bad connection somewere to be causeing that voltage drop. And yes, that then wil not be a good place to have the sense wire, andf you have noticed that already. Haveing the sence wire there were the voltage is low will cause the R/R to controll to too high a voltage, as you have also noticed.

THe orange wire to the rear brake swtich is usally a good place to have the sense wire. Check and see if the voltage there is more like the battery voltage.

.

 

[DimitriT]

Searching old posts I see people reporting that the ignition switch is one place
which needs to be cleaned. What is the procedure for cleaning the contacts in
that switch?

Also noticed that the sense wire draws very little current. Would it harm the RR
if I put the sense wire right on the + battery terminal? I tried that as an experiment
and it regulated to 14.5V very nicely.

 

[duaneage]

Although Duange steadfastly disagrees(he thinks everyone should just keep their contacts clean), using the brake light as a sense point location just opens up the charging system to charging voltage sensitivities do to any of the voltage drops the brake lights might see.

Adding a coil relay modification and using the relay output as a sense point is the only good answer.

I'm pretty sure this has been reiterated about 100 times by now.

If you think doing a relay around bad contacts or connections is the only good answer, go ahead and do so. But don't recommend it to others as some kind of solution. With all the parts available for these bikes it's not hard to replace a switch or connector.

The rear brake light connector represents just one optional switched location which happens to be near the RR and also has connectors which can be used. Seriously low voltage here could result in a dim rear brake light and that would be risky.


And it's Due not Do

 

[duaneage]

Searching old posts I see people reporting that the ignition switch is one place
which needs to be cleaned. What is the procedure for cleaning the contacts in
that switch?

Also noticed that the sense wire draws very little current. Would it harm the RR
if I put the sense wire right on the + battery terminal? I tried that as an experiment
and it regulated to 14.5V very nicely.

It's easy. Buy a can of electrical contact cleaner from Radio Shack or an electronic supply house. Remove the switch from the triple tree with two Allen head screws (6mm) and then you can clean and grease it easily. unplug it from the bike so when you work it you don't flash the lights on and off. Remove the rear cover and you can access the contacts with the spray nozzle. Work it a few times and you should be good.

I got 2 more volts across a switch that was dirty by cleaning it.

 

[Normk]

Haven't read the thread but here's the issue:

The sensor wire indicates the system voltage to the voltage regulator so you need to have that voltage from a source which is identical to the battery or you will have problems ranging from under/over charging, to bulb life, etc.

The 2 volt drop in the tail light or other wiring on a motorcycle is not unusual unfortunately but I recommend that you move the sense wire to a lower loss location. If you are able to read current (ammeter) check to see if there is a draw in the sense line. If there is not a draw/current flow, then this wire can simply be connected to battery +, or better, to the battery side of the starter relay.

If there is a draw in the sense line circuit, it will eventually drain the battery unless the current is a few milli-amps. If there is a significant draw, use your voltmeter to find a convenient connection point which has no voltage drop to the battery +. Connect one voltmeter lead to battery + and the other to the intended point and note the voltage drop indicated with engine running and that circuit active/turned on.

What is happening in your bike's case is that the voltage regulator is producing an output voltage sufficient that it "sees" the desired voltage set point at the sense line. If there is a voltage drop between output and the sense point, the regulator will add on the voltage difference in order that it "sees" the desired voltage. It has no way of knowing that the output and sense values are because of a voltage drop between the two points.

Cleaning various connections is all well and good but that should be secondary to establishing a better sense line location. In some cases we simply attached the sense line (for regulators with a current flow in the sense circuit) to a relay which we also used to provide current for other loads such as the fuse box.

It is quite common for motorcycles to have a high voltage drop in the wiring because the wires are tiny compared to what is really needed. (No conspiracy theories please.....) This is the reason for using a sense line to the VRR in order to compensate for loss in the wiring but this leads to other issues so the system should simply be corrected, IMO.

Try measuring Vd between battery + and the fuse box on any motorcycle and you will see what I mean. One root cause is that power front the battery and alternator are carried through the main fuse, up through the ignition switch, back down to the fuse box, back up front again (in most cases) which adds high Vd because of the small sized wires.

I have written on this subject, literally dozens of times so often become impatient with the subject so please excuse.

Consider the typical headlight power flow: battery/alternator junction point, main fuse, up to ignition switch (should be called "main switch" instead), back to the fuse box, through headlight fuse, back up to the handlebar dimmer switch pod, down to the headlight, through headlight bulb, to ground wire, into wiring harness, all the way back to the ground wire common junction point and to ground. A recipe for losses!

I do many bikes on which the main voltage drop problem is in the battery to ignition switch to fuse box (example: ST1100 Honda and almost any other bike you care to mention), although some are better addressed by use of headlight relays (KLR650). VStrom has a massive voltage drop!

Those who advocate cleaning the ignition switch and other contacts have valid points of view but I wish to caution that one is best advised to locate the voltage drop by means of a voltmeter prior to spending time and effort in blindly cleaning components with which someone else has had a problem.

I am trying to cover some of these issues in the "Basic Electrical" thread although how successfully has yet to be determined.

Apologies to anyone whose posted suggestions may seem to have been shown disrespect by anything I have included as any suggestion of disrespect is simply due to my poor writing ability. I have not read this thread so am unaware of the content of posts other than the initial.

 

[DimitriT]

I put the sense wire right on the + terminal and I am getting 13.9-14.5 volts
charging (at 2K RPM or higher). The system looks healthy.

If there is current flowing through the sense wire it doesn't seem to affect my
battery. I have let it sit for several days and the battery reports 12.4V.

I'm still going to try cleaning the ignition but I think the RR is working well
so I'm gonna leave it alone.

 

[Steve]

My question is why is there a voltage drop? Could the contacts
be bad in the key switch? I guess I can go poking around with
my ohm meter.
I think my problem is I have a bad switch or connector somewhere.

Look at the path for current to get to the tail light:
(Assuming your R/R is still wired in the stock configuration,) power will come from the battery and MAIN fuse (before the engine is started) or the R/R, go through the main contacts in the ignition switch, go back to the fuse panel, through the LIGHTS fuse, go back through more connectors (probably under the tank) split off the main lighting wire, go through another set of contact in the ignition swith, then, finally, to the tail light. Which one (or more) of those connections might you suspect? :-k

The stator goes directly into the RR even with the factory wiring. The RR ground goes directly to the battery..

Are you sure? Most of them have one wire that disappears into the harness, goes to a connector under the tank (or in the headlight bucket), then comes back to the R/R input. That part of the harness is left over from the days when a headlight switch was available, but was still there for the markets where it was still available. To enhance reliability, we recommend bypassing those extra wires.

Adding a coil relay modification and using the relay output as a sense point is the only good answer.

It may be one good answer, but it's not the "only" good answer.

NONE of my bikes has the coil relay mod, but my wife's bike does have an 'accessory terminal relay mod'. I have a terminal strip under the right side cover that feeds power to the CB radio, GPS, XM satellite radio, LED driving lights and the tail light. I moved the tail light feed to that strip because it was responding to voltage fluctuations from the headlight modulator. (I need to clean the rest of the system to prevent that.) Will probably do that when I rewire everything when I install the Eastern Beaver fuse panel this winter.

I put the sense wire right on the + terminal and I am getting 13.9-14.5 volts
charging (at 2K RPM or higher). The system looks healthy.

I'm still going to try cleaning the ignition but I think the RR is working well
so I'm gonna leave it alone.

As previously mentioned, the closer to the battery (electrically) you can connect the sense wire, the better. One suggestion (without adding a relay) would be the orange wire that feeds the fuse panel. If you don't mind adding a relay, you can tap into any of the switched fuses to trigger a relay that does nothing but feed power to your sense wire. Yeah, it's overkill, but very reliable.

.

 

[Normk]

Steve is obviously correct that adding a relay is only one way. I would not install a relay for only this purpose but would do it as part of a feed to the fuse box in order to remove that long run back and forth to the ignition switch as said before. There is certainly more than one right solution here and checking for voltage drops, then dealing with any bad connections or other issues is a given on these old bikes as one should expect problems.

BTW, don't bother with ohmmeters for checking 12 volt electrics other than coils, sensors and the like. They are simply not a reliable means of evaluating a power carrying circuit. You can look far and wide and not find a professional automotive or truck electrical specialist who would use an ohmmeter for this kind of work.

Clip your voltmeter to the battery + and to the fuse box input and turn the switch on with lights also on. If you are reading more than 1/2 volt drop then you should be considering a relay.

Yes, you will likely see 2 volts or more and, "Yes" you can go to all the trouble of disassembling and cleaning the ignition switch contacts but then you will likely see 1-1/2 volts drop. I've seen 5 volts drop to the headlights on many, many bikes due to normal wiring in good condition, just too small sized and too long a runs.

I did automotive, truck and marine wiring professionally for many years and do many bikes so am not guessing about the voltage drops in the wiring. Take a new KLR650 or VStrom, for example and check the voltage drops to the headlight circuit.

One can clean connections and switches (which often needs to be done on old bikes) but find the problem areas by voltage drop, and then decide whether the solution is in using the stock circuitry or using a relay.

I doubt that you will find the sense wire has a draw but didn't want to recommend connecting it live unless that were checked in case I recommended something which would cause a new problem. I do know some automotive systems have a draw in the sense line but don't recall any bike ones. However I also don't recall where I put my socks.....