Charging questions

On a stock system 850 mk2: without headlamp I get 15.3 volts above 3k rpm. With lamp
on I get 14.2 or more at that engine speed.

Is this too much? The reason I ask is that the zener gets warm right away. A minute of
running above 2500 you can feel the zener warm. Not burning hot but distinctly warm.

Rectifier also warm.

This never seemed to be a problem until today when I blew the fuse. Battery usually
shows 12.7 at rest. AGM.

I'm not an electrical guru, but I have been told recently when sourcing replacement fuses for my multimeter (my own dumb fault) that fuses are sensitive to current only, not voltage. So the slight over voltage you have is unlikely to have caused the fuse to blow. You may need to investigate that issue further.

I may be asking more than one question really. The stock zener will pass 5 volts at rest which is of course
a fail. It showed 8.8 volts when the fuse blew.
Zener replaced with known good and fuse doesnt blow but Im still generating what seems to me like
too many volts. Now that sounds like the reverse of what most complain about but there it is.

What can cause high voltage? The zener is clean and well grounded. Battery terms same.
Wiring and connectors new.

Yes, that is a bit high. Your lights will have a rather short life span, and the battery will lose electrolyte quicker than normal. If the alternator is stock, then I would look for another zener. If you have some sort of high output alternator then you can't use a standard zener regulator. It's normal that they get warm, that's why it's heatsinked to the aluminum Z-plate. It's not normal for them to burn out though, so whatever fried the last one needs to be addressed.

Batteries require at least 13.9 volts to charge fully, with a maximum of 14.2 volts. Any higher is trouble as maylar has posted above.

Do you have a high output stator? If the stator is putting out more amps than the Zener can sink, the voltage will exceed the Zener's rated voltage, and the Zener will run hot and ultimately fail.

With a high output stator, you will need an electronic voltage regulator such as a Podtronics.

Slick

Stock alt and rotor. I put in a new zener ( looks like a Wassel) and I see 16 volts at 3500.
Back to a zener off another bike which seems to have no trouble and I get 14.8 with a
momentary spike to 15.
If the zener is the only thing that controls high voltage, is it common for zeners to
be rather all over the map in terms of begin bleed and full bleed?

Slicks numbers are pretty right on. I have seen as high as 14.9 volts in automobiles but I believe anything over 15 volts will start causing problems. I think you have located your problem when you switched out your diode. I would check your connections and ground points at the Zener and beyond just to be sure everything is good.

Onder said:

If the zener is the only thing that controls high voltage, is it common for zeners to
be rather all over the map in terms of begin bleed and full bleed?

Click to expand...

Not really (within reason). They begin to clip (pass current) around 12.7 volts IIRC, then turn the excess current into heat. Once saturated, however, the voltage will begin to climb, as the Zener can no longer pass more current. Pushed hard enough, they'll blow open. As pointed out earlier, that's seldom an issue with our limited charging systems.
If you're getting inordinately high voltages with the headlight off, you might want to check into the cabling from the harness down to the zener. You might have a good, clean connection there, but, if there's a resistance in the line feeding it, it won't be able to sink the excess power to earth. And, make sure the ground wire is equally functional. Merely checking for voltage isn't enough, as the cabling to/from the zener has to be able to handle a fair amount of current for the zener to do its job.

To verify, place your volt meter at the zener and negative post of the battery while running, and, if you see any voltage, there's resistance in that line. A few millivolts is expected, but not much more. 'Same for the earth wire to the zener.

Your describing heat from the zener intrigues me. My system has never produced enough excess power to heat anything!

Nathan

Onder said:

Stock alt and rotor. I put in a new zener ( looks like a Wassel) and I see 16 volts at 3500.
Back to a zener off another bike which seems to have no trouble and I get 14.8 with a
momentary spike to 15.
If the zener is the only thing that controls high voltage, is it common for zeners to
be rather all over the map in terms of begin bleed and full bleed?

Click to expand...

The voltage output of the stator is a function of magnetic strength of the rotor, the number of coils in the stator, the number of wire turns on each coil, and rotor rpm. Without a battery, voltage regulator, or zener diode, the voltage can get very high ... as much as 200 volts or more at high rpms.

To keep the voltage within acceptable limits for the battery and the lamps, the voltage regulator or zener shunts excessive amps to ground when the voltage reaches optimum ... in that 13.9 to 14.2 volt range. So what can go wrong? In lieu of outright failure of the zener or regulator, loose connections at the battery or zener, including the ground connections, can give the spikes you are seeing (read again the last sentence of the above paragraph; loose connections intermittently take the device out of the circuit).

It is not common for zener voltages to be "all over the map". Since you have changed out several zeners, with similar symptoms, the problem probably lies elsewhere. Check your connections. Report back.

Slick

I see that Nater_Potator has beat me to the post. His post more fully explains why a zener fails if the rated amps of the stator exceeds that of the zener. Otherwise, his suggestions are similar to mine, check your cabling/connections.

A Podtronics or similar to replace both the rectifier and zener would be cheaper than a new AGM battery to replace the one you fry.

Make sure your volt meter and resistance meter are very good then:
A bad leg (high resistance/bad connection) from the power generation down to the zener (power or return) will prevent the zener from doing it's job. Therefore high voltage and insufficient current dump will result in cooking the battery due to higher voltage which you say is there. normally 14. 3 is max... if much higher than a few tenths you have a big time problem since it is a stock 120W alternator....
http://atlanticgreen.com/images/zener.gif
All super basic simple stuff IMO :mrgreen: seasoned with 40+ years of repetition.

Ill recheck the cabling by temporary substitution a foolproof way to go.
To make matters more interesting I also have a Triumph exhibiting the exact same problem!
Report will be tomorrow.

Have you checked to make sure your multimeter is accurate?

I more closely read the OP. If the fuse blew for some unrelated issue then the battery is disconnected. The batteryless system is fully functional and it would be normal to run above 14.3 and a bit more based on my chart and the zener would run hot as a pistol...all based on RPM/power out put . A good lead acid battery (at rest) is always 12.8V which is why I suggest to check the calibration on your meter.

If my memory serves me correctly I do remember reading in one of my manuals that the torque of the nut holding the zener to the "Z" plate is very critical in the actual performance of the diode. (this would only be accurate if my memory serves me at all)
Ride On
Dave

Update

Put in new lead from zener to neg term, new lead output rectifier to neg term, new lead
direct from bolt which secures zener heat sink to pos term. Previous leads removed.

Battery at rest, ignition on, 12.8 volts.

With no headlamp or taillamp on, 3500 rpm 15.1 fairly steady. It will go a bit higher
if you suddenly rev it. 15.3 maybe.

With headlamp on high beam 14.2 at 3700.

Zener not noticeably hot after running but only went about a mile.

Added test run and comments:

Another test run.
14.0 volts indicated at 3500 steady cruise with main beam on.
14.2 volts with low beam on. (beams include tail 1157)
15.1 volts to 15.3 volts with no head lamp on.

If you turn off the beam, then turn it back on it may read .1 or .2
higher than it did previously.

The diode gets warm without a doubt.

Now the following is copied from the Triumph T150v factory book:

<The series connected ammeter must indicate zero amps,
up to 12.75 volts, which will be indicated on the shunt connected
voltmeter as engine speed is slowly increased.

Increase engine speed still further, until Zener current
indicated on ammeter is 2.0 amp. At this value the
Zener voltage should be within 13.5 volts to 15.3 volts.

With the specially designed heat sink the Zener Diode
is able to absorb the full output of the alternator.

Provided a firm flat "metal to metal" contact is maintained
between the base of the Diode and the surface of the heat
sink, to ensure adequate heat flow, no maintenance will be
necessary. Ensure that the earth connection to the diode is
a good one.>

The zener base side is clean and uses co9puter heat sink
compound, the ground pin is clean as are the threads and
alloy surface the nut and washer seat against.


Reading this it seems that what is going on isnt unusual and
that Im within the limits. However, 15.3 volts is a lot. Yes it is
dumping into the zener but the system potential still must be
15.3 volts no?

Note: Im using the Trident factory book on this because
1. it is to hand and 2. because functionally the only difference
is Triumph uses a finned heat sink and Norton uses that massive
slab of alloy. I can see no other differences in their electrical systems.

As suggested by someone before, might be a good time to see if you meter is accurate. Could prevent you from chasing ghosts.

As suggested by someone before, might be a good time to see if you meter is accurate. Could prevent you from chasing ghosts.
Is is possible you have a 180 watt unit that came with the MKIII's, they use two diodes instead of one.

Worthwhile to invest $15 in one of these doodads.. fits right into the headlamp shell holes and shows under, correct, and over charge status...