Zenor

Onder

Onder

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If you apply 12v to the spade terminal on the zenor should you read any voltage on
the stud? This is off the bike completely just on the bench.
 
Onder said:
If you apply 12v to the spade terminal on the zenor should you read any voltage on
the stud? This is off the bike completely just on the bench.
Click to expand...
On the bench with battery/meter + to the stud and battery/meter - to the tab you should see the battery voltage. If you see smoke you have a shorted Zener. If the Zener is defective open, you've proven nothing as the Zener's job is to be "open" below its cutoff voltage. If you add a charger to the battery, the voltage should be a little higher than the battery voltage and a little lower than the battery voltage with the Zener disconnected.

On the bike, assuming positive ground, meter's + on ground (the stud), - on Zener tab and bike turned on you should see the battery voltage. The Zener is directly connected to the battery - via wire. The Zener's job is to bleed off the higher voltage from the charging system and to do nothing at the battery fully charged voltage.
 
So if reading Grant's test correctly you will not see any voltage across the Zener until you are over 12.75V as it will not allow current through until the V is 12.75V which makes sense as if it worked below 12.75V you would have difficulty keeping the battery charged.
 
kommando said:
So if reading Grant's test correctly you will not see any voltage across the Zener until you are over 12.75V as it will not allow current through until the V is 12.75V which makes sense as if it worked below 12.75V you would have difficulty keeping the battery charged.
Click to expand...
Nope! The Zener bleeds the higher voltage to ground. Across the Zener you will see the battery voltage if connect like I said since it is basically an open circuit.

Grant's test: https://granttiller.com/zener is different - he is showing the Zener bleeding off the excess. If the supplied voltage is higher than the Zener cutoff voltage then the bulb will start lighting. Of course, he gives a VERY complete answer. I was answering the question asked.
 
It looks like my stash of zenors are all NFG. Wishing to keep the stock charging system, is there anyone out there willing to make an offer
on a working unit? There seems to be one on ebay, claimed new, that goes for 194 quid! Im amazed some one has not made a run of them off shore as they were fit to nearly every brit bike at one point.
Anybody...? I live in hope.
 
Are you sure you are not applying the voltage in the reverse direction. In that direction, the voltage drop should be that of a standard diode, app. .65 volts. Be careful as without a resistance you are nearly shorting the batter since the diode is biased to conduct in a near dead short.

If mine failed I would just convert to an electronic regulator of somewhat greater sophistication. That being said I am still using the gallium rectifier with rather high leakage current on my 20M3.
 
marshg246 said:
Nope! The Zener bleeds the higher voltage to ground. Across the Zener you will see the battery voltage if connect like I said since it is basically an open circuit.

Grant's test: https://granttiller.com/zener is different - he is showing the Zener bleeding off the excess. If the supplied voltage is higher than the Zener cutoff voltage then the bulb will start lighting. Of course, he gives a VERY complete answer. I was answering the question asked.
Click to expand...
I have tried the Grant zener test, on 4 zener's and cannot get the bulb to light. I do not believe all 4 are bad. On another note, how can the zener allow the battery to be charged while on the bike when a charger will have more than the 12.75 breakout voltage?

zener.jpg
 
jimbo said:
I have tried the Grant zener test, on 4 zener's and cannot get the bulb to light. I do not believe all 4 are bad. On another note, how can the zener allow the battery to be charged while on the bike when a charger will have more than the 12.75 breakout voltage?

View attachment 122992
Click to expand...
I would not expect the bulb to light and stay lit, but if you put a voltmeter across it you should see any excess voltage. The Zener does not "turn on", it passes current that is at a voltage higher than it's cutoff.

Grant actually says:

"With the lamp connected as shown in the diagram above, you should see the lamp light up, as the breakdown voltage is lower than the battery voltage, so avalanche current will be allowed to flow.

Very quickly though (around a minute for a 21 watt turn signal lamp, but even quicker for a headlamp) you will see the light go out.

This is because the voltage of the battery has now dipped under the breakdown of the voltage of the zener diode.

If you put your multimeter across the terminals of your battery after this test, you should see that it’s voltage is now under 12.75 volts."

If your battery is under the Zener threshold voltage, you're testing nothing.

If you use the same circuit with a voltmeter across the load (bulb) and you put a charger on the battery that is higher voltage - say 14 volts, then you will see the difference in in voltage between the Zener cutoff and charger voltage.

The Zener's job is to limit the charge voltage to fully charged battery voltage.

In normal use, the Zener is very reliable. I doubt you have four bad.
 
"It looks like my stash of zenors are all NFG."

Seems unlikely that all of them are bad - my original from 1973 still works as designed!
 
MexicoMike said:
"It looks like my stash of zenors are all NFG."

Seems unlikely that all of them are bad - my original from 1973 still works as designed!
Click to expand...
I've seen original zeners die from improper tightening /loosening to/from the frame attachment point .
You need two wrenches , not one . This is to hold fast the central post nut with one , the other to detach/tighten the nut to frame . The small painted wire will break if things are allowed to start to spin .
 
Onder said:
It looks like my stash of zenors are all NFG. Wishing to keep the stock charging system, is there anyone out there willing to make an offer
on a working unit? There seems to be one on ebay, claimed new, that goes for 194 quid! Im amazed some one has not made a run of them off shore as they were fit to nearly every brit bike at one point.
Anybody...? I live in hope.
Click to expand...

Greg Marsh might be a good source for you as he "rebuilds" a lot of bikes in varying configurations.........
 
Torontonian said:
I've seen original zeners die from improper tightening /loosening to/from the frame attachment point .
You need two wrenches , not one . This is to hold fast the central post nut with one , the other to detach/tighten the nut to frame . The small painted wire will break if things are allowed to start to spin .
Click to expand...
I think you are talking about rectifiers?
 
Onder said:
It looks like my stash of zenors are all NFG. Wishing to keep the stock charging system, is there anyone out there willing to make an offer
on a working unit? There seems to be one on ebay, claimed new, that goes for 194 quid! Im amazed some one has not made a run of them off shore as they were fit to nearly every brit bike at one point.
Anybody...? I live in hope.
Click to expand...
all tested.....

www.ebay.com

LUCAS USED + GROUND ZENER DIODE TESTED | eBay

Used genuine Lucas positive zener diode tested and functional. Check back as I am slowly cleaning out a 50 year collection of new and used British motorcycle spares and other stuff collected through the years.
www.ebay.com
 
I couldn't get a satisfactory test using a battery, so I used my Caswell plating power supply, its rated at 15 volts and 25 amps( not sure the amps are really that high and the volts read 15.5 max)

All four zener's got warm, and the breakout voltages were close, however only one passed enough power to glow the filament just a little.

Zenor
Zenor
Zenor
Zenor
 

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