Zenor

marshg246 said:

If you're voltage drop is across the bulb then all four Zener diodes are good.

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This is what I am referring to in Grant's paper, not across the bulb

I keep trying to get the point across - the Zener's only job is to pass excess charge current to ground. Maybe this from a Triumph Workshop will explain it better than I've been able to:

As mentioned in the text - bench power supplies are not expensive and very very handy for playing around with bike electrics. Had my C15 running off a bench power supply for testing.

ilikevelos said:

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.

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Maybe you mean a selenium rectifier?? In the early days gallium was used as a detector diode in crystal sets.

All Commandos should have had a Silicon diode rectifier originally.

Crocodile clips are very prone to intermittent connections or very high resistance, I would repeat the test with the proper lucar connectors and ring earth connector.

Torontonian said:

Correct , rectifiers .
Stopped using zeners and rectifiers a long time ago , thanks to solid state equivalents .

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On my '73 Commando, modern, solid state Podtronics "upgrade" produced .2 volts LESS charging output at all RPM compared to OEM Rectifier/Zener... So it was functionally a downgrade!

At low RPM, below the Zener voltage, the only component (ignoring switches, terminals, battery internals and wires) in the charging system causing a voltage drop is the rectifier.

In that way, the original Zener-regulated charging system is efficient. You may get more electrical power at low RPM than with more complicated transistor boxes.

MexicoMike said:

On my '73 Commando, modern, solid state Podtronics "upgrade" produced .2 volts LESS charging output at all RPM compared to OEM Rectifier/Zener... So it was functionally a downgrade!

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Some Zeners regulate the voltage too high.

Less voltage is an upgrade then.

MexicoMike said:

On my '73 Commando, modern, solid state Podtronics "upgrade" produced .2 volts LESS charging output at all RPM compared to OEM Rectifier/Zener... So it was functionally a downgrade!

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I have no love for PODtronics, but that's not why. Having the correct charge voltage across the battery is what's important, not having the most.

When these bikes were built, Flooded Lead Acid batteries were used. Today it's more likely AGM, GEL, or various types of Lithium and they all have different requirements. Overcharging hurts Lead/Acid or the Zener would not be needed. Overcharging the rest not only hurts them but makes them dangerous.

I would not use GEL or Lithium ION and LiFePO4 must be marked for Motorsports.

HRD said:

Maybe you mean a selenium rectifier?? In the early days gallium was used as a detector diode in crystal sets.

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Yep, I misspoke, I was referring to early 20m3 large disc rectifiers that have a larger leakage current than the later silicon ones.

ilikevelos said:

I was referring to early 20m3 large disc rectifiers that have a larger leakage current than the later silicon ones.

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Should be a silicon type 49072A rectifier according to the parts book that was introduced in the early 1960s like the one in my picture only that's a 49072B.
I'm guessing your rectifier is an earlier 47103A or similar type.

" Having the correct charge voltage across the battery is what's important, not having the most."

I agree but in this case both systems were well within the voltage range for effective charging so I'd prefer the higher voltage. On my Commando "charging" voltage (above 12.6 VDC) occurred at idle (headlight off) with the OEM system but was discharging (12.4) with the Pod. At max charge the OEM was 14.6, the Pod was 14.4.

ilikevelos said:

Yep, I misspoke, I was referring to early 20m3 large disc rectifiers that have a larger leakage current than the later silicon ones.

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my early 126XXX Fastback, 20M3 (since sold but a very original example)had a Zener on a large aluminum disc, did you mistake that for a early rectifier?

Why yes I did. I stand corrected. I will note that the 20m3 seems to discharge the battery faster than later commandos and I had always assumed that the rectifier diodes had a larger leakage current. Never had to work on the charging system. The 20M3 still has its original charging system. and last I rode it it was working fine.

I have a background with Honda who used selenium rectifiers into the seventies so just assumed that norton also used them. It is clear that silicon is materially better and by the early 70s had basically replaced selenium and geranium as a semiconductor.

I have not ridden my 20M3 since 2019 because the tank has failed badly enough that it is time for a new one. One is coming (I hope) from RGM but I ordered it before thanksgiving, it was shipped at the end of november but it still tied up in customs/tariffs today. Customs has the maddening practice of only talking to rgm who has been paid and leaving me in the dark. I imagine I will get the shipment soon but need the parts.

PS picked up a nice mark 3 last week. Will try to title next week.

Happy new year all.