Why not the original rectifier and zener?

Classic Norton Commando Motorcycles.

Re: Why not the original rectifier and zener?

Postby gripper » Sat Jan 28, 2012 1:54 pm

Well worth fitting a couple of mini relays and running the headlight supply direct from the battery. I was loosing 1/2 volt (0.5v) through the ignition switch, ammeter, (now gone) light switch, and dip switch. 0.5 Volt is the difference between yellow and white when it comes to headlights. I bought a HID headlight on ebay for about £40 but forgot about the +ve earth so put it on my Rotary. Now that IS bright. Only uses about 35 watts as well.

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Re: Why not the original rectifier and zener?

Postby ludwig » Sat Jan 28, 2012 2:06 pm

L.A.B. wrote:.;What can you remember?


eh .. the rules ?

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Re: Why not the original rectifier and zener?

Postby bill » Sat Jan 28, 2012 2:09 pm

I answered this in your earlier post. is it a MK3? if it is pre MK3 it will NOT work.

gtsun wrote:I'm fitting a solid state unit with my new Sparx alternator today just because it came with the Alternator & my old one is a bit worn. Still not sure what will happen to my asimilator light. If it just won't come on, or will stay on etc. I'm wiring the alt/reg directly to the battery through fuses.
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Re: Why not the original rectifier and zener?

Postby L.A.B. » Sat Jan 28, 2012 2:14 pm

ludwig wrote:
L.A.B. wrote:.;What can you remember?


eh .. the rules ?


That's encouraging - for a while I thought you might have had a momentary lapse of memory.
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Re: Why not the original rectifier and zener?

Postby xbskt » Sun Jan 29, 2012 7:20 pm

thank you all for the input.
I'll try the originals after they've been tested with my meter.

Jeff
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Re: Why not the original rectifier and zener?

Postby DogT » Sun Jan 29, 2012 7:41 pm

I'm using my original harness with a few new ends, the original rectumfrier and zener on the Z plate. Removed the MC2. With a Yuasa AGM battery from Clubman, less the capacitor, Pazon ignition with no condensers and it's running fine. The Yuasa 9AH battery is sitting on the bench as I write and has 12.8 Volts on it after the summer of riding but only 500 miles and a little charging. Can't complain about that.

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Re: Why not the original rectifier and zener?

Postby Stephen Hill » Sun Jan 29, 2012 10:50 pm

To anwer the questions posed:
Reason 1.
The original rectifier is less efficient than modern replacement bridge rectifiers, so should result in a stronger charge to the battery, when required. In a marginal system, this is a good thing.

Reason 2.
The zener diode is a crude method of disposing of additional voltage. When I connect a smart battery charger to my bike, with the zener diode in the system, the battery never reaches a full charge. Conclusion: the zener is dumping voltage prematurely. In a marginal system, not a good thing.

Having said that, I still run the original items in my bikes and watch the battery voltage like a hawk, especially when riding at night.

Additional details on the "weaknesses" of the original rectifer and zener pasted below.

Stephen Hill


If charging is a problem for you, you may want to replace your probably-dried-out selenium rectifier with a Radio Shack replacement. Bridge rectifiers being a common element in electronics, RS supplies a 10 and 20 Amp replacement in modern solid-state silicon version for less than a 10 dollar bill. Be sure to mount it so that it can bleed the heat it produces into an aluminum plate which you cleverly build as a mount. The earlier RS bridges had spade connections, but the later ones seem to be straight wires, so you'll have to solder the wires on. The terminals are marked + for the one you'll ground, - for the one you'll connect to the battery -, and the ones marked AC may be connected either way to the output from the alternator. Also, be sure to "heat sink" the heat from the soldering iron by using your third hand to clamp a pair of needle nose pliers to the component side of the soldering site. Once you're done, you'll likely find that this little improvement makes quite a difference.

If your system voltage is still low after all this, you may want to try disconnecting your Zener diode. The purpose of this baby is .... wait for it ....... to _dispose_ of excess voltage, so that your charging system won't overcharge your battery, burn out your lights, etc. Although hilariously funny to those who find themselves without the juice to get home on dark nights, this is actually a truth for some. I've had batteries boil with the Zener disconnected, even with the lights full on, so be sure to check your charging voltage after you've replaced the diode, and find out if you need to disconnect the Zener. Theoretically, it shouldn't draw any current at all below it's "knee voltage" of 13.8 or so. The more savvy may want to put an ammeter in the circuit to the Zener, and see if there's any current draw below this voltage.

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Re: Why not the original rectifier and zener?

Postby swooshdave » Sun Jan 29, 2012 11:06 pm

Let's see, the original parts were made by... wait for it... Lucas.

Need I say more?
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Re: Why not the original rectifier and zener?

Postby L.A.B. » Mon Jan 30, 2012 4:13 am

Stephen Hill wrote:The original rectifier is less efficient than modern replacement bridge rectifiers

Additional details on the "weaknesses" of the original rectifer and zener pasted below.


If charging is a problem for you, you may want to replace your probably-dried-out selenium rectifier with a Radio Shack replacement. Bridge rectifiers being a common element in electronics,



There is a commonly held belief that the original Lucas rectifier is selenium type - and this is simply not correct.
The standard Commando multi-plate rectifier is a silicon diode bridge rectifier as fitted to British motorcycles from 1962-63 onwards.

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Re: Why not the original rectifier and zener?

Postby Stephen Hill » Mon Jan 30, 2012 5:06 pm

Right, silicone, not selenium. The question is efficiency. Which is best answered by measuring the output of the old vs the new. Or by somebody familiar with both technologies. Anybody?

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Re: Why not the original rectifier and zener?

Postby motoalchemist » Mon Jan 30, 2012 5:40 pm

Um, My vote for "nothing wrong with the way its is".
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Re: Why not the original rectifier and zener?

Postby Niagara850 » Tue Jan 31, 2012 6:23 pm

Reason 2.
The zener diode is a crude method of disposing of additional voltage. When I connect a smart battery charger to my bike, with the zener diode in the system, the battery never reaches a full charge. Conclusion: the zener is dumping voltage prematurely. In a marginal system, not a good thing.


AHA! I wondered why my Trickle charger would never get the battery to a full charge in the bike but would when I have hooked up the battery on the bench for the winter. Learn something every time here.
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Re: Why not the original rectifier and zener?

Postby L.A.B. » Tue Jan 31, 2012 7:05 pm

Stephen Hill wrote:When I connect a smart battery charger to my bike, with the zener diode in the system, the battery never reaches a full charge. Conclusion: the zener is dumping voltage prematurely.


This is a normal characteristic of the Zener diode which should start to become conductive above 12.75V (check your manual?), the amount of current passed by the Zener increases as the system voltage rises and probably why the charge from a smart or trickle charger won't fully charge the battery with the Zener connected.
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Re: Why not the original rectifier and zener?

Postby DogT » Tue Jan 31, 2012 7:48 pm

Hmmm. I'm not sure when my zener starts conducting, but I'll check, however, I can get 14.4VDC on my zener at 1.5A, which should be plenty to charge a battery unless the charger is not putting out enough current. My charger is putting out about 1.5A, and that's the small one. I usually use a 5A one which will charge the 8AH in 1 or 2 hours, depending on it's state. However, I usually have the fuse off which can make a difference, but a decent charger should be able to handle the current unless it's a 50ma trickle charger.

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Re: Why not the original rectifier and zener?

Postby Niagara850 » Wed Feb 01, 2012 8:15 pm

Very Interesting, I'm using a Schumacher SFM-1562A 1.5a Automatic Charger. According to its specs the Maximum Charge Voltage is 12-14.8 V. The Maintenance Voltage is 12 - 13.3 V. If I am reading the Zener testing section correctly in the manual , the diode in proper spec can be bleeding off 2a ranging from 13.5 -15.5 V, and at a lesser rate down to 12.75V when it should be 0a.

As the specs overlap, a properly operating Zener can bleed off enough current so that this particular charger won't ever charge the battery enough to click over to Maintenance mode. It must be very close to the changeover voltage as the charger never went into Abort mode, which is when the charger determines the battery can't be fully charged. Although I can't say that for sure as no spec was provided to state how the Abort mode is triggered.

I started with a fresh battery at the beginning of last years riding season and would put it on the charger in between rides. I had it on for days and thought the charger was defective and would only hook it up for a few hours every few days. When I pulled the battery for the winter, the charger worked normally. I figured the electrical system was leaking current somewhere, not understanding it is by design to prevent overcharging.
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