Why not the original rectifier and zener?

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xbskt

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Hello to all,

So what is it about the factory rectifier and zener diode?
It seems to be a matter of course that these items are replaced when doing ay electrical rehab on a Commando.
Why?
I
As an electrician I understand the concept of their operation and see no reason they aren't capable of doing the job.
Back in the day was the rectifier found to regularly crap out? Did Zeners fail at regular intervals keeping riders from getting to the watering hole?
If they are junk for a reason then I'll build a wiring scheme on XBSKT 2 without them.
If they have a bad reputation due to poor understanding and bad connections in the past perhaps I'll go ahead and use one of the rectifiers and Zeners that have piled up on the "electrical" shelf.
If I had to guess the rectifier is fine if connected correctly. It's really a basic design but maybe you all and history can enlighten me.
Honestly, I'd rather spend the budget on nice wheels.;]

Have a good day,

Jeff
 
Jeff,
I am running the original gear, but I find the battery does overcharge and looses electroloyte on longer runs. I am contemplating a Boyer powerbox in the future, to fix the charging and also I believe I can get a unit to activate the charging light. So this takes out the dodgy assimilator, that has never worked.

So yes you can use the originals, but keep an eye on the battery?

Cheers Richard
 
xbskt said:
So what is it about the factory rectifier and zener diode?
It seems to be a matter of course that these items are replaced when doing ay electrical rehab on a Commando.
Why?
Click to expand...

Because they could be 40 years old?

There's nothing basically wrong with the original rectifier - except that it can be easily damaged. It is a silicone diode rectifier (not the less reliable selenium type that some people appear to think it is).
 
I'm running the originals as well. Charges fine even when always riding with the headlamp on (local law). I do admit to using a battery tender occasionally in cold months.
 
If they are within specs when checked with a decent meter, they will be just fine.

MAKE SURE TO HAVE A FULLY INTACT BATTERY VENT DRAIN TUBE, AND ROUTE IT CLEAR OF THE BIKE SO YOU DON'T TRASH YOUR EXHAUST AND/OR OTHER BIKE PARTS WITH ACID RESIDUE.
 
L.A.B. said:
xbskt said:
So what is it about the factory rectifier and zener diode?
It seems to be a matter of course that these items are replaced when doing ay electrical rehab on a Commando.
Why?
Click to expand...

Because they could be 40 years old?

There's nothing basically wrong with the original rectifier - except that it can be easily damaged. It is a silicone diode rectifier (not the less reliable selenium type that some people appear to think it is).
Click to expand...

Hi Jeff
+1 on that they can be easily damaged. If the rectifier body twists you damage it. If you over torque the zener or if it is not grounded properly then you may have issues.
Regards,
CNN
 
I seem to remember a diode on my original rectifier going open circuit when it was about ten years old and I replaced it with the solid state unit that's still on there. The twin zeners on my MkIII have been replaced once because they were looking a bit corroded and tatty but they still worked fine. They sit on nice big heat sinks and I've never had trouble with them. I see no reason to change.

The whole charging system is much more reliable than most Japanese bikes of the same era. I really don't know where the bad name came from.
 
ludwig said:
GP : a battery with a vent tube ??
Can"t remember the day I"ve seen one of those ..
Click to expand...


I can't remember ever seeing a wet lead-acid motorcycle battery that did not have a vent for a tube?
 
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.
 
You don't see a whole lot of "survivor" britbikes without acid stains on the pipes due to bad routing of the battery vent tubes.
 
I'm using the originals and they work fine...but also wired in an LED voltage monitor so if they die I'll know right away voltage-monitor-demo-video-t7576.html
have heard of batteries boiling when the zener fails. Electrolytic capacitors often go bad with age, but the rectifier and zener diode should not
 
ludwig said:
L.A.B. said:
..I can't remember ever seeing a wet lead-acid motorcycle battery that did not have a vent for a tube?
Click to expand...

I can't remember that either .
Only , I can't remember the day I've seen one of those .
The last time I fitted a bettery with a vent tube was ..mm ..can't remember ..
Click to expand...

:?

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

gtsun said:
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.
Click to expand...
 
thank you all for the input.
I'll try the originals after they've been tested with my meter.

Jeff
 
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.

Dog
69S
 
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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