Why not the original rectifier and zener?

Stephen Hill said:

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,

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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.

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?

Stephen Hill

Um, My vote for "nothing wrong with the way its is".

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.

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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.

Stephen Hill said:

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.

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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.

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.

Dave
69S

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.

Niagra,
I'm sure the zener could fool your automatic charger, since the charger is most likely working off voltage and maybe even current vs. time if it's smart. The zener could be draining current that the charger thinks is going to the battery. Probably best to charge batteries with the fuze out, especially with smart chargers.

I only use supplies with adjustable voltage and out of the circuit unless I'm charging Ni Cad or Lithium batteries in that case I use smart chargers. Maybe I'm wrong, but sometimes I think I'm smarter that the chargers, but I'm not sure about that, just ask our Terrier, he knows more than I do. I do know that my slow charger for the NiCad battery works better than the fast charger which does all kinds of smart things including measuring the battery temperature while it's charging.

More than you want to know.

Dave
69S