850 Commando Rectifier replacement

I just bought three last week at Radio Shack about 3.34 each. Very small and light you could carry this on the bike (insurance) with you. I used your thread to make a point Mark, you need to find a way to understand a working knowledge of the system alternator to rectifier to battery to ignition and lights via key and kill. And tuning all these to suite you’re riding style. So if you’re riding long straight roads in the day time with no light and you like 80MPH your answer would be different that if you bar to bar with a spare helmet. If you’re old system is not broke and you have not changed over to an AGM than your good. But selecting parts off the self to make a system that has balance for your riding style that is an endeavor that requires more than a volt meter.

bpatton wrote: I've got a BSA C11G that has a huge rectifier that looks like a stack of flapjacks.

That description of a British MC rectifier is the best I've ever heard!

daveparry said:

If you look at the fins you can see the individual silicon diode's attached to them, on the selenium ones the fins themselves were the active component's.
Dave.

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Then I stand corrected. Silicon it is.

So to Mark's original question, the recitifier and zener don't really "wear out", and I would not replace them on principle just for age. The zener can be disconnected if it shorts out on the road, and if you run with lights on the battery won't over charge (you can get home without it). I did have a rectifier fail on the road once (one diode opened), so if you're paranoid about that you could carry a spare Radio Shack rectifier in your kit. They're small and easily changed on the road.

norbsa48503 said:

I just bought three last week at Radio Shack about 3.34 each.

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Part Number?

Dave the part # is 276-1185 a Full-Wave Bridge Rectitier 25 amps 50 Volts.

grandpaul said:

The solid state regulator/rectifiers still do the same old job.

Dump excess voltage in the form of heat.

Hence, "mount in a well ventilated location".

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Not quite, the zener diode takes all the excess and dissipates it as heat, the newer rectifier/regulators are series pass which means they will "pass" the required current on to the output and limit the output voltage to a set value (14.7 volts usually). Sure as more power is drawn, they will heat up, but nowhere near what the zener has to put up with.

The bad thing about the zener, aside from wasting power, is that the electrical system is always working full time, the alternator is at peak, the rectifier is at peak, the wires and connectors are carrying maximum current.

Jean