which uC brand should I use ?

Hero999 said:

But they contained mercury encases in an glass envelope which produced lots of dangerous UV radiation and had to be operated the right way up; not very suitable for automotive used.

Mercury arc valve - Wikipedia, the free encyclopedia

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Hero999 Nil - ThunderChild One

Metal rectifiers, no kind of valves at all - used in battery chargers, rectifiers from alternators, TV's, record players, anywhere a rectifier was required. Easily made larger for higher currents, and easily stacked in series for higher voltages.

BTW - have you googled, and checked sites like this one?

https://ludens.cl/Electron/dynareg/dynareg.htm

Nigel Goodwin said:

Hero999 Nil - ThunderChild One

Metal rectifiers, no kind of valves at all - used in battery chargers, rectifiers from alternators, TV's, record players, anywhere a rectifier was required. Easily made larger for higher currents, and easily stacked in series for higher voltages.

BTW - have you googled, and checked sites like this one?

Dynamo Current and Voltage Regulator

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Nigel, How did those metal rectifiers work ? I never really understood them, I'm aware of them simply because my dads old car battery charger had once which I helped him replace for a silicone one when it blew.

I've seen that website before, it is based on a positive earth system which makes life very easy when designing with semiconductors, unfortunately I have to work to a negative earth. at the end of the day the simplest solution was my original uC version with a little tweaking to the program.

Nigel Goodwin said:

Hero999 Nil - ThunderChild One

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Careful Nigel you don't know what your starting, Hero999 and myself know each other in the "real" world (although me "met" here first and consequently met through other channels as a coincidence)

Here's a quote from a dictionary:

a rectifier consisting of laminated plates of metal, usually iron, that have been coated with selenium on one side, with rectification taking place because the flow of electrons from the conductive metal to the selenium occurs more readily than the flow in the opposite direction.

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so what sort of voltage drop do they have ?, are they less copmpact than Sillicone ? I assume so as we no longer use them and i guess their simplicity would rule

Thunderchild said:

...are they less copmpact than Sillicone ? I assume so as we no longer use them and i guess their simplicity would rule

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Yes less compact. The first place I seen selium rectifiers was in the "transformers" (power pack would be a better term) used in slot car racing. There life span seemed shorter.

Thunderchild said:

so what sort of voltage drop do they have ?, are they less copmpact than Sillicone ? I assume so as we no longer use them and i guess their simplicity would rule

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Voltage drop was considerable, as they were low voltage, so most were a big stack in series. They were MUCH less compact, something similar to a BY127 or 1N4007 would be six inches long and about an inch square. You could often smell when they failed, as selenium gives a VERY pungent odour

As a young engineer a lot of my time was spent replacing faulty metal rectifiers in record players, you removed it and fitted a piece of tag strip with a BY127 and a wirewound resistor in series.

Thunderchild said:

so what sort of voltage drop do they have ?, are they less copmpact than Sillicone ?

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Silicone is used in breast implants and doesn't make very good diodes.