I have followed this discussion with great interest and with an
increasing sense of Dj vu.
When the issue of regulator/rectifier failures occur withing the Rotax
community, the standard fix seems to be to simply replace like with like
(at elevated Rotax pricing) and fly on until the next unit fails.
Up until about five years ago, nearly all modern Japanese motorcycles
used the same technology as that found on the Rotax 91x series engines,
permanent-magnet generators controlled by SCR rectifier/regulators. It
may come as some surprise that for an industry renowned for precision
and reliability, nearly all of these major motorcycle manufactures have
at some time, been plagued by problems with their SCR based
rectifier/regulators failing and burning out alternators and wiring,
cooking batteries and in extreme cases, squirting unregulated AC into
the wiring loom and blowing up ECUs. It was just such a failure that
"sparked" my interest :-(
Known as "Shunt Regulators" the SCR technology runs extremely hot and
requires more cooling air than modern styling and space allows.
The solution was a move towards MOSFET controlled regulators and the
numerous web-based one-make discussion groups were full of information
and advice on the reasons for failure, the benefits of the change and
practical advice on how to convert.
It was by trawling these groups that I was able to build up a good
understanding of how these R/Rs worked, what was causing the problem and
what the potential solution might be. I compiled what I considered to be
the best informed snippets of information into the attached document.
The first half gives an overview of a typical design of an SCR
Rectifier/Regulator for use on a permanent-magnet generating system and
the second half discussed the relative merrits of SCR versus MOSFET.
It would be interesting to know which technology the the after-market
Schicker and Silent-Hektic R/Rs use.
Nigel
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