dlj04(at)josephson.com
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 Posted: Wed Sep 07, 2016 3:00 am Post subject: Ducati R/R deficiencies |
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On Sep 6, 2016, at 2:04 PM, Bob Nuckolls wrote:
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I took some time to finish an article I started some
years ago explaining my perceptions of thermal management
deficiencies in the Ducatti R/R supplied with Rotax
engines.
http://tinyurl.com/zvkoh4p
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Indeed, and thanks. I have disassembled a couple of these and found the same problems. There seem to be two heat-related failure modes: (a) the semiconductors get too hot for the thermal resistance between junction and free air, and (b) the solder joints are poor between the leads of the devices and the pc board, and between the pc board and the connector, leading to localized heating. In two of the cases I have, the solder had melted often enough that the board was charred, and the component leads were not well cleaned so the solder had dirt and oxidation in it. They are no doubt caught up in European lead-free solder requirements too.
To be fair these are inexpensive regulators designed for motorcycles where they are often installed in free air -- at the top of the firewall where they are usually found in airplanes is not a particularly cool place for them. Charging a motorcycle battery, plus a headlight, and ignition, is something they can handle well. Rotax can't design/build everything, it would be even more expensive than it is if they did (ever priced a wastegate controller for a 914?) and with proper cooling and low current drain the Ducati r/r is not too bad. Once it starts to fail due to heat however it's downhill from there.
The Silent Hektik device seems to be a good replacement although I have not used one -- they will not ship to the US and seem not too interested in the light aviation market anymore.
I have designed a more robust version using low Vf diodes and scrs and will probably have some test hours on one by the end of the year. The basic design is OK, I agree with Bob that it just needs better thermal management.
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