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1. 11:15 AM - Re: Ducati Regulator (Robert L. Nuckolls, III)
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Subject: | Re: Ducati Regulator |
At 01:27 PM 9/1/2016, you wrote:
>For those interested in learning more about the
>Ducati regulator used in Rotax installations,
>the following post appeared on
><http://rotax-owner.com>rotax-owner.com forum.
>Note that there is an embedded link that goes to some technical
information.
>
><snip>
>The 22A "Max" is a=C2 continuous=C2 current rating.
>
>Ducati uses a power MOSFET as a switching
>regulator for the DC output. See the=C2
><http://www.futurlec.com/Transistors/BUZ60.shtml>BUZ60
>datasheet=C2 ... But if you peruse the graphs
>there, it appears that the device's 22A 'pulsed
>current' rating is dependent on pulse width
>(duty cycle), and more than anything the ability
>of the device to dissipate heat. The device
>itself can only (safely) supply its maximum
>rated output if its own case temperature is kept
>to 47C or below. Assuming the module package is
>100% efficient at drawing the heat away from the
>MOSFET, you can extrapolate from the MOSFET
>performance curves that it shouldn't put out
>more than about 17.6 amperes at the "maximum"
>allowable module temperature of 80C.So I think
>your estimate of 16A continuous is a very good 'conservative real-world
number'
I checked the article cited. Unfortunately, a few
items of fact cited are poorly interpreted. The BUZ60
device is inappropriate to this task. It's a HIGH
voltage, LOW current device with very HIGH on
resistance. There are hundreds of devices more suited
to this kind of service.
The Ducatti regulator is demonstrably under-cooled. The
samples seen in a disassembled condition appear to
depend on POTTING COMPOUND to conduct heat energy from
the switching devices to the outside world via what radiating
fins do exist on the housing. This is a mystifying concept
that was tried by this writer only once . . . a long time
ago and never since.
My friendly CNC driver has carved out some parts that
fit into this proof of concept package
http://tinyurl.com/zcxn6lr
I'm exploring options for a PM r/r wherein the
ability to control generations and rejection
of heat are know quantities and tailored to
design goals. Thermal resistance between the
silicon junctions and outside world will be
minimized . . there will be no potting
compound.
It is a mystery as to why the Rotax/Ducatti marriage
has persisted for so long . . . but the answer
is immaterial. It time to figure out how to do
better.
Bob . . .
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