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kenryan
Joined: 20 Oct 2009
Posts: 426
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 Posted: Thu Sep 01, 2016 10:29 am Post subject: Ducati Regulator |
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For those interested in learning more about the Ducati regulator used in Rotax installations, the following post appeared on rotax-owner.com forum. Note that there is an embedded link that goes to some technical information.
<snip>
The 22A "Max" is a continuous current rating.Ducati uses a power MOSFET as a switching regulator for the DC output. See the BUZ60 datasheet ... 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'.
We haven't tested it in our lab here, but I suspect if the rectifier-regulator module was actively cooled with a small computer fan mounted to the heatsink, you would get closer to the rated performance. And I'm not an electrical engineer but I have a feeling that the longevity of these regulator units (aside from heat dissipation factors!) is directly proportional to the quality of the 22,000uF Capacitor that smooths the ripple from them.
<snip>
For me, this prompts the question: How does one determine the quality of the 22,000uF capacitor?
Ken
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edpav8r(at)yahoo.com
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| Posted: Thu Sep 01, 2016 12:50 pm Post subject: Ducati Regulator |
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On Sep 1, 2016, at 11:27 AM, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
| Quote: | For me, this prompts the question: How does one determine the quality of the 22,000uF capacitor?
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As I recall, our tutor here on the AE-List isn't convinced-by-data that this capacitor adds value to the airplane electrical system design equation, but he can chime in with those details.
That said, if I were going to use one, this is how I would narrow it down:
Pick from among the well-known top-tier manufacturers of aluminum electrolytic capacitors (Panasonic, Nichicon, Rubycon, United Chemicon, EPCOS, Cornell-Dubilier and Würth Elektronik). Anything sold by a reputable electronic component supplier will be fine. Avoid suspiciously cheap parts on eBay, AliExpress or similar outlets.
Some key specs to look for:
- Rated voltage. For a 14V airplane, you'll want a capacitor rated 16V minimum, and you'd be safer with 25V. Higher voltage ratings drive up cost.
- High ripple current rating, hand-in-hand with low equivalent series resistance (ESR). Generally, as ripple current goes up, ESR goes down. This spec expresses the capacitor's ability to absorb and release current as demand varies.
- Good temperature-over-time value. This spec starts at 85 deg C for ~1,000 hours and goes up from there. The higher the temp and longer the time, the greater service life you can expect.
- For ease of mounting and connection, you'll probably want a capacitor with screw terminal connections, rather than PCB pins.
A quick search of Digi-Key shows five options that meet all of these criteria, ranging in price from $25 to over $300. The $25 EPCOS part would be my choice. It's rated for 40V, has very low ESR of 13mOhms and a ripple current rating of 15A, and connection is via screw terminals. It's rated for 20,000 hours at 105 deg C, so it will probably outlive us all behind your panel.
See here: http://preview.tinyurl.com/jyf4nhs
Eric
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nuckolls.bob(at)aeroelect
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| Posted: Sun Sep 04, 2016 10:14 am Post subject: Ducati Regulator |
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At 01:27 PM 9/1/2016, you wrote:
| Quote: | For those interested in learning more about the Ducati regulator used in Rotax installations, the following post appeared on rotax-owner.com forum. Note that there is an embedded link that goes to some technical information.
<snip>
The 22A "Max" is a continuous current rating.
Ducati uses a power MOSFET as a switching regulator for the DC output. See the BUZ60 datasheet ... 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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