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steve(at)tomasara.com
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 Posted: Thu Dec 11, 2014 1:53 pm Post subject: Alternator Disconnect Z17 vs Z20... |
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Greetings,
I'm currently working on wiring up a Quickie with a Rotax 503 (and a
glass panel, go figure...). The two architecture diagrams that look
appropriate to start from are Z17 "Small Rotax System" (sounds right...)
and Z20 "Small Jabiru System".
They are basically the same EXCEPT they way the alternator is
disconnected (Z17 is downstream of regulator, Z20 is upstream of the
regulator).
I might be mistaken (please correct me...) but it also appears both
diagrams are assuming more of a diode bridge than a real regulator as
they both show a 20,000uF cap on the output of the regulator.
My questions: 1) What's the significance, if any, of the different
approaches to the alternator disconnect? 2) If I use Rotax 264 870
regulator (as opposed to the 866 080 bridge) is the cap still
appropriate (it's not shown in Rotex's wiring diagrams?
All thoughts welcome.
Thanks,
Steve Stearns
LongEz N45FC (working on a Quickie)
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user9253
Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan
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| Posted: Fri Dec 12, 2014 2:57 pm Post subject: Re: Alternator Disconnect Z17 vs Z20... |
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The Z-17 and Z-20 diagrams that I have both show the relay between the regulator and the battery side of the starter contactor. Z-16 has the relay between the dynamo and the regulator, thus switching the AC current. Either way will work.
The 20,000 microfarad capacitor helps to smooth out the pulsing DC from the single phase dynamo. Even if it is not required (but probably is), installing it will not hurt anything. Z-17 and Z-20 have voltage regulators which also rectify the AC into DC. I found this article: http://www.pra.org/publicdl/engines/477%20electrical%20output.pdf
I think that a voltage regulator should be installed rather than just a bridge rectifier.
Joe
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Joe Gores |
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nuckolls.bob(at)aeroelect
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| Posted: Sat Dec 13, 2014 9:43 am Post subject: Alternator Disconnect Z17 vs Z20... |
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Greetings,
I'm currently working on wiring up a Quickie with a Rotax 503 (and a
glass panel, go figure...). The two architecture diagrams that look
appropriate to start from are Z17 "Small Rotax System" (sounds right...)
and Z20 "Small Jabiru System".
They are basically the same EXCEPT they way the alternator is
disconnected (Z17 is downstream of regulator, Z20 is upstream of the
regulator).
I might be mistaken (please correct me...) but it also appears both
diagrams are assuming more of a diode bridge than a real regulator as
they both show a 20,000uF cap on the output of the regulator.
All z-figures for permanent magnet alternators depict rectifier/regulators as the device of choice for converting the PM alternator's output to DC and then controlling it in a manner friendly to batteries and avionics. Specifications for the 503 state:
GENERATOR OUTPUT: 170 W AC at 6000 rpm and 13.5 V RMS
RECTIFIER- REGULATOR: (optional) a.) #9103 requires min. load 12 W (1 amp) to regulate b.) #9251 requires no min. load
Are you planning to use one of these two rectifier/regulators or some other product? 170 watts of output probably translate to about 14A maximum available output from the r/r . . . do you plan electric start? Have you conducted a load analysis of all planned accessories to determine that you have enough engine driven power to support the load?
My questions: 1) What's the significance, if any, of the different
approaches to the alternator disconnect?
None
2) If I use Rotax 264 870 regulator (as opposed to the 866 080
bridge) is the cap still appropriate (it's not shown in Rotex's wiring diagrams?
Where might I find data on these two products? They're not cited as one of the two options in the spec sheet I downloaded. I'm not sure why anyone would ever use an ordinary bridge rectifier between their PM alternator and any other accessory. Can you point me to any literature that describes/recommends this?
The capacitor has been a legacy feature of Rotax installations on airplanes for decades. But the little testing I've been able to do on PM alternators and rectifier/regulators cannot confirm the value of adding this device. I'm planing to get another look at the question with more sophisticated equipment in the not too distant future.
Bob . . . [quote][b]
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steve(at)tomasara.com
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| Posted: Sun Dec 14, 2014 7:51 am Post subject: Alternator Disconnect Z17 vs Z20... |
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Bob N. asked:
"Are you planning to use one of these two rectifier/regulators
or some other product? 170 watts of output probably translate
to about 14A maximum available output from the r/r . . . do
you plan electric start? Have you conducted a load
analysis of all planned accessories to determine
that you have enough engine driven power to support
the load?"
Steve replies:
The 264 870 regulator is listed in the engine manual (all I have is hard copy) and on line from rotax suppliers. I don't have a spec sheet on it but given the pictures (big module with a heat sink) it's more than a diode bridge. The engine manual says it doesn't require any load to be in regulation. Our configuration will have electric start and it looks like it needs a good bit of juice per the manual (16AH min battery 10mm2 wire, which looks to me like 2AWG. Engine up front, battery in back so 20' of heavy cable. <sigh>. The load analysis shows there is plenty of juice (Dynon D60, low-power transponder, radio and engine monitor, LED tip lights and only one halogen on the tail).
There are clearly (at least) two version of the 503 (as older one removed has one spark plug per cylinder and the newer one installed has two). If I run across a link for the manuals I have I'll forward them to you.
New sanity-check question:
The rotax documentation specifies a 16A fuse between the regulator and ship loads (including battery). I'm assuming the location of this fuse is determined by the same factors as an ANL on an alternator equipped ship and, as such, I've put the fuse next to the battery in back, not up front with the regulator. Is there anything about a PM dynamo/regulator combination that would drive putting the fuse up near the regulator? (I still would want something in back near the battery...)
Thanks for your help,
Steve.
[quote][b]
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steve(at)tomasara.com
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nuckolls.bob(at)aeroelect
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| Posted: Sun Dec 14, 2014 8:19 am Post subject: Alternator Disconnect Z17 vs Z20... |
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| Quote: | Thanks for your help,
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Good data dump! Need to run a mini-van load
of grandkids to ICT but will pray over your
posting a bit this evening.
Bob . . .
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user9253
Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan
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| Posted: Sun Dec 14, 2014 9:11 am Post subject: Re: Alternator Disconnect Z17 vs Z20... |
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Perihelion Design sells lightweight copper-clad cable. http://www.periheliondesign.com/fatwires.htm
| Quote: | | Is there anything about a PM dynamo/regulator combination that would drive putting the fuse up near the regulator? |
Alternators and dynamos are self current limiting. A dynamo rated at 13 amps will not put out much more than that even if the output is shorted. So there is no need to put a fuse near the dynamo or regulator. A fuse is needed near the battery to protect the wires from excessive battery current if a wire is ever shorted to ground.
Joe
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