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Jan=2C and others=2C
Thanks for cleaning up my jargin. In my feeble mind the thyrister disconne
ct is just dumping the power from the output. Your explanation shows true
knowledge of these components. Whether it dumps or shorts or snorts=2C I
agree that the problem is not worth repairing. One could try to fix the Du
cati=2C but as you say=2C if its broke=2C it is best to just replace it...
Great idea from Kevin on putting the regulator on the 914 duct=2C or Remi
's idea on an aluminum plate to absorb more heat. However=2C what is the tr
ack record on the others using the GR6 or SH. Without testing on a plane w
ith known current draw=2C specifics on the RPM variations=2C battery condit
ion etc. what is good for one may not work for all. I know Paul has a fair
ly high draw aircraft (probably close to 15 amps)=2C and some extra data wo
uld be nice... However=2C I would like to see all of us not throw good mo
ney after bad or waste our time. My plane just doesn't draw enough power t
o kill the Ducati so I must experiment on more electrically thirsty planes
and listen to the lessons of others.
I have now completed quite a number of aircraft=2C nearly all are running a
nd working well. From the electric side=2C it seems to me we should set a
basic guideline for what to do electrically from the bus supply side for ou
r new owners/builders. Lord knows I have made many compromises using every
thing from split busses to dual alternators to get enough power to run stuf
f. Every client/builder has his own desires on the type of equipment he wan
ts=2C but usually doesn't have a clue on what really happens when all the t
oys get turned on. The Rotax install manual gives one the impression the n
ew Rotax/Ducati combo is a 22 amp 14.2 volt system above 1000 + 250 RPM. I
haven't seen that output at 2000 RPM except before the avionics were turne
d on. (That data was upgraded from the old 13.6 above 2000RPM from my old r
egulator). We know the Rotax / Jabiru charging systems do not produce enoug
h power to charge=2C at low RPM as during taxi=2C pattern=2C and landing ro
ll out with all the stuff on. There is nothing worse than an electrical sy
stem that is depleted due to low RPM running with a slightly old battery=2C
and on final=2C when you key the mic=2C the radio shuts down and EFIS rebo
ots due to a low battery condition brought on by running only 30 minutes at
or below 4000 RPM. On landing roll out you have to shut down everything a
nd run the engine up to talk on the radio. My rule of thumb is "the Rotax
charging system can only produce 15 amps at 13 volts above 4000 RPM" (at 1
8 amps the voltage just begins to drop off a bit) and electrical power requ
irements must be reduced below 4000 RPM or you must have a battery of suffi
cient capacity to supply the deficiency of the charge system. I build a
power requirement sheet with each panel I build or supervise. That works g
reat at cruise=2C but doesn't give the full picture at low RPM/High current
draw phases of flight=2C so we hope the battery was fully charged well pri
or to pattern entry. If you are an amp zealot=2C but still want an aux fuel
pump=2C pitot heat=2C 100 watt landing light=2C strobes=2C heavy draw radi
o (Garmin 430 type)=2C Aux Radio=2C Mode S transponder continuously working
=2C autopilot=2C stereo high quality music system=2C external power plugs f
or our phones=2C I-pads and inflight video system=2C the Rotax charging sy
stem is not going to hack it. Perhaps in the situation above=2C it would be
prudent for a 914 builder (914 can draw 11 amps on its own with both pumps
running) to consider a belt driven alternator of 40 amps=2C and simply red
o the cowl front and keep the Rotax as a backup in case of belt failure. If
you build a 912S airplane with all LED lighting=2C Garmin 255 or Becker Co
m=2C Simple digital Transponder=2C Aux Boost=2C and maybe an autopilot for
cruise only and a paper map=2C then the Rotax / Ducati should be fine. The
GR6 or SH may be better and longer lasting to boot. In my opinion the Rot
ax system can't put out much more than 15 amps or so and as the current inc
reases=2C the voltage output starts to diminish (at least it does in my poo
r old airplane) . Just my thoughts.Bud
> Date: Mon=2C 20 Jan 2014 16:40:25 +0100
> From: jan_de_jong@casema.nl
> To: europa-list@matronics.com
> Subject: Re: Europa-List: Re: Ducati rectifier/regulators
>
>
> Re two-phase bridge rectifier/regulator.
> The 2 thyristors in the rectifier bridge do not short the AC input or
> "dump" anything.
> On the contrary=2C they disconnect the DC output from the AC input when
> the output voltage threatens to exceed the set voltage.
> All output current passes through one branch of one diode and one
> thyristor in series half the time and through the other identical branch
> also half the time.
> Heat development is proportional to the output current and the voltage
> drop across a branch.
> Voltage drops increase somewhat with current=2C so heat development
> increases more than linearly with output current.
> In the Ducati device the diode is reportedly a MR2510 pill (typically
> 0.75V at 10A=2C 0.8V at 20A)=2C the thyristor can be a 2N6504 (typically
> 1.1V at 10A=2C 1.3V at 20A).
> So at 10A the two branches of the bridge are each expected to generate
> 0.5 x (7.5 + 11) = 9.25W (total 18.5W) of heat.
> And at 20A the two branches of the bridge are each expected to generate
> 0.5 x (16 + 26) = 21W (total 42W) of heat.
>
> (
> a failure mode for the Ducati device is reportedly the loss of
> continuity of a diode pill attachment through thermal cycling=3B fitting
> external parallel diodes has been proposed as a solution=3B replacing the
> whole device seems more sensible
> )
>
> Cheers=2C
> Jan de Jong
>
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