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kevann(at)gotsky.com
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 Posted: Wed May 06, 2009 5:21 pm Post subject: Radio Noise Problems - Rotax 914 with Dual Bolt-on Alt. |
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Hi Darin,
I have the same setup on my 914 Europa
Do you have a good ground strap (fat wire) from the engine block to the
battery?
Kevin
On Wed, May 6, 2009 at 8:32 AM , darinh wrote:
| Quote: |
<gerns25(at)netscape.net>
I am having a problem I hope someone can help me with. I am not an
electronics guy by any means but I did wire my panel and everything
has worked well up to this point. Here is a description of the system
and the problem:
System:
The engine is Rotax 914 UL and has 40 hours on it since new along with
all components. I have a 40 amp alternator (Nippondenso modified by
Flightcrafters I will refer to as the ND Alt.) mounted to the back of
the gearbox where you would typically mount a vacuum pump. The gear
ratio is .43:1 so the alternator does not really come alive until
about 3200 engine rpm or so and then will not produce quite its rated
capacity due to the gearing. I have set the engine up as a dual
alternator system for redundancy so the backup is the Rotax (onboard)
generator. Both the ND alternator and the Rotax generator are wired
to a relay and a 3 position switch for selection of Main Alt (ND Alt.)
- Battery - and Aux. Alt. (Rotax Generator). I have the large
capacitor installed on the Rotax generator lead and was under the
impression that the ND alternator does not need the capacitor as it is
rectified and regulated internally. Again, everything has worked
great up until now.
Problem:
Now the problem. At about 38 hours total time my "idiot light" lit up
while cruising at 5000 rpm and 31" MAP. The EIS indicated that my oil
pressure was too low - 18 psi (55 - 65 psi is normal). Litterally in
the course of a couple seconds, the indication went from 18 psi to 75
psi and continued to fluctuate rapidly between the mid teens to mid
90's. I new at this point that is was a faulty indication and not
actual loss of oil pressure. Upon landing my suspicions were
confirmed as all oil lines were tight and I had lost no oil. A quick
check of the system indicated that oil was still circulating. The OP
sender was suspect and was replaced and moved from the engine to the
firewall to minimize vibration and heat fatigue. The next flight
showed OP as normal. All good right? Wrong. The next flight the oil
temp sensor started fluctuating rapidly also...210 degrees to over 300
then back to 210 within a second or two. I really didn't think that
the temp sensor was going!
bad but really didn't have any other idea of what it could be. As I
was sitting there idling, I switched from the ND alt. to the battery
position and the temps immediately stabilized. Next I switched to the
Rotax onboard generator and everything stayed normal....then went back
to the ND Alt. and the problems came back. With this, I pinned the
problem on something to do with the ND alternator.
On the ground I did some run up tests and found that when the ND
alternator is providing power my oil temps are either abnormally high
or abnormally low depending on rpm setting (high rpm = high temp. low
rpm = lower temp). Again, with the Rotax onboard generator providing
power, all is normal. Then, during one of my runups, my indicated
system voltage plummeted while running on the ND alt. I switched back
to the Rotax generator and voltage came right back to 13.8 so I knew I
had some type of alternator failure. I removed the ND alt. and found
that one of the copper output leads from the coil was completely
broken. At this point I thought I had found my problem as obviously a
broken lead would cause weird voltage issues and possibly mess with my
engine sensors. The alternator was repaired by a reputable shop but
because it has a spline gear he could not turn it up to check the
rectifier/regulator.
I installed it and am still having the problems with oil temps
fluctuating wildly and to add to it, I have a ton of noise in my radio
when at cruise power settings. During a test flight today, the tower
told me my transmissions were broken and unreadable with a high
pitched wine. Isn't this classic alternator interference? By the
way, I have traced all grounds on the senors (most ground through the
engine) and this has checked out. So I don't think it is a grounding
issue. Everything worked fine before this and I haven't changed
anything with the electronics with the exception what is mentioned
here with the sensors.
Sorry this is so long winded but I wanted everyone to have a complete
picture of the issues.
Now the questions:
Could or will broken output leads cause the voltage regulator on the
ND alternator to fail? If so, how can I check if it is toast?
> From my description above does anyone have any advice or comments
> that might help?
I am getting pretty frustrated so any help would be greatly
appreciated!
--------
Darin Hawkes
Series 7 914 Turbo
Kaysville, Utah
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p 42934#242934
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darinh
Joined: 20 Apr 2006
Posts: 327
Location: Utah
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| Posted: Wed May 06, 2009 9:48 pm Post subject: Re: Radio Noise Problems - Rotax 914 with Dual Bolt-on Alt. |
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Kevin,
Yes I do. Keep in mind this all worked great until the leads on the alternator failed on me. The only thing I can think that has happened is when the leads failed it somehow damaged the built-in regulator. Problem is, I know next to nothing about alternators and regulators so I don't know how to check if it is good or not.
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_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah |
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