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nuckolls.bob(at)aeroelect
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 Posted: Tue May 26, 2009 2:47 pm Post subject: Rotax 912ULS voltage . . . |
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At 12:38 AM 5/26/2009, you wrote:
Thank you for the information Bob.
I am trying to trouble shoot my low voltage problem to determine its
cause (i.e.; the regulator, wiring, or the internal engine
alternator) so I can take corrective action.
There is nothing in the Rotax 912 manuals to assist in doing this. I
checked the internal engine coil resistance reading and found it to
be .7-ohms. The DC voltage at the regulator is the same previously
reported (still under 13-volts). Finally I measured AC voltage coming
from the coils. The voltage varied as follows:
Idle (1900-RPM) was 12.8 volts
2500-RPM was 16.0 v
3000-RPM was 19.0 v
4000-RPM was 24.5 v
cruse(5000-RPM)was not measured.
Bob, Am I correct to think that the AC voltage looks adequate and the
problem is likely a faulty Rotax voltage regulator?
Thanks again for your help.
If you have ANY voltage from the alternator's output winding
at any speed, and the winding is not shorted to ground (very
unlikely) then the alternator is fine. Rotax PM alternators are
exceedingly simple, rugged and reliable. I'm not aware of any
failures.
The Ducati rectifier/regulator supplied with these engines
is another matter. They are of marginal thermal design and
sadly lacking in adjustability. Two conditions VERY
easy to fix if anyone with responsibility for the product
cared.
Unfortunately, replacing it with an identical OEM R/R has
a high probability of installing a similar problem right
out of the box. I've heard that John Deere has a single
phase, PM alternator regulator that is rated for up to
35 amps. Goto http://matronics.com/search
Search the AeroElectric List for AM101406 and you'll
get several hits by folks who discussed it some time
back.
Here are some after-market clones . . .
http://www.watercraftstarter.com/Lawn%20Garden/Regulator%20Rectifier/?nocache=1
http://www.amazon.com/Replacement-Voltage-Regulator-Deere-AM101406/dp/B00169H3E0
I don't see a voltage adjustment mentioned or
shown . . . unfortunate but perhaps understandable.
Most of these regulators are used on small tractors
and most users are not skilled in the use of such
features.
Wish I had my alternator drive stand running. Building
a 'real' PM r/r for aircraft is not a big task . . .
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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lgold(at)quantum-associat
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| Posted: Sun May 31, 2009 11:21 am Post subject: Rotax 912ULS voltage . . . |
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Bob,
Here is another twist in the strange continuing low voltage problem saga in
my Rotax 912 / Figure Z16-designed electrical system.
I purchased and installed a new Rotax voltage regulator (called a
regulator/rectifier by Rotax), which provided identical low voltage results.
Just as I was getting ready to return the "defective" regulator I accidently
switched on the endurance bus and, what do you know, the voltage shot up
from 12.9V to 13.8V (as measured through my Dynon glass cockpit and Lowrance
GPS instruments). While still a little low, I can certainly live with 13.8V
under normal working load since this should adequately charge my battery.
Ok, so now it looks like there is something wrong in the Z16 electrical
configuration. I'd rather not leave my endurance buss on all the time
(although I don't think this would hurt anything??) so I would like to fix
the issue. I suspect the problem is associated with the diode that attaches
the two busses shown under "Note 12" on your Z16 diagram. Do you concur? Do
you think I should change this diode, do further testing, or should I look
elsewhere for the problem? The my diode came with a heatsink from B&C. If I
need a new one, and you make them, I need one ASAP since I plan a 1000-mile
trip next weekend.
Thank you again for your help.
Les Goldner
510-549-1622
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nuckolls.bob(at)aeroelect
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| Posted: Mon Jun 01, 2009 8:13 pm Post subject: Rotax 912ULS voltage . . . |
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At 02:18 PM 5/31/2009, you wrote:
| Quote: |
<lgold(at)quantum-associates.com>
Bob,
Here is another twist in the strange continuing low voltage problem saga in
my Rotax 912 / Figure Z16-designed electrical system.
I purchased and installed a new Rotax voltage regulator (called a
regulator/rectifier by Rotax), which provided identical low voltage results.
Just as I was getting ready to return the "defective" regulator I accidently
switched on the endurance bus and, what do you know, the voltage shot up
from 12.9V to 13.8V (as measured through my Dynon glass cockpit and Lowrance
GPS instruments). While still a little low, I can certainly live with 13.8V
under normal working load since this should adequately charge my battery.
Ok, so now it looks like there is something wrong in the Z16 electrical
configuration. I'd rather not leave my endurance buss on all the time
(although I don't think this would hurt anything??) so I would like to fix
the issue. I suspect the problem is associated with the diode that attaches
the two busses shown under "Note 12" on your Z16 diagram. Do you concur? Do
you think I should change this diode, do further testing, or should I look
elsewhere for the problem? The my diode came with a heatsink from B&C. If I
need a new one, and you make them, I need one ASAP since I plan a 1000-mile
trip next weekend.
|
Nothing needs "fixing". For the purposes of knowing
your alternator's setpoint voltage, you're measuring
the system voltage at the wrong place. Yes, the e-bus
is KNOWN to run about 0.7 volts lower than the main
bus and it doesn't matter. When a voltmeter is fed
from the E-bus, it becomes something of an electrical
fuel gage for battery-only operations. When you're
down to 11.0 volts battery only, the battery is 95%
used up. If you want to use this voltmeter to check
the main bus . . . then you momentarily close the
alternate feed switch as you've discovered.
13.8 is still pretty low for charging a battery but
if you're going on a trip and will spend hours per
flight cycle at cruise RPM then 13.8 will get you by.
The system is working as designed. You can either
mentally add the 0.7 volts of known diode-drop or
do your low voltage and/or voltage display sensing
from the main bus. Any LV Warning should ALWAYS be
driven by the main bus when such systems are installed.
I'd say you are good to go on your trip.
Bob . . .
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