Today's Message Index:
----------------------
1. 02:44 AM - unsubcribe (Michael Dawson)
2. 11:22 AM - OV protection (paul stewart)
3. 01:20 PM - Re: OV protection (James H Nelson)
4. 08:21 PM - Re: OV protection (Fred Fillinger)
5. 08:25 PM - Re: OV protection (Fred Fillinger)
6. 11:04 PM - 150th Anniversary (david.corbett)
Message 1
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--> Europa-List message posted by: "Michael Dawson" <mtd@ilkley.fsbusiness.co.uk>
unsubscribe.
Message 2
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--> Europa-List message posted by: "paul stewart" <paul-d.stewart@virgin.net>
All
I have had some very helpful emails and photos from Gerry Holland recently about
electrics, which included some discussions about the EXP bus. This had me going
back to re-read 'lectric bob, the club overvoltage protection mod and EXP
bus latest web site - don't know if it's helping or not.
Control vision on their web site say that the EXP bus now provides overvoltage
protection. My understanding is that the Rotax has a PM alternator and so no field
circuit to simply 'turn off', thus the OV protection requires a relay capable
dumping the whole alternator output to ground (as per the club mod). Their
website suggests if using an alternator without a field input that the circuit
may be used for any 5 amp application. I'm not clear that the EXP bus does
provide the OV protection to prevent boiling the battery in the event or regulator
failure.
Anyone with experience of the EXP bus or more understanding of it than my basics
care to comment.
Regards
Paul Stewart #432
Message 3
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| Subject: | Re: OV protection |
--> Europa-List message posted by: James H Nelson <europajim@juno.com>
Paul,
When trying to use a OV protection with the Rotax alternator you
need to send the output from the Rotax through a relay. This relay is
part of the OV control using "lectric Bob's" system. All you have to do
is make sure that the output from the Rotax is connected to the 2500mfd
capacitor all the time. This capacitor is the stabilizing "load" that
must be on the output. I am using my designed 40A alternator with the
Rotax unit as my backup. So my Rotax alternator is basically "just
there" with no work being done. (Until my 40A goes "south"). When the
OV functions, the load is not "dumped to ground" as it is just
"disconnected" and left hanging. The OV unit goes to ground to blow the
fuse that holds the relay in the system. With the relay "off line" and
the output not putting any power, all is stable. Yes, I guess you put
the output to ground but it is through a fuse that is designed to blow.
The battery will take over now for a short time. IF you are going to
use any strobes and running lights, you WILL need more than 17A from
Rotax.
Jim Nelson
N15JN
Message 4
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| Subject: | Re: OV protection |
--> Europa-List message posted by: Fred Fillinger <fillinger@ameritech.net>
James H Nelson wrote:
> When trying to use a OV protection with the Rotax alternator you
> need to send the output from the Rotax through a relay. This relay is
> part of the OV control using "lectric Bob's" system. All you have to
> do is make sure that the output from the Rotax is connected to the
> 2500mfd capacitor all the time. This capacitor is the stabilizing
> "load" that must be on the output.
I think we need to be careful here. The only cause of overvoltage will
be a defective regulator. If OV protection opens the relay, thus also
removing load, there is potential to place AC voltage voltage across the
25,000uf Faraday device of maybe 100V P-P. The result will be one heck
of bomb shortly exploding within the airframe. If the regulator is
defective but all load disconnected, the capacitor simply isn't needed
to protect something which has failed. The relay should be placed
"upstream" of the capacitor.
> So my Rotax alternator is basically "just
> there" with no work being done. (Until my 40A goes "south").
We don't know what's inside the Rotax regulator, but the only way to
achieve what you describe is either a series regulator or "classic"
switching regulator, which the Rotax reg neither clearly is not. If
under no load, the regulator runs hot, power not used is being
dissipated therein. If cool, then there's some substantial portion of
250 watts dissipated in the generator coils, augmented by engine heat.
The only possible problem is that's within the same stator assembly
that's providing spark voltage! An AC ammeter inserted in the AC line
to the regulator will divulge the truth. Approximate current, as the
ammeter will read RMS voltage drop for an assumed sine wave, which the
generator output ain't (10-phase 1/2-wave?).
Regards,
Fred F.
Message 5
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| Subject: | Re: OV protection |
--> Europa-List message posted by: Fred Fillinger <fillinger@ameritech.net>
paul stewart wrote:
> Control vision on their web site say that the EXP bus now provides
> overvoltage protection. My understanding is that the Rotax has a PM
> alternator and so no field circuit to simply 'turn off', thus the OV
> protection requires a relay capable dumping the whole alternator
> output to ground (as per the club mod). Their website suggests if
> using an alternator without a field input that the circuit may be
> used for any 5 amp application. I'm not clear that the EXP bus does
> provide the OV protection to prevent boiling the battery in the
> event of regulator failure.
I find it hard to believe that one should short either the regulator or
generator output to ground. Good grief!
EXP's Rotax schematic says the relay is connected to what I guess is a
control voltage to the regulator. The innards of the regulator are not
in the public domain, so we'll have to take EXP's word for it that this
arrangement works.
"Boiling the battery" is really not the concern. It will take a while
to do that, and in fact in the short run it's beneficial in that it's a
recommended method of desulfating the plates! The concern is avionics,
but I've not seen a schematic on modern avionics where overvoltage will
quickly cause damage such that instant protection is needed. Except
maybe some 30-cent illuminating lamps, and on some VHF comms please
don't key the mic during a severe OV condition.
Bob Nuckolls thus has writ that for Rotax PM generators (not an
alternator!), it's sufficient due to limited output to provide for panel
indication of overvoltage with visual/aural alarm. The overvoltage
problem on mechanical alternator regulators has to do with frozen
"buzzer" contacts, but of many dozens of solid state power supply
failures I've seen they've all gone open and thus to zero output. At
least I've never found any anecdotal report on the net that the Rotax
Reg fails in overvoltage.
My OV scheme for the avionics and electric gyros is just a 17V, 50W
stud-mount, heat-sinked Zener diode across the bus. The theory is that
most of the generator output is being sapped by devices on the bus, so
there's plenty finite time before that $12 puppy blows to allow for an
aural overvoltage indication to dictate corrective action.
Regards,
Fred F.
Message 6
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| Subject: | 150th Anniversary |
--> Europa-List message posted by: "david.corbett" <david.corbett@fwi.co.uk>
About 2 weeks ago there were some messages posted on this forum about Sir George
Caley's glider, and reference to the intended flight of a replica.
I am now able to update you all about the actual event, which was witnessed by
two of my friends, both PPL's of much experience who live close to the late Sir
George's home, Brompton Dale, near Scarborough, North Yorkshire; a descendant
of Sir George still lives in the house.
It was decided that the original 1853 glider, which is housed in the Museum at
Elvington airfield, Yorkshire, could not be taken out for this anniversary. British
Aerospace agreed to make a replica in their factory at Brough, and this
was completed on time. (Brough is the home of BAE Hawk manufacture).
The day itself - Friday 4 July I believe, but it may have been the following day
- was overcast with solid cloud cover at 1000ft or less agl. All the active
participants were in period costume. A dummy run was made to start with, about
20 men pulling the glider downhill so that the pilot (who had a beard!) could
get the feel of the machine, which is controlled by a "paddle" rather than by
elevator and ailerons.
A second run was then made and the pilot successfully completed a flight described
to me as about 6 feet.
An additional attraction, not quite at the same moment, was the appearance below
cloud level of a Virgin Atlantic Boeing 747/400, which did several graceful
circuits around the site before disappearing almost silently into the cloud.
As those who followed the original thread will have guessed, the pilot with the
beard was none other than Richard Branson.
Oh to have been there!
David
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