Been on a REAL vacation to visit my brother and his new bride in
Oregon for the past ten days. Spent some time camping out in the
mountains and wading in some VERY cold water at the shore. Will
be home for 10 days before starting our FAKE vacation at Oshkosh
for another ten days . . . blowing the whole wad in one month
this year!
The following are some tidbits I've picked up from various postings
to the list while we were gone . . .
>Address for free catalogue for heavy duty plugs/sockets and fuses with
>plastic holders etc is:-
>Merv Plastics
>201 Station Road
>Beeston Nottingham NG9 2AB UK
>Tel 0115 922 2783
When shopping for fuseholders or any other products fabricated from
plastic, check into temperature ratings. The automotive audio market
here in states offers a variety of what appears to be heavy duty
fuse holders, terminal blocks, etc. Turns out the plastics for some
products get brittle and crack and or won't stand under-the-cowl
temps. Also, be wary of "gold" platings offered by some vendors of
automotive audio products . . . these are not truly gold plated and
have higher resistance than plain ol' tin plating.
>Graham said, "But if they blow, there is probably something
>seriously wrong.
This is the reason that circuit breakers on the panel don't make much
sense. You need to ASSUME right up front that everything you install
is subject to failure . . . if you don't need it for comfortable
completion of flight, don't worry about it. If you DO need it, have
a back up. In either case, don't fiddle with breakers or fuses until
you're on the ground.
>I forgot to say that another good reason for having access
>to the fuses on the firewall from the cockpit side is that
>you can pull them and then plug in leads to charge the
>battery without having to remove the cowling.
Ground power connectors should be wired directly to the battery
via small contactor and reverse polarity protection diode (in
series with contactor coil) and o.v. protection (crowbar module
across contactor coil). Contactor is controlled from cockpit with
one of the FEW places where I recommend a switch-breaker. This
arrangement (1) allows charging battery without powering up
entire airplane (2) gives pilot control of ground power independent
of operator (3) prevents damage to airplane in case of reversed
polarity or inadvertnet application of 24 volts to your airplane.
>you need to provide a good earth somewhere
Yes . . . from ground power jack minus (-) right to airframe
for rear mounted battery or crankcase for front mounted battery.
>Perhaps you could even jump start it ?
You bet!!!!
>If a fuse/cb with big numbers on it blows there will be
>an overwhelming urge to land pretty quick regardless of
>how easy it is to reset. Believe me!
Agreed!
>Like the idea of access from the cockpit side for charging
>Graham2. I appreciate the point Graham1 brought up about his
>obviously working instruments and AC at the panel, but given
>the choice, i will still keep the leads forward of the firewall
>and as short as possible hopefully to limit any interference
>to radio/transponder.
Main advantage of short wiring is limiting interference to compass.
Keeping as much stuff forward of firewall as possible contributes
to short wiring and isolation from radios, intercom, etc.
>Bob Nuckolls writings make a lot of sense and are very
>useful to have. See his email from a few days ago for
>further info.
Thank you for the kind words . . .
>Why is AC behind the firewall a problem? Many of us have 26V
>400Hz single phase and 200V 400Hz 3 phase running separate
>instruments. Not a problem.
. . . mostly because the aircraft ac is low current, sine
wave power delivered on twisted pairs . . . very low noise
source. Rotax PM alternator output is high current,
lousy waveform, and best kept as short as possible between
alternator output leads and rectifier/regulator.
>We like the idea of the alternator CB on the firewall,
>resetable if you really need to. You only have to land
>if you are IMC or the mechanical fuel pump quits.
Again, assume the alternator is going to fail for LOTS of
reasons which may or may not manifest itself by blowing a
fuse or breaker. You need to carry enough battery to
run essential equipment until flight can be comfortably
concluded. If these criteria are met, it doesn't matter
where the breaker/fuse is located.
>Ignition is independant of charging. There are two
>separate dedicated coils. Rotax, it seems thought it out.
Except . . . be sure the four screws holding alternator
stator stack to crankcase are periodically pulled,
bonding areas cleaned and re-installed to proper torque
every annual. These bolts are single ground for ignition
system and under certain conditions causes BOTH ignition
systems to fail. (See Service Bulletin specific to this
issue . . . don't have it immediately at hand but if anyone
needs to know, I'll dig it out and get number and date).
>Ask for Europa's new circuit diagram. It will surely be
>improved but it's a good base from which you are unlikely
>to come unstuck and I doubt you will need to change much
>to perfect it.
Hmmmmmm . . . you haven't spent much time about Bob Nuckolls,
have you?
>BTW Bob Nuckoll's published remarks have almost pursuaded me
>that it's daft using expensive 1930s technology CBs except
>for special jobs, like perhaps the alternator supply and main bus.
The main bus doesn't normally get any sort of fault protection.
These wires are FAT guys that tend not to acquire hard faults
that need protecting. For example, 50,000 Cessnas have batteries
in the tail and a FAT wire bringing power up front but NO fault
protection. I could write a few paragraphs explaining why but
trust me . . . it works! Alternator supply lead protection
is to protect wires from battery current in case of diode failure
in regulator . . . if the diodes short, the the show's over,
might as well make it a fuse cause reseting the breaker will
just get you another pop . . .
>Goldwing Strobes don't like them either . . .
Don't like circuit breakers???? Probably because fuses generally
open faster than a breaker . . less likely to precipitate damage
to wiring inside the unit in case of hard fault failure.
> . . . and pose the question "Why no CBs on modern high
>tek cars?"
EASY . . . 1 cent per automobile saved over a production run
of 1,000,000 cars is $10,000 saved. $20 per automobile
for fuses versus breakers (they can make 'em cheap!) is a
whole hell of a lot of dollars . . . their choices have
nothing to do with operating logistics . . .
>It looks like Europa (and R&D) decided to bring the full alternator
>load through the firewall and into the panel (Rotax output is 25A).
Actually, I think it's a 250 watt alternator which works out to about
19 amps at 14.0 volts dc. . .
>This is also the noisiest electrical field on the plane, so
>Alan Thorne and myself decided to change things slightly to
>keep the run as short as possible.
Got that right !!!!!
>Am I right in thinking the rectifier part of the Rotax is a
>separate entity to the field coils (unlike a car where
>this is combined). Presumably the reason for keeping the
>circuitry on the engine side of the firewall is because its AC.
The Rotax alternator is permanent magnet excited versus regulated
field excited in automobiles . . . hence very different regulation
schemes.
>A large chunk of my current is used up on the Wheelen strobes.
Hmmmmmm . . . what strobe system are you going to run? Average
current for even the BIG systems is under 5 amps.
>Regarding the matter of fuses versus CB's, it can only
>be said that fuses also fail occasionally
MUCH less often than fuses . . .
> . . . and it would be a pity to have to terminate a
>flight if this was the only problem.
That's why battery capacity is chosen to run essential
equipment for duration of maximum fuel capacity when
worn down to half capacity . . . This means that you have
to replace a battery because it's capacity is low . . .
NOT because it didn't crank the engine on any given day.
A proper attitude toward battery maintenance provides a
VERY reliable source of power. I've flown long cross
country trips with a DEAD alternator by starting with
ground power and running one radio. Got to replace the
alternator with my own spare instead of one costing $750
---From an enroute repair facility.
>The trouble is that if this was mounted on the engine
>side you would have no option but to land.
Design it right and the only reason you HAVE to land is
because you're about out of fuel!
>Since this is such an important circuit perhaps it
>would be an idea to protect it with two CB's in parallel
>(but to keep one off as a standby). . . . .
This scenario is so remote in order of probability that
it's not worth the concerns . . .
>Goldwing say don't use C/Bs with their strobe it may
>cause failure. Really? They reckon sometimes faulty
>ones develop high resistance. Need a good excuse to usefuses.
Fooey . . .
>Worked for a co. that made CB contacts for a while -
>they also reckoned they could develop high resistance -
>this was domestic applications tho - I thought it was a
>reason to sell more CB's - didn't work since they went bust.
If you DO choose to use circuit breakers, please do use good
ones . . . the miniature aircraft breakers from Mechanical
Products, Klixon, etc are suitable and have every probability
of lasting the lifetime of your airplane. But . . . they ARE
$20 a pop!!!!! Fuses on the other hand are $0.25 a pop and are
inherently more reliable than breakers (lower parts count, lower
mechanical stresses, etc.)
> . . . been looking for plug and socket . . . .
What's the application????
> and decent fuseholders.
Check out Bussmann fuse blocks with built in bus bars. They should
be avalable in Europe . . . if not, I can supply via B&C specialty
products. $32 worth of holder and $5 worth of fuses replaces
$400 worth of miniature breakers and saves many square inches
of panel space and HOURS of assembly time.
>Anyone got any thoughts on this one? The Europa
>circuit shows a 40A breaker for the alternator on
>the cockpit side of the firewall.
30 amps is plenty big and an inexpensive, inline fuseholder
(Bussmann HFB or equal) right next to starter contactor
is fine . . .
> . . . . . . . . . In fact I planned to
>combine this with a switch - I suppose mainly because
>the aircraft I fly has an alternator switch. Is there
>any real need for an alternator switch - and why
>40A since I suppose this is only the field winding?
You bet! But how about putting a small, high current relay
in series with alternator output before it traverses 30 amp
fuse to starter contactor. Then, power relay via panel mounted
2 amp breaker and a panel mounted switch. A crowbar ov module
across the relay coil then affords overvoltage protection that
Rotax chose to leave out of their regulator designs. In most
airplanes the alternator switch does indeed control alternator
field circuit . . . in Nuckolls/Rotax designs it controls a
disconnect relay.
I think that's all the stuff I have to comment on. If anyone is
going to be at OSH . . . drop by the B&C Specialty Products
booth in North commercial building south of control tower.
I'd like to get a copy of Europa's electrical system and associated
text from the builder's manual. Rather than have a bunch of folk
send it, post your offers to do so here on the list and I'll respond
to the first one I receive so that the efforts are not duplicated.
Regards,
Bob . . .
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