Inconsistent Aeroelectric?
Hi Guys,
The Aeroelectric is such a proponent of Autocar Fuses instead of breakers because if it trips he says you should not attempt to put it back on while in the air, hence fuses makes sense...but in his diagrams he still adds a 5 amp breaker (RED) to alternator field instead of (BLUE) Fuses.?
WHY??? What am I missing??? Thanks Rudi
Bob talks in absolutes. When there is over lap or preference, it gets a little confusing. Remember some of Bob's ideas are more in the preference area than technically necessary.
The main reason for the ALT CB is when using a "crow-bar" or B & C regulator, which has a crow bar in it. The CB is an integral part of the "crow-bar system", an over voltage protection device as you know. The crow bar works by dead shorting the CB and tripping it. The Plane power alternator that I recommend, also uses or needs a CB. You could still use a fuse from any CB, however, a CB makes more sense, if you plan on occasionally tripping circuit "normally". (read on)
Here is my interpretation of Bob's CB/Fuse philosophy.
Since the OV "crow bar" might trip "accidentally", the ability to reset it, is desirable; the CB is obviously more desirable than a fuse for something you expect to normally trip on occasion. Bob denies the crow-bar is finicky or subject to nuisance trips. OK? If its true, it never tripped unless, than you could use a fuse, right?
Well the crow-bar is not that stable. There are other ways to protect from OV, and this is one that Bob likes, and it needs a CB to work.
In general his "logic" or philosophy on "fused" items, is you can live with out them or should if it blows, with proper design of your system. In most production planes (read all) only CB's are used or resettable thermal current limiting devices. Bob is right, fuse are cheap, simple, light and work to protect the wires as good as any CB. The down side is you have to carry extra fuses and it's difficult to fix or re-set in flight.
However the latter issue, resetting in flight, is moot in Bob's opinion. He proposes you don't want to replace a fuse, ever, until you land. Obviously if a CB pops, you might consider not resetting it, like if you smell something. At least you let a CB cool and only allow one reset. So bottom line, if a fuse blows it's OK to leave it blown till you land since you don't need the device and it might harm something to reset that circuit, in the scenario in his mind.
(IMHO, for heavy current items like gear retraction motors, CB's are generally preferred. A electric motor can have a transient overload and be fine. So CB reset is hand.)
The Alternator is a little different?
You could use a fuse. Bob makes grand statements of philosophy or "Bob rules", but than it "appears" he contradicts himself or changes the philosophy to fit his current opinion. That is not a criticism, we all move the goal post sometimes. However if you think you can live with out your alternator, say fly on battery power, than the fuse on the ALT is not critical. You could sub in a fuse for simplicity and less cost/weight. If you have a stock internal voltage regulated alterantor the CB on the "IGN" lead is even less useful. The current is like 0.10 amps or less.
If you are using an internally regulated alterantor than the fuse can be say 0.5 or 1 amp since the "IGN" lead is only a 'signal' to wake up or sleep the alternator, not a "field wire" or power to the voltage regulator. All the power goes through the b-lead. If you are using a Plane Power, than use a 5 amp (or what ever size) CB they suggest, since that is also a "crow bar" type CB popper as well. As you might know a crow-bar dead shorts the CB to trip it, removing power to the regulator, which removers power to the the alternator "Field", which de-energizes the alternator, if its miss behaving.
Bottom line: Bob's way is not the only way or best way, just his way which is totally fine. Some times its over kill. Some times the reasons he gives are opposed to other opinions (but there is always a justification). It's just not that important, and if you follow his philosophy you will be ok, albeit may be on the overkill side. The only thing I really think is wrong is putting a crow bar & over voltage relay on the b-lead of a internally regulated alternator. That is heavy and a Jury Rig. It also will damage the alternator in the event of a nuisance trip. If you are worried about your internally regulated alterantor (and you will be if you believe everything Bob says, which he does not have proof of) than get a Plane Power unit. Also good is B&C alterantor with an external regulator, but I would get a Transpo V1200 regulator not a B&C voltage regulator. The Transpo V1200 uses solid state OV protection and not a CB tripper crow bar. It also cost 1/3rd or 1/4th the cost of B&C voltage regulator price.
