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Posted for "Jeffrey Liegner, MD" <liegner@earthlink.net>:
Four Points from B&C Tech Support Tim Hedding "<thedding@BandC.info>:
1. The field circuit breaker should not be 7.5 Amps; it should be 5 Amps. The
field current should never exceed about 4 Amps unless the over-voltage crowbar
has tripped in the regulator. At this point, the regulator is temporarily a
direct short circuit on the field circuit breaker, with the intention of
shutting the alternator down by tripping the breaker. Increasing the circuit
breaker size increases the stress on the regulator circuit board traces and
increases the chance of damaging the regulator.
2. The alternator-warning lamp is voltage dependent and its threshold is
approximately 12.6 Volts. When ever the bus voltage (as sensed on Terminal 3
of the regulator) reaches 12.6 volts or less, the lamp will flash. This will
happen any time the alternator output does not cover the demand, and the
remaining current is drawn from the battery. This could happen if engine speed
is low, the load is very high, or there is a charging system problem. Charging
system problems could include, poor connections, poor design, bad alternator,
slipping alternator drive, etc.. Chances are that if the regulator holds the
system at the correct voltage during all normal usage, the regulator is fine.
3. Any time there are major transients in the charging system, such as are
caused by bad connections, or large inductive loads, there is a chance of
tripping the over-voltage crowbar. This is especially true if the regulator
"Bus Sense" terminal is close to the load's source and isolated from the
battery. I'd suggest moving the regulator's Terminal 3 connection from the bus
near the gear motor circuit breaker to the switched side of the master relay.
Since the battery is the main system transient suppressor, this will decrease
the likelihood of nuisance O.V. trips. In fact, I have had this make all the
difference on a Lancair before.
4. See if your regulator is an LR3C-14. An LR3B-14 or earlier version is more
susceptible to such nuisance trips. If the regulator is an older model, it may
be possible to upgrade, depending on the exact vintage. Any unit newer than
year 2000 should be upgradeable.
My guess is in this case, that during the gear transit, the alternator does
not cover the entire load. The remaining current is drawn from the battery
until the gear switch is satisfied. At that instant, alternator is (and should
be) in a full-fielded condition. When the load is suddenly removed the bus
voltage spikes upward over the over-voltage limit, firing the O.V. crowbar,
and tripping the field circuit breaker. The moving of the "Bus Sense" source
as describe above may help or even cure the problem. If the battery is old,
replacing it may also help. If these ideas fail to cure the problem, call me.
We might need to perform the regulator modification mentioned above or add
some transient arresting diodes on the gear motor contactor.
Tim Hedding
Electrical Engineer,
B&C Specialty Products
316-283-8000
Lancair IVP. TSIO550E. Standard 65amp primary alternator. Buss A.
Alternator with Hydralic Pump Problem:
Sometimes when my hydralic pump (gear, flaps) is running for more than a brief period (ex, when flaps/gear are coming up on a go around), my 7.5amp circuit breaker "FIELD" for the main alternator pops. Of course, the alternator output then ceases.
An added observation: In addition to the HYDRALIC ON lamp illuminating during pump action, the alternator's WARNING LIGHT always flashes during (and only during) hydralic pump running (regardless of whether the CB will pop).
Of course, with hydralic pump on, it uses some 40 amps (as seen on the JPI ammeter). If this is sustained any more than briefly, the Field CB pops. The 50 amp Hydralic CB does not pop (annd is perfectly happy).
QUESTIONS:
FIrst...is 7.5 amp field CB correct? I thought it was, but maybe not?
Second, warning light should come on when battery voltage > alternator output. Does this mean the Voltage Regulator for the alternator is failing me when the hydralic pump demands exceed capacity of voltage regulator to do its job? Should I replace the voltage regulator?
Third...or does this mean that I have some sort of current misdirect, when output demands (ie,hydralic pump) exceed supply (alternator output), such the current must come from the battery to make up the difference, and it does it through the FIELD circuit (inappropriately), exceeding 7.5 amp CB tolerance? Of course, the battery is directly hooked up to the BUSS, and the hydralic pump can be run without engine or alternator tuning, directly from the BUSS. A short somewhere?
Who among us understands alternators and can tell me where to look (more than what I've done)?
Jeff L
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