Message-ID: <3718B260.799D043A@regandesigns.com>
Date: Sat, 17 Apr 1999 09:10:08 -0700
From: Brent Regan <brent@regandesigns.com>
To: lancair.list@olsusa.com
Subject: Alternator Fuse Protection
References: <19990417043732.AAA21556@truman.olsusa.com>
Mime-Version: 1.0

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Fuses and breakers protect the WIRE from turing red hot and starting a fire.

Alternators convert mechanical power into electrical power but they don't store
much (a little in the magnetic fields, and a little in the inertia of the rotor). A
60 amp alternator will produce about 65 amps maximum whether it is at 14.6 volts
charging the battery or 0.05 volts into a dead short. The alternator is "current
limited" and if the wire connecting it to the electrical buss is sized for 65 amps
without damage then the alternator can not overheat it.

The battery is another story. It stores energy and can deliver hundreds of amps
into a short. If the alternator B lead shorts, the battery will fry it. The
alternator B lead must be protected with a fuse or breaker AT THE BATTERY. You
won't fix a shorted B lead in the air so there is no need for a breaker in the
cockpit. A fuse at the master solenoid is best. Carry a spare.

The alternator also produces electrical noise. To minimize the noise conducted to
the electrical system, the alternator should be connected to the aircraft side of
the master solenoid and not the buss behind the panel.

Regards
Brent Regan

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