Kellym
Joined: 10 Jan 2006 Posts: 1705 Location: Sun Lakes AZ
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Posted: Fri Dec 24, 2010 4:40 pm Post subject: Alternator output voltage vs usable voltage at the bus |
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Your reasoning is correct, but the goal is not. You want 14V +/- 0.2 at
the battery when you have enough rpm for significant positive output
from the alternator. Your avionics and most everything else electrical
will function fine at 12 to 14 V and are not that picky. Voltage is set
to fully recharge the battery, so you have maximum endurance time
available if the charging system quits. The rest of the electrical
system doesn't care that much once the minimum voltage is present. So
the cable size(s) from the alternator to the battery via the regulator
and any resistance induced at connections are what matters.
On 12/24/2010 3:03 PM, Neil Clayton wrote:
Quote: | Is my reasoning correct here?
On my pusher, the _internally_ regulated alternator puts about 13+
volts on the bus behind the panel.
If there is 10 feet of #6 wire between the alternator and the battery
(alternator, all the way forward to the 40A panel breaker, then to the
bus).
10 feet of #6 wire at 0.004 mOhms/foot pulling 15 amps of current
would see a voltage drop of 10 x 0.004 x 15 = 0.6 volt drop. Add a few
more losses along the route and 13v is a reasonable expectation at the
bus. So if the electrons start out their journey from the alternator
at 14 volts, I'd see about 13.0 volts on the bus.
Furthermore, if I _externally_ regulated the alternator using +14 bus
voltage as the target voltage, the regulator would compensate for the
line voltage drop, and I'd see 14+ volts at the bus?
Right, or is this Mech Engineer counting electrons wrong?
Thanks
Neil
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_________________ Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD |
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