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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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 Posted: Tue Jul 22, 2014 4:47 am Post subject: Alternator and Battery ON & OFF |
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7/22/2014
Hello Joe (Unknown) and Bob Nuckolls, The B&C wiring diagram accessed by the link given below by Joe has this warning:
“Important – Battery contactor and alternator should come on and off together.”
Can someone please explain to me why that is important? What bad things will happen if they don’t come on and off together?
Thank you,
OC
'O C' Baker says "The best investment you can make is the effort to gather and understand information."
PS: My procedure: On start up, Turn the alternator ON after engine is running. On shut down, Turn the alternator OFF while engine is still running to get a flashing low voltage light to confirm that my low voltage warning system is working. I have entirely separate Battery (battery contactor) and Alternator switches.
=====================================
Time: 07:41:41 AM PST US
Subject: Re: Are 'serial' contactors really needed?
From: "user9253" <fransew(at)gmail.com>
| Quote: | it says to hook the ovm to regulator in & to the master switch
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No it doesn't.
B&C schematic link: http://www.bandc.biz/pdfs/OVM_wiringdiagram.pdf
The B&C schematic shows the black wire of the O.V. module connected to ground.
They just happened to use the same ground that the master switch is connected
to. You can connect the black wire to any convenient ground.
I think that B&C drew the schematic that way for two reasons: 1. It is easy to
draw. 2. It is easy to wire directly at the master switch because both ground
and the alternator field circuit are available there (if your master switch is
wired like B&C's switch is wired).
As for the colored wire (orange?) of the O.V., B&C shows it connected to the alternator-field
half of the master switch. Electrically speaking, this is the
same as connecting to the voltage regulator input. In either case, power is coming
from the 5 amp breaker.
Now if you want to connect the O.V. module directly to the 5 amp breaker, I see
no reason why that will not work. I hope others will correct me if wrong. Just
make sure that it is connected to the down stream side and not the always
hot side of the breaker.
In summary, connect the O.V. black wire to ground. And connect the other wire
to some point between the 5 amp breaker and the input to the voltage regulator.
Joe
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Tue Jul 22, 2014 6:23 am Post subject: Alternator and Battery ON & OFF |
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At 07:45 AM 7/22/2014, you wrote:
7/22/2014
Hello Joe (Unknown) and Bob Nuckolls, The B&C
wiring diagram accessed by the link given below by Joe has this warning:
"Important Battery contactor and alternator
should ccome on and off together."
Can someone please explain to me why that is
important? What bad things will happen if they don't come on and off together?
Hmmmm . . . hadn't noticed that. It's a not-so-accurate
acknowledgement of the history of alternators in airplanes.
When our vehicles with big fans and wings carried
generators, there were two relatively independent
sources of power. A battery and a generator. Generators
were by nature self-exciting (after the field was
'flashed') and output from the machine was relatively
smooth. Ship's electro-whizzies would run well on
battery, generator or both.
When we pressed the Ford alternators into service
on airplanes in the 60's, two noteworthy differences
in the alternator's characteristics took center
stage. Alternators were reluctant to self-excite;
you couldn't simply turn a spinning alternator ON
and expect it to come on line. Further, voltage
regulation dynamics for alternators was a fledgling
technology . . . having a battery on line aided
in the task stabilizing bus voltage and the battery
prevented the alternator from suffering a stalling
event should it be hit with a large inrush like
klieg-lights on the wings or an electro-hydraulic
landing gear system.
It was clear that the legacy separation of BATTERY
and GENERATOR switches was fraught with some risk
for confusing pilots familiar with how the electrical
system worked in the older airplanes. What's an
itty-bitty airplane factory to do?
The airplanes at Cessna were already being fitted
with the stylish rocker switches from Carling. The
pilots, engineers and switch-guys put their heads
together and the split-rocker DC MASTER switch
was birthed. Mechanical linkage between the rockers
allowed you to operate battery-only but that the
alternator could not be on without having the battery
on also.
EARLY in the history of AeroElectric Connection
architectures, the split-rocker was replaced with
a two-pole, ON-OFF switch to operated battery and
alternator together. The crowbar OVM called for
use of a field supply breaker . . . which could
be pulled for battery-only operations either
airborne or ground test.
Later, I discovered the Carling catalog and sources
for the three position 2-10 switch that would emulate
the split-rocker functionality . . .
http://tinyurl.com/q9pbjks
Over the years, the simple DPDT+breaker configuration
was replaced with the DP3T, ON-ON-ON (2-10) switch.
Now that you have the history, I can explain that
the admonition on the B&C drawing is an artifact
of the "days before 2-10 switches" and was further
mis-interpreted as an imperative . . . don't recall
now who wrote those words but they are in error.
Now that you have the "Rest of the Story" you are
free to select from the whole array of available
switches including (1) simple, DPDT+breaker (2) DP3T
ON-ON-ON, or (3) a living artifact of the early days
of alternators in light aircraft, the split rocker switch.
Bob . . .
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Tue Jul 22, 2014 7:09 am Post subject: Re: Alternator and Battery ON & OFF |
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| Quote: | “Important – Battery contactor and alternator should come on and off together.”
Can someone please explain to me why that is important? What bad things will happen if they don’t come on and off together? |
I think that it is good operating practice to turn the master contactor and alternator on and off simultaneously. But I do not think that bad things will happen if not operated that way. TC aircraft have a split master switch and the Z figures have a progressive transfer master switch that allows the alternator to be shut off.
Most pilots expect the the master switch will shut off every single electrical circuit on the airplane. If the master contactor and alternator are controlled by separate switches and if only the contactor is shut off, then it is possible (or even likely, depending on the alternator) for the alternator to keep supplying power to the aircraft. This is not necessarily a bad thing, but could be if the pilot does not understand how the aircraft is wired.
Another consideration is flying with the master contactor on and the alternator off. The battery will not be recharged. If the alternator is then turned on, could there be a voltage surge? I do not know. Maybe Bob N will answer that.
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Joe Gores |
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jmjones2000(at)mindspring
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| Posted: Tue Jul 22, 2014 1:01 pm Post subject: Alternator and Battery ON & OFF |
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Most of the split alt/bat switches that I have experience with allow the battery to be on without the alternator but not the alternator on without the battery. The function is an internal mechanical function in the switch itself. I like to call it army proof.
On Jul 22, 2014, at 7:09, "user9253" <fransew(at)gmail.com> wrote:
| Quote: |
> “Important – Battery contactor and alternator should come on and off together.”
> Can someone please explain to me why that is important? What bad things will happen if they don’t come on and off together?
I think that it is good operating practice to turn the master contactor and alternator on and off simultaneously. But I do not think that bad things will happen if not operated that way. TC aircraft have a split master switch and the Z figures have a progressive transfer master switch that allows the alternator to be shut off.
Most pilots expect the the master switch will shut off every single electrical circuit on the airplane. If the master contactor and alternator are controlled by separate switches and if only the contactor is shut off, then it is possible (or even likely, depending on the alternator) for the alternator to keep supplying power to the aircraft. This is not necessarily a bad thing, but could be if the pilot does not understand how the aircraft is wired.
Another consideration is flying with the master contactor on and the alternator off. The battery will not be recharged. If the alternator is then turned on, could there be a voltage surge? I do not know. Maybe Bob N will answer that.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=427139#427139
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