nuckolls.bob(at)aeroelect
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 Posted: Sat Nov 23, 2019 6:22 am Post subject: Battery/alternator interlock required? |
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At 10:02 PM 11/22/2019, you wrote:
| Quote: | | I admit I'm fuzzy on the ways batteries and alternators interact. I'm adding a backup alternator and using Z-12 as my guide. I have one of those standard red split rocker switches which doesn't allow the alternator to be on without the battery master being on. Would it be bad to have the battery go off with the alternator on? The standby has a field switch but it's not connected to the other one so it would certainly be possible to have that on and shut off the other one. If I want to replace the rocker with a toggle, should I use a switch that can do off - batt - batt + alt or could I use two separate toggle switches? |
The 'split rocker' switch was birthed
in the 60's when alternators first began
to replace generators. Alternator/regulator
combinations of the time were not as well
behaved as modern machines. They might not
self-excite. A heavily loaded alternator
might stall and quit if subjected to a
large transient like landing gear pump
or fat landing light . . . recall that the
well fitted aircraft of the time had a panel
full of vacuum tube radios.
While not so critical today (solid state
radios, fewer radios, incandescent landing
lights flying off into the sunset with dodo
birds . . .) having a battery on line any
time alternator ops are needed is not a
bad idea.
The split rocker made sure
that any time the alternator operation
was desired, there would be a battery on
line to keep it happily ginning out electrons
under the worst case conditions.
In my not so humble opinion, from a fabrication
standpoint the rocker switch is a pain in the
you-know-what . . . never did like to cut
rectangular holes when a spot-facer (or now a
step bit) in a drill motor would make such neat
work of the task for mounting switches. Hence, the S702-10
toggle switch substitution for the rocker
switch for performance of the same action.
If it were my airplane, I'd wire up as
suggested in Z-12 using toggle switches.
You have a option of incorporating an
auto-switch feature for the standby alternator
utilizing the SB-1 regulator in which case
normal flight operations are conducted with
BOTH alternators ON. Or fit the standby
alternator with an LR3 or other generic
regulator and do the standby alternator
selection manually as needed. Either works
just fine and the later is less expensive.
But in any case, I suggest you strive to have a
battery on line at all times whether you use a
progressive transfer OFF-BAT-BAT+ALT switch or separate
switches. For my money, the fewer holes in
the panel the better . . . and round holes
are 10x more desirable than square ones.
Bob . . .
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