The 12 volt generator/alternator will be at 14-15 volts
nominal when within the working range of RPM. The voltage
regulator should keep the voltage within that range without
any significant variation.

Just what are you intending to be warned against? The load
meter gauge shows the load being carried by the generator
system, the ammeter shows whether the generator or battery
is supplying the power being used, An ammeter should be
showing only a slight charge all the time as it keeps the
battery "topped off." If the battery is any good, the
ammeter will return to low indicated charge within a few
minutes after starting the engine. At a low idle, the
battery will show a discharge because the generator is not
carrying the load and the battery is discharging to carry
what the demand is at the time. This is not a problem in
the short term, such as a power-off landing or glide, but
anytime that the engine is in the power range, the generator
[alternator] should be carrying all the load.

Power relays need about 10 volts to stay engaged. If you
are building a home-built airplane, you could have a yellow
warning light at less than 13.9 volts and a red warning at
12.8. Open cell no-load voltage is 2.2 volts or 13.2 volts
on a lead/acid battery.

Certificated aircraft require certificated parts. You can
get a cigarette lighter plug-in monitor.


--
James H. Macklin
ATP,CFI,A&P

--
Merry Christmas
Have a Safe and Happy New Year
Live Long and Prosper
Jim Macklin
"markp" wrote in message
...
| Hi All,
|
| I'm looking for recommendations for a low battery warning
voltage level. I
| was going to use 12.8V - is this liable to be triggered by
noise/dips in the
| bus voltage? My guess is when heaters or motors kick in
there could be a
| momentary drop due to high current that could trigger my
low voltage
| indicator. Also it it worth putting a long time constant
filter on this?
|
| Thanks!
|
| Mark.
|
|
|