How long on an alternator?

On Dec 3, 10:34 am, wrote:

The Lonestar 'Eliminator' filter (http://www.lonestaraviation.com/
eliminator.htm) that goes in line with the power feed to the avionics
does do a great job of stopping alternator whine that comes riding
along the power wire into the radio/intercom/whatever. I used to fly
an old Cherokee that had the little Terra NAV/COM radios and the
alternator whine was terrible. The owner had one of these Lonestar
filters installed into the power feed to the Terra and intercom, and
it stopped the whine completely.

My Piper Pacer had one of these filters in it when I first got it. It
had just a single ValCom, and a Sigtronics SPA400 intercom.There was
so much alternator whine and strobe squeal that it almost drove me
nuts. I thought the filter had failed so I took it out. That made
absolutely NO difference. I had to unground (isolate) all ten mic/
headphone jacks, the cabin speaker, the PTT switch on the yoke, as
well as rewiring the SPA400 and moving some other grounds to separate
them from the avionics grounds. That got rid of 95% of the whine/
squeal. Reconnecting the filter got rid of about half of the remaining
noise.

Subsequently, I removed the ValCom and replaced it with a Narco Mark
12D. That got rid of all the remaining noise, with or without the
filter hooked up, so I removed it. My conclusion is that the filter is
not effective in curing the overall problem, which in this case was a
ground loop. The ValCom obviously was worse at rejecting ripple on its
supply line than the Narco that replaced it. It could be that Terra is
also sensitive to ripple.

I recently installed a PSE PM3000 stereo intercom in a friend's 172.
PSE claims right on their PM3000 spec sheet that the attenuation from
the power input to the audio output is a minimum of -65db. Since there
is about 100mV of ripple on the bus of the typical aircraft, that
would mean that the amount of ripple that would appear on the audio
out would be about 56uV. Since the normal listening level at the
output of the intercom is about 2vp-p, the noise would actually be
90db below 2V. Almost any IC chip audio amp made has a power supply
rejection ratio (PSRR) of 60db, so the designer of any avionics that
is sensitive to power supply ripple (and would benefit from the
Lonestar filter) has to be a total idiot. I know from experience that
COMS like a KX170, KX155, Mark12D, SL30, SL40, audio panels like the
PSE, King KMA20/24/26, intercoms like the PSE PM1000 & PM3000 do NOT
need the Lonestar filter.

MikeM

On Dec 3, 5:38 pm, "Mike Gilmour" wrote:

An EI UBG16 and a zero-centre ammeter would also be good belt & braces
monitoring with the advantage of data logging. It would be interesting to
know the minimum supply voltage the UBG16 unit itself operates at? The unit
should have sufficient storage or an internal battery system to continue
logging a number of lengthy low voltage anomalies. A worst case scenario
perhaps but its reassuring to know of its minumum supply specification e.g.
does the display shut down at low voltage but data storage continue.

Per the UBG16 Installation Manual (downloadable at www.buy-ei.com),
the UBG16 operates on 10.5 to 35V. The MUX8 data logger module
requires 7.5V to 35V. Since the UBG16 sends RS232 to the MUX8, I
suspect that the data stream from the UBG16 will quit first.

If I have an inflight alternator failure, I will try to be on the
ground long before the battery discharges below 12.0V. Since I know
within seconds that the alternator trips off line, by shedding loads,
I should easily have 30 to 45min of battery life to run essentials,
like Gyros, GPS, NAV, COM and Transponder. I do a battery capacity
tests as part of the annual inspection. I replace nominally 25AH
batteries if their capacity degrades below 18AH. This test is
described in the "continuing airworthiness" section of both Gill's and
Concorde's Battery Manual.