On 7/31/11 8:23 PM, Tony V wrote:
On 7/31/2011 10:58 PM, John Derosa wrote:
Tony,

I am with Darryl on this, with your seemingly modern electronics and a
new
9AH battery, you "should not be having a problem". But of course you do
apparently seem to be having an problem. I say apparently as you say your
Dittel display disappears when you transmit but it still "... gets out
OK...". This seems like a problem with your radio, not with your battery
or wiring.

So it appears. When it happened again today, I switched the 302 to the
battery voltage screen and when I was transmitting (with the blank LCD
display), the 302 was registering 11.6 volts. So, it appears that I have
a radio or wiring problem.

What is the gauge of your wiring from the battery to your instrument
panel?
If you are using small gauge wiring, and drawing considerable amps when
transmitting, then the voltage can drop considerably between the battery
and your radio. I use 12ga wiring. 14ga generally works just fine.
Anything smaller and you are throwing away voltage, which we glider
pilots
cannot afford. So measure the voltage of your power system at the radio
when you hit the transmit key. If the voltage drops considerably (i.e.
from 12.5VDC to 11.5VDC) then you either have a wiring/connection
issue or
your battery is bad. BTW: Only use Tefzel wiring in aircraft:
http://wingsandwheels.com/tefzel_coa...kers_louds.htm.

I will be checking the wiring to the radio very closely.

Battery Testing - Testing your batteries each year is a good idea. Darryl
mentions a very nice battery tester which does a quick job of determining
good from bad. Unfortunately, it costs $150 which is a bit steep for a
once a year effort. So here is my (slow) poor man battery testing method
that should not cost more than $10-$15:
http://aviation.derosaweb.net/#batterytest

This is nice. I typically test by putting a 1 Amp load on the battery
(using a 1156 automotive light bulb). My charger is an
accumate(http://www.accumate.com/612/), which IMHO is quite good.

Thanks for the advice!

Tony, LS6-b "6N"

It actually has to be _really_ thin wire to drop significant voltage at
transmit current draws (because that current is just not that high -
with modern radios typically about a bit over 1 - 1.5 amp @ ~12VDC
transmit draw, say worse case 2 A all up, you can draw that through 10
feet of 24 AWG wire (finer than you should find in a glider) and only
drop around 0.25 volt. So its worth checking the wiring and using
heavier wiring can be good practice, but thickness of wiring causing
this problem is kinda unlikely.

One thing I would look out for if the wiring seems suspect is corrosion.
Especially hidden behind heat shrink tubing and inside poorly made crimp
connection. So if you can't sort anything else out carefully inspect
connectors. Sometimes it hides in places like inline fuse housings and
their connections etc.

But overall I'm also suspecting your radio. It also may be worth
thinking if this effect is temperature dependent (happens after the
radio bakes in the sun for a while?). I've seen LCD displays exhibit all
sorts of weird problems when they get hot enough.

Darryl