D180 Battery Voltage?

[rdockery_3]

During flight my voltage shows normal and I had never really paid attention to it during pre flight with the engine off. I happened to notice the other day that the voltage with the avionics switch on (only way for voltage to show up with my D180) it shows 12.1 volts with the engine off. When I turned the fuel pump and landing light on during pre flight it temporarily dropped to 11.9 volts. I know that is low for a good battery at rest but I'm wondering if that is just because of the draw from the avionics, fuel pump, lights, etc. The battery is a PC680 and is only around 6 months old. When I went to start the plane it started right up like it always has.

 

[Carl Froehlich]

Normal reading for the condition you discribe.

Carl

 

[Piper J3]

With D-180 EFIS, you may have an early SN RV-12 that has CDI ignition without the auto-spark-retard startup feature. Early CDI modules without the retard feature have green stickers for identification.

The reason I mention this is possible damage to the starter engagement if the engine backfires or struggles thru compression stroke when starting. The starter motor on 9-series Rotax uses an over-running clutch (one-way rollers) instead of a Bendix. The rollers are easily damaged (and hard to replace). Best practice is to always have a fully charged battery for strong starter motor cranking.

I have an Odyssey battery charger connected to the airplane when in the hanger to insure battery will provide strong engine start. The Odyssey charger is not a trickle charger, it monitors and only charges when voltage falls below threshold. Odyssey say 24/7 is fully acceptable practice for their battery / charger combination. I have been doing this for over five years…

 

[rvbuilder2002]

Very good advice from Jim above.
Starting with an undercharged battery is risky.
Replacing the Sprague clutch for the starter, requires splitting the case of the engine.
A fully charged battery should have a voltage of 12.7 to 12.8.
It is possible you have an indication error. Measure the battery voltage on its terminals with a meter and see how that compares to what the D180 indicates.

 

[rdockery_3]

I believe mine has the newer ignition modules because the logbook shows they were replaced recently but I didn't pay attention to the sticker the last time I had the cowling off. You don't think that voltage would be normal because of the draw from the avionics and lights being on as the second poster suggested?

 

[rvbuilder2002]

I believe mine has the newer ignition modules because the logbook shows they were replaced recently but I didn't pay attention to the sticker the last time I had the cowling off. You don't think that voltage would be normal because of the draw from the avionics and lights being on as the second poster suggested?

If your comment was directed to me…. Very close to fully charged battery voltage should be displayed with only the master switch on and the EFIS powered up. As you turn on other devices, the voltage will go down but should still be in the 12.4-12.5v range, depending on how many things you turn on.

 

[Carl Froehlich]

If your comment was directed to me…. Very close to fully charged battery voltage should be displayed with only the master switch on and the EFIS powered up. As you turn on other devices, the voltage will go down but should still be in the 12.4-12.5v range, depending on how many things you turn on.

This assumes you are measuring battery voltage at the battery. Most setups measure buss voltage very downstream of the battery, so there will be both a battery droop and line loss depending on what is running.

A good science project - put your good multimeter on the battery terminals and compare that to the EMS voltage reading after you power up all you normal stuff.

Carl