Keep alive circuit power usage

[Jake DeHaan(Guest)]

I am building an RV9A with Eggenfellner Subaru engine. I noticed that my aircraft batteries were going down with the aircraft just sitting (not flying yet). Checked the power usage and with the Dynon EFIS keep alive wire (pin 2) connected to the EXP bus keep alive terminal the ammeter read 215 mA. This seems excessive. The other strange thing is that when I disconnect the remote compass this value drops to 95 mA - it should not be connected to the keep alive circuit. When the keep alive wire is disconnected from the EXP bus the usage drops to zero.

 

[dynonsupport]

The keep alive wire can draw quite a bit of power, but it will only be for short periods of time.

The primary use of the keep alive is to keep the clock running if there is no internal battery. This is microamps of current.

The secondary use of the keep alive is to charge your internal battery. This can be up to an Amp of current, but only until the battery is charged, and decreases as the battery charges.

When you first plug in the keep alive wire, the EFIS turns on (internally) and checks for a battery and sees if it needs to be charged. If it does, it charges it. If it doesn't, it shuts off after a few minutes. After that, it powers up periodically and checks to see if the battery needs a charge, but this only takes a few mS every few minutes.

The reason you see a current difference with the remote compass is because the EDC is connected to the EFIS power supply and we can't turn on that supply to charge the battery without also powering the EDC. This is expected behavior.

In order to see the real standby current of the EFIS, you need to hook it up to your ammeter and leave it all hooked up for at least 10 minutes, assuming your battery is completely charged. You'll see that after a few minues, the unit shuts back down and the current drops to basically zero. The only reason that you are seeing this is because you are disconnecting the EFIS from all power as you put the ammeter in-line, and thus the unit is booting up cold and figuring everything out.

We've had plenty of customers use the keep alive line with no problems.

On the other hand- if you have an internal battery, there really isn't any need for the keep alive line, as your battery will keep the clock, and the battery will charge whenever the EFIS is on.

 

[jtdehaan]

I kept the ammeter in place for 15 minutes and it constantly cycles about 27 times per minute to about 127 mA. In addition the remote compass does not seem to be working, when doing the test with the headset the compass moves about 10 to 20 degrees whether the remote compass is plugged in or not. There is power going to the remote compass, but the communication does not seem to work.

 

[Frank(Guest)]

Just a thought but presumably if you have the keep alive circuit wired up and you end up having an alternator failure in flight...presumably the keep alive circuit will attempt to recharge the battery as you draw it down?

With my 8 amp standby alternator I need to rely on the internal battery of the EFIS, i.e not draw from this standby source.

Presumably in this case one should NOT connect the keep alive, or at least have a way to disconnect it in the event of an alternator failure?

Presumably the same is true of the EMS (even though it does not have an internal battery, I am toying with the idea of providing a small battery dedicated to the EMS so it will run independantly in the event of power loss).

Thanks

Frank

 

[dynonsupport]

Frank,
If the EFIS is ON, we will not draw any power from keep alive. It doesn't matter if we are on master power or battery. So keep the EFIS on battery backup during an alternator failure and we won't draw any power.

The same is true of the EMS. In the EMS the only thing keep alive is used for is the clock, which only draws microamps, so this shouldn't be an issue. If the EMS has master power, the KA circut doesn't draw anything.

 

[Vern Little(Guest)]

I have the keep alive circuit connected to the main battery through a shottky diode. When I power down, I see the expect 100 to 200 mA of current that is used to charge the internal battery.

However, after several weeks, my main battery was completely discharged and the D10A was 'ticking' (powering up and down internally?).

Do I have a defective unit, or is the in-line shottky affecting the behaviour of the D10A. Under no circumstances should it discharge the main battery... this is a serious problem and can damage the battery.

The recommendation to not use the keep alive function with an internal battery may be the only fix.

Comments?

 

[dynonsupport]

The shottky diode won't affect anything in your installation.

The ticking you hear is part of the power supply and does not indicate a defect.

We are looking into the battery discharge issue and agree that the EFIS should not be doing this to your aircraft battery. While we investigate, please disconnect the keep alive line from the EFIS (or battery) to ensure that the EFIS can not excessively drain your aircraft battery.