Is 'clock power' required or just desirable?

[BillinDurham]

My (3) HX panel is wire so that 'clock power' is supplied 24/7. Originally, as I recall, it was required if the systems clock was to retain the time of day.

Recently, went I had left clock power disconnected, it seemed that the system retained the correct time, or at least picked it up from the GPS signal or something.

Can someone speak to what 'clock power' powers in the current system?

Thanks.

[katieb]

I wrote about this a while ago in the Sport Installation manual- so rather than rewrite it I took the lazy way out and pasted it here for you. (It is Friday afternoon, after all...)

Internal GPS memory may be maintained when the aircraft is parked on the ground by connecting
Pin 21 on the EFIS, formerly referred to as “Clock Power,” to the aircraft battery. The draw is less
than one milliamp, but it may draw the aircraft’s battery power down over periods of inactivity.
When Pin 21 is not hooked to the battery, the GPS may take 2-3 minutes longer to find its position
after startup. Pilots who do not fly at least once per week should leave the GPS memory power
wire disconnected.

When the GPS knows what time it is and where on the Earth it is, it takes a shorter time to find the satellite constellation. I could be wrong, but I believe the newer GPS units make "clock power" obsolete. The GPS chips that we are using now have a tiny internal battery that maintains their memory for up to 3 weeks after the unit is powered off. I don't know if older GPS units had this or not-- but I did read it on the data sheet for the chips we use now. So, your HXs probably have it. In my airplane, I will not hook up the Clock Power. I'd rather take a chance on waiting a couple minutes for the GPS than have my battery slowly drained, especially in this colder northern climate.

[BillinDurham]

Thank you Katie! Exactly what I needed to know.

Since normal ops depend on the G430 GPS, I'm thinking that I won't even notice the search time. I will be discoing the line to all 3 ASAP... am hoping that I have them fused separately so that popping a fuse is all that will be required.

Thanks.

Bill

[GRT_Jeff]

On the HX and HXr, clock power connects to the main processor to keep the time, date, and possibly other temporary boot information. On a PC, this is normally powered by a 3V coin cell battery, but I don't know how efficient our circuit is. If the clock is not powered, the EFIS will pick up the time and date from a GPS or weather source as soon as it's available.

The Sport clock power only connects to the internal GPS module as a backup to the internal battery in the GPS. It is not normally connected.

[BillinDurham]

I have disco'd the clock power lines and taken a few flights. Didn't miss it a bit. All is fine now.

Having (3) HXs installed, and therefore 3 clock power lines, I think the draw was just too much for my battery. I've flown over 150hours each of the last 2 years but my flights are often 3-4 weeks apart. I have dual Odyssey 960s and was finding the life on the one hooked up the clock power lines was unexpectedly short and I was in the process of killing a 2nd battery. I've been recording no-load fully charged voltages on all my batteries since half way thru the build so I had a pretty good data track of what to expect from the batteries. I'm pretty sure going without these power draws will fix the battery problem.

Thanks for the additional detail.

[RV-10flyer]

I have a PC 680 aux battery in the back and on my second one in 125 hrs. I have two HX's connected. After 3 -4 weeks of no flying, my aux battery always reads less than 11.5 vdc. I will check amp draw next time at the hangar and disconnect mine too. I also have cabin and glareshield LED dimmers wired in, but mfr says amp draw is nil with rotary switch off.

[chal3oye]

I will be discoing the line to all 3 ASAP... am hoping that I have them fused separately so that popping a fuse is all that will be required.