Hi guys!
One question keeps running through my mind: how does the internal car clock, mostly inside the BCM, is secured to powerloss? What do you think?
I have teared down some BCMs of Ford Cars (built 2007 onwards) and never found a lithium battery oder such. Well maybe it is all inside a uC which only needs some picoampere to run an internal clock, which may come from an elco. But maybe it is just that simple that there isn't any. So making the car powerless by disconnecting the battery will result in an unset clock. Most modern cars use their radio or navigationsystem to retrieve and set the time.

 

One question keeps running through my mind: how does the internal car clock, mostly inside the BCM, is secured to powerloss?

I've never seen one that is. There may be enough capacitance onboard to provide power across a brief interruption but disconnecting the battery for more than a few seconds will wipe out the clock, and often the radio presets also.

 

Probably has a capacitor that can hold enough charge to keep the clock powered for a day or so. There are clock circuits that only draw current in the picoamp range. Or maybe, it does lose power and once power is re-applied, quickly receives a clock signal and properly resets itself.

 

DALLAS time chips are not likely to be used in a car, but take a look here: https://www.maximintegrated.com/en/app-notes/index.mvp/id/52 especially at the Phantum time chip. So, you have about 10 uA that can be used to keep time.

Microcontrollers on their own can keep time.

Way back when, e.g. 1965, it actually was a wind up clock. A pulse wound the clock when it wound down.

Later you might find the radio or a separate clock keep time. They need a power always and a IGN power. Powe runs the clock chip and other power runs the radio or displays.

I can see where a GPS could do timekeeping, but not all cars come with GPS.

 

Hi guys!
One question keeps running through my mind: how does the internal car clock, mostly inside the BCM, is secured to powerloss? What do you think?
I have teared down some BCMs of Ford Cars (built 2007 onwards) and never found a lithium battery oder such. Well maybe it is all inside a uC which only needs some picoampere to run an internal clock, which may come from an elco. But maybe it is just that simple that there isn't any. So making the car powerless by disconnecting the battery will result in an unset clock. Most modern cars use their radio or navigationsystem to retrieve and set the time.

Most everything I've worked on resets with a power loss, including trip mileage. Typically you can measure 20ma of battery drain with everything turned off. There 9v operated cigarette sized plug units that will provide a "keep alive" voltage while the battery is disconnected

 

There are 9v operated cigarette sized plug units that will provide a "keep alive" voltage while the battery is disconnected

Anyone know the minimum keep-alive voltage to avoid memory loss? Would a 9V PP9 type battery with a 1N4007 series diode (to prevent the PP9 charging), connected permanently across the main battery terminals do the job?

 

Most automotive systems will work until voltage goes under 6V, and start working if voltage goes up over 9V.

 

There are two different circuit types in a car, 1. ignition switched(goes on and off with the key) 2. always on, this is for all of the memories in the car and the other things like the lighting circuits and remotes, things that work without the ignition on. The clock and radio presets falls under the second.

 

For #1. During start, there are some IGN circuits that die when the car is actually starting. Notice that your radio and heating blower goes off when your starting the car. Now, if the ECM went off while starting, you could not start the car.

 

The satnav of my Ford Mondeo (called Fusion outside Europe) built end 2010 facelift, switches off the display and mutes the sound while cranking. It does not really switch off, because it would normally play some intro screen in such case. Oh, btw. my Xenon headlights switch off while cranking also.
I guess this is to protect the electronics from failing due to low voltage and also to reduce load for the battery while attenator is running.