Frequently Asked Question
BIRDHOUSE - What is the Lithium Coin battery for ?
Last Updated 6 years ago
If the coin cell goes dead the processor cannot keep time and may not "wake up" properly after "sleeping".
Sleep cycles shut down the processor to reduce battery current drain when AC power is lost (i.e. - running on internal power).
The (coin cell) backed clock allows it to "wake up" every few minutes for a few seconds, just long enough to check the situation.
If everything is OK and there still isn't any AC, it simply goes back to sleep.
If it didn't "sleep" the batteries would only last a few hours rather than a few days.
Most people have reliable AC so it never sleeps so this is typically not a problem.
What happens if the coin cell falls off or goes dead? I don't believe anything will happen at all - that is until it loses AC.
The worst scenario I can think of is that it loses AC and when AC is restored the processor is sleeping but it can't recover because the coin cell is dead. So, the processor never recharges the main batteries. Yes, software monitors the main battery charging.
Add to this a customer that doesn't test their system regularly, so a couple years later corrosion from four dead NiMH batteries damages the control board. I admit that this scenario is pretty far-fetched. It still is a possibility.
Note that there are redundant circuits that will "trip" the disconnect without the processor even operating. For that reason I don't see any safety risk. The manual tells users to test their system regularly and to open up the case every once in a while to change batteries and / or inspect for corrosion.
Sleep cycles shut down the processor to reduce battery current drain when AC power is lost (i.e. - running on internal power).
The (coin cell) backed clock allows it to "wake up" every few minutes for a few seconds, just long enough to check the situation.
If everything is OK and there still isn't any AC, it simply goes back to sleep.
If it didn't "sleep" the batteries would only last a few hours rather than a few days.
Most people have reliable AC so it never sleeps so this is typically not a problem.
What happens if the coin cell falls off or goes dead? I don't believe anything will happen at all - that is until it loses AC.
The worst scenario I can think of is that it loses AC and when AC is restored the processor is sleeping but it can't recover because the coin cell is dead. So, the processor never recharges the main batteries. Yes, software monitors the main battery charging.
Add to this a customer that doesn't test their system regularly, so a couple years later corrosion from four dead NiMH batteries damages the control board. I admit that this scenario is pretty far-fetched. It still is a possibility.
Note that there are redundant circuits that will "trip" the disconnect without the processor even operating. For that reason I don't see any safety risk. The manual tells users to test their system regularly and to open up the case every once in a while to change batteries and / or inspect for corrosion.