RTC Backup Battery Holder CR-2032 Issues
#3
(09-06-2016, 07:49 PM)MarkHaysHarris777 Wrote:
(09-06-2016, 06:34 PM)steveslim Wrote: I have no electrical circuit experience, but have been trying to search on the web for answers (maybe "Electrical Circuits for Dummies" would help me?), but am having trouble, so I turn here for help.

The CR2032 is a 3 volt lithium ion coin cell typically used on computer mother boards to hold the RTC and CMOS.  

The RTC on the PineA64 requires 3 volts.  The CR2032 battery holder (with switch) is designed to hold two CR2032 cells (in parallel) so that the 'battery' provides 3 volts and 'twice' the available current of one cell.  In this configuration the plus(+) of each cell is tied together (on red) and the negative ( - ) of each cell is tied together on black.

If the cells are installed properly three volts +3v will be present on the plus (red) wire relative to the black (ground) wire when the switch is ON.  If the measurement across the red and black wire is either zero ( 0 ) or six ( 6 ) volts ( or if the polarity is reversed ) then the cells are inserted incorrectly. 

If six volts is plugged into the RTC connector, or if the polarity is reversed damage may occur to the RTC or to the Pine board in general.

Hello MarkHaysHarris777 and thank you very much for the explanation.  In a perfect world, there would be some more detailed instructions on how to use the battery holder when you purchase one.  But even with instructions, my situation appears odd since for one holder I have the battery closest to the red/black wires with the ( - ) terminal on the battery face up and the second battery in that same holder with the ( + ) terminal face up, and for the second holder I have the battery closest to the red/black wires with the ( + ) terminal on the battery face up and the second battery in that second holder with the ( - ) terminal face up.  They are opposite of each other.  Yet both holders only work when they have batteries oriented this way, and so far, neither seems to have burned up, exploded, or otherwise gone up in a puff of smoke.

For what MarkHaysHarris777 has posted, I have to assume that for any given holder, the parallel configuration of the batteries (as opposed to a series configuration, I guess) is done by having one battery with the ( - ) side face up in the holder and the other battery with the ( + ) side up (at least with these holders).  I guess that doubles the current (amperage), while leaving the voltage at 3 volts.  I guess this makes the batteries last longer while controlling the RTC.  I'm assuming that if I WAS really sending 6 volts down the RTC circuit, I'd have noticed it by now (snap, crackle and pop, followed by blue smoke and a noxious odor), even if I don't have a meter.  And some voltage and current must be going down the circuit since the RTC keeps working when I disconnect it from AC power and then reconnect it.  I think I've ruled out 6 volts or 0 volts going down the RTC circuit.

But I still don't know if the battery next to the black/red wires should be inserted with the ( - ) side facing up or down and the second battery (in that same holder) facing in the opposite direction.  Or, in the opposite orientation.  I also don't understand why my two holders seem to require different orientations to work at all.  If the batteries are inserted in the opposite way in either battery holder, then they don't work at all.  This IS a good thing since otherwise, they may fry my board or RTC circuit it seems.  And I still have no idea how to tell if the polarity is reversed.  Is positive polarity always how things should be configured?  Or do some devices require negative polarity to operate?  Guess I do need an electrical meter to really troubleshoot this.  If I did have a meter, would I want to ensure that the circuit has positive polarity?   And could inserting the batteries in the wrong orientation cause the wrong polarity (negative polarity)?  So many questions.

Apparently not a project that a person with my current expertise should dabble in.

Since so far, neither Pine has suffered any ill effects, I'll chalk it up to magic, and update the post if either of them fry.

If all of this is just nonsense, feel free to just ignore it.  But if anyone has anything to add that might help explain this to this ignorant person, I'd be happy for additional lessons.  Thanks again to you, MarkHaysHarris777.  I do appreciate your post.  It did explain some of the puzzle.


Messages In This Thread
RE: RTC Backup Battery Holder CR-2032 Issues - by steveslim - 09-06-2016, 08:46 PM

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