What about using a micro relay instead of a diode?

Opens circuit when 5v is present somehow.

Or… a pcb that installs a usb port and uses a 5v usb power pack as a voltage source

Sphere478 wrote on 2024-01-26, 03:38:

Tony359 recently did some work on one of my boards and was able to identify a diode I beleieve near by that when removed stopped 5v from reaching the battery terminals. And the rtc functioned properly with a 3.3v battery. So simply removed the diode and installed a coin cell holder.

Can you post a a picture?

douglar wrote on 2024-01-26, 12:51:

Sphere478 wrote on 2024-01-26, 03:38:

Tony359 recently did some work on one of my boards and was able to identify a diode I beleieve near by that when removed stopped 5v from reaching the battery terminals. And the rtc functioned properly with a 3.3v battery. So simply removed the diode and installed a coin cell holder.

Can you post a a picture?

I can do better, here’s the video! :p went live today!

https://www.youtube.com/watch?v=yVg2pvyYbn0

Thanks Tony!

There are three main concerns when doing a mod like this that never really get covered on YouTube.

1) making sure the RTC keeps accurate time after leaving the system off a day or two - low standby voltage can save the NVRAM settings just fine and still not run the RTC properly

2) making sure the RTC still ticks with the system powered ON and NO battery installed - you want to ensure you're not powering the clock exclusively from battery when you attempt to disable charging

3) making sure the coin cell has the requisite capacity to last more than a year - many old RTC chips are NOT standby power efficient and really require the capacity of a 3xAA pack or equivalent

maxtherabbit wrote on 2024-01-27, 02:32:

There are three main concerns when doing a mod like this that never really get covered on YouTube. […]
Show full quote

There are three main concerns when doing a mod like this that never really get covered on YouTube.

1) making sure the RTC keeps accurate time after leaving the system off a day or two - low standby voltage can save the NVRAM settings just fine and still not run the RTC properly

2) making sure the RTC still ticks with the system powered ON and NO battery installed - you want to ensure you're not powering the clock exclusively from battery when you attempt to disable charging

3) making sure the coin cell has the requisite capacity to last more than a year - many old RTC chips are NOT standby power efficient and really require the capacity of a 3xAA pack or equivalent

Excellent advice! I will see if I can check this when I get the board. Thanks man!

I recently found a VLB card that kills coin cell batteries. If I leave the vlb board in the system with the power off, the board loses its settings in about a minute and the coin cell will die in about a week if I leave the power off. Its that UMC 85C418f card I’ve been messing with.

Kinda makes me wonder if we should use something like this with a li ion cell 5v in, 3.7-4.2v out.

The charge circuit can hook direct to 5v psu

The battery can be direct to the remote battery terminals

maxtherabbit wrote on 2024-01-27, 02:32:

There are three main concerns when doing a mod like this that never really get covered on YouTube. […]
Show full quote

There are three main concerns when doing a mod like this that never really get covered on YouTube.

1) making sure the RTC keeps accurate time after leaving the system off a day or two - low standby voltage can save the NVRAM settings just fine and still not run the RTC properly

2) making sure the RTC still ticks with the system powered ON and NO battery installed - you want to ensure you're not powering the clock exclusively from battery when you attempt to disable charging

3) making sure the coin cell has the requisite capacity to last more than a year - many old RTC chips are NOT standby power efficient and really require the capacity of a 3xAA pack or equivalent

Thanks for the advice, I'll bear that in mind!