Hey everyone I'm working on a project where I want to be able to power a thin mini-itx motherboard two different ways. Here is what I'm trying to do:
19V battery will be connected to a relay which is connected to the DC input of the motherboard. The port for the power adapter will also be connected through a relay to the DC-IN of the motherboard and to the charging port of the battery. When the adapter is present the adapter relay is closed and the battery relay is opened. When no adapter is present it closes the battery relay and opens the adapter relay. The goal being that the motherboard always has power and I can charge the battery without discharging the battery at the same time since the power adapter can handle both powering the motherboard and charging the battery.
Since the battery voltage will vary based on its charge i'm concerned that there may be short periods of time where a <19V battery will be connected to the constant 19V power adapter.
So my questions are:
In the case of a <19V battery being connected to the 19V power adapter do I need to worry about current flowing back into the battery? The battery has both a charging port and a output port. I'm not really sure what electronics are present on the output port. Maybe use Diodes to prevent current flowing back into the output port of the battery?
Do you think that when a adapter is connected I could switch the battery relay off and the adapter relay on fast enough to not interrupt power to the motherboard? This question somewhat effects the one above. Because I don't really have a feel for how much time I have. I don't have that much experience with relays. I was thinking of using a microprocessor to control the relays in which case I could disconnect the battery relay first then milliseconds later activate the power adapter relay which should mitigate the problem of connecting the adapter and battery together. However, I'm not really sure if that will be fast enough to maintain power to the motherboard.
Lastly do you see other concerns with this method that I have not yet thought of? Mainly safety concerns for the equipment.
Hopefully this is understandable. First time posting this type of question on a board.