selecting between 2 different sources

Hello all...my first time posting. I need to create a circuit that selects between 2 dc power sources (PS A and PS B) with a push button. It is ok if cause an slight interruption in power during the switching process. I can fire the relay to switch power sources well enough, but as soon as I press the button to switch, the relay dies and it defaults back to the PS A. (assuming PS A is where I am starting from.) I know it has something to do with keeping the relay coil energized during the switchover. I also need to be able to switch from PS B to PS A again after that, with the same button. I am stumped. any ideas? thanks in advance.

Can you post a schematic of your circuit so far?

If your supplies are fairly low current you could use a latching changeover switch for the pushbutton, if it is acceptable to have a switch that bulky. That way you wouldn't need anything more than the switch itself.

A change-over switch, rather than a button, seems the obvious answer. Couldn't you use that?
If you must use a relay to do the switching then perhaps you could supply power to the relay from both sources via diodes.

If you must use a push button, use a "push-on/push-off" type.
View attachment RLY.PDF

alec_t said:

A change-over switch, rather than a button, seems the obvious answer. Couldn't you use that?
If you must use a relay to do the switching then perhaps you could supply power to the relay from both sources via diodes.

Click to expand...

View attachment RLY1.PDF

The cct looks good, Mike odom, but can the +RLY_PWR be driven from PS A and / or PS B?? I want to keep this thing kinda self-contained.
thanks

dvandlp said:

The cct looks good, Mike odom, but can the +RLY_PWR be driven from PS A and / or PS B?? I want to keep this thing kinda self-contained.
thanks

Click to expand...

see circuit in post #5