Yeah my diagram not as clear as it should have been. The diagonal line pointing in the direction of the smaller power supply was ment to denote that. My bad.
Pin 30 will go to stereo via the Nc/ coil? As in my diagram. And the switch I was thinking the same the way I currently have it would require 2 switches. So from my main power in, put the 30 amp fuse, then split the live, and put the switch on the 30amp supply cable and that should be that?
* what type of capacitor should I use and where should I place it?
Not quite. Your diagram showed a potential problem.
Pins 85 and 86 are for the coil and does not appear to be polarized, so ground and power can be provided forward or backward on these two pins.
Pin 30 is 'common', pin 87a is the Normally Closed contact, and pin 87 is the Normally Open contact.
The diagonal line you have drawn merely shows the 'internal connection' of the relay. That diagonal line will toggle between 87a and 87 as power is added or removed from the coil on pins 85/86.
At any time, the relay Pin 30, will be internally connected to either 87a or 87, but never both, and there is a very very small time-frame where it will not be touching either one while it's changing state.
Your drawing shows that both power supplied are connected to Pin 30. This is a bad decision in itself immediately because you run the risk of having one power supply back-feed into the other. If both power supplies are connected in such a manner you *must* use a diode as protection against backward current into either one of the power supplies. By putting power *into* Pin 30, you are also limiting yourself to no longer choosing which power supply to use, but you are building a circuit which *redirects* power to pin 87a or 87.
Additionally, your drawing shows that both 87a and 87 goes to the stereo amplifier... This in itself is incorrect as well, unless you want to toggle providing power to either the Power input or Standby input of the amplifier. The standby voltage simply holds clock values, and the Power input will turn the unit on and provide the current required to drive the speakers and internal circuitry.
Instead of redirecting power to go from one input to another of your stereo, you must take care of it a different way.
You *must* keep power to the Standby input 24/7.
Power only needs to be supplied to the Power input when you want to listen to music.
The question now is: How do you want to control the device?
Option A: Turn off the big power supply.
Option B: Toggle a separate switch.
So, with that said. I'd encourage you to simply leave the 30A supply on, and put a switch in-line with the Power input on the Stereo and leave the Standby input connected directly to the 30A supply... Easy. The 30A supply is capable of 360W, but it will not run like that all the time! It's simply a converter. When the stereo is on and wants 200W, the power supply will pull 210W-220W from the wall. When the stereo is off and may be drawing less than 1W, the Power Supply will be pulling substantially less as well. The exact amount will depend on how efficient the Power supply is.
*It's possible that your more capable 30A Power Supply draws less current when supplying standby power to the stereo than the less capable supply... I can't say for certain without seeing specs on the supply, but unless the 30A supply is a horribly cheap inefficient beast there really is no need to disconnect the stereo from it and connect it to a lesser power supply with a relay.
If you are still set on making it work your way:
- Connect the 30A supply + to a Fuse Side A.
- Connect Fuse Side B to Switch Side A.
- Connect Fuse Side B to Relay Pin 87.
- Connect Switch Side B to Stereo Power Input.
- Connect Switch Side B to Relay Pin 85.
- Connect the 0.5A supply to Relay Pin 87a
- Connect Relay Pin 30 to Stereo Standby input.
- Connect Relay Pin 86 to Ground.
- Connect Stereo Ground to Ground.
Sorry for lack of diagram.
The switch sits on the Power Input of the stereo. This switch is responsible for turning the stereo *and* relay on and off.
When the relay is off, it will connect the Standby input of the Stereo to the lesser Power Supply connected to pin 87.
When the relay is on, it will connect the Standby input of the Stereo to the more capable Power Supply connected on pin 87a.
In this way, the less capable supply is only ever allowed to connect to the standby input *if* the more capable supply *or* switch is turned off.
The capacitor may not be required, you can test it without first. If you need it, you should put Side A on the Standby input, and Side B on ground.