2x 12 volt dc power supplies.

[Alex Ayris]

I'm wondering if this would be OK to do. I have A 30 amp 12volt power supply that powers a stereo system that I have made. The issue is that every time I turn off the unit at the switch on the stereo I lose all my settings. I'm wondering if I can wire in an additional 12 volt supply that bypasses the switch and takes the power direct from the mains in, the stereo has a constant live which is what keeps all the settings and a remote live which it uses when I have the stereo turned on but only 1 negative. So can I wire the additional power supply to the constant live and to the same negative that the other power supply is using? The secondary power supply is on 0.5 amp. Any advice would be appreciated.

 

[duke37]

That sounds all right to me.
You could consider a small 9V NiCad battery to hold the memory instead of an extra power supply. It depends on the voltage and current needed and how long your holidays are.

 

[dorke]

What kind of memory device holds the setting?
If you had used a "permanent memory device" like a FLASH , it would have solved your problem.

 

[Alex Ayris]

Thanks for response. It's actually a heads unit from a car so the memory function is built into that somewhere. I had thought about the 9 volt option. Although I have no idea how long that would last. I suppose I could try and find out.

 

[Alex Ayris]

So I have just found out that what I'm trying to do would not work. Let me explain what I'm doing. So I'm trying to convert an old car stereo system into a stereo in my house. The trouble I am having is I can't get my radio to keep its presets. ( it doesn't bother me but it bugs the hell out of my wife). So the above solution was to keep the presets. However I have found out that the constant live is the live that also supplies the power. And the remote live ( when you switch the ignition on) is just a switching live. I still have not tested this to see if this is true but it makes sense. I could wire the 2 together that would solve my problem, but the trouble is I don't want a 40 amp power supply sitting on all day every day. Could I still use an additional.0.5 amp power supply that has some sort of bypsss when the main power supply is turned on?

Any help would be appreciated.

 

[Alex Ayris]

I have been doing some sole searching and have maybe had a eureka moment. Would it even matter if I had the 40amp supply running all the time if the stereo is off then it would only be drawing the minium current required by the stereo to keep the presets and settings. My only concern would be the power supply getting hot. So the question I'm posed with now is would it? I'm guessing not as it would be drawing such a minimal current. If someone could let me know if I have this wrong please let me know same go's for if I have it right. Lol.

 

[Alex Ayris]

So I have decided I do want to run 2 power supplies. Is there a way of wiring in a relay that switches supply when the main supply is turned off?

Any help much appreciated.

 

[Alex Ayris]

??

 

[duke37]

Just connect the relay coil across the power supply. If you have a change-over relay you can make or disconnect a circuit as required. A relay of considerable switching capacity will be quite thirsty.

 

[Alex Ayris]

Just connect the relay coil across the power supply. If you have a change-over relay you can make or disconnect a circuit as required. A relay of considerable switching capacity will be quite thirsty.

Any suggestions on what type and how to wire it. I'm a bit of a novice as you may have guessed. The max start up current will be around 25-30 amps dc but actual running amps closer to 15 amps.

 

[Alex Ayris]

http://www.ebay.co.uk/itm/12V-Micro-Automotive-Changeover-Relay-30A-5-Pin-Car-Bike-Van-/261993828001. I was thinking this might do the trick?