Trying to wire 2 power sources into 1 stereo

Thread Starter

Thismetalmess

Joined Dec 6, 2017
12
Hello!
I have a VW Bus I'm working on. My stereo is located in the cab area, and wired standard, so it turns on when the ignition turns on.
I have another battery solar powered, that I want to be able to flip a switch and power on the stereo, without having the ignition on, and have it running off the SOLAR battery..
Heres the catch.. I already have installed the wires for a SPST switch and mounted the switch in the cabinet.. In the rear of the vehicle.. So we have current running from the rear up to the cab.. I want that wire, when it's switched on, turn the stereo on. The only, ONLY issue I have so far is that, of course, if I wire both the hot leads, one from the ignition switch, one from the aux battery together, issues occur. So how do I isolate the two power sources?
 

Reloadron

Joined Jan 15, 2015
5,669
Without looking at a drawing my best guess would be the addition of a SPDT switch or SPDT Relay. The radio being connected to switch Common allowing selecting either power source. This also could be a ON OFF ON SPDT allowing a center OFF position.

Here is a basic drawing allowing battery select:
Battery Select.png

Ron
 
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Thread Starter

Thismetalmess

Joined Dec 6, 2017
12
Without looking at a drawing my best guess would be the addition of a SPDT switch or SPDT Relay. The radio being connected to switch Common allowing selecting either power source. This also could be a ON OFF ON SPDT allowing a center OFF position.

Ron
Thanks for the swift reply. I drew a drawing but it further baffled my electrical engineering friend.
If I could try to explain in simpler terms:
I have a powered stereo, assume it's constantly powered, or switched either way. I would like that when the OTHER power source becomes available, the stereo becomes powered by the second source.. Isolated, obviously so both power sources never "touch"
Attached is my potentially confusing drawing. The "theoretical device" labeled "SPDT RELAY?" in the drawing is the magical device that in my mind, ignores one current for the other, and connects it to the stereo.
Thanks, I apologize for my ignorance in these matters. Screen Shot 2017-12-05 at 5.31.44 PM.png
 

Thread Starter

Thismetalmess

Joined Dec 6, 2017
12
OK yes I realize this would work flawlessly, but I am more difficult than that haha

All the RadioShacks in town shut down and I can't order a SPDT switch just gambling it'll fit in my already cut hole I have for the SPST switch I have installed... Can I link a SPDT Relay AFTER the SPST switch and accomplish the same thing??

Thanks:)
 

Reloadron

Joined Jan 15, 2015
5,669
I have a powered stereo, assume it's constantly powered, or switched either way. I would like that when the OTHER power source becomes available, the stereo becomes powered by the second source.. Isolated, obviously so both power sources never "touch"
With that in mind I would use a SPDT automotive relay very commonly available. You can buy relay and socket from any parts store. I can likely work up a simple drawing if you feel you need one. It would allow the aux battery when selected to power the radio. In your drawing the SPST switch in addition to how you already drew it would also energize the relay. Pretty much as you have it drawn.

Youcan also get any switches from an auto parts store. :)

Ron
 

Thread Starter

Thismetalmess

Joined Dec 6, 2017
12
With that in mind I would use a SPDT automotive relay very commonly available. You can buy relay and socket from any parts store. I can likely work up a simple drawing if you feel you need one. It would allow the aux battery when selected to power the radio. In your drawing the SPST switch in addition to how you already drew it would also energize the relay. Pretty much as you have it drawn.

Youcan also get any switches from an auto parts store. :)

Ron
OK sweet then I think we've got the answer! If you have the time to draw that out, just for me to confirm, then I would be very appreciative! I can probably figure out how to wire the terminals of the relay, with troubleshooting..
 

dendad

Joined Feb 20, 2016
3,625
Would a couple of diodes work ok for your application?
Use a bridge rectifier module, connect the ignition fed line to one AC terminal, the solar battery to the other AC terminal, and the radio to the + terminal. leave the - terminal not connected.
Bridge2.jpg
 
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