powering car stereo from computer PSU. how to keep settings??

hello. i am using a high end car stereo, powered by my compouters PSU. i have sorted the red and yellow cables from the head unit, so it powers, but the problem is, that everytime i turn off the computer the car stereo looses settings. Since no one has done it on the instructables i have seen, i guess its hard to be done. has any one done it? i dont want to have the PSU 24/7. i would prefer an external battery...

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verence4 years ago
The car stereo should have (at least) two +12V inputs. In the automotive world, there are (mostly) fixed contact numbers for them.

Contact 30 is the permanent power that is always connected to the battery. (your stereo needs a battery here)

Contact 15 is the switched power, that is only on, when the ignition is on.

So, what you can try is:
- get a small 12V lead battery.
- connect the PSU directly to contact 15 of the stereo. (This will power the stereo)
- connect the PSU to the battery via a diode (make sure, the battery is precharged or invest in a charge controller) The diode will stop any current from the battery backwards through the PSU if the PSU is switched off.
- connect the battery to contact 30 of the stereo. This will preserve the settings if the PSU is switched off. You may want to put a diode between battery and stereo to prevent current bypassing the charge controller.
- off course, connect all ground pins i.e. minus of the battery and contact 31 of the stereo
settra (author)  verence4 years ago
Thanks! this seems like it would work.. but its "allot" of work. i was wandering, wouldn't the 5v standby (purple) from the PSU work??
RavensCraft4 years ago
I may be wrong ,but it seems to me that a radio's settings memory would be like a computers bios memory in that it doesn't require a big high amp battery to maintain settings when the power is off.

I suggest using a 23A size battery which is 12 volts. they are used in garage door opener remotes. Just make a battery holder for the
23A battery and connect it only to the permanent power pin
or whatever pin is for memory.

Note: "23A"  is the actual battery size.  It does not  mean 23 amps.
That should work. Just put a diode between plus of the battery and the permanent power input (contact 30) of the stereo. If you can't get a 23A battery, you may try 8 AA cells in series.
Use a couple of diodes to connect from your PSU and your battery.