Radio memory wire

Thread Starter

enbarnes357

Joined Oct 7, 2013
4
first let me say i am glad to be part of this forum, have a project i am working on and need some help, i have taken a in dash car dvd player and installed it on my tailgating cart what i am using is a 12dvc regulated switching power supply which gives me 12 volts. the problem i have having is keeping memory to my radio presets, so i installed a battery which after time has to be charged so i got to thinking what if i could install some type of relay,which would allow the 12vdc regulated power supply to power the memory wire and once i cut off the system the 12vdc battery will kick in does this sound possible?
 

Thread Starter

enbarnes357

Joined Oct 7, 2013
4
ok but i wanted to know what type of circuit would i need to switch the radio memory from the 12vdc power supply to the 12vdc battery not about the radio.
 

#12

Joined Nov 30, 2010
18,187
This isn't a car modification in my opinion.

A couple of 1N4001 to 1N4007 diodes should work, or just leave the memory wire powered by the battery all the time.
 

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adamclark

Joined Oct 4, 2013
472
thats an easy fix with a standard spdt automotive relay.. ill draw you up a picture if this is what you need... and don't you get some hum through the power supply?
 

adamclark

Joined Oct 4, 2013
472
here is the picture I promised, you need a standard 20/30 amp spdt automotive relay(if it has 5 pins its spdt)... heres how it works,,, the 85 pin comes from the psu power switch to turn the relay on, the 86 pin is the ground for the relay, pins 87 and 87a are normally connected when the relay is off, and pin 30 is the 12v output from the psu. when the psu is off pins 87a and 87 are connected, when you turn the psu on the relay turns on connecting pin 30 with pin 87 letting the psu run the memory.. turn the psu off and the relay turns off letting the batt run the memory wire... hope this is what you needed....cheers
 

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#12

Joined Nov 30, 2010
18,187
I would like to mention that diodes are cheaper than relays and don't eventually get contact resistance build-up.

I also think the memory circuit takes very little current, does it?
 

adamclark

Joined Oct 4, 2013
472
I would like to mention that diodes are cheaper than relays and don't eventually get contact resistance build-up.

I also think the memory circuit takes very little current, does it?
no more than 2 amp. relays are about 6 bucks at the autoparts stores. if you use a quality weather resistant terminal, and don't turn it on and off 100 times a day the resistance build up shouldn't be a problem for 5 years.. I have relays on my boat that have been there for 5 years without any corrosion yet... but I like the diode idea.. I use diodes at work to isolate things, but its mainly ground feedback im isolating. Im just now starting to learn more about electronics and circuits and such so relays have been my main solution for a lot of things in the past..lol
 

Thread Starter

enbarnes357

Joined Oct 7, 2013
4
would like to thank everyone for their help, i will be trying this out today, as for how i turn on the psu it is thru a switch thanks.
 

#12

Joined Nov 30, 2010
18,187
If the memory circuit requires, "more than 2 amps", or, "no more than 2 amps" I called out the wrong diodes. You would need "3 amp" diodes like 1N5404 or STP3150RL.
 
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