Diodes & 12V stereo "memory" (1 Viewer)

[jblueridge]

I wanted to figure out a way to use any 12V radio in my 24V truck without the stereo setting "memory" pulling my batteries down too much.
I found that my cheap Pyle 7200W 24-12V converter used at least 200ma while providing the tiny amount of current needed to feed the radio memory: 6 days without driving meant not enough power to start the truck.

By combining a tiny 500ma converter with some diodes the stereo works as it would in a 12V car.
If you know how to solder and have heat shrink tubing, you should be able to do this.
I think I spent about $40 for all the bits.

Here's the wiring diagram

The 2 pin connectors let me unplug all this stuff and run power right to the radio if I feel like it.


Stuff to buy:

15SQ045 Schottky 15amp 45V
Amazon product ASIN B079KK5KXN

1N4007 diode 1 amp
Amazon product ASIN B0068AEU0W

Recom 78W12-0.5
R-78W12-0.5 Recom Power | Power Supplies - External/Internal (Off-Board) | DigiKey

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[jblueridge]

I tested the diodes and found that they work well as long as the current is not too high.
I think my cheap Jensen mech-less stereo uses about 4 amps most of the time.

As usually happens with me and wiring, I left the wires too long and made a spaghetti mess.

Using this setup I feel like I could buy a 12V unit with back-up camera for my BJ74 and run it with no problems.

 

[cruiserdan]

There may be a small fly in your ointment. In some cases the continuous power feeding the memory is also the main feed when the radio is powered up. In these cases the feed circuit fries, interrupting power to the radio. Ask how I know

 

[jblueridge]

For my radio, the yellow memory IS the main power line. It is a larger diameter than the red “power” wire. The red wire merely switches the radio on and off.
I used two diodes in parallel to handle the larger current.

A while back I tried the mini converter without the diodes, that setup did not last.

 

[paul r]

I really like the idea behind this. I assume the parasitic draw from the smaller unit is ~20-milliamps? Have you measured the total parasitic draw of the system with and without this in place?

 

[jblueridge]

Sperry digital multi meter showed no current draw at all, which is impossible.
I plan to get a non digital ammeter from our schools science dep’t... measures 0-1 amp I think.

I’ll update with results.

 

[jblueridge]

Student-quality analog ammeter was useless.
More expensive digital self-ranging multi-meter showed a low draw as expected.
Digital ammeter at first showed a spike up to 175 ma, then a decline to 70ma, settling out at just under 22 ma.
I re-tested many times. Final answer was always just under 22 ma.
See pics

 

[jblueridge]

Just posting to say this setup has worked perfectly for 6 months now.
Stereo "remembers" all settings and in every way behaves like it should.