Keeping station pre-sets when hooked up to dc power supply?

Electronic circuits that contain presets have a small trickle power feeding those presets at all times. When you shut off the deck, or a TV or a radio, you're really only shutting down the main circuits like amplifiers, etc. The presets remain energized. So, in your case, to retain the presets, don't turn off the dc power supply. It's that simple.

So if I leave the dc power on and install a switch to act like a key ignition then it should save them. There is a yellow wire for constant power and there is a red wire ( I assume it is to allow a low current to save the pre-sets but power down the deck to lower current draw from the battery). Am I correct in my assumption. The reason I ask is because the deck stays lite up when it should turn off. Thanks for your help.

I believe you are correct that usually car stereo's have a "switched" hot that turns off with the key or in a lot of newer cars the RAP or Retained Accessory Power which allows you to use accessories such as power windows, stereos, etc. for a fixed amount of time after turning off the car. Then there is a constant hot to power the clock, keep presets if they are stored in volatile memory, etc. I'm not sure of the colors for Panasonic but the "switched" hot should be a heavier guage wire then the constant hot.

I'm not sure why you would see so much current draw if you turn-off the stereo but putting a properly rated switch on the switched hot to simulate turning the car off and leaving the constant hot connected to the DC supply which remains on should save your presets.

Shawn

Are you talking about a car radio? I'm not really clear on your application and why you would have a separate power supply. Please provide more information.

We do need fuller infos before we go marching off into the distance using the wrong directions, don't you think?

Yes it is a car stereo that I what to use in a garage. The yellow wire is a heavier gauge wire than the red. So which should be hooked up to the switch?

>>So which should be hooked up to the switch?

Without the schematic there is no way to know. email crutchfield and have them send you a copy of the installation schematic. Then you'll need information on your car about where the accessory hot points are. You may be able to find something on the web or you'll have to use a voltmeter to figure it out.

As has been said newer vehicles have three accessroy power points: instantaneous switched, delayed off switched and always on. You'll have to wait 5-10 minutes with the voltmeter on the hot point to be sure you have always on and not delayed off.

Of course the other option is to take it to an installer, but that will probably cost $100 unless they are feeling generous...

Good luck.

I would guess the the yellow wire would be hooked up directly to the source and that the red would be the switched wire. This is only a guess and it could be the other way around. An internet search on your model # stereo might yield a wiring diagram. If it were me I would try it that way and see if it works as you want it but (disclaimer coming) do so at your own risk. Chances are it won't hurt the stereo if the wrong one is disconnected but I make no promises or guarentees expressed or written.

Shawn

The last two posters have it, without the diagrams, you will have to experiment, but the correct one for permanent live is usually the red wire in my very limited experience. That way, you keep your presets active.

But you then need to have your power supply active all the time. So a better bet may be a dual power supply that has a tiny 12 volt source for when you are "switched off" or you need to find a car radio that has presets that do not care if the 12 volts are removed.....an older model of 20 years ago or more for example.......!

Or, you place a 12 volt car battery between say a charger and the radio, that way (once you have correctly identified the permanent live connection) it will work like a car so to say.

BUT DO PLEASE ONLY use a charger that does not overcharge as all cheap chargers sadly do!! Or put a voltmeter in place and switch the charger off and on as needed to maintain the charge (but this is liable to be forgotten!!). Or use a 12 volt power supply, that ONLY supplies 12 volts exactly, that way the battery will never charge fully.....

12.6 volts would actually be better (adjustable power supply with a good voltmeter) for the battery and absolutely perfect, as radio presets usually only need a few milliamps anyway.....not more! 12.6 will stop sulfating of the battery better....

Overcharging ruins batteries and causes a dangerous explosive gas to be formed.....

Remember, using something in a way for which it was not originally designed is usually fraught with problems.....!!

You are correct about wiring the constant power lead to save your presets. I have done the exact same thing in my garage. I didn't want to spend good money on a stereo system just to put it in my hot humid garage. Of course I didn't go out and buy an aftermarket deck, either. Instead, I used the old Chrysler radio (with a digital tuner and presets) that I had laying around after putting an aftermarket CD player in my Dodge truck.

I have the radio power lead switched and have a constant 13.2 volts going to the memory lead to keep my presets and the clock correct. As to the memory lead being yellow and the swithched red (or vice versa), I have seen them both ways. I would imagine that the thicker one wourld be switched power, but I would check with the manufacturer of the deck to be sure. Better yet, try switching one and see if you lose your presets. If you do, it's obviuously the other one ;)

My power supply consists of the transformer from an old UPS, a bridge rectifier and a few larger filter caps that I had laying around. (oh yeah, a fuse too)

This simple setup, driving a $20 truck speaker box (from WalMart), has been working flawlessly for about five or six years now. Another cheap junk box project that has exceeded my expectations.

...but did it need constant 12 volts for the presets?????

Sort of. It needs constant power for the clock and to stay on a preset. When there is a power loss, the clock loses it's time setting and the radio comes back on tuned to 540 AM, regardless of what channel it was tuned to previously. The actual presets seem to keep though. I just have to hit the FM button (if I am listening to an FM staion) and push the correct preset button to get back to where I was before.

The power supply has been powered the entire five or six years with no problems, though.

Typically a car sterio with an LED read out keeps it's presets because there is a separate constant power wire going to it. This way when you turn off ignition power to the LED readout, there is still constant power to the preset memory

Downloaded the wiring diagram from crutchfield. Yellow goes to the battery and red goes to the acc power lead. Am I correct in assuming that the red wire can be connected to a switch between the power supply and the deck to get the desired result or vise versa. Thanks for you input everyone.

You are correct, put a switch in series on the red wire and the stereo should turn off as if you turned off the car.

Shawn

What type of switch should I use? The power supply is 13.8 V with 3 amp draw. The deck when hook-up to 4 speakers will draw 2.2 amps. Should I use a 3 amp switch or 0.5 amp switch?

The 0.5 amp switch will be fine. The red wire is a relatively low current remote turn-on, the major current draw is on the other wire.

Shawn

thanks everyone for your input. got it hooked up today and works perfect. thanks again.