Is it possible to connect an AC/DC power adapter's ground (-) to a battery's negative side?
I am powering a car radio with a 12V AC adapter. That works fine. However, if the radio loses power, it also loses it's programmed FM stations etc. There is a separate cable to provide constant +12 V. from the car battery, but there is only one "-".
Would it work if I connect both the AC/DC "-" and the battery's "-" together to the car radio "-" lead, and the "+" sides of the adapter and the battery to their respective leads?
Or would this fry my battery, my adapter, my radio, or burn down the house 🙂 , or just plainly not work?
Edit:
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I was thinkinkg of any small cheap 12V battery. Probably non-rechargeable. Maintaining settings memory should draw very little power.
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I have no idea whether the 2 separate +12V leads are eventually shorted inside the car radio or not.
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The main difference in my setup from the normal use in a car is that in a car, these 2 power leads get the same voltage (from the single car battery). In my case, they would get a different voltage (possibly up to 2-3 volts of difference?).
Best Answer
Yes, of course it would work. If you think about it for a moment, that's exactly how it's wired when it's used in the car.
Regarding the additional issues raised in your edit:
Inside the radio, there are two kinds of electrical loads: those that get swtiched on and off with the ignition, and those that need continuous power, such as the clock and the memory for the frequency presets.
If the radio works without any power applied to the "unswitched" power input, that means there's some sort of diode (or equivalent) that powers the unswitched loads from the "switched" power input.
In a car, there are other loads on the unswitched power bus, and the radio designers would not have wanted to power those loads through the diode inside the radio, so there will also be a second diode that prevents this. (You should be able to use a multimeter to verify this.)
Therefore, if you replace the switched power with an AC power supply, there's no way that the AC power supply can try to charge the battery you have attached to the unswitched power input. Everything will be fine. In fact, if you want to use a rechargable battery, you'll have to provide an external charging path.