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Yes. The voltage will drop immediately when you draw current, try using a resistor just to be safe.
Most cheap power supplies work this way...sadly...
Check the input voltage rating range on your led strip. If it's made for an automobile, then it's probably rated for up to around 16 or 17 VDC, since alternators produce more than the nominal battery voltage for charging, which *often goes unfiltered (aside from the primary rectification and smoothing) into the DC aux bus. If so, then it may already be within compliance for use directly with your supply. If not, then you will need to pre-load it as Steve indicated, to draw the voltage supply into its compliance range, or push it through an intermediary voltage regulator before powering your strip if preloading isn't an optiuon and the led strip does not provide enough load to draw the suply into compliance on its own.
I can understand you do not want to risk damage to your LED strip !
Here is a very simple Unknown PSU Test that you can quickly try to best answer your question.
Start with a simple load of a 40 watt incandescent light and measure the PSU DC voltage. If it is still high try a 60 watt resistor and so and so.....
More than likely. Is it a modern small switchmode supply, or the old heavy wall wart that has a nice iron transformer in it and no regulating circuitry whatsoever?
If it is the older type, then it most likely cannot deliver more than 500mA while maintaining the output voltage, and I would not worry about it, as once it is connected to enough load (the LEDs in this case) that voltage will drop and things should be fine. (with these old unregulated blocks, usually the output is a lot higher than the rating, and the rating is only accurate when the correct amount of power is being drawn. Another way this saggy effect can be described is to say that the output impedance of the supply is high. It can appear like a 16.8V supply with a resistor in series, even if no such resistor is actually present.)
If it is a regulated supply, the output voltage should be pretty close to the nominal rating regardless of load. (Thats called the load regulation, and the better it is, you can say the output impedance is low, so that virtual resistor described earlier is smaller, so it looks more like a constant voltage source.). In your case, that means the open-circuit voltage of the switching regulator should be like 12.6V or something, and loaded down, it might not even drop by as little as 1 volt! 17V on the output of that could mean that it is broken, or that you have not met the minumum load requirments.
Yes, but you need to use a controller for it. Depending on the kind of lights and how much control you want to have over them.
This one is for a single color and it takes anything from 5 to 24 volts. It has an RF remote control.
If you are using a set of RGB (multi color) you might want one of these.
Both of these items have ended but you can search for ones just like them.
The nice thing about them is that the voltage control and resistance is all built into them and they are very reasonable in price. There are some manual ones also which work the same but with out the remotes.
I'd second Vyger,
Your Power supply issue is most likely because there is no load on it. Hook up a simple 12v lamp to it and test again, it should drop down the the specified 12V rating
Try it, briefly, the load of the LEDs will /should pull the output down to 12V.
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