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First of all, I have limited experience with electrical components (and theory), but I know exactly what I'm trying to accomplish and why (just not entirely how).

Get this, I'm working on a "battery eliminator" for a portable audio device in my car (which will replace a 1.5v AAA battery with 1.5 volts drawn from the car battery).

Here's the jist:

[12v to 1.5v converter/power adapter]--[fuse?]--[1.5v portable audio]--[auxiliary input adapter]--[factory radio]

Anyway, my question has to do with fuses (I think). At this point, I'm wondering how to determine what size (or kind) of inline fuse is needed to protect the 1.5 volt device from potential overexposure to voltage. However, all fuses seem to go by amps, so I'm not sure if they even respond to voltage like I want them to. In that case, what might I put between the converter and the player to prevent too many volts from going to the player (if the converter should fail, or is on the wrong setting)?

 
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fuse size depends on wire size. its to protect the wire from failure due to power surges or too much current. now the device's amp draw will determine what thickness of wire you need. if you pick too low of a wire/fuse combo, the fuse will blow and you will need to switch to a thicker wire with higher amp fuse. or just pick a larger wire size that will work for sure like 14 gauge. heres the table of how to pick fuses depending on the wire size. they are a bit conservative, and usually you can increase the fuse rating by 1-2 amps for a given wire size and still be okay. im not sure what to do with the voltage regulation. maybe you should post this on hidplanet.com/forums, there are more electronics guys there. im not sure if what you have drawn out will work or not.

 
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Thanks, the fuse information helps. I think the plan will work, of course. Although I'd like it to be fail-safe, because I'll probably use that setup for a long time...