morganw
11-20-2003, 03:12 AM
Anyone know if the Belkin auto-kit & other power adapters regulate and/or filter the power from the cigarette outlet to the iPod?
Someone took apart an Auto-kit and shoved it inside the dash to hardwire it in, but I can't find the page.
My commute's short enough now that I'm happy using the battery: no ground loops-- but it would be nice to have tunes for longer trips.
kman1666
11-20-2003, 11:30 AM
I'm sorry, I guess I do not understand your question. But I have read nearly all the forums and the only one I remember where someone took apart the auto kit was too remove the light on the back of it so it would not drain his battery. I think there might have been one taking it apart to do something with the amp in it.
morganw
11-20-2003, 03:15 PM
I'm wondering whether car power adapters for the iPod regulate and/or filter the power from the car.
The "12 Volts" from a car might actually be 11 to 13.8 Volts, it might droop significantly when you switch the car from ON to START (starter motor draw) and it might have a lot of noise of significant amplitude on it. This is usually ignition related (thousand volt pulses in the engine compartment are somewhat mitigated by resistors in the spark plugs, but there might be enough noise to be audible), but can also come from other sources. For instance, my VW Passat has fluorescent dash lighting and the inverter kicks out electromagnetic noise in the audible range.
The alternator is AC, rectified to DC, but it might have significant ripple left if the filtering isn't very good.
The solution is to use a large-ish capacitor to make up for droop and ripple, a regulator to keep the voltage from going over 12V and filters (maybe a simple choke or a common-mode choke) to keep noise in the car's power supply from finding its way into the iPod and your audio.
A really trick supply might be a switcher that uses a transformer so the car ground and iPod ground are isolated. You're better off breaking a ground loop there than putting an inductor in your audio path.
I'm guessing that the iPod takes a pretty wide range of voltages for charging, but based on complaints I see around here, it sounds like it's noise rejection might not be so hot.
---
This guy (http://forums.nasioc.com/forums/showthread/t-447148.html) opened up his Belkin Auto-kit to hardwire it, but he doesn't mention what's inside. I thought I'd seen a picture of an opened up one somewhere, but now I can't find it.
-M