Morning all,
I have an older first gen XM radio in my car that I'm tired of coaxing to change channels, so I'm switching to a newer one that the wife just abandoned because her new car has XM built in. A long time ago, I plunked down 70 or so dollars for a box that both powered my radio and was a FM modulator directly to the antenna wire when it sensed the radio's load. I would like to continue using this box because a new one is 30+ dollars, the old one still works, and maybe I'm just feeling cheap today.
Here's my conundrum: old radio is 6v 1A, new radio is 5v 2A. I'm going by the fuse ratings on the two power supplies as I haven't been able to find any sort of current draw information for either radio and my current multimeter can only handle .5A... bummer. So, assuming that I simply cannot cheat and drop the voltage down (with something like a 1N4001 rectifier or a 7805 regulator) because the new radio is hungrier, I figured I would just run one of those 12v accessory outlet extensions to behind the dash and plug the stock DC power adapter for the new radio to step it from 12v down to 5v. However, in order to keep on using the FM modulator, I need to fool it with a dummy load so the modulation circuitry runs. I was fiddling around with some spare resistors and figured out that the sensing circuitry picks up the load somewhere around .5A... but my little 1/4W resistors get real hot real quick.
If I understand Ohm's law correctly, the maximum wattage on that 6v circuit at 1A is 6W - so if I were to use this Rat Shack 8-Ohm Non-Inductive Resistor (rated for 20W) as my dummy load, then it should not only limit my current to .75A (thus saving me from possibly blowing fuses) but also handle the heat generated from the 4.5W as a result. Is that correct logic? Or am I running the risk of melting something behind my dash if I try this? Should I wire 2 in parallel? Obviously I wouldn't bundle it in the middle of a rat's nest of wires, but there's only so much air for radiating heat back in there... also, I'm not worried about draining the car's battery since the magic modulator box is already on an accessory circuit.
Appreciate the insight!
I have an older first gen XM radio in my car that I'm tired of coaxing to change channels, so I'm switching to a newer one that the wife just abandoned because her new car has XM built in. A long time ago, I plunked down 70 or so dollars for a box that both powered my radio and was a FM modulator directly to the antenna wire when it sensed the radio's load. I would like to continue using this box because a new one is 30+ dollars, the old one still works, and maybe I'm just feeling cheap today.
Here's my conundrum: old radio is 6v 1A, new radio is 5v 2A. I'm going by the fuse ratings on the two power supplies as I haven't been able to find any sort of current draw information for either radio and my current multimeter can only handle .5A... bummer. So, assuming that I simply cannot cheat and drop the voltage down (with something like a 1N4001 rectifier or a 7805 regulator) because the new radio is hungrier, I figured I would just run one of those 12v accessory outlet extensions to behind the dash and plug the stock DC power adapter for the new radio to step it from 12v down to 5v. However, in order to keep on using the FM modulator, I need to fool it with a dummy load so the modulation circuitry runs. I was fiddling around with some spare resistors and figured out that the sensing circuitry picks up the load somewhere around .5A... but my little 1/4W resistors get real hot real quick.
If I understand Ohm's law correctly, the maximum wattage on that 6v circuit at 1A is 6W - so if I were to use this Rat Shack 8-Ohm Non-Inductive Resistor (rated for 20W) as my dummy load, then it should not only limit my current to .75A (thus saving me from possibly blowing fuses) but also handle the heat generated from the 4.5W as a result. Is that correct logic? Or am I running the risk of melting something behind my dash if I try this? Should I wire 2 in parallel? Obviously I wouldn't bundle it in the middle of a rat's nest of wires, but there's only so much air for radiating heat back in there... also, I'm not worried about draining the car's battery since the magic modulator box is already on an accessory circuit.
Appreciate the insight!
