the secret is all in the converter.
and there is a slight fly in the ointment.
cars don't really run on 12v it's more like 13.6 when operating.
The output of the converter is +16V~24V.
so in a worst case scenario the radio sees the low end of the converter output which 16V and the high end range of voltage from the alternator of 13.6 and the radio sees 2.4 to 4 volts volts across the input terminals.
you'd need to put a large isolation cap across the output to prevent droop under load.

 

^So would you say it is not worth trying this? I have to think that if it worked, there would be kits readily available becuse there is a pretty good demand for a solution to this situation.

 

you would need to know the current load drawn by the radio.
Output Vout 16 Volts 18 Volts 19 Volts 20 Volts 24 V
Output Iout 3.5 Amps 3.3Amps 3.0 Amps 3.0 Amps 2.5 Amps

keep it below 2 amps draw and you should be ok with the small converter.
that was with the 60 watt converter.

the design principle doesn't have a lot of margin for rolloff.
I could easily be wrong but I just don't know if the demand is out there for them.
It would be easy enough to derive a regulated output switcher that could maintain the 12V rail relative to ground.

 

Jerry, i just want a basic radio deck that plays CDs. Can you recommned a converter? Maybe you know where to get these things. I don't.

 

I haven't hunted at all.
been many a moon since I bowed before the dark prince.

if I remember tomorrow I'll nudge some of the power guys.

 

Thanks, but not to worry. I thought you might know. I'll figure something out.