Does there exist a Victron dc to dc charger capable of drawing solely off a car cigarette lighter without more complex wiring? Perhaps the Orion 12/9? The use case would be to charge a 100ah LiFePo4 battery in my ultra-portable diy solar generator during the long drives between camp sites. Jackery products can charge this way, so I'm trying to figure out how add similar capacity to my diy build, understanding of course that charge times would be slow.
I just did exactly this, with the 12/9 unit. It will do what you expect, but consider the behavior carefully.
First, be aware that there's no low voltage shutdown. Or rather, there is, but it's like 7 volts, well beyond the point that your car battery is trashed. So make sure you unplug it, or your lighter socket is switched, when the engine is off. (Or use the remote-enable input, but that's not conducive to lighter-socket operation.)
Second, assuming the output is basically constant voltage, (driving into a discharged LiFePO4, it will be), the input is basically constant power. If either the car battery gets low, or the wiring develops a high resistance fault, your happy 12v/9A converter might find itself fed with 9v and will therefore draw 12A. I've seen mine draw up to 15A when the source was around 7.5v.
I had ordered some cheap "16AWG" lighter-socket cables, which came close to melting during testing, especially in this low voltage high current situation. (I suspect they were 1.0mm^2, midway between 16 and 18 AWG.) I replaced them with some "14AWG" cables, which feel much closer to their advertised thickness, and they only get moderately warm.
The Orion TR Smart units have configurable input voltage lockout, but the smallest one is 18A and there's no setting to limit the input current, so I don't think these are suitable for lighter-socket operation at all.
Cigarettes lighters outputs are normally rated for 10A max. I advise you to use a good quality connector as they can get hot when using over longer periods.
