There seem to be a load of 12v to 5v 3A USB converters around (the vast majority of which seem to be produced by a chinese OEM and then rebranded).

However I want to do something a little different......

Given the number of electronics devices you can add to cars these days (phones, tablets, GPS, cameras, etc....) I want to add a single USB converter circuit to my Jeep Wrangler which will allow me to run 12 USB ports to various points around the car.

Given the demands of the assorted devices can be anywhere from 0.3A up to 2A I want to try to use a single step down converter that handles say up to 12A, I'm looking at wiring this into a separate unused fuse point in my fusebox and then running the wiring invisibly as possible to each point, that way it keeps the interior of the car tidy.

I don't want to just plug in a converter to my 12V Cigar Lighter socket as I want to keep that free for other potential uses (no I don't smoke....but occasionally have had to use a compressor to pump up tyres or use a vacuum).

I want the step down adapter to be shielded to avoid creating noise (the 3A ones commonly available appear not to be shielded as a number of reviews have commented on radio interference once fitted) and also to account for and prevent any surge issues or ignition coil issues causing problems.

If no 'off the shelf' device exists how difficult would it be to breadbox one....while I'm not an electronics engineer I have a rudimentary to fair understanding or electrical issues (I understand capacitors, resistors etc...for example).

Shoot me down if what I'm asking for is too difficult, but I would have thought if 3A versions of the circuit exist it would likely not be too difficult to scale that to 12A and add the shielding?

  • \$\begingroup\$ Since found this....amazon.co.uk/DROK-1-25-36V-Converter-Voltage-Regulator/dp/… not confident this won't generate noise so how best to shield and add the ignition coil protection? \$\endgroup\$ – tezzy Nov 20 '16 at 17:45
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    \$\begingroup\$ I'd suggest you are better off running 12v (at lower current) around the car and putting convertors on each outlet point. This allows you to set the output short circuit protection to just 2A or so per point. If you put a central convertor you will have to set the short circuit protection to more than 12A and you expose more low voltage ( 5 V and closer to your devices) wiring for noise (RF interference) transmission. \$\endgroup\$ – Jack Creasey Nov 20 '16 at 18:08
  • \$\begingroup\$ just a remark: It's generally capital "V" for Volt, and capital "A" for Ampere, like you use it in the second half of your question. \$\endgroup\$ – Marcus Müller Nov 20 '16 at 18:08
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    \$\begingroup\$ Jack has it. Car batteries are 12V for a reason, if you try to run 3m of wire to your trunk and you want 4A capabilities (2 ports), and say you can accept 10% load regulation (a lot), even if your converter does not have load regulation (not true), your max resistance must be about 40mOhm/meter, about .7mm diameter (AWG21). 1mm to get 5V-5%. And 2W dissipated along the way. \$\endgroup\$ – Vladimir Cravero Nov 20 '16 at 18:41
  • \$\begingroup\$ I suggest you start with one 12V to 5V, 3A, converter. Shield it and provide for two USB ports. Test it. if satisfactory, repeat 3 more times to get your 12A, 8 USB ports. \$\endgroup\$ – Guill Nov 26 '16 at 0:38

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