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Hardwiring USB devices for power

Discussion in 'Car Repairs / Maintenance' started by ikearns, 26 Jul 2018.

  1. ikearns

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    Good Afternoon All

    As like many others (I guess) I have a dashcam, DAB adapter, SatNav etc in my car and only find that I have one or two USB power outlets via my cigarette lighter. As some of these toys are in the car all the time then it would make sense to connect them to a power source which is semi-permanent (not the adapter in the cigarette lighter). This would also mean I can run cabling much tidier and make a better installation.

    My question is 'whats the best way to install this'?

    Can I splice into the cigarette lighter power and earth behind the dash or should this run back to a separate fuse? My issues are that I would put myself as a confident amateur, have a reasonable background in IT, can follow a wiring diagram (most of the time) but dont really want to get into the realms of messing with looms or doing serious auto-electrics.

    Any help is appreciated.

    Cheers
     
  2. SFK

    SFK

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    Ikearns,
    I have always connected my 12V to USB convertors onto the cigarette lighter power for the reason that if the USB is shorted it will take out the cigarette lighter fuse (which is not uncommon) and not some other critical item.
    So I have always used Blue wire connectors to splice onto cigarette lighter cable.

    However, I have always USB devices to cars whose cigarette lighter power goes off when the car ignition is off, and not to cars whose cigarette lighter power remains on when car ignition is off. This is becuae of my worry that the USB will continue to take power when not in use and drain the battery.

    I have used the following devices:
    https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=12V+to+USB&_sacat=0
    and
    https://www.ebay.co.uk/sch/i.html?_...12V+Car+Cigarette+Lighter+Socket+USB&_sacat=0

    SFK
     
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  3. ikearns

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    Like those links especially where I could install a spare lighter socket and USB sockets in the glove box and run the cables back to there.


    Appreciate your reply.



     
  4. SFK

    SFK

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    Ikearns,
    pleasure.
    One word of warning, some have complained that the 12V to 5V convertor used in these devices creates radio interference/noise.
    I have not had this issue (yet - noting that these are all Chinese ebay items), but might be best if you first loosely connect it and try it with you car radio before taking dashboard off.

    Also, these are the Blue T splice connectors I was taking about:
    https://www.ebay.co.uk/sch/i.html?_...hape+Wire+Cable+Connector+Terminals+&_sacat=0
    SFK
     
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  5. ikearns

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    Do you think it is viable to connect an additional four USB sockets without any detrimental effect?



     
  6. SFK

    SFK

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    I see no issues with 4 USB sockets as I doubt that you will ever using all four at full power, and even then that is less than a single Cig lighter can provide.
    And eitherway you are protected by the Cig lighter fuse so all is protected.

    Key item is to use wire from Cig lighter to your Glove compartment that is same thickness as the wire going from car to Cig lighter (ie do not use a smaller wire).
    SFK
     
  7. EddieM

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    Those 12v to 5v transformers (shudder) are usually rated at 25w or 5A. Therefore 4 USB ports off one of them would not be advisable or even be able to supply enough power.
     
  8. SFK

    SFK

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    Eddie,
    Agreed these Chinese DC-DC convertors are not the best.

    But the links I showed were 5V @3A for two USB and 5V for 2.1A for 2 USB.
    So doubling to get 4 USB that is 5V @3A x2 for four USB which is 6A.

    And this is 6A at 5V, so it will be less amps at 12V.
    And all is protected by the Cars Cig Lighter 15A fuse.

    Although I do use these, I am more worried about them being Chinese and failing catastrophically or swamping car with electrical noise, than the Current wiring limits.

    And these use the same electronics as used in the stubby Cig lighter to USB convertors that are normally used:
    https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=car+port+usb+charger&_sacat=0
    SFK
     
    Last edited: 26 Jul 2018
  9. EddieM

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    Huh? They can only supply a certain 5v wattage to their max rated output.
     
  10. rsgaz

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    My preferred method is to look through the manual at the list of fuses and find a feature that your car doesn't have. So, for example, you might find "Heated seats - 20A". Then use an "add-a-circuit" fuse tap where the missing fuse was...

    [​IMG]

    ...and wire your new hidden cigarette socket(s) into that. The negative can be connected at any grounding point you find or if you are confident, you can even drill your own one. That way you're not cutting any existing looms, you don't need to be concerned about maximum amps, etc. You have a totally independent socket with it's own wiring, rated at whatever circuit you find 'empty' in the fusebox. (check it actually switches with the ignition!)

    I have done exactly that in my van, found the "rear wiper - 10A", which it doesn't have and hooked it up to some heated mirrors (which it didn't come with when new).
     
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  11. JBR

    JBR

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    Although the 'proper' method would be to use a fuse tap on the fuse board, I found it much easier to wire my dashcams (front and back) to the power sockets (cigar lighter socket). I am lucky to have one in the boot as well as between the front seats.
     
  12. ikearns

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    Never seen one of these before. Looks like I havent meddled with auto electrics in recent times to need one. I take it they just run from the fuse box?? I guess YouTube will be my resource on this one.



     
  13. DaveHerns

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    I've hardwired my dash cam using an "add a circuit" I'd recommend them.
     
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  14. rsgaz

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    Yes, they are intended for when there are no spare places in the fusebox. So, let's say your cigarette socket is on a 20A fuse, you plug this in, put a 15A fuse(for example) in one side for the existing circuit, then a 5A fuse in the other slot for your new circuit, so it totals the existing Amps.

    But that's why I said about finding a spare fuse position, you don't need to downrate the existing circuit then. Things like an in-car coolbox have a very high (but very brief) startup/inrush current, and can blow a smaller rated fuse, so I try to not reduce any existing circuit's current rating.
     
  15. ikearns

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    Okay so having a quick look on ebay and YouTube it seems using one or two dual USB outlet sockets with a fuse tap then this shouldnt be a major job.

    I am looking at either of these sockets:-

    https://www.ebay.co.uk/itm/12V-24V-...948294&hash=item3ac5d95f95:g:YLcAAOSwOVpXYrmB

    And a fuse tap. My query about the fuse tap is if it is worth using the existing cigarette fused connection on the fuse box as all I am doing is moving the load from the actual cigarette socket to the newly used USB sockets. I am not a smoker, I dont give lifts to smokers so in essence the cigarette lighter is redundant.

    As for running an earth then should I just tap into an existing earth or just ground on somewhere on the car body in the engine bay?

    One final thing, if I am going to use a spare slot in the fuse box then how do you know if it is one which is only on when the ignition is on? Plug it in and see??

    Thanks again to all
     
    Last edited: 27 Jul 2018
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