USB protection circuit

Discussion in 'General Electronics Chat' started by oznick, Jul 31, 2014.

  1. oznick

    Thread Starter New Member

    Jul 31, 2014
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    Hi everyone!

    I was hoping to get some help with the following problem I encountered (I am a 2nd year Electronics Eng student, so if you can, please be kind, I'm still learning...;).

    I'll try to describe the problem in a lot of detail:

    I am installing an expensive stereo head unit in my car and it has a rear USB and an HDMI port for ipod/smartphone connection. According to the manual, you connect the USB cable and HDMI cables to an MHL adapter and plug that in to your smartphone - that's easy:)

    But (!) the usb port on the rear panel is capable of supplying just 1A. I was hoping I could also attach and charge other devices, such as tablets, which require at least 2A current. So my idea was to buy a basic 12V to 5V converter from ebay and splice that into the VCC wire of the USB cable coming from the stereo. I believe, that should work (correct me if I'm missing something).

    Now the question:
    What is the best way to protect the stereo, in case the cheap 12V-5V converter fails?
    Do you think just a 2-3Amp fast fuse going to be enough? or some dedicated protection circuit would be better?

    Thank you!!
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    That's just stupid.

    Buy the 2 A charger that plugs into cigaret lighter.
     
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the best protection for an expencive item is to use a cheaper one instead. use the car power to charge things, it is made to supply power, and the usb in your usb in the stereo is just another backdoor into your expensive stereo for problems and surges to enter.
     
  4. oznick

    Thread Starter New Member

    Jul 31, 2014
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    Yes, that's an option too. And I already have one.

    The problem is that the usb socket on the stereo is also used for data - in the end, I'd still have to connect the two usb supplies somehow.

    Edit:

    In fact, for this stereo there is a OEM kit available which includes it's own 12V to USB converter. This is where I got this idea from in the first place. I'd actually get the kit, but it costs $100 and includes other cables that I already have.
     
  5. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    I am kind of wondering about the 2 A requirement to charge phone/tablet. I realize that if you use higher current, you will charge the device faster. But... if you just want to charge the device and don't care how quickly it will charge, would the device work with the 1 A usb you already have? I mean, if the device does not receive 2 A, will it just sit there and do nothing? Or will it take that 1 A and charge anyway?
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    It just won't charge as fast from my experience.
     
  7. alfacliff

    Well-Known Member

    Dec 13, 2013
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    lots of static in cars, have you aver gotten zapped when putting in your key? plastic, fabric and such mean a static prone car. do you want to zap your stereo when plugging in chargers?
     
  8. oznick

    Thread Starter New Member

    Jul 31, 2014
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    This is another reason why I would like a hard-wired solution instead of sticking a charger into a cigarette lighter socket.

    Although I'm sure there should be some protection from static discharge in the stereo. It's probably the contact voltage spikes when you plug in the charger you should be more worried about.
     
  9. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    If I and mcgyvr are correct, then I would very highly advice not to eF with your car, not to eF with your stereo, and just charge your phone/tablet from the 1 A USB. Yes, it will charge more slowly, but you actually will not eF up anything which is far far far more preferable.
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Just buy a cheap cig lighter USB adapter and a "Y" usb cable and receive power from both ports at the same time using off the shelf parts.
     
  11. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Well, yes, but they said they want the device also "talk" to the stereo, that is why they want to do the charging solely from stereo USB port, get the power and do the "talking" from/through one port/connection.

    I think the Y USB cable would work, I say that because I use one for external hard drive and I can move data back and forth between pc and external hd. Would be interesting to see if it will work with car stereo and cigaret lighter charger and phone/tablet.
     
  12. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    "typically" the cig lighters just don't use the data pins at all.. So the radio would be using the data pins and the power pins from both devices would be powering the tablet..
     
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