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USB 5V power from 12V car supply

john2k

Jun 13, 2012
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I have a 12v to 5v(3A Max) converter. I'm planning to hook this to charge my Nexus Android tablet as part of a car in-dash install. My question is: The converter seems to be regulated in terms of voltage but the current says 3A max. Therefore there doesn't seem to be any form of current regulation. Does that mean the tablet will only draw what it needs to charge and the device will only give 3A max? What are the chances of too much current being delivered to the tablet?

Thanks
 

Martaine2005

May 12, 2015
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Hi John2k,
Your assumptions are correct..
The Max is 3a.
Your tablet will only draw the current it needs.
You could use a 5v 5a and the same applies. A device will only draw what is required.
Martin
 

Martaine2005

May 12, 2015
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Your 12v to 3v adapter probably has a 1a fast blow fuse.
Mine has a 1.6a 250v fast blow fuse. Don't worry about 250v, it's just a maximum voltage.
It should be located in the 12v end of the adapter like this picture. Where the spring is..

charger.jpg
 

john2k

Jun 13, 2012
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The 12v to 5v converter i'm looking at is like this: not sure if it will have a fuse inside that housing. So considering maybe to add an inline blade fuse maybe on the red wire. Is that ok? and what amp fuse would be recommended?

$_12.JPG
 

Martaine2005

May 12, 2015
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Amps = Watts / Volts
15w / 12v = 1.25amps
I doubt if your tablet will even draw an amp. The fuse should be the 'weakest' link to protect the device.
 

john2k

Jun 13, 2012
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Yes. But a fast blow fuse.
Martin

Do they sell fast blow fuses in blade format? I think they just in the glass style. Should I just put an inline glass 1A fast-blow fuse then instead of blade fuse?

Many thanks
 

Martaine2005

May 12, 2015
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Without searching the internet, I have no idea.
I don't see any reason why they would not sell them..
But if not, a glass inline would be perfect too.
Martin.
 
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