USB 5V power from 12V car supply

[john2k]

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]

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

 

[john2k]

Thanks Martaine2005

 

[AnalogKid]

All true, but an inline fuse would be prudent.

ak

 

[john2k]

All true, but an inline fuse would be prudent.

So if converter is rated at 3A max, should I put a 5A fuse or a 3A fuse?

 

[Martaine2005]

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..

 

[john2k]

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?

 

[Martaine2005]

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]

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.

So a 1A mini blade fuse should do the trick?

 

[Martaine2005]

Yes. But a fast blow fuse.
Martin

 

[john2k]

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]

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.