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usb in car Answered

PLEASE HELP. i am trying to find a way to install some usb ports in my car to be used as power supplies for various devices (mp3, nav systm,phone).  i hate clutter, so i'm trying to stay away from adapters for the cigarette lighter plug.  im pretty sure i need to reuce the volts and amps so i do not harm the devices.  please help. i dont even know where to begin.


. All you need is 5VDC. A 7805 or similar should do the job.

will i need to worry about it heating up too much...ive read that it might require a "heatsink" (whatever that is). just wanna be sure it wont mess up my devices.

. Yes, it will require a heatsink. I have a 7909 (-9V) driving the gauges on an old Mustang and use one of the dash supports as a heatsink. . USB devices are rated for up to 500mA (½A) each. Make sure your regulator will handle the load (500mA × numberOfDevices + a little extra for headroom). You should be able to find what you need by searching for "5V regulator".

thanks so much nacho. all i need to know now is how to hook up a heatsink. also...are you saying that he since the 7805 has a output of 5v 1A and most usb devices are rated for up to 1/2A i should be able to power 2 ports/devices from 1 regulator?

. The 7805 had a metal tab that you bolt directly to the heatsink. For my car, I just found a hole in the support that was the right size, scraped a little paint off the support, put a little thermal compound on the regulator, and bolted everything together. (BTW, it may be a 7809, but I'm too lazy to crawl under the dash and check.)
. Exactly, but you probably want to have some breathing room for inrush current and such, so I recommend using one less device than the regulator is rated for.
. There are other voltage regulators besides the 7805 - that's just a very common one. According to Wikipedia: the 7800 family is "generally not appropriate for applications which require more than a few amps of current".

ok....it sounds like the heatsink is nothing more than a piece of metal that i can bolt the tab to...correct?also...should i run a separate power supply with its own regulator for each usb input. i would like at least 2 ports to plug into. finally...any recomendations on in-line fuses for this application? as always...thanks sooo much for your help and your time

the heatsink should contact well with the entire back surface of the 7805. if you use thermal compound it should be in very thin layer beween the 7805 and heatsink. good amount is small drop for the entire surface aluminium piece of few cm (from window frame etc) is excellent heatsink since aluminium conducts heat well 1 A slow blow fuse on the 5 V side of each 7805 1 main slow blow fuse for all 7805s together on the 12 V side. 2 A x amount of 7805s (you may use individual fuses too) connect 1000 uF 10 V electrolytic and 1 uF polyester capacitors in parallel on the poutput of each 7805 to protect your usb devices from voltage spikes after assembling load it to the max (devices and usb hubs) and hold your hand on the 7805s to see if they overheat (if you can hold your hand on it continuously after 5 min of work its ok) do the test when the car engine is running - the voltage is higher and 7805s heat more