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5v 2amps from a 12v 110amp leisure battery? Answered

whats the best way to get a power supply to my raspberry pi b+ which is 5 volts 2 amps from a 12 volt 110 amp leisure battery?

the method ive thought of so far is to connect a 12v cigarette lighter socket straight to the battery and put a 2amp usb charger in there, i cant see why this wouldn't work but is there a better way of doing this as i intend on using the Pi for playing music and if i don't get a good power supply it could interfere with sound quality.



they turned up today, thank you for you help.

Using a 2A USB charger sounds like a solid idea. Just to be safe, put a fuse (1A, slow) between the charger and the battery. 110A x 12V are A LOT of energy in the short circuit case. Put a low ESR capacity between 5V and ground to filter out any switching noise.

sounds good verence, what does 'slow' mean in the 1A, slow that you mention

and what size low esr capacitor would you suggest?

A 1A fuse will not trip in the first instant the current goes over / reaches 1A. There is a little wire that needs to be heated up and melt. Depending on how much thermal mass the fuse has this may take a longer or shorter time.

A fast fuse will blow (almost) immediately while a slow fuse will tolerate a short period with a higher current. This is useful, when a circuit has a high in rush current when switched on. See here.

The capacitor is not critical. Something 1,000µF and up. 

sorry just to make sure ive understood i need to solder the capacitor to the 5v and ground of the usb charger?

Yep. Most likely, the capacitor's negative pole will be marked with a band of "-". This goes to the 0V/Gnd/Minus output of the charger, the other side goes to 5V of the output. Put the capacitor close to the charger if you have long cables between charger and Raspi.

im just looking at getting a capacitor from ebay now verence does it matter what the voltage is? they seem to vary quite a lot

At least the voltage it is used at. As the USB output is regulated to 5V, a 5V capacitor is just okay, 10V are better. Anything higher is okay but will not be better. If you order more than one piece to get a better price, Downunder35m's 16V are a good value, you can use the leftovers in 12V circuits as well.

16V electrolytic will do, anythin up to 50V is fine too, above that they just get beigger in size with no benefit to you.