echo951357
Posts: 13
Joined: Thu Jul 14, 2016 10:28 pm

use voltage regulator to power supply a pi2

Mon Jan 30, 2017 12:15 am

hello guys,
i don't find a section better than this to post my question, if i'm wrong please correct me.
i want to supply my raspberry pi 2 with power using a 12V DC batteries via the micro-usb, i thought that i can use a LM7805C voltage regulator to convert the 12V to 5V, i measured the current consumption of my pi it never excesses 500mA and the 7805 can support up to 1A as a maximum, theoretically it can make it, before i try it, i came here to be sure to note damage my pi or do something stupid, so is this a good idea?, will 7805 dissipate a significant amour of power ?
thank you for trying to help

mosespi
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Re: use voltage regulator to power supply a pi2

Mon Jan 30, 2017 12:25 am

A linear regulator will work, but you need a heatsink. It needs to 'burn' off 7 volts to give you 5v from 12v. At half an amp your heat dissipated at the regulator will be.. 0.5A * 7 = 3.5 watts.

I would skip the linear regulator and get an adjustable switching DC-DC converter. Likely no heatsink needed at your current levels and your battery will last twice as long. They are cheap now and plentiful on most electronics sites or major e-commerce sites. Search for "DC-DC converter". Make sure to adjust it to 5v.

Regards,
-Moses
Power problems? MoPower UPS for the Pi
http://www.allspectrum.com/mopower/

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mahjongg
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Re: use voltage regulator to power supply a pi2

Mon Jan 30, 2017 11:09 am

Buy a standard car cigar plug to USB converter, they come in different models, buy one that can deliver 2.0 Amps. Its probably the cheapest 12V to 5V switching converter you can buy, as they are ubiquitous.
You could also buy a battery-replacer AKA UBEC from a shop that sells Radio controlled toys, but these are more expensive and not sold everywhere, and do not have an USB output, just wires..

the thing you need to know about the cigar plug adapter is that the +12V goes to the TIP of the "cigar plug", and GND goes to the side springs.
You can often unscrew the tip, leaving two wires, a (probably) red one goes to the tip, and a (probably) black one goes to a spring.
The output is already an USB connector, so that is easy.

echo951357
Posts: 13
Joined: Thu Jul 14, 2016 10:28 pm

Re: use voltage regulator to power supply a pi2

Mon Jan 30, 2017 4:28 pm

hello,
thank you guys for your help, i really appreciate it, 3.5 W is huge ... i will purchase one of these DC-DC converters or a cigar car.


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