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5V UPS for Raspberry Pi: Difference between revisions
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Fortunately there are UPS devices for alarm/camera systems which you can buy for few dollars from [http://www.aliexpress.com/ AliExpress], just search for ''ups 12v output'' and looks for example these rated at 35W (these are the smallest possible but still more than enough for any USB device). I was able to buy one of these in Prague in local store called [http://www.t-led.cz/ups-zdroj-12v-35w-s-nabijenim T-Led] around 20USD personally. But you can get them directly from China to anywhere in the world for around same price including shipping. The UPS power supply I bought has 110-230V AC input and two 12V outputs. One 12V output is for battery charging (0,5A) and second is for your DC-DC converter to USB (we will talk about this later). If you connect battery to UPS it would not automatically start but wait for power supply to be connected. Once power supply is connected it will start and if there is an outage it will automatically keep voltage without any downtime (tested, Raspberry Pi did not went down when I disconnected main power and it switched to battery supply). If you need a cold start (start from battery without any external power connected) there is a small button (unfortunately not external one) connected solely for this purpose. | Fortunately there are UPS devices for alarm/camera systems which you can buy for few dollars from [http://www.aliexpress.com/ AliExpress], just search for ''ups 12v output'' and looks for example these rated at 35W (these are the smallest possible but still more than enough for any USB device). I was able to buy one of these in Prague in local store called [http://www.t-led.cz/ups-zdroj-12v-35w-s-nabijenim T-Led] around 20USD personally. But you can get them directly from China to anywhere in the world for around same price including shipping. The UPS power supply I bought has 110-230V AC input and two 12V outputs. One 12V output is for battery charging (0,5A) and second is for your DC-DC converter to USB (we will talk about this later). If you connect battery to UPS it would not automatically start but wait for power supply to be connected. Once power supply is connected it will start and if there is an outage it will automatically keep voltage without any downtime (tested, Raspberry Pi did not went down when I disconnected main power and it switched to battery supply). If you need a cold start (start from battery without any external power connected) there is a small button (unfortunately not external one) connected solely for this purpose. | ||
== DC-DC Converter from 12V to 5V USB == | == DC-DC Converter from 12V to 5V USB == | ||
[[File:12-to-5v.jpg|200px|thumb|DC-DC 12V to 5V converter]] | |||
At first it might seems as a good idea to use power stabilizer but problem with this solution is that all diference (12V-5V = 7V) would be converted implicitly to heat. So not only you would need to have some cooler but also a lot of power from battery would be lost without any usage. This is a reason why usage of DC-DC power converter is recommended. DC-DC converter has one large advantage specifically low power lose and high efficiency. If you put 12V at 2A to input you will likely get minimally 5V at 4A. One disadvantage of DC-DC converter is price which is slightly higher than using stabilizer but still pretty low if you buy it on [http://www.ebay.com/ Ebay.com]. Just try to search for ''DC-DC step-down buck converter 5V USB 3A'' (or 2A of your choice) and you should get some for as low as 2-3 USD. | |||