How do I build a UPS-like - battery backup - system?

Question

As we all know, the Raspberry Pi doesn't really use that much power (5v + 700mA is the spec).

I'd like to build a battery backup for power outages in a DIY-ish fashion. I don't need surge protection or any other fancy options, just security from minor power outages and brownouts.

How can I put a battery backup between the Raspberry Pi and the phone charger I'm using to run it?

Answer 1

You question is more suited for the Elictrical Design Stack - Because you can always rely on the Gurus there, like Oli to help design easy, up to date circuits.

I think that this question will be asked by many more Raspberrians to come so this is actually a very good place to answer your question.

My answer will go more into engineering your own circuit so that you can have full control of what you want it to do.

The circuit should handle...

1. Initially deciding what kind of circuit you need. Powered by USB 5v? or maybe by a 12volt source? You can also power it from a lower power source like 3.3v/1.5v but is very inefficiently in converting power. This decision also fundamentally contributes to what kind of voltage regulator you are going to use.. if any.
2. Keeping the battery charged up druing normal operation (also each type of battery requires have charging characteristics, Lead Acid, Ni-Cd, Li-Ion, etc)
3. The circuit needs to sense when primary power (usb +5v) stops providing power or similar.
4. The backup circuit to charge your type of battery and an embedded circuit to possibly route power back into the main circuit when the main power is off.
5. Optional. Build a trigger into the circuit that connects to the Raspberry PI's I/O system to send you and email,text message, make a phone call, trigger an alarm or turn of your kitchen lights.

Searching around the internet most UPS circuits and schatics will include a transformer to reduce 110v/220v down to DC 12 Volts.

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• Here is a very simple circuit used with Lead-Acid batteries (They are easy to charge and they keep charge for a very long time) Do not attempt to charge any other kind of battery with circuit.. they will blow it up!

Part List:

• R1 - 39 ohms 1/2W
• D1, D3, D4 - 1N4001 or similar diode
• D2 - 13V zener rated 1W
• C1 - 220uF electrolytic capacitor rated 25V
• C2 - 10uF electrolytic capacitor rated 10V
• IC - 7805 or similar 5V regulator
• BAT - 12V lead acid battery rated 1.2Ah minimum
• DC Input - 12 Volt DC

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• I found this circuit while rummaging through the internet. This guy pretty much rips apart a notebook and recycles a few parts to make a decent system - Just remember to regulate the output voltage to 5v

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• Finally circuit - on of the easiest and most probably the one that many people would prefer to use is a USB charged UPS circuit using some small lithium batteries. This was answered at Engineering SE, please refer to the answer for details.

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Do not feel like building you own circuits. There is this MUPS available for purchase that does pretty much what the final circuit design outlines.

References

• You can find allot more circuits on this website
• Using search engines will also find allot of other interesting facts and solutions
• Visit Electrical Engineering Stack if you have any circuit design questions.

Answer 2

I have built a converter from 12v to 5v

That's enough for RaspberryPi's 5v requirement. IT also gives power for fan with adjustable thermostat (12v) and even active usb hub (in the future). Everything (Raspberry Pi, converter and thermostat) is enclosed in a router-box (I even have space for an additional 2.5" hdd, 3G modem and/or GPS unit ;) )

Such a converter can convert power from a battery pack (for example from 5 or more AA batteries) and SAFELY give 5V for Raspberry (watch out for voltage!). The converter is pretty small (i think 3 x 10 x 1.5cm). But if you are good at soldering and building circuit boards you can do it smaller.

This is the converter I use with a sample schematic.

It works great, you can attach from 7 to 40V from batteries. And we got max 3 amps on 5v side.

If you need to switch between phone charger and battery pack, you must build a switch (when power from charger goes down, the battery-pack power is connected and vice versa). I think that's pretty simple (transistor, capacitor... just few elements). Or do it manually ;)

Answer 3

I found the question very interesting but my self am not really interested in soldering and fiddling with resistors and stuff and I am sure other people might stumble upon the OP question with hope of a ready product.

So I did find this which for my needs would actually be great. Buy, wait a few days, plug in and viola.

I found it on DX.COM

As pointed out in comments. It seems like there could be an issue with high power consumption.. so end of day it looks like it will have to be opened and messed about with. But it is suitable for the Model A.

Answer 4

I would like to know if this product would work well as a UPS for the Raspberry Pi. It looks like it can both keep its battery charged as well as power the PI while doing this. It would power the PI in battery mode if AC power failed.

Power Supply

In my application the PI will be used as part of a weather data-logging system in a somewhat rural location where the AC power is not very reliable, the AC power is available about 98% of the time but visible voltage glitches occur several times a day and if the PI lost power completely I assume someone would have to manually restart it which might not happen for a week or more.

I think the maximum time for a power outage would be 9 to 12 hours.

Answer 5

Here is a UPS for the Raspberry PI: http://www.eevblog.com/forum/projects/raspberry-pi-server-with-diy-ups/

Also, with sufficient changes and safety circuits, lithium rechargeable cells can be float charged. In this case it is best to use a single cell and a boost converter so that balancing circuits are not required. Here is some info on float charging lithium cells: http://www.electronicsweekly.com/Articles/01/02/2006/37528/Float-charging-lithium-ion-cells.htm

Answer 6

The LiPo Rider Pro was meant for solar applications, but the USB port can also charge the battery, so you don't really need a panel. Coupled with a larger LiPo battery, it should keep the Raspberry Pi alive for a number of hours.

Answer 7

Yes I can confirm a lipo rider pro board from seeedstudio works like a charm. It has usb in + batter + solar charge if so desired. Single usb out. Basically takes main in if available, otherwise battery. All for under 20 dollars including battery. The only downside is its only 1amp out so if you have some usb devices drawing power, it may not supply enough.

Answer 8

So you want a SIMPLE reliable DIY ups like powersupply for your RPi:

1. get a sealed 12v Pb battery ( I use a 5Ah battery)
2. get a 220Vac to 12v switched mode power supply (I use 12v 4A )
3. get a car lighter to usb plug (8v--24v input, out = 5v 2A) switched mode
4. get a diode which can handle 4A and a 0.5 ohm 5 watt resistor to limit the current by empty battery recharging
5. get a usb to universal cellphone charge cable it has 10 different plugs with short cables, 1 goes to power the RPi,an other one for the usb hub , an other for whatever jumps in mind.....still many left

Wire it as follows:

• from the +12v of the power supply to the anode of the diode

• from the cathode of the diode to the 5Ah Pb sealed battery, this protects against the power supply draining the battery when no 220v

• Then from the + of the battery to the "lighter plug to usb " +5v 2A

, plug in the usb cable

I was liking to put a picture of all parts needed, but i'm not allowed by this website until received 10 points... when this will happen, then i will post the picture

Results of running the RPi(running ssh,wospi,lighttpd) + Davis VPro2+ console (console added 300mA) + usb hub : after 20 hours on the battery , the battery voltage was dropped from 13.08v to 11.77v ! considering 10v as empty this means enough juice for at least 32 hours on a 5Ah battery total costs 30 usd, everything brand new