Hi!

I am making an arduino project where i am monitoring the temperature of my cabin, and obviously i would like that system to work during a power loss. I plan to use an GSM-shield with the arduino, that will send me a message if the temperature drops under 4 celsuis.

So, i want to make som kind of UPS-system for my arduino, to make sure that it can stand a 1-2 day long power loss. I want it to be fairly cheap, (sub 50 usd), and i wonder if you have any ideas for easy circuits?
It doesnt need to be perfect, so it doesnt matter if there is a small delay when it switches over to the battery.

I have acssess to a 9/12v (1 amp) charger, and unlimited supply of resistors, leds and transistors. Do you have any good, easy ideas for me?

 

So, i want to make som kind of UPS-system for my arduino, to make sure that it can stand a 1-2 day long power loss.

Hi, and welcome.

I might not know the answer to you question, but I'm curious.

Is the arduino supposed to stay on for 1-2 days? Or, is the computer supposed to stay on for 1-2 days?

 

Only the arduino, and the gsm-module will mostly be in standby, where it only draws 1.5 mA. So i dont think i would need the largest battery in the world.

 

Ok, thanks for clearing that out.

Good luck on your project.

 

In thinking about your problem it occurred to me that some batteries behave better at low temperatures than others. It might be worthwhile to investigate how long various batteries last in their projected environment. The results might surprise you.

 

[...] I plan to use an GSM-shield with the arduino, that will send me a message if the temperature drops under 4 celsuis.

So, i want to make som kind of UPS-system for my arduino, to make sure that it can stand a 1-2 day long power loss. I want it to be fairly cheap, (sub 50 usd), and i wonder if you have any ideas for easy circuits?


[...] Do you have any good, easy ideas for me?

To receive, you have to give...
So, besides an 1.5mA sleep current for the GSM, and the temp at below 4°C, would you be so kind as to let us in on the full set?
Current and voltage demand of GSM active and for how long?
Current and voltage demand of your particular Arduino, in sleep/idle and active (plus length of non-sleep/idle periods)?
Voltage of your present supply?
Are you willing to break into the low voltage side of the voltage regulator?
Lowest temperature that you need it to work at (be realistic)?

Please understand that we're not oracles (we just look that way to the uninitiated ), so we really need this info to give you a proper solution and I for one, don't wanna have to ask repeatedly to drag this kind of info out of you, so please answer all of the above.

NiMH will typically work at 0°C with ~80% of nominal capacity, but if you have to go further down, Sanyo Eneloop is the answer - can't say anymore 'till the necessary info ticks in

 

Current and voltage demand of GSM active and for how long?
I actually have no idea how much power it draws when it is on, but it runs on 5 volt

Current and voltage demand of your particular Arduino, in sleep/idle and active (plus length of non-sleep/idle periods)?
I dont have the arduino or the gsm yet, so i dont know

Voltage of your present supply?
9 or 12 volt ( i have two)

Are you willing to break into the low voltage side of the voltage regulator?
I guess so

Lowest temperature that you need it to work at (be realistic)?
0 degrees celsius

it will be some time before i have written the code for the arduino, but i will post the power drain when it is done. I really doubt it will use much power, and a battery around 10+ watt should be able to run it for some while i think. I just have no idea have to make a ups

 

I played with an Arduino Uno. Awake, it draws ~55mA (pretty bad) at 5V to 12V input. I then transitioned to a Mini, and in sleep mode, with most of the power hungry peripherals turn off, I could get it down to ~200uA. I set a timer for it to awake. While awake, it draws about ~2ma while doing an A/D conversion (temperature reading?) which takes less than 100msec, after which it can go to sleep for another 30sec, or so.

You only need to wake up the GSM if there is something to transmit... I'm guessing that the GSM will draw a good fraction of an Amp while it is doing its thing.

I'd be looking for a several-Ah 6V SLA. Close to the 5V needed by the Arduino and GSM. The Arduino has its own LDO regulator; easy to add one for the GSM. Easy to float-charge a SLA while AC is available, while more exotic batteries are a bitch to manage. Even its cold temp performance isn't too bad.

 

I dont have the arduino or the gsm yet, so i dont know

Aha, then your questions are a bit premature - if you don't know, how would I?
Anyway, you must have a rough idea of how often a wake up is called for in the 2 days you need it to work.
One way of running it leaner would be to just sample the data when it's on back-up power and then transmit the logged data when main power returns.

Voltage of your present supply?
9 or 12 volt ( i have two)

Lowest temperature that you need it to work at (be realistic)?
0 degrees celsius

it will be some time before i have written the code for the arduino, but i will post the power drain when it is done. I really doubt it will use much power, and a battery around 10+ watt should be able to run it for some while i think. I just have no idea have to make a ups

OK, then I'd recommend NiMH cells, as they're only out-matched in low temperature use by (expensive) Enelopes (which are NiMHs further developed with a slightly spiced up chemistry) and regular NiMH can be charged just as easily as the SLA's that Mike mentions.
The actual circuit can be fairly simple (hope there's no errors - it's past bedtime)...

You may get away with 1N400n for D3..D6 - Hard to say when peak current isn't stated.
Use the largest capacity AA's you can get.
If you want it to use one more cell, to be able to drain the cells fully and thus get a longer run time, you need a higher voltage in, say 15V (plus change R5 to 1k8 and adjust VR1 for 11.2V).
Any questions or anything unclear, just ask