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12V UPS supply for embedded systems

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Member level 5
Aug 16, 2014
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I want to provide uninterrupted 12DC power to my raspberry pi based remote system. Rather than using a traditional UPS, I thought a LV DC UPS makes more sense which removes the unnecessary AC-DC-AC conversion.

If I'm not wrong, I need a simple charge controller that charges a 12V battery protecting it against overcharging and over draining. It should also supply the load which I suppose will not exceed 1-1.5A. It will be always on and when power goes out, the battery will supply the load.

Will a simple 12V transformer's rectified output feeding an off the shelf solar charge controller be OK? Say something like this:

**broken link removed**

that solar charger can be connected with your transf-rectifier output.

only problem is size of transformer compared to SMPS.

and it is low cost too.

I presume that you intend to use a three stage charging. U didn't mention the battery capacity so i'll explain it in general.
Suppose you are using a battery of 12v and 7AH so the maximum charging current would be 7/10 = 0.7Ampere.
And at the same time the load on the battery will be drawing a current of 1.5 ampere . So the maximum current that your charger should supply should not be less than 1.5 + 0.7 =2.2 Ampere . Now let's choose a power supply of say 2.5A , 14.4 V rating, now you have to measure the input current going to the battery and output current that is drawn by the load. And according to that, you have control the charging current by some microcontroller or some analog circuitry.
Now suppose at some instance the load is drawing a current of 0.5Ampere, you have adjust the input current to (0.5+0.7) = 1.2Ampere.

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