A quick question on backup power

Question

Hi everyone, im making a model house with a solar panel and a rechargable battery.I've been looking on the internet for a while, but i cant really find out if what im planning to do is correct in terms of wiring. Idealy you will have the external power disconnected and the battery will be charged by the solar panel and drained by the consumers (servo+ a few LEDs) and when the energy is not enought the external power will charge the battery/ or if the power network is down- rely on the solar energy to charge the battery alone. Is this schematic applicable? Im not sure if i have to put any diods around to limit the current's direction **For some reason i cant insert an image so im attaching it as a file! Thans in advance! 
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ntewinkel · Answer

I've been looking into this sort of thing a little bit, as I need to do something about the solar setup in my outbuilding (wife's art gallery) now that the charge controller seems to have died. From what I understand, as long as the maximum charge amps of the solar cell is at a rate small enough compared to the total battery capacity (ie, the equivalent of a trickle charge), you don't actually need any circuitry (other than that diode I guess) - the battery will just dissipate the extra energy in the form of a small amount of warmth. But I'm using basic lead-acid batteries in my setup, so that might not apply to your NiCd battery. I could also be very very wrong, and if so I hope someone will correct me before I blow up my wife's art gallery Cheers, -Nico

shabaz · Answer

Hi, Unfortunately you've picked a relatively advanced topic, and it will be very hard to make this work (at good efficiency) without a fairly complex circuit. You could try to just stick a diode and resistor in series and then connect the solar cell to the rechargeable battery, and it may trickle charge the battery somewhat, but at low efficiency. I take it that the solar cell is fairly small if this is a model? If you want to do the advanced design, search for MPPT. An alternative may be to purchase a ready-made solar cell with battery, e.g. something like this possibly (no recommendation, I just googled this one).

A quick question on backup power

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