The core parts are how to safely charge a 12V nominal voltage lithium battery pack (say, three 18650 cells in series) from a solar panel, whilst providing all the protection needed against over-charge, over-discharge, etc.. There are loads of "12V" solar panels around, and any that can deliver around 15V to 18V will probably work, and they don't need to be very large. I used a relative large one (this one: https://www.ebay.co.uk/itm/361482859520 ) for the water pump, but smaller ones are fine for solar PIR triggered lights, as long as their voltage is within the acceptable range (15V to 18V is ideal, the MPPT is OK up to around 25V).AE-NMidlands wrote: ↑Tue Sep 27, 2022 6:20 pm I'm definitely interested in the solar-powered porch light
(but not so sure about the solar butt pump though... I shall not try to sell it to SWMBO!)
A
The MPPT modules I've been using are these ones: https://www.ebay.co.uk/itm/254657000347 They deliver around 3A (if the panel can deliver that much current, none of mine come close) and they voltage limit at 12.6V, ideal for a 3S lithium battery. This module takes care of the charging, but doesn't give any protection from cell over-charging or over discharging and doesn't provide any sort of cell balancing, all of which are essential for safety.
The 3S BMS modules I've been using are a massive overkill, in that they can handle a LOT more current than needed (10A maximum), but they aren't too costly and I feel it's nice to have a safety margin: https://www.ebay.co.uk/itm/403872715490
These fit neatly on the end of a 3 cell 18650 battery holder, like this, although the battery holder needs slight modification to lead out wires from each cell for balancing): https://www.ebay.co.uk/itm/143971215201
18650 lithium cells are widely available from many outlets, best to buy the ones with no protection, as the BMS board provides all the protection needed, plus cell balancing.
The wiring up is pretty straightforward. The solar panel is wired directly to the MPPT module (no diodes needed - night discharge prevention is built-in). The 12.6V maximum from the MPPT is connected to the BMS board, and all three cells are also wired to the BMS board. Any load (lights, pump, whatever) is wired to the BMS board output (not directly to the cells).
To run the solar lights, with PIR switching, I use a PIR switch module that includes a relay to handle the high current to the LED strip. There are a few of these around, but IIRC the ones I've used are these: https://www.ebay.co.uk/itm/401597373785 These are more versatile, as the PIR sensor can be sealed into a hole in the case and the module mounted a couple of inches away. These modules only draw a very tiny current when not triggered, I believe that mine were using around 30µA or so. not enough to worry about. The relay will switch several amps at 12V, more than enough for most LED lighting applications.
Finally, the LED strip I used for the front door light was similar to this stuff: https://www.ebay.co.uk/itm/294807784233 Just need to make sure it is the encapsulated outdoor stuff, that is weatherproof and has a transparent flexible over-moulding in some sort of clear resin, Bit fiddly to solder wires to the ends, and needs a bit of waterproof (glue lined) heat shrink sleeving to make sure water can't get at the connections.
Happy to try and add more details if needed. Here's a repeat of the photos of the light and also one showing some solar flood lights that are down the East side of the house, where I'm currently fitting a solar panel covered canopy (exactly same power system as the front door strip light):
- East side solar floodlights 2.JPG (51.72 KiB) Viewed 527 times
- Gable Solar powered lights 3.JPG (37.25 KiB) Viewed 527 times
- Gable Solar powered lights 2.JPG (242.58 KiB) Viewed 527 times
