Adding a solar panel to a game cam, circuit question

Thread Starter

skeer

Joined Oct 28, 2022
19
So I've got a game cam and a 5V 4W panel that I'd like to add to the cam to help maintain the 8 AA's a bit longer. The cam holds 8 AA's but only runs off 4 meaning 6vdc. I haven't taken it apart yet so I'm unsure how it handles the other 4 batteries.. electrically speaking.

Anyway so the idea I've got currently is that I'd need to add a diode inline with the panel's positive side so the batteries don't backfeed. And the placement of this will ensure the panels not producing at 100%, more like 50-60%. So I don't believe I need to worry about over-charging especially since it's output is less than the requirements of the camera itself.

Am I missing anything here?
Thanks!!
 

Ya’akov

Joined Jan 27, 2019
6,854
Welcome to AAC.

Are the cells Alkaline? The PV panel is not going to produce enough voltage charge a 6V battery, nor to operate a device that needs 6V and adding a diode will lose you the best part of a volt. I don't really understand how you intend to use the panel. Could you provide a schematic or wiring diagram?
 

Thread Starter

skeer

Joined Oct 28, 2022
19
Thanks Ya'akov. So right now Im running regular alkaline yes. But if this works I'd switch over to Lithium Ion.

I do not yet have any sort of schematic drawn up.. but I thought the idea was simple enough. Tack on a solar panel to trickle charge and help maintain.. or at a bare minimum extend the charge life of the batteries.
I realize it won't top them off but this camera eats AA's like candy. If I can even extend the charge/replacement period by a week it'd be worth it.
I also did not realize a diode would consume that much.. wow. I toyed with this idea last year by creating an array from the tiny solar cells from those cheap solar LED outdoor lights. Each one produced around 1.2v in perfect sun. I strung together probably 8 over those tiny cells and almost burnt them up when I connected to the battery. Once I added a diode then it solved that problem.
 

bassbindevil

Joined Jan 23, 2014
631
There are diodes with lower voltage drops, like Schottky diodes. There's a good chance of finding one in a scrap switching power supply. The "diode check" function on a DMM will reveal which have the lowest voltage drop. Some are even dual diodes, which are handy if you want to connect two solar panels. But many small solar panels already have isolation diodes built in to them. I don't know what a 5V solar panel really is. It may be much more than 5V open circuit followed by a voltage regulator, or just 5V at a specified load current. The typical "12 volt" panel is around 20 volts open-circuit, and 17 volts for maximum power.

If you're going with lithium, they're not a great match to 6V. 7.2V for lithium iron phosphate fully charged is the closest match. But I'm not aware of a chip that handles 2S LiFePO4 charging. The MAX745 does 2S lithium ion, and modules have a voltage trim pot, but I don't know if it can be tweaked to work with LiFePO4.

It's possible that 5V is close enough to 6V, and if so, the battery could be a 4.2V nominal lithium-ion, and be boosted to 5V using a power bank chip. Then the MAX745 or other chip (SY6912, TP5000) could handle charging from solar.
 

bassbindevil

Joined Jan 23, 2014
631
And then there's the obvious answer that I overlooked: 6V sealed lead-acid battery with a 6 volt solar charge controller. Those charge controllers can be found on ebay for under $10.
 

Hemi

Joined Mar 17, 2012
28
If the camera eats batteries quickly, your original idea should work to extend the battery life a bit longer. I would use NiMH AA batteries, (e.g., Eneloop) because they're more tolerant to charging when cold and the same form factor (and voltage) as the alkaline AAs. Like others suggested, a schottky diode will reduce the Vdrop, like a 1N5817
 
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