Trying to use the parts I have available...

I have a wel-bilt #28650 12v solar panel (Max: 7 watt / 583mA / 15-17v) I have 2x 12v 7Ah sealed Lead-Acid batteries in series for 24v (from a APC UPS #APCRBC123).

I also have a number of components from the recent RadioShack closures. Various diodes, transistors, caps and so on, but nothing specific for this.

I want to make a charger from the 12v solar panel to charge the 24v battery that will then run a 24v security camera and PtP wireless station.

At current the camera is run from POE but it is tethered to a ethernet cable that is then in turn tethered to a 120v extension cable. This is no longer acceptable because I want to move the camera. Further, there is no point in having it on a wireless system if still having to use a cabled power source.

The wireless PtP device and camera are both using 24v POE (https://www.ubnt.com/airmax/nanostationm and https://www.ubnt.com/unifi-video/unifi-video-camera-g3) and I can't see any reason not to make it solar powered.

I've looked at a number of IC555 step up tripplers and a few other circuits. But they all seem to provide very low mA (as in less than 100mA). The PtP wireless device is rated at a max of 8 watts (but i'm only using it at a 1/4 of its max power output) and the camera is rated at max 4 watts.

UPDATE: assuming my meter is correct, the equipment is using 220mA with IR off (day) and 250mA with IR on (night).

This may not work out at all. The solar panel is rated max at 7 watts. So I don't see it being able to charge the battery and provide enough power to run the equipment.

Some advice here would be greatly appreciated. I'm only a beginner here but I want to learn and it's fun to build things!

  • 1
    \$\begingroup\$ What you want is called a boost converter. The control circuitry for one is a good bit more complicated than a 555, but it works on vaguely similar principles. Plus, boost converters are so common that you can get all the requisite circuitry already put on a chip for you, just add inductor. \$\endgroup\$
    – Hearth
    Apr 26, 2017 at 17:44
  • \$\begingroup\$ yes - I saw 100s of them on amazon and ebay. How hard to build one? The ones I saw are simple to grand. I only need a fairly simple circuit. \$\endgroup\$ Apr 26, 2017 at 18:02
  • \$\begingroup\$ Run the batteries in parallel to simplify charging from solar panel. Just use a simple over-voltage disconnect to avoid over-charging the batteries. Use a 12V to 24V boost converter to supply power to your load. \$\endgroup\$
    – user57037
    Apr 26, 2017 at 19:31
  • \$\begingroup\$ something like this will get you from 12v to 24v cheaply and relatively efficiently... \$\endgroup\$
    – dandavis
    Apr 26, 2017 at 19:57
  • \$\begingroup\$ @mkeith good idea. so just use the solar to charge the 12v battery (instead of charging 24v) and then use a boost converter to power the rest. I could use a zener diode or 7612 to keep the solar charge voltage at 12v constant unless sun is down. \$\endgroup\$ Apr 27, 2017 at 20:38

1 Answer 1


So I don't see it being able to charge the battery and provide enough power to run the equipment.

I think you know you've already answered your own question! Using the wireless station at less than maximum isn't going to save enough power to make this work, especially as the boost converter won't be 100% efficient. 7W maximum generated during daylight hours only, maybe 10W or 11W required all the time. And the battery charging circuits will also use up some of that valuable power.

You could use it to provide camera power during daylight but that's about it - at my electricity prices that would save you about £2 a year. I'd have to suggest that the economics just don't make sense.

  • \$\begingroup\$ yes i figured i had already answered myself, but i was hoping someone would tell me a way around this limitation! lol. the entire reason for solar power is to make this portable with no limiting power extension cables. the PtP wireless can go up to 15km (and I want to use it about a 1/2 mile away). \$\endgroup\$ Apr 27, 2017 at 20:44
  • \$\begingroup\$ UPDATE: assuming my meter is correct, with IR off the equipment uses 220mA and with IR on it uses 250mA. thats a max of 6 watts. MAYBE THIS IS STILL POSSIBLE? \$\endgroup\$ Apr 27, 2017 at 22:19
  • \$\begingroup\$ I'd love to give you hope and encouragement, but for starters your meter is only showing you an average consumption and not the peaks in current that radio equipment can need, and if you're right on the limit supplying the average there's nothing left for the peaks and you're likely to suffer from voltage dropouts. Even without that, your 7W panel output is an absolute best case maximum and you'll only get it during the brightest hours of sunlight. Outside those brightest hours you won't have enough and there's nothing spare to charge a battery to get you through them. \$\endgroup\$
    – Finbarr
    Apr 28, 2017 at 8:33
  • \$\begingroup\$ ANOTHER UPDATE: I just found out that these devices work at voltages all the way down to 9 volts! This has put a whole new light on things. I just tested the equipment with a single 12v battery and the 12v solar panel (without the battery) and all works well. I was reading on their website of other people using 12v supply voltages with no problems. \$\endgroup\$ Apr 28, 2017 at 17:05
  • \$\begingroup\$ Is it still 250 mA at 12V? \$\endgroup\$
    – user57037
    Apr 29, 2017 at 4:48

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