12V solar/battery project

HI there,
I have a solar/battery power project going that requires monitoring of the 12VDC battery & PV cell, as well as the capability to open & close relays, controlled by a Pi Zero.
I’m looking at the Pimoroni Automation pHAT but just wanted to make sure I’m buying what’s required. It looks like it may well measure 12VDC from a couple of sources and has a relay already for LED lights, am I correct?
Also on my list is the Adjustable Switching Power Supply Module IN 4V-35V OUT 1.5V-30V LM2596S which looks like it’s suitable to take 12VCD in and charge a 3.7V lithium battery?
The project requires the LED’s to come on after dark, so i have a photo transistor light sensor - would this be the most suitable in Sydney CBD, or the analog option, or would you suggest i experiment with both?
many thanks,

I think the pHAT would work just fine. The relay on the pHAT can only handle 2A, so it’s not really suitable to directly control LED lights. Unless of course, they draw less than 2A. If you want to charge a Lithium battery you need to have a Lithium battery charger as well. But you could use the switching power supply to provide the correct voltage to a battery charging unit.

I really need to know a little bit more about your project to give a more detailed answer. Could you please provide:

  1. A brief summary of what you want your project to do
  2. A clear diagram showing how it all comes together. This could be accomplished with the following tools:
    a. Fritzing – A easy to use, Open Source tool (Free Download required - http://fritzing.org/home/ )
    b. TinkerCad Circuits – Another free & easy to use tool, but this one is browser based and requires a login ( https://www.tinkercad.com/circuits )
    c.Draw a simple block diagram of what your circuit should do, alongside a picture of a top down shot of your circuits (Pen, Paper and Camera Required)

It would also be helpful to know any of the relevant voltage/amps of the components. Such as the solar panels and the battery you intend to use.


Hi Stephen,
thanks for that, I was needing the Fritzing software.
The Fritzing file wouldn’t upload in the forum so here’s a link
password is Stephen
Let me know if it makes sense.

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Hi Ben,

There are a lot of moving parts to this project, a number of issues with this diagram spring to mind straight away. It would be best to build one bit at a time, keeping the variables down along the way. Learn, test and iterate. Perhaps don’t try everything all at once.

Some feedback:

  • Pi Zero isn’t the best board for really low power stuff. Its power footprint is fairly high compared to something such as a Particle Photon using sleep mode etc. With a bit of math for power over time, you would arrive at this outcome pretty quick.
  • The LM2596S will not charge LiPo. Search for LiPo Charger and explore some options. Choose something within your requirements. Most also have regulated voltage outputs as well.
  • The LDR would be dependant on lots of physical environmental factors. Sure, either would be fine. But “what if” something interrupted the physical path of light and created a false trigger (be it for a short while, or a long while). If the device was internet connected (which the Particle Photon very well could be) then you could instead make a web request to find the sunset time for each day and go from there. Or just use a sensor, either would be fine - it’s the fun of DIY
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Hi Graham,

Thanks for recommending the Photon - are the Particle Relay Shield for Photon relays rated for DC?

The good news is I have a working solar kit, it is only missing the control. And I have someone to help with coding.


Hi Ben,

According to that relay datasheet, the relays are rated for 5A at 30v DC Max.

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I don’t think Ben was referring to that product, Stephen.

Perhaps Ben was referring to this, if so, then the details are listed on the product page:

If you are new to Particle, then check out our tutorials for a range of topics here

Also, this is a good getting started kit for IoT projects:

Graham and Ben,

The Datasheet I posted is for the relays on the Particle Relay Shield. I got the link from the Particle website.

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Thanks guys, I appreciate your advice.

I’ve made an order for Particle bits and will have a crack at a couple of options.

I’ll let u know,

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Hey guys,

So far so good. The Particle Photon/Electron would appear to be ideal not only for the application but also my limited level of knowledge. The prototype is up & running and I’m following the steps on the Particle website, I’m confident I’ll have most of it operational soon without any outside help (which is better than expected).