Solar relays - best practice?

Builds / Use Cases
42

This Looks Amazing Keith! I’ve been wanting to do something exactly like this for the last month. I’m very interested in what your working on.

2 Likes
43

Do you have any idea on the price for these LTO chargers?

44

I’m still figuring out price since I don’t have a final manufacturing cost yet.

I have both the charger and regulator prototype boards in hand and I’ve been testing them rigorously. There’s a couple things I will update on the regulator board (to help reduce output voltage ripple at low current) and then I will send them off to get manufactured. I should have them available in 4-6 weeks.

This is the regulator board prototype (the production version will look a little different). It has a buck/boost IC from 1.8v-5.5v with selectable output at 3.3v, 4.2v, 5v. It comes with an optional UVLO circuit at 3v with selectable release threshold at 3.3v or 3.8v (to support li-ion/LFP or 2S LTO). I added reverse current blocking to the LOAD output so the board isn’t damaged by external voltage added to LOAD. For the voltage sensor I went with an INA3221 which has 3 channels. Battery and solar power are wired to two of the channels so you can monitor the health of your node remotely (voltage/current).

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Here is the charger and regulator board stacked as a unit (the production boards will align properly so we can use headers to connect them).

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And here’s a test node I’ve been monitoring with LTO batteries and a 2W glass panel. I’m happy to report the unit restarts after a dead battery without issue.

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7 Likes
45

Nice!

That looks really good. I hope I can afford one when you release.

1 Like
46

Thank you for the great work!! in the example above with the two LTO cells are they hooked up in parallel to solve the need for the balance circuit or is that something that still needs to be figured out? Excited to test this out! Been wanting to deploy the solar nodes I have built but didn’t feel comfortable letting LiPo bake in a hot enclosure.

47

Yes! You are correct. It’s running in 1S2P for two reasons:

  1. There is no 2S balancer solution available on the market. I’m looking into this but it’ll probably require a custom circuit to make this happen.

  2. I’m running 3.3 directly into the RAK battery port so I don’t really need the higher voltage you would get from a 2S configuration.

These modules are now ready for deployment. My first production-ready batch is already sold out but I have another batch on the way. I expect it to arrive in a couple weeks.

You can read more about it here and get on the waitlist:
https://voltaicenclosures.etsy.com/listing/1609406536

48

I came across this earth battery build for remote repeater which could be helpful in extreme cold conditions if battery is buried deep in ground where temperature is above freezing year around. It produces above 3 volts at 145 mA with 2 cells and easy to build with some Home Depot parts. This is the most efficient earth battery I have seen. It may work standalone without solar panel recharging itself using moisture only or small solar panel can recharge it.

Thanks.

49

With 3 cells buried in ground he got 7 volts at 130 mA as shown in his second video. It is quite impressive free energy perfect for 3.3 V or 5V devices for very remote hard to reach places like mountain top lora repeater. The added bonus is it is buried under ground so not noticeble.

Thanks.