Solar Relay Build - Ireland

My wish list for building this relay, was as follows.

Able to get sufficient sunlight to run the relay year round, even with diminished sunlight in Winter.
Battery insulator and/or heating circuit to keep the batteries above freezing to avoid temporary or permanent loss of capacity.
A casing, water and dust proof.

Download this link for an excel spreadsheet of below with hyperlinks, pricing, instructions, images and diagrams.
Link with diagrams, excel spreadsheet with pricing, instructions, photos etc

Never ever, power up radios without an antenna connected, if fries the circuit.

Shopping list - Solar Powered Relay:

Solar Panel - Dokio 12V 20W Small Solar Panel China 18V Solar Charge Polycrystalline Silicon Solar panel DSP 20M/20P|18v solar|polycrystalline siliconsilicon panel - AliExpress
LiPeO4 Batteries - 2pcs/LOT Soshine 3.2V 18650 LifePO4 Battery Cell 1800mAH Protected Positive nipple for Led Torch Headlamp Bicycle Light|soshine 18650|cell 18650soshine 18650 lifepo4 - AliExpress
Cable from Solar Panel to Charge Controller (1m) - Square 0.5mm Black Ultra Soft Sheath Wire 2 3 4 Core Silicone Rubber Cable Insulated Flexible Copper High Temperature Power Line|Wires & Cables| - AliExpress
18650 x Parallel battery holder - Holder Box Case 2x 18650 3.7V Parallel Corded Akku Battery für Arduino Raspberry | eBay
Solar MPPT Charger Controller - Buy with optional Thermistor & 3.07A Version -
Antenna - SDD21-868-SMA - Ideetron
Radio - LILYGO® TTGO Meshtastic T Beam V1.1 ESP32 433/868/915/923Mhz WiFi Bluetooth ESP32 GPS NEO 6M SMA 18650 Battery Holder With OLED|Circuits| - AliExpress
Electrical Waterproof box with waterproof plugs to allow aerial to be mounted out through the casing and same for wiring for solar panel - (Best to buy from local electrical store, buy last when you have your antenna and solar cable to get the right sized plugs)
Resistor to be used as battery heater - RESISTOR 150 Ohm 3W Metal Film Resistor (LOT OF 10) | eBay
(Hammond Box 1591xxCBTU) Casing to act as insulation box for batteries and mppt charge controller - Genuine Hammond Blue & Black ABS Plastic Enclosure Project Box Case | eBay

2017-06-28T22 02 46.993Z-LiFePO4wered-Solar1-connections


Solid list. The Soshine / Lifepo4 combo is good.

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Hi @ohcdh ,

I’ve noticed from your drawing that you’re not using the LOAD output of the MPPT charge controller, instead the T-Beam is wired in parallel with the battery. This way you’re not benefitting from the low voltage battery disconnect feature of the controller.

Since I’m using the same controller I’m curious to learn your reasoning behind that.


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I’m a novice to this, so perhaps your suggestion is a better way to do it? It sounds like it might be. I wasn’t aware of this feature, what does it mean or do?




The TBeam has battery management built-in and will power down when the battery voltage reaches 3.0v. What I have found with the T-Beam, if it does power down on low voltage, you have to physically press a button to wake it up again when the voltage returns above 3.0v. The other option is to break the connection to the battery and reattach it. Depending on how the MPPT disconnects the load to the TBeam the TBeam might turn back on when it is reconnected. But looking at the board C10 will prevent the TBeam from seeing the load disconnect and you may still have to press a button to power it back up.

The ideal situation is to size the battery bank big enough that you never encounter a brownout. You might be able to lower the voltage setting in the battery management of the TBeam too, which might prevent the TBeam from going to sleep. This may allow the load disconnect to function without user intervention. I have not played with programming the power management board myself, so Im not able to assist further.

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As per the official features list:

Low voltage load disconnect at 2.7V battery voltage to prevent over discharge and maximize battery life.

Yes, I’m aware of that, that’s why I hope to find a way around it :grin:

@IZ1IVA So should I connect from load output on the mppt charge controller and solder two wires to the positive and negative terminals of the single battery holder on the back of the t-beam? And then solder the parallel battery holder wires to the LiPeO4 connections on the mppt charge controller?

Thank you so much for your help. This community is fantastic, everyone is so helpful.

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@IZ1IVA I don’t know if this has made a difference in my case. But I have two LiPeO4 in parallel and the relay has been operating continuous without interruption. I know concerns were raised about the low voltage threshold kicking in, but fingers crossed it hasn’t happened yet. Will continue to test it at home for another week or so, before placing it into position.

Shame there ain’t a way to configure the battery capacity in the firmware to give some indication of the charge left

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@IZ1IVA This morning I attempted to connect to the relay and it had powered down. I don’t know if it it the radio or low voltage, but I’m not taking any chances. Once this is in place I want some degree of certainty it will stayed powered up and working. Can anyone suggest a charge controller suitable for Li-ion or a charge controller suitable for Li-Titanate (which don’t lose capacity to below freezing temperatures)

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Or could I for example place a buck controller between my LiPe04’s and the t-beam and it would set it above the threshold that the t-beams battery management kicks in? Or is there a way to bypass the power management on the t-beam?

You certainly could if your system can tolerate the consequent loss in efficiency.

I’m afraid no.

Update: This relay seems to be functioning ok, I replaced the t-beam radio, as I suspected it may have had a faulty power management chip, so no brownouts due to low voltage. Using 2 x Soshine LiPeO4 batteries 1800mah in parallel. Relay has remained continually powered up for 7 days.


FYI. The battery cutoff voltage can be set in the power.h file.

When it drops below 3250mV, it triggers deep sleep and I couldn’t find anywhere that wakes it from this state hence the requirement for a power cycle.

Try reducing this value to a very low value and letting the charge controller take care of the low voltage cutoff.

Thanks @Chiumanfu that is great to know. Is it possible to set this “define MIN_BAT_MILLIVOLTS 3250” via a terminal command such as “meshtastic --set is_router true”? Or does a custom build have to be built?

it is default build in general firmware (standard command)

I don’t see anything in the proto-bufs. The only variable related to power is ChargeCurrent

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I have been testing the relay now for over 4 weeks and it has remained consistently on without any power outages. Launching the small community network, with a total of 8 households shortly to see how the network meshes. Initial tests have connected our most remote member at 50km away


Great to hear it’s working. Did you connect heater pads for the batteries? Not that relevant now, but will be in October…

For new installs, I’d look at the Wisblock rather than the Tbeam as they are more power efficient WisBlock Starter Kit | WisBlock basic kit – RAKwireless Store

Thanks @sam_uk . No I stuck with the 150ohm resistor as I was advised the heater pad would draw too much energy and reduce charging. It’s in situ on a mountain top doing it’s stuff ever since. It’s working, but I suspect that an earlier incarnation of the firmware was transmitting at a greater distance, as the range is much reduced, despite a power increase in transmission output on the code. Most of the participants on the network are not picking up the relay and if not for one user, I wouldn’t have connection to the others, he bridges my messages for me. I am not a coder, else I’d get stuck in, but I hope in the coming months many of the bugs will be ironed out and I can upgrade the firmware once again and install a more powerful antenna, but it is working and that is great, delighted with that. I looked at the Wisblock and it looks promising.

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