Stationary relay nodes for newbies

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In many instances, an A/C electrical outlet won’t be available, so a different energy source will be needed to persistently-power the stationary relay node. The most common approach is to use a solar panel to charge an “always on” external battery pack, and to connect the external battery pack to the goTenna Mesh by a micro-USB cable. The external battery pack selected will need to be capable of simultaneously accepting the charge current from the solar panel, and sending the discharge current from itself to the goTenna Mesh unit. Not all battery packs can operate in this manner, so make sure your external battery can do this before using it in your setup.

Naturally, there are a number of questions that arise when you consider setting up such a system. “What power generation output do I need from my solar panel to keep my external battery pack from fully discharging?” and “How do I determine the external battery storage capacity that I need to ensure that the goTenna Mesh never loses power?” These questions will be answered in turn.

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What power generation output do I need from my solar panel to keep my external battery pack from fully discharging? The answer is that it depends upon three considerations: (1) Your geographic location; (2) The orientation and quality of sun vs. shade throughout each day of the year; (3) The highest number of consecutive overcast days anticipated during the poorest power-generation month of the year for your location.

Fortunately, there is an excellent article with a link to a free online photovoltaic calculator that can help you calculate your needs, thus avoiding the costly and time-consuming process of experimenting to determine them through trial and error: https://www.voltaicsystems.com/blog/estimate-solar-irradiance-iot-device/

When entering input to the photovoltaic calculator, use the “off-grid” tab of the calculator. Enter the solar panel’s peak output in watts into the field labeled “Installed peak PV power [Wp]”. Enter the external battery’s storage capacity in watt-hours into the field labeled “Battery capacity [Wh]”. Enter the discharge cutoff limit for the battery into the field labeled “Discharge cutoff limit [%]”. If you don’t know the discharge cutoff limit for your battery and you are using a Lithium ion polymer battery, a conservative assumption is to input 40 into that field. Enter the power consumption per day in units of watt-hours into the field labeled “Consumption per day [Wh]”.

Since the goTenna Mesh device’s internal battery has a storage capacity of 0.589Ah, and the battery voltage is 3.7V, the amount of power you would need for one day is 0.589Ah x 3.7V = 2.1793Wh. That’s the power you would need if the energy conversion between the output of the solar panel to the input of the external battery, and back again to the output of the external battery, to the input of the goTenna Mesh was 100% efficient. In real world conditions, the energy conversion is far less than 100% efficient. The linked article states “With lithium batteries, we typically assume 50% of that power is lost going into the battery and back out to the device. That power loss comes from heat as electrical energy is transferred to chemical form and back again, as well as from regulation.” If you want to assume 50% efficiency due to energy conversion and regulation, then you’ll need to adjust your input to the photovoltaic calculator. You would enter “4.3586” into the field labeled “Consumption per day [Wh]. (That is 2 x 2.1793Wh = 4.3586Wh)

Next, enter the angle that the solar panel is raised above horizontal into the input field labeled “Slope [degrees]”. As noted in the linked article, the optimal angle for power production varies with month and geographic location. Be sure to recalculate the power production at various slope angles to determine the optimal slope for the worst power-producing month of the year, which will be December in the northern hemisphere, and June in the Southern hemisphere. If you exercise the photovoltaic calculator for Brooklyn, New York, you’ll find the optimal slope in December is a tilt of about 70 degrees up from horizontal. Next, enter the Azimuth angle in the input field labeled “Azimuth [degrees]”. In the Northern hemisphere, if you are able to orient the solar panel so that it is aimed directly to the South, that will provide the best power-production. In this case, enter “0” into the Azimuth input field. Finally, click the button labeled “Visualize Results” to obtain a bar graph that illustrates results expected for each month of the year for the power consumed (labeled “energy output”) and for the excess power delivered by the panel (labeled “energy not captured”).

One final consideration: If the solar panel will not have an unobstructed view of the sun throughout the day each day of the year, you will need to scale down the power output value you enter for the solar panel in the photovoltaic calculator. (i.e., if the sun tracks behind trees, buildings, and/or clouds during the course of the day, you’ll need to make a conservative assumption about the reduction in power production that will be output from the solar panel to the external battery.) Let’s say that you know the panel will be placed in a location where it will only have direct line of sight to the sun for 50% of the daylight hours on a clear day. Let’s also say that passing clouds will cause intermittent exposure to the full intensity of the sun during the periods of the day when there should be an unobstructed line of sight. You might make the conservative assumption that the output power of the solar panel is only 25% of the rated peak value, and adjust the input field in the photovoltaic calculator accordingly to help you understand expected performance under these conditions. The idea is to take these things into consideration to ensure that the panel you purchase has a high enough energy output to prevent full depletion of the external battery pack and the goTenna’s internal battery. As previously mentioned, you need to keep your relay node up and running continuously, or a manual intervention will be necessary to depress the power button and to place the device in relay mode once the solar panel recharges the batteries in the system. For this reason, it’s best to err on the side of selecting a solar panel that produces too much, rather than too little power. (It will save you the aggravation of periodically visiting your stationary relay nodes to reset them. Depending on the difficulty of accessing them, this may be “priceless”.)

In the end, you’ll still need to try out the system you design to verify adequate performance in the varying conditions at your location, but the photovoltaic calculator and the tips above will help you select the right solar panel for your needs the first time.

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How do I determine the external battery storage capacity that I need to ensure that the goTenna Mesh never loses power, in conjunction with the solar panel selection that I have made using the photovoltaic calculator?

You need to consider the maximum number of days of overcast weather in your location expected during the month of the year that produces the least amount of power from your solar panel. So in the Northern hemisphere, you should be looking at the most consecutive days of overcast weather in the month of December. In the Southern hemisphere, consider the most consecutive days of overcast weather in the month of June. This type of information can be obtained by querying a historical weather database for your location. One such database is linked here: https://weatherspark.com. Studying the historical data will allow you to estimate the worst case. If, for instance, you are in Brooklyn, New York, and the historical data indicates that the highest number of consecutive days of overcast weather on record in December was 15 days, here’s a conservative method for determining the external battery storage capacity you’ll need to ensure that your goTenna never loses power.

You start with the conservative assumption that the energy output from your solar panel on an overcast day is zero. This means that you’re assuming your external battery is losing power at a rate of 2.1793Wh per day. In a 15 day period, the external battery would lose 15 x 2.1793Wh = 32.6895Wh of power. A 44Wh external battery, such as this one: https://www.voltaicsystems.com/v44, used in conjunction with the goTenna’s 2.1793Wh internal battery, would keep the system powered through the rough patch of weather, and when the sun once again emerges, the solar panel will gradually recharge the external battery pack. If you are in Brooklyn, New York, using a solar panel with a 6 watt output, a slope of 70 degrees, an azimuth of 0 degrees, and you have unobstructed line of sight to full intensity sun throughout your December day, you can expect to replace the 32.6895Wh of power that was drained from the external battery pack in about 3.1 days of full intensity sun exposure. Then your system will be ready to endure just over 21 days of zero energy production from the solar panel without the goTenna Mesh ever losing power.

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That pretty well sums it up in terms of panel, as well as battery pack, sizing. The calculator gives what I consider to be minimum values. In making your final hardware choices, go for the next size bigger IMO and experience. At 40 degrees North latitude, I’ve found that a 6W minimum size panel is what you need as reliable starting point.

For more info on such basic user friendly set-ups, along with lots of pics, visit the UMESH thread: Urbana, Illinois, Now a goTenna Mesh Ambassador City!

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@MeshTheWorld Wow, will have to come back after work hours to read everything but thanks for this primer & call to mesh! :slight_smile:

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I have one stationary set up and connected to A/C power but I would love to know if there is a way to see if I am actually doing anything to help anyone. I know I’m the long run someone will use it, but how can I get a stats sheet listing the amount of jumps passed through my GoTenna to show mine is being useful and not just sitting there?

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@Kaf2321 you don’t. If you watch it you can see the light when it is relaying messages. But AFAIK there are no counters on how many times you’ve relayed. It is a numbers game. We need more people out there with mesh to get more hops available and better end to end connectivity.

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aspexin is correct. Look for the flashing lights. In fact, look for them on your personal goTenna Mesh, because if you’re near your relay, you will see the LEDs on it flash 3 times when the node relays nearby. When you’re not sending or receiving a message, paired nodes also relay whatever they pickup unless it’s the 6th hop already.

Another thing to do is to post your relay on the node map at https://imeshyou.gotenna.com/ . Not everyone does, but the more people are aware of what others may be doing, the more the mesh gets used.

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Thanks for your reply - I hope you find this information helpful, and that you decide to set up some stationary relay nodes of your own. :smile:

Don’t hesitate to ask for advice from the folks in this community if you have any questions. We’re here to help.

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It would be really helpful to have a setting for the Mesh node to automatically power it back up in relay mode when power is restored, particularly since there is no way for a normal user to determine whether the node is running without physically pressing the button. That the node stays powered off after power is restored after a battery discharge makes it less appealing to place nodes in hard-to-reach-but-rf-favorable places with intermittent power sources.

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Your concern is shared by goTenna and those of us who operate relay nodes. At one point it was hoped this functionality could be effected by a firmware update, but it was eventually concluded it could only be done with a hardware change in the device itself. I hope this change becomes effective soon, but this will require a slight redesign in production to accommodate a new switch.

Right now my 8 nodes are sitting under a diminishing layer of snow that is supposed to be replenished on Saturday. I’m looking at some work once conditions to climb improve, I suspect.

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+1 to that, Mike – I would LOVE to see a product improvement released that permits a goTenna Mesh to power itself back on in relay mode once power is restored. Even if I have to purchase new goTenna Mesh units to get this capability for my stationary relay nodes, I would do it to improve the tenacity of my solar-powered relay nodes. Seeing the volume of posts asking for this across many past topics, it appears that many others feel the same way.

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You got that right. Lots of us want this. I too will invest in new hardware if I have to. I had to move my nodes I had out of the attic as I developed a bum knee and climbing up to replace the battery packs when they eventually die (solar power during winter only bought me about 14 days of juice) is no fun. The nodes are on the 2nd floor but they lost about 12’ of height with the move.

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Can you communicate with others on the stationary relay node? I set on up a couple months ago, it’s always on, using both electrical outlet, and an anker battery and solar panel, and nobody every responds when I shout to the public channel… super bummer

Shouts do not relay. They only go directly to another GTM device that is within range of yours without aid of a relay.

MikeL is correct - shouts do not relay, they simply transmit out from the goTenna unit paired to your Android or iOS device. So if you have your stationary relay node operating in “relay mode”, it will not retransmit any shouts it receives. On the other hand, if you pair your Android or iOS device to your stationary relay node, and remain in Bluetooth range without setting it into “relay mode”, it will be the goTenna that originates your shouts. (But your shouts will not get retransmitted by any other goTenna’s in-range that receive the shout.) Make sense?

In one of MikeL’s latest posts [Here] he mentions his concern about whether the battery capacity in his solar powered relay node will be sufficient to keep the node up and running until the snow and ice clear from his solar panel to restore normal power output to recharge his external battery pack.

It’s a concern I have as well, since I have to deal with snow and ice accumulation during the winter months – and I know that during some periods of severe winter weather, it can take weeks before the temperatures rise sufficiently (and for a long enough duration) for the snow and ice to melt away and clear the solar panel and the dry box that contains the goTenna Mesh relay node.

Early in the linked post, Mike notes, “When the snow first came down, it’s effects were very minor, mostly involving needing to resend a message where it was typical to get a confirmation returned after a several hop connection. Things aren’t so good two days later. Apparently, the melting of the snow compacted it, which had a bigger effect on RF signals getting out consistently.”

Mike’s experience is that once the snow partially melts and refreezes, the operational effectiveness of the relay node is compromised – or fully defeated – because the layer of dense snow pack and ice hampers the radio signal.

So the rest of this post contemplates options to consider that will help stationary relay node owners keep their nodes powered and operational under winter conditions, while avoiding the need to visit the setup to restore power or operational performance.

  1. Keep the dry box containing the goTenna Mesh elevated off the surface where snowfall will accumulate. Do the same for the solar panel too. If the historical extreme for snow accumulation in your area is 4 feet, then make sure you mount the solar panel and the dry box containing the goTenna Mesh at least 4 feet above the surface of the roof or platform. This is necessary to keep them from getting buried in snow pack. Make sure you consider the worst-case extreme total accumulation from multiple consecutive snowstorms in your area.

  2. Install a small angled wooden “roof” over your goTenna Mesh’s dry box. If you’re mounting your setup to a pole that’s on top of your building’s roof, put the angled wooden goTenna “roof” highest on the pole, with the goTenna’s dry box underneath. Below that, mount the external battery’s dry box (assuming it’s separate), and underneath the battery dry box, mount the solar panel.

  3. Make sure you mount the solar panel at a steep enough angle to facilitate rapid clearing of snow and ice when temperatures get above freezing. As noted in a previous post in this topic, mounting the solar panel at a tilt angle of 70 degrees up from horizontal is optimal for power output in New York City during December when the periods of daylight are the shortest. This mount angle will also nicely facilitate rapid clearing of ice and snow from the panel when temperatures rise above freezing.

  4. Install a higher capacity external battery to keep the relay node powered longer - ideally until the solar panel is operating at full power output again.

  5. Use a larger solar panel with higher output power. Even when not operating at full output power, it will sustain power to the relay node longer than if you choose the bare minimum panel wattage needed in good weather conditions.

These are all options to consider. They involve classic design tradeoffs between cost, setup complexity, and system reliability. Some people have tighter financial constraints than others, and will decide that they are willing to trade away higher system reliability to have lower setup complexity and lower cost, even if it means they’ll need to perform more work to maintain the uptime of their stationary relay nodes. Each stationary relay node owner will have to make a personal decision on the optimal compromise of complexity, cost, reliability, and maintenance obligations. I’ll leave you with the following questions to contemplate as you seek to make the optimal decision for yourself:

a) What’s my primary purpose for setting up stationary relay node(s)? (Experimentation? Expanding the local mesh presence for everyday use under routine circumstances? Establishing an off-grid emergency communication system for disaster preparedness?)

b) Depending on my answer to a), what is my tolerance for dealing with lower reliability and/or system outages of my stationary relay node(s)? Can I live with periods of lower reliability, or will it be inconsistent with my primary purpose for establishing the stationary relay node(s)?

c) If I have decided that I want to maximize uptime but minimize setup cost and complexity, how do I feel about tending to my stationary relay node(s) if they experience reduced operational performance or lose power due to severe winter weather? Are they placed in locations that are safe for me to access when there is ice and/or snow present?

d) How much can I afford to spend to set up my stationary relay node(s)?

When you answer these questions, you’ll have a clearer concept of the tradeoffs that are optimal for you.

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That’s a great summary of issues in snow country. Depending on where you’re at, this may be less of a factor with climate change, but keep in mind that one result of that is a greater intensity of precipitation. If you’re in snow country, it might even get deeper than is now typical in many places. Here in the Midwest, the trend has been toward higher temps through winter, so I am hoping that this winter’s experience is unlikely to be repeated in the future.

It’s also important to keep in mind that gloom can be almost as bad an enemy as snow. Between November and February, overcast days often far outnumber sunny ones. I tend to have a chuckle over people getting their calculators out to see just how small a panel they can get away with. That works fine in the summer, but estimating what is needed to get through winter is much trickier, when panel output is most likely a small fraction of what is available on a bright sunny day. Best to go big as seems reasonable, as you’'ll need it all on the darkest days of the year.

The pole mount idea is one that makes a lot of sense, but also requires more material, a more complex set-up, more potential points of failure, and is less likely to be found visually acceptable by node hosts. In fact, that’s what I have here at home, because one more antenna at my place won’t stick out…

In this pic, it’s the small box on the mast in the middle, before solar power was added. Looking the other direction…

For long periods of snow blockage of solar panels, only a really large battery will work for weeks at a time. Seems economically unfeasible for most installs, but if it’s where comms are needed it is possible.

This makes me wonder about whether panel heaters are available? How would they be controlled, etc? There’s some possibilities there, but seem costly and would require their own dedicated batteries.

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You got that right. Lots of us want this.

I don’t get it. Why doesn’t someone just change the firmware to do this? I’d do it like this:

  • On mode change to relay, push some bits into EEPROM storage that says “we are in relay”. (And on going back into non-relay, push bits in that say “we aren’t in relay,”)
  • When you power up initially from battery power loss, read the location above to determine if we should go straight into relay.

This is really straightforward. Simple enough that it likely can just be tacked onto the existing firmware. (Don’t get me wrong, this is “really really hard” without the source, but not impossible. It’s just ARMv7 opcodes. Especially if it’s a feature that nearly everyone wants and for some reason goTenna doesn’t provide or doesn’t know how to provide.)

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couple of years on, wondering if there has been any movement on this, perhaps with bray’s recommendation? to build a resilient, self-healing mesh network you really need to be able to deploy relays that will reboot when power is restored, otherwise the network will naturally decay as remote links drop out because they need someone to go restart it