Minimal, Individual Preparation for EMCOMM

Computers for EMCOMM

Configuration of an EMCOMM Power Supply

If you are simply a concerned citizen with a ham radio license, you should read this: Minimal, Individual Preparation for EMCOMM

This article is about serious preparations for emergency communication.

Contents

• Intro
• First Step: Define Electricity Requirements and Operating Time
  • Participation in EMCOMM with handheld FM Tansceiver
  • Participation in an EMCOMM Network With a Mobile Transceiver
  • Operation of a Simple FM Relay
• Dimensioning of Solar Modules and Batteries
• Using the Emergency Power Supply for the QTH
• Why DIY and not a Power Station?
• Why not Just a Proper Solar System?

If you want to do emergency communication (EMCOMM) as a radio amateur, you need a suitable emergency power supply. The easiest way is to operate your handheld FM transceiver with external, possibly rechargable, batteries. If you want to do a little more, you will quickly end up with a solar power system.

Tips on how to build emergency power supply is available in a separate chapter (not yet translated).

Solar modules are particularly important if you want to use the special advantage of amateur radio: After 2-3 days off-grid, the communication networks of the emergency bodies should be quite at the end because the diesel for the power unit gets scarce. I do not believe that the replenishment works without a functioning power grid:

• Fuel depots have to pump and bill the fuels.
• The traffic in the cities collapses without traffic lights.
• A storm may have blocked the access to a site on a mountain...
• Apart from the fact that an essential part of the diesel generators does not start anyway or fails at short notice.

If you complement the battery with solar modules, off-grid operation is practically possible for unlimited times. If you want to do the rest, you can buy an emergency generator of the 1-kW class for EUR 300 and a charger for 100 EUR. So you can reload the battery every few days. However, an emergency generator must be serviced regularly.

What I describe here is based on several years of experience. I started working on my first experimental system in 2017, using old solar modules and lead-gel batteries. In the meantime I switched to LFP batteries. Their prices came down considerably, making any lead technology not worth considering – at least on the long run.

See also the references on the left in the navigation column.

First Step: Define Electricity Requirements and Operating Time

Participation in EMCOMM with handheld FM Tansceiver

A handheld tranceiver should often be enough to reach the next relay. During reception, such a unit needs maybe 100 mA at 7.2 V. During transmission it quickly reaches 2 A – depending on the required transmission power. At 10% TX this means 0.3 Ah per hour, based on 7.2 V.

If you take a lead-gel battery of the 20 EUR class, i.e. 12 V/7 Ah, you can use about 4 Ah. A small switching regulator as in the picture reduces the power consumption from the battery to about 0.2 Ah/hour. So you get around 20 operation hours from the battery. If you assume 5 standby periods of 10 minutes each day, this means less than 1 operating hour a day. So you can take part in the EMCOMM network for 20 days if no further activities are necessary.

Participation in an EMCOMM Network With a Mobile Transceiver

There are reasons to do EMCOMM with a mobile transceiver, from connecting the station antenna to greater transmission power to special functions, such as cross-band relays.

But this means a significantly higher power consumption. Lets estimate 500 mA RX and 6 A TX, everything on a 12 V basis. This means at a 12-V consumption of about 1 Ah/hour – factor 5 more than with the hand TRX. The above battery would be discharged after 4 days. If you drive the battery to wear, you get a week. If the radio still works under 11 V.

If one assumes that the disaster protection services only remember us after the breakdown of their own communication infrastructure, that is not enough. After all, you could have done welfare traffic by then, that is transporting information for the population.

Operation of a Simple FM Relay

I see no crucial reason why a simple relay should consume much more electricity than a mobile station. I see the difference more in the operating time and thus the necessary battery capacity. The control could easily be done by an Arduino or a small Raspberry Pi.

My suggestion is to equip relays for at least 20 days of off-grid operation. Solar operation can expand the operating time almost arbitrarily. At 12 V/1 A that means 12 V/500 Ah! In LFP technology this would cost around 1000 EUR. However, this can be significantly reduced:

• Modern handheld transceivers should also be suitable as relay RX.
• In an off-grid situation, the relay falls into emergency operation. Then little more than the handheld radio in the RX path and the processor system are powered. When the relay is accessed, it takes a few seconds to power it up. This delay happens only at the first activation, not during a QSO. As soon as there was no operation for 3 minutes, the relay is powered down again.
• It is unlikely that the weather will always be gray in gray for two weeks. With a standard 450 Wp solar module for 100 EUR, a charge controller for a similar amount and 200 EUR small stuff around it, a 200 Ah battery for 400 EUR should be sufficient for availability beyond 95%. If the relay has a realistic occupancy of 30 minutes per day in normal operation, the power grid connection can be completely omitted.

Integrating the relay into a network using HAMNET methods requires only a slightly larger power supply.

Dimensioning of Solar Modules and Batteries

Only in very sunny areas with more than 300 sun days a year or so, a solar installation can provide energy year round. But solar modules can extend the operation time of emergency equipment considerably.

The following observations were made in southern Germany, 50 km north of the Alps. For Germany, this is a relatively sunny area. On the other side I have to cope with quite some shadows, not only from 20 m high trees 25m south of my house. You should consider that even minimal shadows on your solar modules can cost you 50-90% of the output as a single wafer (single silicone sheet) can define the current through the whole solar module.

• On a cloudless day, the solar modules should provide up to 3-5 times the energy needed per day. This will not only charge the batteries quickly but also provide enough energy during overcast days.
• Consider mounting the solar panels vertically. This certainly reduces the energy that can be harvested over the year. But this is not the primary concern for an emergency power supply: You need a certain minimum of energy for as long as possible.
  • Mounting can be easier and cheaper. Solar modules are cheap so you can trade in more solar modules for all the aluminium and work costs – provided you have the space.
  • Vertical mounting shifts the time with the maximum output away from the summer when you do not know what to do with all that energy anyway.
  • If you get snow now and then, all other solar modules will stop providing any energy. (In the photo, 40 cm of wet snow within 24 h brought down my shortwave antenna, as you can see.)
• If you go the solar way, dimension the batteries to at least two days of maximum solar output. Example: Your installation consumes 1 kWh/day which is a mean consumption of around 40 W. This means, according the guideline above, an energy harvest of 3-5 kWh/day and 6-10 kWh of storage capacity. It makes no sense to trade more solar power for less batteries: During the winter you might have weeks without any noteworthy solar harvest.
• Without solar, get a gas generator and dimension the batteries to store enough energy for a day. This reduces gas consumption and operating hours. If everything is dark and quiet, this might be important.

If you dimension your solar system this way, you should be able to operate your emergency equipment 24/7 from March to October from solar only. During the winter you can operate the emergency equipment for at least 8-14 days. Only if the emergency might last longer you would have to limit operating hours. I need around 20 kWh/year to bridge the winter gap, for the shack and the fridge. A small gas generator could fill the gap for a few 100 EUR while 20 kWh of battery storage would cost several 1000 EUR.

You can compute that my installation conforms to the lower limits of this guideline.

• Plan A is to operate both installations in the shack and in the basement. See next chapter.
• Plan B is to operate one of these installations, perhaps with moving some charge with a switching voltage converter and the 12 V line between the basement and the shack.
• Plan C is using my 2 kWh power station. Normally I keep back the power station as it is my only portable power source.

Using the Emergency Power Supply for the QTH

This chapter is provided as a reference for your own installations. It describes the different components, their purpose and their usage.

If you are already setting up an emergency power supply: Why should you set it up just for hobby use and the unlikely event of an emergency? For this reason, at the end of February 2022 (why then?), I considered a larger power supply. I wanted to have at least 500 Wh/day available under all possible conditions, despite the rather unfavorable conditions. See image:

• My shack consumes around 20 W or 500 Wh/day. The QRP transceiver and the Wi-Fi access point do not make much of a difference, but a small Windows computer does.
  I have the radio running 24/7 while I am at home – usually with VarAC on 40m or 20m. Using Winlink Express, I can send and receive emails, which I might do as welfare traffic during a disaster. I can also use FM on 2m and 70cm, of course.
• I can charge USB devices on a dozen ports. I might want to offer this to the neighborhood.
• Normally, my refrigerator-freezer is also connected to the emergency power supply. It has an EU energy rating of A and cost well over EUR 1,000. However, this refrigerator only consumes a good 200 Wh/day, while its 13-year-old predecessor consumed at least 600 Wh/day more.
  At 0.30 EUR/kWh, that means savings of EUR 65/year. The additional cost pays for itself over its lifetime, if I run the refrigerator on the mains.
  Due to its low power consumption, I can also run it on the solar emergency power supply. With the inverter losses, however, it consumes about 400 Wh/day.
• In an emergency, I would either rely on sunny weather or turn off some of the equipment. Then I can, for example, run my central natural gas heating for a few hours.
   

Output of two 335 Wp solar modules vertically on the house wall July/August.
Red box shows time frame of the next diagram, a rainy period. You can estimate the energy consumption of the fridge through the inverter.

State of charge (blue, 100% = 240 Ah)
power in/out of battery (red)
In the upper diagram the newest data are on the left, in the lower diagram on the right.

Based on my experience with my old experimental system, I purchased the following components:

• 1 kWp solar modules, see picture above. I screwed them vertically to the house wall. This was quite easy because the house is clad in wood. This means I lose some energy harvest in the summer, but I want to harvest as evenly as possible throughout the year.
  Originally, the limiting factor was the solar charge controller. I over estimated the losses by their vertical mounting of the solar panels. The charging current is limited to 35 A, which at 13.5 V means about 480 W. Even with the vertically mounted solar modules, I still get more than half of the rated power! At least in central European climate, few will be able to achieve more than 80% of the rated power. This is due to the measurement method.
  These days, two of the solar modules are connected in series, which results in a solar voltage of around 70 V. Through 20 m of cable running down to the basement they power the fridge and possibly a few kitchen appliances. At a typical current of 5 A and a maximum of 8 A, I can easily use 2.5 mm² cables.
• 35 A/150 V MPPT solar charge controller. This delivers up to 3 kWh/day, despite the shading visible above. So, a cloudless day can provide energy for up to 6 days to the kitchen.
• 15 A/70 V MPPT solar charge controller. This provides up to 1.5 kWh/day. So, a cloudless day can provide energy for three days of 24/7 operastion of the ham radio station.
• 12.8 V/300 Ah LFP batteries in the basement, or just under 4 kWh. Considering parallel consumption, I can store the energy of two cloudless days.
• 12-8 V/200 Ah LFP batteries in the shack, or about 2.5 kWh. Considering parallel consumption, I can store the energy of two cloudless days.
• 600/800 W inverter in the basement: This inverter has an 8 W self-consumption, which is relatively low. This was important to me because I want to achieve the longest possible runtime. It is sufficient for most devices. Only the dehumidifier in the basement does not run on it. See below.
• 200/250 W inverter in the shack: This is from the same line as the inverter above, but is normally turned off. I can use it to power the computer monitor in the shack that I hardly ever use. It could also power the soldering iron or the oszilloscope. Most often I use it when the batteries in the shack are full. Then I run the computer in the home office from solar.
• No further voltage conversion in the shack as everything runs directly from the battery voltage: QRP transceiver, WLAN access point, Windows computer.
• 2 kW inverter in the basement: In the summer, I often did not know what to do with all the solar power in my stand-alone system. A sale at a local hardware store came at just the right time: The inverter only delivers modified sine wave power, but that was enough for me. With it I feed around 200 kWh/year to the dehumidifier in the basement. The problem is not the normal operation at around 300 W, but rather the startup current of the compressor. The 2 kW inverter was not originally planned, but it will pay for itself in about 4 years. It also gives me redundancy: Inverters contain power electronics, which often fail.

The design decision for 12 V was made to reduce losses around the ham radio station. The 2 kW inverter exposed the limits of a 12 V system: 2 kW means more than 150 A to the inverter. To limit losses I had to dimension this current path with 32 mm² (AWG2).

I have a 12 V line between both systems. With a switching regulator I can push energy from one system to the other. For some time I had LFP batteries in the basement and AGM (lead) batteries in the shack. The voltage level of the AGM batteries is generally lower that that of LFP batteries, especially when the AGM batteries are mostly depleted. Through the 0.4 Ω of the line I got up to 1.5 A charging current to the AGM batteries.

Bottom line: From end of February to begin of November I can power shack and fridge completely from solar. For the rest of the year I need 10-20 kWh of grid power. For normal operation I do not use the lowest third of charge. At all times I can operate the station for at least 24 hours without any solar energy.

Why DIY and not a Power Station?

DIY saves you hardly any money, but it does give you more flexibility. If you follow evaluations of power stations on tech-savvy YouTube channels like DIY Solar Power with Will Prowse, they are usually poorly suited for our purposes:

• You can hardly ever get direct access to the battery voltage, which is the most important application for me. LFP batteries with 12.8 V nominal voltage have the optimal voltage for the shack. Therefore no voltage converters are needed, optimizing efficiency. For good reasons, power stations with more than 1 kW AC output operate at 24 V or even higher voltages. A good guess is (stored energy / 100 Ah) as this is the standard capacity for LFP cells.
• The inverters are too power-hungry for emergency power supplies. Power stations are generally designed to drain the battery in an hour. This certainly makes sense on a construction site or similar, but it leads to high self-consumption. This can easily reach 25 W. This might be more than the EMCOMM equipment needs.
• If power stations include a solar charge controller, 36V modules can only be connected in parallel or not at all. I wanted to have the emergency power supply in the basement, which would have required rather thick cables at 500W/15A. I could not have put them in my conduits.

I also do not want to hide the fact that I also see the whole construction as an appropriate toy for a retired electronics engineer :-)

Why not Just a Proper Solar System?

Warning! Even setting up my solar system required a certain amount of specialized knowledge, from the generator junction box to double-insulated cables to grounding. Anyone who wants to make any changes to their large solar system should only have it done by a qualified electrician.

In my case, this is due to the trees that tower into the sky south of my property line. From the beginning of November until February, all suitable roof surfaces are in shade. The roof visible in the picture belongs to my neighbor, but mine does not look any better. The ridge is just not visible. I cannot harvest more than a few hundred Wh/day under these circumstances. It would be a bit better with solar modules mounted several meters higher. I did not want to go through the hassle of scaffolding, etc.

Most grid-connected solar systems are unsuitable for emergency purposes: The solar modules only power the inverter. As soon as the power grid fails, these systems are dead, even if they contain batteries, because the batteries are only connected to the grid.

The alternative is a power path from the solar modules via a charge controller directly to the batteries and from there to an inverter. The system should be able to feed into the power grid and also independently power the house after switching over.

The simplest option is to connect a standalone inverter to the batteries, which then supplies power to individual devices: a refrigerator not defrosting during a power outage, or the shack, are good options.