Repeaters: sufficient backup power?

[K3MRI]

I'm wondering how much backup power is available to most VHF/UHF repeaters around the country and around the world. I'm also curious to know how many repeaters have battery only /vs\ solar+battery /vs\ generator?

Is it one-hour – to avoid losing the repeater during a quick power drop or failure – or is it several days in the case of a major power outage like after a storm or during a pandemic when, potentially, workers might not show up to a power plant to fix an outage?

[W3TDH]

The primary repeater that is used by Skywarn in the Washington  Baltimore Metropolitan area and Northern Virginia ,which is the WA4TSC 147.300 repeater at Bluemont, Virginia, has battery back up power but no automatic means to recharge it. The repeater’s output power is reduced automatically when electrical utility supplied power is lost. For some types of Skywarn Activation that has meant that I have had to change the net to one or both of the Secondary Repeaters. One of those is the Montgomery Amateur Radio Club’s KV3B repeater, Which See.

The WA3YOO repeater, in central Rockville, is maintained by the Montgomery County Radio Shop for use by the Auxiliary Communications Service which is a cooperating agency of the Office of Emergency Management and Homeland Security. It is hosted in a County facility which has a legally required Emergency Generator.

The Montgomery Amateur Radio Club’s (MARC) KV3B repeater system is hosted at 6 sites. All of those sites have a legally required Emergency Generator but at one of the sites it has not been possible to obtain the use of a circuit which is supported by the Emergency Generator. That leaves one of the remote receiver sites of the 146.955- repeater without emergency power.

Emergency Power Systems are required to pickup their full load in 10 seconds or less. The MARC Repeater Committee is attempting to bring the KV3B repeater system up to full functionality over the next 6 Months. Once that is done the committee plans to install continuously connected battery supply which will be sufficient to get the equipment located at each of the repeater sites through generator transfer without any interruption in repeater function. At the site were a circuit supported by the Emergency Generator is not available we will move toward sufficient battery capacity and solar charging capability to assure continuous operation of the repeater and the remote receiver situated there.

Tom Horne W3TDH

[K3MRI]

Thanks Tom @W3TDH! In your opinion, if someone were to come to you asking for the 'ideal' power setup for a repeater, what would that look like? What source combination, duration of power, and switch over options? I realize that much depends on budget and repeater usage, but for the sake of this discussion, high traffic and a multi-purpose usage profile including emcomm, rag chew, and some packet.

Thanks!!

PS. Congrats on your new ARES role 👍

[W3TDH]

From only my own point of view a repeater that is realistically expected to carry emergency communications would be running directly off of a bank of Lithium Ferro Phosphate batteries [Note 1], with no transfer mechanism that has any likelihood of failing in an open condition; Schottky barrier diodes leap to mind. The battery bank would be sized to carry the repeater at 100% duty cycle for 24 hours. The battery bank would have three sources of recharging. Solar panel array sufficient to carry the recharging at 100% duty cycle on cloudless days. A modest wind generator with sufficient output to carry the recharging at the wind speeds historically experienced on cloudy days. and a utility powered charger / conditioner.

All equipment, including computers if any, able to run directly off of the 12 volt DC power supplied by the batteries or a voltage converter from 12 volts. No inverter powered equipment in the repeater system. An AC power inlet located at an accessible location for connection of a portable or mobile generator, to supply the battery charger / conditioner, fitted with a transfer mechanism Listed by a recognized testing laboratory. A utility powered visual signal, such as an always on emergency light, to show when AC power is present at the utility supply of the facility's step down transformers, were such as system is used, that supplies the circuit which carries the Charger / Conditioner. [Note 2]

Explanatory notes:

[1] The choice of LiFePh4 batteries is based on their; much higher number of charge/discharge cycles prior to needing replacement, much flatter discharge curve which obviates any need for voltage boosters, lighter weight for carrying beyond the top floor which has elevator access, and their inability to support combustion.

[2] Larger buildings receive utility power at a variety of voltages which can be used directly to power the buildings heavier loads such as; Heating Ventilating & Air Conditioning (HVAC), Fire protection systems, production processes... In such buildings power for 120/208 volt receptacle outlets is usually produced by a transformer that is part of the facility's electrical plant. These transformers are owned and maintained by the facility's owners.

[W3TDH]

Further thoughts on the desirable characteristics of a repeater which is realistically expected to carry emergency communications.

No part of the repeater system should depend solely on the Public Switched Telephone Network (PSTN), power from a public utility, internet connectivity, or any other resource beyond the control of the repeater's operators. Remote links for reception, control, and monitoring should all be radio based but secured against unauthorized use by a digital squelched control signal receiver. The control signals themselves should be digital as working with digital media is less likely to be within the skill set of the brainless twits who engage in malicious interference with emergency communications drills and possibly even actual emergency communications.  If possible that receiver should be on Federal Communications Commission Part 15 frequencies so as to make encryption of the control codes lawful. The side benefit of using Part 15 frequencies is that it may be possible to tie that control chain into an alternative internet pathway such as a radio linked IP system like the one being constructed by the Mid Atlantic Internet Protocol Network (MAIPN).

FWIW Your Millage WILL Vary.

Tom W3TDH

[W3TDH]

6 hours ago, K3MRI said:

Congrats on your new ARES role

Thank you for the kind words. I'm trying to come up to speed on the job under these very unusual circumstances.

Tom W3TDH

[W3TDH]

On 3/26/2020 at 11:36 AM, W3TDH said:

The battery bank would have three sources of recharging. Solar panel array sufficient to carry the recharging at 100% duty cycle on cloudless days. A modest wind generator with sufficient output to carry the recharging at the wind speeds historically experienced on cloudy days. and a utility powered charger / conditioner.

The Repeater Committee is considering my suggestion that we add an AC power inlet and manual transfer switch to the remote receiver site which does not have a generator supported electrical supply. That would allow a generator at ground level to supply the repeater's Battery Charger-conditioner long enough to recharge the battery bank if the Solar Array and wind generator were to fail. Think severe ice storm or hail. We may place the inlet in the stairwell near the Fire Department Emergency Electrical Circuit outlet. That supply takes the form of a simple conduit run in the stair well with an inlet plug at the bottom and a receptacle outlet on each floor. We would need to have adapters for the Fire Department's 20 ampere locking receptacle and inlet but I had planed to include those in the Montgomery County Auxiliary Communications Service's standard generator accessory kit accessories list. Since No is the easiest word to utter in the English language I have devised an alternative. There is a conduit run to the building's roof from the repeater equipment which is not yet in use. We could reduce the exposure to theft or tampering by locating the generator inlet on the roof and running the inlet wiring down to the repeater with the Photovoltaic array's wiring. If the elevators were not available a Honda EU1000i could be hauled up by rope using a tyrolean traverse if the emergency power team were short staffed. With the use of such a small generator it should be possible to just carry it up the stairs if there are 3 or 4 people on the team. Since there would be other heavy equipment to carry; such as tools, a service monitor, and an extended run generator fuel tank; it might take 3 or more people to carry it all.

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Tom W3TDH

Edited October 1, 2021 by W3TDH
Left out needed context.

[K3MRI]

On 10/1/2021 at 10:54 AM, W3TDH said:

The Repeater Committee is considering my suggestion that we add an AC power inlet and manual transfer switch to the remote receiver site which does not have a generator supported electrical supply. That would allow a generator at ground level to supply the repeater's Battery Charger-conditioner long enough to recharge the battery bank if the Solar Array and wind generator were to fail. 

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Tom W3TDH

Tom, trying to understand what you mean. Does that mean that the manual transfer happens 'after' a power failure? That means that before be useable you'd have to wait for the battery bank to be recharged?

[W3TDH]

10 hours ago, K3MRI said:

Does that mean that the manual transfer happens 'after' a power failure?

The Manual Transfer Switch would be used as an alternative way to recharge the site's back up battery array to full capacity. If severe weather, such as a damaging hail storm, put the solar array and windmill out of service the APRS beacon located at the site would report the loss of DC charging current for the battery array to the repeater committee members who are monitoring for such reports given the occurrence of that severe weather.  A support team from the MARC Repeater Committee would go to the building that houses the KV3B North remote receiver for the 146.955 MHz repeater and the KV3B D-STAR repeater to determine how to keep some or all of the site's equipment in service. The team would determine whether the photovoltaic array or the wind generator could be rapidly returned to service. They would also check the state of charge of the battery array which stores the solar and wind power provided by those 2 outdoor power production systems. If restoring one or both of the on site power generation systems was not immediately doable then the utility AC electric supply to the converter charger for the batteries and the normal DC power to operate the site would be switched from it's building electrical system receptacle outlet to a dry (non-energized) fixed plug electrical inlet. Because of the small size of the circuit to be switched the transfer assembly would be made from regular electrical parts such as the ones shown in the attached photographs. Those include a Double Pole, Double Throw, Center Off Switch, a fixed plug inlet to except the cord from another AC power source, with the boxes and parts to put them together into a complete transfer assembly. Factory built transfer assemblies are not manufactured in such a small size. By throwing the switch to the down position; because that is the position customarily used for that purpose; the Charger Converter AC supply would then be connected to the inlet which will except an extension cord's receptacle end cord cap which is supplied by another source of AC power. The Generator used would have to run long enough to charge the battery array to it's maximum capacity. That would have to be repeated as often as needed until one or both of the alternate sources could be repaired and brought back on line, a suitable extension cord was run to an power outlet elsewhere in the building which is supplied by the building's emergency generator, or utility power was restored. Since access to the topmost roof of that building is controlled by security it might be possible to leave a small generator with an extended run tank on the roof and replenish the fuel and lubricant oil as often as needed to keep it running.

If you think of the photovoltaic array as the belt and the wind generator as the suspenders then the alternative AC power inlet is a BIG safety pin that can make the waist of the pants tight enough to stay up. It's not elegant nor even convenient but it allows the wearer to keep working.

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Tom W3TDH