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K3MRI

Repeaters: sufficient backup power?

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EXPERT ELMER

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?

solar panel.jpg

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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

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EXPERT ELMER

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 👍

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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.

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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

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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

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