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Discussion in 'Electronic Basics' started by Brock Manville, Aug 1, 2003.

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  1. We need an uninterruptible power supply, functionally similar to the sort we
    use on our computers, but with 24vac input and output, and of the smallest
    possible size. Output at 24vac will be less than 5 watts, for no more than
    10 minutes. Can we buy one? And if not, then can we make one?

  2. Tom Biasi

    Tom Biasi Guest

    Hi Brock,
    The answer is a definite maybe.
    What is the application? Control circuitry, security/fire detection?
  3. The application is control circuitry. We are HVAC service technicians
    in south florida, and we have problem with systems using solid state
    controllers that default either to 'off' or to an undesirable setting
    after a power interruption.

  4. Why don't you install a standard UPS before the 120 to 24 VAC
    transformer? That way it is an off the shelf part that is easy to find,
    and easy to replace after it dies of old age or a too close lightning

    Instead of hard wiring the transformer, see if the building inspector
    will let you install a single outlet for the UPS, then use a high
    temperature cord to plug into the UPS. Add a clamp to hold the AC plug
    into the outlet, then post a warning that it is not to be disconnected,
    except to service the system.

    I see low end UPS new for under $60 quite often, and have seen a few
    250 watt for $40. harbor freight had some not too long ago, and Staples,
    Office Depot and Circuit City have them on sale quite often.

    The only problem I see is that you ay need a sine wave supply, or at
    least a stepped waveform to prevent heating the transformer.
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