Battery charger for Comet CAA500 Mark 2 ant. analyzer

Discussion in 'Computers, Hardware, and Operating Systems' started by KK6FYE, Sep 15, 2020.

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  1. WA9SVD

    WA9SVD Ham Member QRZ Page

    That's very true. "Wall warts" come in a myriad of types. ALL have AC INPUT; SOME (such as for some answering machines, and many (old style) external modems ) have unregulated AC output, with filtering and (often multiple voltage) regulation internal to the device. SOME are DC output, with or without significant filtering be a single electrolytic capacitor after a rectifier to DC. Still others will be either positive OR negative center contact of a barrel connector (of various sizes) , and some even use a 3/8" or smaller plug, or (worse) a proprietary connector that is unique to a particular piece of equipment.(TI calculators, fand small Sony TV's (REALLY old!) or instance, use proprietary connectors, but probably other brands do as well.)
    Some will actually be switching supplies, with a regulated output at a fixed value, regardless of load. The voltage, current and usually positive and negative connections are usually printed (or stamped) on the "wall wart" itself, either on the top or bottom side. This is where your DMM (or VOM) is your friend; CHECK first to determine polarity of the connector, THEN check the voltage. If it is exactly (+/- about 10%) of the voltage indicted on the "wall wart' is most likely a regulated switching supply; add a load (about 50-100 mA or so) and if the voltage remains constant, it IS almost certainly a switcher, or otherwise contains regulation. (Highly unlikely as that may be.)
    Last edited: Oct 9, 2020
    KB0MNM likes this.
  2. KB0MNM

    KB0MNM Ham Member QRZ Page

    Very true: See posts #3,4,6 regarding possibilities for external or internal charging plus cautions about wrong battery chemistry. 12-14 VDC center positive, if using the original provided cable- center conductor is insulated white. Verify with a multimeter and load, eg. 60 ohms ( rated current- high wattage ) that the polarity and voltage are correct. Verify that the A.C. ripple is not enough to trip the internal regulator 'top' of 16 VDC. Please note that we have NOT heard from the author since post #1.
    Math: 12/60=.2 Amps or 200mA. Batteries should not draw beyond 250mA per manual. 5 watts* maximum expected through load resistor, A.C. ripple measurements needed.
    *Simple 12 x .2 D.C. calculation of resistor wattage results in 2.4 watts, yet 5 watt resistor would be more readily available. Use 20W resistor instead for testing safety -and- precautions to avoid nearby paper, contact cleaners, etc. in bench area to prevent a fire. Same is true if using incandescent lamps for automobile applications ( Cold resistance of bulbs may open fusing, if any).

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