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. KB0MNM

    KB0MNM Ham Member QRZ Page

    I sent you the manual regarding Post #1, as he did not leave an e-mail address on his profile. You will note that there are two versions. They are pretty clear in the second version that A.C. is not to be used on the supplied D.C. cable. If the supplied D.C. cable is correct, the white conductor should correspond to center positive. Since some battery chargers actually do impress an A.C. voltage or ripple in addition to D.C., that and connector size are a very good point. I did say "Theoretically", not practically regarding the one from "Batteries America", cable of supplying 300mA compared to 200mA or 250mA minimum. With an output voltage of 12 V.D.C., it should* be safe to say that the voltage to the internal regulator *under load* should not exceed 16 V.D.C.
    Since I own one of the *variable supplies* mentioned, I have examined the output with an oscilloscope. The A.C. ripple of the B & K 1610 which I own is nearly undetectable.
    *Theoretically, that is. A 'load tester' could be constructed easily following ohm's law. 12 V.D.C. divided by 300mA ( .3A) means than 40 ohms or more should be the load, at less than 5 watts. If that load reflects more than 300mA current or more than 14 V.D.C. under load conditions- the "Batteries America" supply might not be appropriate. More resistance could be added, outboard to the analyzer. If the initial specifications of 200mA ( or more! ) are correct, 60 ohms should be the correct series impedance of the system. Then two 47 ohm resistors in parallel to each other, yet series to the circuit could be connected for charging.
     
  2. WA9SVD

    WA9SVD Ham Member QRZ Page


    I guess you misunderstand. AC is NEITHER "Positive OR Negative." Or is my electrical understanding all wrong?
     
  3. KB0MNM

    KB0MNM Ham Member QRZ Page

    From my somewhat limited experience, the D.C. level of a power supply which starts as an A.C. transformer is never perfect. There is always a certain amount of A.C. ripple on the supply voltage, often seen under certain load conditions: fully loaded or lightly loaded. Thus if you were to select a 'wall-wart' ( Class 2 ) power supply/charger such as the one illustrated, there is a good chance that on an oscilloscope- one could see a volt or two of A.C. ripple riding on the D.C. For this reason, it might not be prudent to select one with a 16 V.D.C. output. The internal filters sometimes also account for a certain additional capacitance in the load. So to give the illustrated 'charger' a fair 'load test', one might have to use an LM7805 series regulator, resistor to drop around 3 volts on the input at 300mA, and Nickel-Cadmium cells (4) in series. Since the regulator in the analyzer should also include capacitance, that may not be necessary. The D.C. polarity of the plug supplied with the analyzer should be positive in the center, and if it is the original cable, then Comet documentation says the white-colored lead is positive. The A.C. 'ripple' on the D.C. voltage contributes to the energy at the input of the analyzer regulator, which can not exceed 16 V.D.C. What the maker of the analyzer is saying is this- folks have erroneously thought that there is a rectifier circuit on the input to the internal NiMH charger circuit- and this leads to destruction. Thus a 'wall-wart' known to supply an A.C. voltage is unsuitable. So also may be one that produces excessive A.C. ripple on the D.C. output. The illustrated one will work- theoretically. A.C. ( alternating current) alternates between positive and negative about a center reference. That reference may be ground, or a positive voltage. If it is an undesired result of an imperfect rectification and filtering, that A.C. current can be called ripple. The regulator in the analyzer theoretically can deal with some A.C. ripple. How much? Ask Comet.
     
    Last edited: Sep 17, 2020
  4. WA9SVD

    WA9SVD Ham Member QRZ Page


    Sorry, but all I saw was an "eHam" review, which wasn't specific about batteries. Dis d you send anything else?
     
  5. KB0MNM

    KB0MNM Ham Member QRZ Page

    Do you have an e-mail that matches this ( specified here on QRZ under your profile ) :
    wa9svd@verizon.net
    ???
     
  6. WA9SVD

    WA9SVD Ham Member QRZ Page

    Last time I checked, YES.
     
  7. AC2KV

    AC2KV Ham Member QRZ Page

    To answer KK6FYE’s original question any 12 volt power source should be fine. Per the users manual I use NIMH AA cells with the supplied charge cable connected to the same supply used for my base rigs, (13.8v). 12 or so hours fully charges the batteries which last a long time. Never had any issues. The charge circuit is built in to the analyzer.
     
    Last edited: Oct 7, 2020
  8. JOHNEMMONS

    JOHNEMMONS QRZ Member

    To the point, the simple answer to your question is KK6FYE’s any 12-volt power source should be fine. For further, you can check these two sites where you get this easily if you want. The first one is batteriesameric, and the second one is batteryhuntersblog. But the choice is yours.
     
  9. WA9SVD

    WA9SVD Ham Member QRZ Page


    One thing to pay attention to: (if you pardon my English.) There are "wall warts" and then there are "wall warts." SOME (many older) warts have a simple transformer, rectifier, and (possibly) a moderate sized electrolytic capacitor. They are un-regulated, and a 12Volt/1Ampere wart will (hopefully) put out 12 Volts @ 1 Ampere, but under a lighter load, the voltage CAN (and usually does) increase, sometimes over 15-16 Volts. Newer power supplies, even those that LOOK like old style "wall warts" may well contain switching power supplies, and put out a fixed, regulated voltage, regardless of load (or lack thereof) up to it's maximum current rating. Use of an old-style, unregulated "wall wart" with equipment that NEEDS a regulated power supply from it's "wall wart" is asking for a clear amount of smoke to be released.
    (Many of the "ultra-low priced" imported H-T''s are on the type that have, and need, such a regulated supply.)
     
    KB0MNM likes this.
  10. KB0MNM

    KB0MNM Ham Member QRZ Page

    See post #19. WA9SVD made a very good explanation of the problem. This is also quite clear in the manual. In the analyzer manual, it very clearly states that an A.C. supply is not suitable. That means that though AC2KV never had a problem with a particular supply, not all supplies are suitable. When in doubt read the manual... which can roughly be abbreviated RTFM. I do not doubt that you 'never had a problem'... yet want to ensure that others do not end up with melted plastic battery compartments or worse.
     

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