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I'm a beginner trying to use one of my two CB radios as a "base station." The problem is that the power cable is just two wires (no connectors/12v car plug) and a 2A fuse along one. Is it possible/safe to splice these to one of my million extra AC converters (pic below) and plug it into the wall? I know that the CB runs off of 12v, not sure about current. The adapter has a DC output of 12v 0.3a. This stuff is probably really obvious but I just want to be extra careful not to fry things. Thanks!

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    $\begingroup$ Howdy, welcome to ham.se. I'd imagine 300mA would be enough to power the unit on and recieve/listen, but not enough to transmit anything. I bet a 2A PSU would do it, though if it's a poorly-filtered switch mode supply you will likely end up with a pretty noisy system. $\endgroup$
    – user14945
    Jun 30 '20 at 6:14
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    $\begingroup$ The manual specifies a power supply capable of supplying 2 A. $\endgroup$
    – rclocher3
    Jul 6 '20 at 15:48
  • $\begingroup$ I see that this question is flagged as off-topic. But since a few of us decided awhile back that we would accept questions about CB radios, I did not vote to close it. If anyone disagrees, please open a question in meta, where we can revisit this matter. $\endgroup$
    – Mike Waters
    Jul 6 '20 at 19:23
  • $\begingroup$ I also did not vote to close it, because general questions about radio equipment and stuff like power requirements sort of falls under the "technology of radio", which is definitely on-topic for this site. I say the question is on-topic $\endgroup$
    – Scott Earle
    Jul 9 '20 at 2:55
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CB radio service transmitters are limited to 4 watts output power. Figure that that output circuit is only 50% efficient at most, and in round numbers you'll need probably at least a 10W input if not more.

For DC circuits the power (watts) is equal to the voltage times the current (amps). Your 12V, 0.3A adapter is therefore rated to supply 3.6 watts which is not nearly enough. When you try to transmit, the voltage into the radio will likely drop and cause the radio to "brown out". (This probably won't permanently damage anything except maybe the power supply, but the radio won't "work" while it's happening either and might need a power cycle to clear any lingering control circuit glitches…)

The 2A fuse on your radio is a clue that you'll probably want at least a 1A power supply for it. Is there a sticker somewhere on the radio that gives a specific current expectation?

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Those "wall wart" style power supplies are likely to lack the power needed here. As others point out here the radio will likely somewhere between 1.5 to 2 amps to operate as intended. I don't recall seeing a 12 volt wall wart that can provide more than 1 amp. Do you have a "soap on a rope" kind of power supply in your parts bins? That would be the kind where the power supply is a brick with a 120 VAC cord to the wall outlet and another for the low voltage DC. It doesn't have to be 12 volts either, that's just the nominal voltage of a typical car battery. The actual voltage will vary from about 11 volts when the car is off and close to 14 volts when running. Double check the specs on the radio to make sure but it's likely built to handle 15 or 16 volts. This can widen your options if you can't find a 12 VDC supply rated for sufficient current.

As an example I have an old 15 VDC power supply from a long gone laptop just waiting to be put to use. I already put a 12 VDC @ 4 amp laptop supply into service for running and testing automotive electronics at home. 5 VDC supplies will be far too low of voltage. 9 VDC supplies are common and might light up the radio but I wouldn't even try. Laptop supplies in the 12 VDC to 15 VDC range should be easy to find, and provide enough voltage and current for your CB radio. There's lots of laptop power supplies, especially as laptops are getting more powerful and more people are switching to USB-C, in the 16 VDC to 20 VDC range. 16 VDC is likely too much, and anything over that is asking for something to start smoking.

Any wall wart supply is not likely to work for you. That doesn't mean give up on them, it means think bigger. It doesn't have to be exactly 12 volts, but not too high or too low. Check the manual or manufacturer website, it should give a safe range of voltages for you. If at all in doubt then keep it below 13.8 volts, that's the regulated voltage of a standard car alternator, and above 11 volts.

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Galaxy, there are a number of things to watch out for when connecting power to your Cobra 29LTD AM only CB radio.

  1. The power supply must be a regulated DC power supply, which outputs between 12 and 14 V DC. An adapter which outputs AC is no good. Note that many adapters like the one in your picture are not regulated, and when nothing is connected to them they can output a few volts higher than what they have printed on them. Any DC output voltage in excess of 15 V will damage the radio.

  2. The power supply must be at least 2.5 A. That radio draws about 0.5 A on receive and about 2.5 A when transmitting. If you power it with say a 500 mA plug pack, it will receive ok, but when you try to transmit the lights on the radio will all go dim and TX won't work.

  3. Do not connect the plus and minus power wires around the wrong way. If you do the fuse will blow, or if the fuse is the wrong one and rated too high, there is a reverse polarity protection diode inside the radio that will go short circuit and it will need to be replaced.

  4. CB radios need a special matched CB antenna. If you transmit while using the wrong antenna or one that is not tuned properly the radio will get hot and you risk damaging the main RF output transistor in the radio. Any antenna can be used if you are only receiving without any risk to the radio.

Hope that helps.

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  • $\begingroup$ Not sure why this was downvoted, except that the part about the antenna --while great advice-- doesn't really help answer the question. But since the rest of the answer is good, IMHO you don't have to delete it. $\endgroup$
    – Mike Waters
    Jul 6 '20 at 19:09
  • $\begingroup$ Thanks Mike, i seem to have a serial down-voter / fan who down votes every post i make on Ham Stack Exchange, i have sent a complaint to site support, hopefully they will deal with it. $\endgroup$
    – Andrew
    Jul 6 '20 at 21:30
  • $\begingroup$ " The power supply must be at least 2.5 A. " The original post says the radio has a 2 amp fuse so this is likely unnecessary. Experience tells me that the fuses often have a 50% to 100% margin to avoid burning out too easily. This is a "rule of thumb", perhaps the 20% to 25% margin you give on current capacity is your own "rule of thumb". Perhaps you missed that detail. A quality 1.5 A supply should suffice. Double checking polarity is always wise. If in doubt check with a volt meter. $\endgroup$
    – MacGuffin
    Jan 4 at 11:37

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