20A Cigarette Lighter socket

Discussion in 'Mobile Radio Systems' started by KC3U, Oct 3, 2013.

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  1. M3KXZ

    M3KXZ Ham Member QRZ Page

    John, a lot of people with very high power car stereo systems use similar - a supercapacitor. The good thing is that they charge virtually instantly, unlike a battery, and can provide a high current. They help with the peak current draw. Can't think of any reason it wouldn't work with radio.
  2. KF7VXA

    KF7VXA Ham Member QRZ Page

    It might just be a good thing for him to use then unless he's using some of the digital methods. I've never had any experience with the MFJ unit and am not sure how big their capacitors are compared to the audio unit that you are talking about, but thought I would mention it, I'd hate to see him just use the outlet and run into a problem. Hopefully he reads your reply. I think they run about $110.00 give or take. Thanks

    Myself, I like to go with the tried and true method. If his additional battery works for him, then all is good.

    73's John KF7VXA
    Last edited: Oct 31, 2013
  3. K0BG

    K0BG Ham Member QRZ Page

    Seemingly, everyone here is missing the point.

    The main failure typically isn't the wire size (albeit important, as in voltage drop), nor the fuse size (≈20 amps). Rather, it is the plug's positive contact assembly. It relies on spring pressure (as does the somewhat larger negative contact), and a very small contact area. That point of contact is what causes the heating.

    The MFJ unit, is nothing more than a buffer. When the transceiver is transmitting, theoretically, the current imposed on the contact assembly would be whatever the average current draw is. We really don't know that with any certainty, as there are many variables we don't know (transceiver power draw, compression and/or high mic gain use, SWR, and the list goes on). If we assume the average draw is about 8 to 10 amps including the cooling fan, then our rather small contact assembly has to carry that current. The truth is, it can't.

    Anyone here who has an adequate DC power supply (≈30 amp capability), can go out and buy a lighter socket, and a plug to mate with it. Doesn't make any difference where you get it, or what the brand. Wire it into your transceiver's power supply cable, and transmit into a dummy load. Use SSB, or CW (it doesn't matter). After about 5 minutes, feel the back to the socket. If you do, you'll get a rude awakening. If you wish, repeat the tat using the MFJ buffer. The results will be the same.

    If you REALLY want a rude awakening, add about 15 feet of #14 wire to the length of the cable, and feel the wiring when you get done.

    If you do these things, you'll prove to yourself why using the accessory socket is a big gamble!
  4. AE7RZ

    AE7RZ Ham Member QRZ Page

    I nominate this as "Post of the Year" :)
  5. KF7VXA

    KF7VXA Ham Member QRZ Page

    I second that. The cigarette lighter plugs really are the weak point. Maybe if he were to splice in a power pole fitting under the console and run it out from the space between the console and the floor, no pinching of the wire and a good solid contact.
    I guess my whole problem with this is the need to use the power port. Anyone who will take a little time can run wires just about anywhere they want in a vehicle. If nothing else, have a car stereo shop do the wiring, they are experts at it if he finds a reliable shop. Then the problem is solved, it's safe and there is no damage to the vehicle. To me it's a no brainer and it can be done with the correct wire for less voltage/amperage drop and no heating of the wire/contact point allowing the radio to put out full power. It would also allow an accessory or two to be connected without overloading a 14 ga wire.
    I use the 8 ga wire and if I need 13.8 volts for a very short time with the vehicle not running (Using car starting battery), I'll put a voltage booster in line. For extended use, a deep cycle battery can be put into the mix or just leave the vehicle running.
    It's not my set up, the OP has got some very good info from more than one person, so at this point, the OP can do as he wishes. It's just better to do it right the first time and avoid problems.

    73's John KF7VXA
  6. KK6GMN

    KK6GMN Ham Member QRZ Page

    Using an SLA battery as a buffer between the cig port and the radio works well for me. No heating of any components even at high draws by the radio. Battery charges from the port, large amp loads are delivered by the secondary battery. Happy with this method for me.
  7. KF7VXA

    KF7VXA Ham Member QRZ Page

    You are still missing the problem with the plug in connector. They just have a small spring inside that pushes on the plunger. It will fail in time and will get quite hot. It is yours, do as you wish, glad it is not mine. The previous post warned about the same thing. I have had one of the inside springs fail some years ago and the plug got very hot. Kind of like when you were a kid and put a piece of wire between the positive and negative posts of a battery and watched the wire glow red hot.

    John kf7vxa
    Last edited: Nov 2, 2013
  8. KK6GMN

    KK6GMN Ham Member QRZ Page

    Ok, so it is the plug... I have my GPS plugged in and my cell plugged in most of the time to the CIG socket. Will they cause fires? If so, it seems more cars would be burned up.
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    Cigar Lighters and Power Points are made different.

    A Cigar lighter socket is made of metal, and a Power Point is made of plastic.

    A Cigar Lighter is a Option on many autos and will have heaver wiring, and a ashtray. Power Points are standard, and you get a cupholder.

    Whatever is attached should have its own built in fuse, and should not rely on the fuse in the autos fuse box.

    I would be more concerned of RF getting into the computer system, because of the DC path that goes thru the Dash Board wiring.

    Have Fun.
  10. AA4HA

    AA4HA Ham Member QRZ Page

    The cigar lighter plug in a car was originally designed for a very intermittent, high current load to heat up a coil of wire. The socket was made of metal so things would not catch on fire.

    That being said they did not care about voltage drop, great electrical connections or continuous duty. It was only depressed for 10-20 seconds to get things hot and then the button would pop out.

    To me they are fine for charging my cellphone, plugging in the adapter for the Yaesu handheld or a GPS, those loads are all less than 1 amp. If I get a bad connection it is easy to reseat the connection.

    For a radio there is a continual load of 1/2 to 2 amps to run the receiver (like an FT-857). When transmitting the current can get up to 10,15,20+ amps and depending upon how much of a ragchewer you are you are doing this for up to a minute or so at a fairly high duty cycle. That pesky loose connection is bouncing around, giving you intermittent connections, voltage sags and spikes and generating heat.

    Taking apart a plug and you see that the tip is just a sleeve with a spring to apply tip pressure. They are all cheaply made, not a very good electrical connection, wrapped up in an even cheaper plastic shell that sort of holds things together.

    The annoyance factor of constantly reseating the plug, intermittent connections, random radio resets and low voltage alarms pretty much wipe out the advantage of convenience. It is a pig in a poke; in a rental car I will use the plug for a few days. For my own personal installations I run the dedicated wiring, DC circuit breaker under the hood, power pole connectors and fusing on individual radios.
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