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Author Topic: Can I run a Mobile rig from a Cig Lighter ?  (Read 1630 times)

Posts: 65

« on: January 05, 2008, 09:02:42 PM »

I have an ICV8000 and I would like to know if its possbible to run this off the cig lighter in my BMW ? Someone said if I do I can only transmit 30 watts max safely. Is this true? Do I buy a specific type of cig lighter adapther to wire it in to?

Posts: 4464

« Reply #1 on: January 05, 2008, 09:33:09 PM »

You'll have less alternator whine and noise if you connect across the battery terminals, but for a temporary plug & play setup the cigarette lighter is about as handy as it gets.

Cigarette lighters are typically fused at 5 to 8 amps (?) so you'll want to stay on low or mid power TX. A standard lighter plug should work fine, center pin positive. TEST THE POLARITY WITH A DC VOLTMETER BEFORE CONNECTING IT TO THE RADIO.

...and don't bypass the fuse(s) in the radio power cord. That can get expensive. Wink

The end of the world will occur on April 23, 2018 ( the day after Earth Day. Go Figure ).  If you're reading this on April 24th look for updates coming soon.  If you're reading this after June first, fuhgedaboudit.....

Posts: 2415

« Reply #2 on: January 05, 2008, 09:41:10 PM »

They are not even called cig lighters anymore. Most newer vehicles are calling them "Aux" power outlets for running equipment.
The GM vehicles I have used in the past few years have been fused for 20 amps, And I have never had any problem powering 50 watt type VHF/UHF radios from them.

Do get a decent plug, Capable of the 15 or so amps, that has nice heavy wire coming from it.

(I would use caution in an older vehicle that the cig lighter was actually used to light cigs, And has ash residue in the socket. That may cause a high resistance contact)

Is it the best way to do it? No, Of course not. But it does work out just fine.

Posts: 17479

« Reply #3 on: January 05, 2008, 09:49:21 PM »

Yes, but...

I did this for several years in two different vehicles.  At 50 watts you
are probably pulling 10 amps: while the socket may supply this much
current remember that the cigarette ligher itself generally has very
intermittent duty - perhaps 15 seconds every 10 minutes for a heavy

There were several quirks that I ran into.  First, many lighter plugs are
not designed for high current - some are only fused at 2 amps, and
even if you can change the fuse the internal construction may not be
suitable for high currents.  I had to change the plugs about every year
or two when it got overheated and no longer made good contact.  Also
there often is excessive voltage drop in the wiring because it isn't
designed for high current (the lighter still works even when the voltage
across it drops to 8 volts.)  Not only are you much more prone to noise
on the DC line that can modulate your signal, but in one case the
voltage dropped enough at high power that the rig would lock in
transmit mode.  (It even did this at 25 watts when the engine was off.)
Once I had to DF my wife's car to shut the radio off when it was parked.
Radios vary a lot in how well they handle low input voltage, but it isn't
uncommon for mobile rigs to show some quirks when the voltage drops
below 12V or so, as can happen due to voltage drops at high current.

So, yes, you can do it, but it isn't a good long term solution, particularly
if you plant to run more than 25 watt or so.

Posts: 110

« Reply #4 on: January 06, 2008, 05:25:54 AM »

Take a look at the thickness of the wiring in your car then look at the poor contact arrangements in the cigarette lighter connectors. I would not like to pass more than five amps through such an arrangement.

Alan, K0BG has something to say about this on his website but I can't locate it right now.


Posts: 6252

« Reply #5 on: January 06, 2008, 05:51:44 AM »

A cigarette lighter socket/plug is not made for constant high current useage such as a mobile rig may demand.  Neither is the 'aux. power' outlet--even if it is fused at 20 amps.  Cigarette lighter plugs are notoriously bad for lousy contacts between the plug and the shell, heating up because of the bad contacts, and melting, causing a short circuit--and damage to the underdash harness.

If you insist on using the lighter or power socket for such high current applications, be prepared to possibly spend plenty of your hard earned money to fix your ride.

Posts: 10248


« Reply #6 on: January 06, 2008, 06:07:43 AM »

Aside from what's already been mentioned, there is another aspect often overlooked; Ground loops. They occur when there is a potential between two paths to ground or power. They can, and do cause the appearance of alternator whine, but the biggest effect is what they do to on-board electronics. The resulting malady acts and sounds like an RFI issue, when it isn't. This makes finding ground loops very difficult. Thus, the best offense is a good defense, and you do that by wiring your radio the right way the first time around.

An adjunct to this, folks like MFJ have come up with devices which are supposed to make this type of wiring safe. If you opt for such a device, you're on your own. And as alluded to above, no automobile repair is more costly that a wiring fire.

Alan, KØBG


Posts: 14491

« Reply #7 on: January 06, 2008, 01:18:32 PM »

In spite of all the above comments, I've sucessfully run many a 2M transceiver from the lighter plug for temporary installations. Many of the newer vehicles indeed have lighter and/or ACC jacks fused and wired for 20A continuous. Most of the "Radio Shack" type lighter plugs have internal 2A fuses but but you can get lighter plugs rated and fused for 15A. Try automotive stores, Best Buy, an electronics wholesaler, or the Internet (Mouser or DigiKey).

See if there is a lable near the Lighter or ACC jack that says 20A. If not, check the owner's manual or lastly the acutal vehicle fuse size. If its rated for 20A I would have no hesitation about connecting the radio via a 15A lighter plug. If you have hum from a ground loop then do something else but odds are it will run fine.

Bob  AA4PB
Garrisonville, VA

Posts: 6642

« Reply #8 on: January 06, 2008, 02:56:17 PM »

Most of these are fused at either 10 or 15 amps, so you can get away with the 7 amps or so at 30 watts.  50 or 75 watts output will normally draw over 11 amps, too close in my book!
The specs for automotive wiring are different than house wiring, and a smaller gauge wire is used.  You really do not want to melt a single wire in an automotive wiring harness... messy and expensive!
If possible, I DO recommend running directly to the battery!  Less noise, and you KNOW what the wiring is!
Take a look at K0BG's website... he recommends real cabling and explains why!
As I recall, you were concerned about modifying your car in any way.  If that is the case, the lighter plug can supply under 10 amps fairly safely.
Do you REALLY need all those watts on FM?


Posts: 17

« Reply #9 on: January 06, 2008, 11:33:07 PM »

The YL has a Subaru forester, and there are 3 "cigarette lighter" style power jacks.  One is the actual cigarette lighter, the other two are simply power jacks.  The jack in the cargo area is fused at 20A, and has 14 gauge wire running to it.  In the "deluxe" optioned models, this is where the 110V plugs are, and the inverter is mounted right beside it (where she has the separated radio base mounted)  Both the lighter jack and the power jack in the passenger area are fused at 15A, and still have 14 gauge wire running to them.  They are, however, on the same fuse, so if you want to run them both, it won't be at 15A.  Her FT-2800 runs about 10A in the 25W "mid" setting, so all is well, just be sure not to get a connector rated below that.  I made that mistake about 10  years ago when I replaced the fuse in a Radio Shack 7.5A adapter, and tried to run my FT-8500 through it.  All was well until that first REALLY long rag-chew where the connector got pretty hot, and all of a sudden there was alternator noise on my transmitted signal.

So, buyer beware, but you might be able to get away with it.  Just keep a watchful eye on the health of the system as a whole.

Posts: 6252

« Reply #10 on: January 07, 2008, 04:24:21 AM »

"See if there is a lable near the Lighter or ACC jack that says 20A. If not, check the owner's manual or lastly the acutal vehicle fuse size. If its rated for 20A I would have no hesitation about connecting the radio via a 15A lighter plug....."

If there is a label there, that means that the protection is a 20 amp fuse, not that you can pull 20 amps continuously through the connector.  In modern cars, there are several things pulled through that same 20 amp fuse.  In a great many, the interior lamps are wired through that fuse as well, and those alone may pull 5 to 7 amps.

You want a better indication?  Look at the WIRE attached to the CENTER CONNECTION of that power plug.  Chances are it is just a 14 or 16 gauge wire--on foreign cars, possibly only an 18 or 20 gauge.

You start pulling 15 amps through a 16 gauge wire, and you'll 'have a hot time in the old town tonight', and possibly a B-B-Q.  

Do yourself a favor and take the time and the $10 and run wireing to the battery.  The possible headaches and the car repair bill you may well avoid makes it well worth it.  After all, you're only buying insurance.    

Posts: 5639

« Reply #11 on: January 07, 2008, 06:39:05 AM »

Can you? Yes.

Should you? No.

I would do it ONLY in a very temporary installation - a borrowed or rented vehicle in which I absolutely had to have a radio.


Lon - W3LK
Naugatuck, Connecticut

A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.

Posts: 293

« Reply #12 on: January 07, 2008, 09:33:24 AM »

As other posters have pointed out, 10A may not be 10A at 13.8V or 12V or even 11V due to the thin wire used to connect the outlet. I ran a 10M Radio Shack HTX-10 just fine off the lighter outlet in my Honda CR-V - only a 25W radio, not sensitive to under voltage. But my IC-706 will not transmit, at any power level, because the voltage drop at just 4 or 5A current turns it off.

Posts: 14491

« Reply #13 on: January 07, 2008, 03:15:26 PM »

Well, it would take 0.5 ohms of resistance in the wiring to drop 13.8V to 11.5V at 5A. That's quite a bit of resistance. I suspect you may have some corroded connections, likely on the lighter socket or the fuse block.

Bob  AA4PB
Garrisonville, VA
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