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Author Topic: cigarette lighter type power outlets  (Read 685 times)
KG6WNG
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Posts: 27




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« on: November 02, 2004, 11:43:21 AM »

     I have a Toyota Tacoma small pick up truck and it has two dedicated cigarette lighter type power outlets at the bottom of the dash. The covers on these outlets state that they can handle a max. of 120 watts. Would it be safe to run a Kenwood g707a (max output 50 wts) off of one of these outlets instead of installing a seperate power cable to the battery? If so, who makes an adapter for the Kenwood to a lighter type plug?

               Thanks, Kim
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AA4PB
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Posts: 12688




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« Reply #1 on: November 02, 2004, 01:07:37 PM »

In general, it is not a good idea to power a permanent installation from the lighter plug. First off, your 50W radio probably draws 100W or more at 13.8 Volts (50W is the output power, not input). That brings you pretty close to the limit of the outlet. Secondly the voltage drop and noise in the lighter plug circuit is likely more than you would have by a direct run to the battery.
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WB2WIK
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Posts: 20547




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« Reply #2 on: November 02, 2004, 01:20:36 PM »

A 50W "output" FM transceiver normally draws 9-10 Amps at 13.8Vdc = 124.2 to 138.0 Watts.  I've seen a few that draw more than 11 Amps (which is 151.8 Watts).

I wouldn't power a 50W transceiver from a cigar lighter accessory outlet other than very temporarily, like in an emergency.  Much safer for the user, the rig and the vehicle to run the wiring to the battery.

WB2WIK/6
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K7JBQ
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Posts: 80




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« Reply #3 on: November 02, 2004, 01:59:07 PM »

While it's certainly best to wire direct, lighter outlets can be used in some circumstances (rental cars, for example). Radio Shack carries them (wirh a 10 amp rating).

The following, from a Daimler/Chrysler service bulletin, may be useful:

">For low or medium power transmitters (up to 55W FM or 110W SSB or
CW), the power outlet or cigar lighter feed may be used. Use a 1/4"
jumper terminal at the socket or splice (solder and heat shrink or
tape). For higher power transmitters, including amplifiers, connect
the power (battery +) lead at the battery or at the power
distribution center or at the positive jump-start post, if the
vehicle has one. An appropriate terminal should be used. If the
terminal is exposed to the weather, solder and apply a commercial
protectant (wheel bearing grease is an acceptable alternative.) to
retard corrosion. This lead should be fused as close to the battery
as practical to protect the wiring (and the vehicle)! If the power
connection is underhood, use a weatherproof fuse holder. Motorola
Communications Division supplies a weatherproof holder, part number
09-84277B01 for 5AG cartridge fuses that is part of their standard
installation kit. Packard Electric Division of Delphi Automotive
Systems makes an insulator, part number 12033769, terminal number
12020156 with cover 12033731 for standard SAE plastic fuses.

>Vinyl-insulated wire, typically supplied with transceivers is not
entirely suitable for the higher underhood temperatures in modern
vehicles. Route underhood wiring away from all hot areas. Body sheet
metal, away from the exhaust, radiator, A/C liquid line and engine is
usually the coolest location.

>DO NOT FUSE THE GROUND LEAD. If the ground-side fuse were to open,
the entire supply current would be conducted by an alternate current
return path, which could cause the feedline to overheat, with
possible resulting damage.

>For low or medium power installations, connect the ground (battery -
) to body sheet near the power feed point. If you use a screw through
the floor, put body sealer over the underbody projection. (Stamped
acorn nuts, filled with sealer are available at most body shops for
this purpose.) For high power installations, connect the ground
(battery -) lead at the battery connection to the body. This is
usually a 6 or 8 AWG black wire from the battery negative terminal to
a screw at the wheelhouse or radiator support. If a separate sheet
metal ground is used, clean the paint off a one inch or so diameter
area of body panel where the ground lead is to be connected (usually
the case with commercial trunk mount radios). An awl is the best tool
to use to pierce a starting hole for a #12 or 5mm, minimum plated
ground screw. A ring terminal with lockwasher serrations of the
proper size for the screw or a separate serrated (not a split or SAE)
lockwasher should be used between the terminal and the screw head. As
above, some grease or protectant should be used if the connection is
in an unprotected area.

>If the power cable must pass through the dash panel, try to find an
existing hole with a grommet that is unused. If none is available,
pull the carpet back from under the dash panel in the passenger
footwell in the cabin. Locate a place where there are no other
components on either side, as high up as possible. An awl is the best
tool to use to punch a small hole through to the engine compartment.
If the position is good, enlarge the hole by driving the awl in up to
the shank. If this is not large enough to easily pass the cable,
enlarge it by using a larger tapered punch. This will leave an
extruded hole with no sharp edges. Install the cable and seal the
hole with silicone RTV or commercial body sealer on both sides. Seal
any extra holes that you may have made. Dress the underhood wiring so
that it is sate from all hazards, which include the following:
exhaust manifold, steering shaft, throttle linkage, fans, etc. Tie
wrap as required"

73,
Bill
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AA4PB
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Posts: 12688




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« Reply #4 on: November 02, 2004, 03:32:48 PM »

The Daimler/Chrysler service bulletin is wrong! A 110W SSB transceiver draws 20A peaks - certainly more than acceptable for a 10A ligher plug. Even a 55W FM transceiver as stated earlier will draw at least 10A and likely more - also not suitable for a lighter plug rated at 10A.

If you are in a rental car and must use the lighter plug for temporary use then cut the power back to 25 watts output.
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AA4PB
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Posts: 12688




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« Reply #5 on: November 02, 2004, 03:40:00 PM »

In reading closer it appears that the Daimler/Chrysler service bulletin is advocating tapping into the lighter circuit at the back of the ligher socket (thereby not using the socket itself). Perhaps their vehicles use a wire suitable for 20A and use a 20A fuse even though lighter plugs are only rated at 10A. I wouldn't count on that being the case with other vehicles.
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KG6WNG
Member

Posts: 27




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« Reply #6 on: November 02, 2004, 04:11:20 PM »

     Thanks for the replies. I did the math in my head and obviously got it wrong. If I had used pen and paper I probably could have avoided bothering you all with this question. Thanks again for setting me straight.
                    Kim
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N2MPT
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Posts: 71


WWW

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« Reply #7 on: November 03, 2004, 09:06:31 AM »

kim,

i have the same truck (specifically a 2002 xtracab 4wd TRD tacoma) and have a 2m mobile in it.  if you need any info about where to hook stuff up to or how to run the antenna downlead let me know.

jim / n2mpt
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K7JBQ
Member

Posts: 80




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« Reply #8 on: November 03, 2004, 10:20:07 AM »

PB,

Exactly right. And the bulletin doesn't mention any particular plug, or amperage rating.

Many vehicles, including my Pontiac, fuse the lighter circuit at 20 amps.

73,
Bill
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K1CJS
Member

Posts: 5884




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« Reply #9 on: November 06, 2004, 02:13:13 PM »

It really isn't a good idea to power anything from a cigarette lighter type plug for any length of time.  Even though the "circuit" for the lighter socket is fused at twenty amps, the lighter is just one of the items using that fuse for protection.  

In some cars, that fuse also protects the dome lamp circuit and a couple of other things as well.

Unless the car you are putting the equipment in is a rental or a car you are just using for a short time, it is always a better idea to run wires to the battery for ANY rig.  Remember also to fuse both wires at the battery to prevent damage to the rig and the car.
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K1CJS
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Posts: 5884




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« Reply #10 on: November 06, 2004, 02:35:28 PM »

Sorry, I missed one earlier post which said not to fuse the ground lead.  The reason for that fuse is to prevent damage to the rig in case the chassis ground connection became bad or disconnected.  The power usually going through that connection would then go through the one alternate path available--the rigs negative connection.  Can you say burned up rig?

If the shield of the co-ax being used can't handle the power in the case the negative fuse should blow, then you need to replace it with better co-ax--only the cheapest co-ax made couldn't handle that power.  Also, you should be able to notice

The radio manufacturers put a fuse in the negative lead for a reason.  If you want to question that reason, go right ahead, but its not a good idea to advise anyone else to--unless, that is, you want to pay for their ruined radio.  
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K1CJS
Member

Posts: 5884




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« Reply #11 on: November 06, 2004, 02:37:14 PM »

Sorry, I missed one earlier post which said not to fuse the ground lead. The reason for that fuse is to prevent damage to the rig in case the chassis ground connection became bad or disconnected. The power usually going through that connection would then go through the one alternate path available--the rigs negative connection. Can you say burned up rig?

If the shield of the co-ax being used can't handle the power in the case the negative fuse should blow, then you need to replace it with better co-ax--only the cheapest co-ax made couldn't handle that power. Also, you should be able to notice the reduced performance of the rig.

The radio manufacturers put a fuse in the negative lead for a reason. If you want to question that reason, go right ahead, but its not a good idea to advise anyone else to--unless, that is, you want to pay for their ruined radio.
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