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Wattage limit via cigarette lighter plug?


WRDB702
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13 minutes ago, ldcarson said:

You didn't say which radio, but cigarette lighters normal rule of thumb is no more than 8-10 amps.

I noticed that after tapping "Submit". 

Wouxun KG100G  - Medium power can be set to 20w or 30w.

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Most cigarette lighter sockets are fused to 10 Amps, and most vehicles alternators run between 13 and 14 volts.  Being conservative, you should be able to manage 130 Watts max. The question is how long will the socket/intermediate wiring hold up under long term use at that wattage.  If you've got a good quality vehicle, I'd stay under 100 watts.  If you've got an economy job, maybe 60?

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5 minutes ago, Blaise said:

Most cigarette lighter sockets are fused to 10 Amps, and most vehicles alternators run between 13 and 14 volts.  Being conservative, you should be able to manage 130 Watts max. The question is how long will the socket/intermediate wiring hold up under long term use at that wattage.  If you've got a good quality vehicle, I'd stay under 100 watts.  If you've got an economy job, maybe 60?

No chance of going that high on the wattage.  The radio is limited to 50w.  I do not wish to risk any damage to the vehicle, so even the 50w is not being considered on a cigarette lighter connection.

Mentioning the alternator brings up another question though. Will the alternator introduce additional noise?

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7 hours ago, WRDB702 said:

I don't know how many amps the KG1000G pulls at 20w or 30w.

It comes with an inline 15amp fuse for use at 50w, so...?

My 45 and 50 watt rated radios tend to be between 10 and 11 Amps draw on high power. I want to say around 4.5 amps for the 20 watt rated anytone at779uv (twin to the retevis ra-25 @back4more70has). You should be okay on medium on the wouxun, whether you have it set for 10 or 20 watts.

One thing to bear in mind looking at watts the outlet can handle, vs radio power output is everything else that needs power between input to the radio, and output to the antenna. 50% is good for a very rough estimate of input vs output when looking at wattage .

Alternator noise is a possibility, but not as common an issue at gmrs frequencies. (Both of my at779uv are powered from the 12v sockets in the truck and beater car)

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29 minutes ago, back4more70 said:

I'm running a Retevis RA25 "20 watt" (not quite) at full power through a DC inverter at home, rated at 12V/10A.  The radio is showing 12.5V. I imagine you would be okay running your radio to the cigarette lighter, but like it was said, watch the amp draw?

Thanks.  That helps.

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7 minutes ago, WRDB702 said:

Mentioning the alternator brings up another question though. Will the alternator introduce additional noise?


I'm no radio expert yet, but I've seen a number of posts saying that if you ground to frame, rather than battery, you can avoid most of that noise.  YMMV!

I run a 20 watt Radioddity DB20-G from my lighter socket, and experience no noise I can detect with my ears.

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Posted (edited)
22 minutes ago, wayoverthere said:

...You should be okay on medium on the wouxun, whether you have it set for 10 or 20 watts. ...

My options are 20 or 30 watts.  So, sticking to 20 sounds like the safe route.

Thanks

(Connecting & disconnecting the HT is getting old.)

Edit: 

"You should be okay on medium on the wouxun, whether you have it set for 10 or 20 watts."

You are correct. I got my info mixed up.

Edited by WRDB702
Error Correction
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18 minutes ago, WRDB702 said:

My options are 20 or 30 watts.  So, sticking to 20 sounds like the safe route.

Which radio are you using for 20 watts?

As noted above the Radioddity DB-20G a/k/a Anytone AT-779UV a/k/a Retevis Ra-25, all use a cigarette lighter plug for power and transmit up to 20 watts.

I use the Anytone in my EV through the cigarette lighter plug.

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46 minutes ago, MichaelLAX said:

Which radio are you using for 20 watts?

As noted above the Radioddity DB-20G a/k/a Anytone AT-779UV a/k/a Retevis Ra-25, all use a cigarette lighter plug for power and transmit up to 20 watts.

I use the Anytone in my EV through the cigarette lighter plug.

The radio is a Wouxun KG1000G.  The consensus seems to be that as long as I don't exceed the 20 watt medium setting I will be fine.  

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Thank you all.

Unless someone posts a compelling reason to do otherwise, I will be installing the KG100G using the cigarette lighter as a power source and transmitting only on 20 watts or less until I get it wired through the firewall to the battery.

Then again...  I might leave it configured this way with a mag mount antenna and move it from vehicle to vehicle when desired. 

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1 minute ago, Over2U said:

One “safety” would be to change the in-line fuse to the radio (there is one, right?) to one with a (much) lower rating.

So maybe a 10 amp fuse, just in case I bump the power button and accidentally transmit at 50 watts?  

Makes sense.

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On 6/17/2022 at 4:13 PM, WRDB702 said:

So maybe a 10 amp fuse, just in case I bump the power button and accidentally transmit at 50 watts?  

Makes sense.

If that happens I would be more worried about the Fusible links going up in smoke. Unfortunately, cigarette lighter plugs tend to be 12 gauge or less on the back side.

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7 minutes ago, kidphc said:

If that happens I would be more worried about the Fusible links going up in smoke. Unfortunately, cigarette lighter plugs tend to be 12 gauge or less on the back side.

I wouldn't worry about the wire on the plug. 12 ga wire will handle 30A with no issues. In fact, 14 ga silicon insulated wire will handle 30A but PVC or rubber insulated wire can get over 200 degrees Fahrenheit when carrying that much current.

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3 minutes ago, BoxCar said:

I wouldn't worry about the wire on the plug. 12 ga wire will handle 30A with no issues. In fact, 14 ga silicon insulated wire will handle 30A but PVC or rubber insulated wire can get over 200 degrees Fahrenheit when carrying that much current.

Sounds like you did the math and experimenting. I'll trust you on it :)

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48 minutes ago, BoxCar said:

I'm not that good with the math. I cheated and got the information on the Internet from several different sources.

Those currents result in raised temperatures in the wire and insulation. For house wiring, which is admittedly conservative, 12 ga. is rated at 20 amps. 

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10 minutes ago, Sshannon said:

Those currents result in raised temperatures in the wire and insulation. For house wiring, which is admittedly conservative, 12 ga. is rated at 20 amps. 

And that's where the NEC and Ampacity tables have their largest differences. In radio work, at least with the radios we are dealing with on this site, wire lengths don't come into play so there is no regard to the internal resistance of the conductor and any losses that result from length. I believe the NEC formulas are set to keep the insulation temperature below 60C where the ampacity tables allow temps up to 130C. The most common PVC coating will withstand a temp of 160C while silicon will allow a temp of 600F which can light paper. Additionally, we are normally dealing with amp draws of 16 - 18A max as the radios are limited to 50W. 100W amateur radios will draw 28A which can be run on 14Ga wire, but I build all my harnesses with 12Ga silicon.

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5 hours ago, BoxCar said:

And that's where the NEC and Ampacity tables have their largest differences. In radio work, at least with the radios we are dealing with on this site, wire lengths don't come into play so there is no regard to the internal resistance of the conductor and any losses that result from length. I believe the NEC formulas are set to keep the insulation temperature below 60C where the ampacity tables allow temps up to 130C. The most common PVC coating will withstand a temp of 160C while silicon will allow a temp of 600F which can light paper. Additionally, we are normally dealing with amp draws of 16 - 18A max as the radios are limited to 50W. 100W amateur radios will draw 28A which can be run on 14Ga wire, but I build all my harnesses with 12Ga silicon.

Here’s an ampacity table for automotive applications:

https://jascoautomotive.com/automotive-wire-amperage-capacity-chart/

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Thank you for all the information (some of it way over my head).

I checked the vehicle's manual and found my cig lighters are on a 15 amp fuse.  Does that mean the radio, which also has a 15 amp fuse in the cable, should be ok at the full 50 watts if nothing else (cellphone) is plugged in to the same circuit at the time? (Amperage ratings appear to match...?)

I plan to use the radio at 20w most of the time, but may occasionally consider using the 50w setting.  

 

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