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eHam Forums => Amplifiers => Topic started by: KU7I on March 19, 2013, 11:09:58 PM



Title: current rating of automobile cigarette lighter plugs
Post by: KU7I on March 19, 2013, 11:09:58 PM
Anyone have any idea how much current you can draw from the cigarette lighter plug in most automobiles? I want to push ~ 400 watts mobile but not sure if this is too much current draw.

Lane
Ku7i


Title: RE: current rating of automobile cigarette lighter plugs
Post by: TANAKASAN on March 20, 2013, 01:18:22 AM
The contacts on a lighter plug are not very good, the fuse may be rated at 10A but I doubt that you could pull more than 2A or 3A from one without it getting hot.

A 400W amplifier (assuming 50% efficiency) will draw 800W @ 13.8V. This is a 58A load and a fire waiting to happen unless you do it right. Head for Alan's site and do the job properly.

http://www.k0bg.com/wiring.html

Tanakasan


Title: RE: current rating of automobile cigarette lighter plugs
Post by: KF7CG on March 20, 2013, 04:40:54 AM
If you have a newer Pickup or SUV, it may have 12V power points in addition to or in place of the cigarette lighter sockets. Same appearing connector but more solid contacts, ratings should be in owners manual. They won't exceed ten amps so won't power 100 watt HF rigs (18-22 amps).

KF7CG


Title: RE: current rating of automobile cigarette lighter plugs
Post by: AA4PB on March 20, 2013, 05:35:27 AM
I've seen some labeled by the mfg for 20A - but I don't think it is suitable for radio use at that current. One issue is the voltage drop in the small guage connecting wires in the vehicle.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: AD4U on March 20, 2013, 05:44:18 AM
The auto manufacturer may accurately rate the accessory 12V jack at 10 amps or 120 watts, but the typical cigarette plug found on many accessory cords will not "handle" that much current without a major voltage drop.

Dick  AD4U


Title: RE: current rating of automobile cigarette lighter plugs
Post by: W8DPC on March 20, 2013, 05:49:20 AM
Head for Alan's site and do the job properly.

http://www.k0bg.com/wiring.html

Tanakasan

Definitely read that page. What you are planning to do is simply a fire waiting to happen. It's a bad idea to even run a rig barefoot through the cigarette lighter plug, let alone an amp.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: K6AER on March 20, 2013, 09:57:07 AM
Wire directly to the battery. Fuse at the battery. If the battery is over three years old replace the battery with one that has the highest cranking amprage rating. At 400 wattts you can draw 50-60 watts on voice peaks. Also run the negitive lead from the radio and amplifier all the way back to the battery.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: NO2A on March 20, 2013, 10:38:38 AM
There`s a picture on Alan`s site of a fire started by an ht using a cigarette plug. Hard to believe. It did much damage too.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: W9MMS on March 20, 2013, 11:30:07 AM
If you cannot do it right the first time, then don't do it period!

As K6AER so correctly stated .......

<snip>>>>> Insert Quote
Wire directly to the battery. Fuse at the battery. If the battery is over three years old replace the battery with one that has the highest cranking amprage rating. At 400 wattts you can draw 50-60 watts on voice peaks. Also run the negitive lead from the radio and amplifier all the way back to the battery. <<<<<

Also, be mindful of your ALTERNATOR. ......... www.k0bg.com

If you are going to be "Cheap" about it then forget it as well.

Do it right and save yourself a lot of grief!

just my $0.02 worth

((((73)))) Milverton.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: KU7I on March 20, 2013, 05:42:52 PM
Got it. The cigarette lighter plug is a terrible idea and will not be pursued. Thanks to all for the intel.

Lane
ku7i


Title: RE: current rating of automobile cigarette lighter plugs
Post by: KM3F on March 20, 2013, 06:19:21 PM
Always look in your owner Manuel for fuse sizes per the function.
The auto wiring is in a harness, not large enough in size and can melt into the other wiring creating a big problem beside the voltage drop.
Anything that draws more than 8 amps needs to have a dedicated feed.
Many 2m FM radios that have a high power setting of 65 watts or more can't be run out of a lighter socket unless set on lower power.
You need to know that running a fuse at or near it's rating will fail in a short time from heat fatigue.
Goodluck.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: KU7I on March 20, 2013, 09:11:03 PM
Ken,
My previous call was KM3G, non-vanity from ~ 1983.

Lane


Title: RE: current rating of automobile cigarette lighter plugs
Post by: G7DMQ on March 25, 2013, 08:26:49 AM
I had a similar problem - but running a cool box which kept melting plugs & sockets!

I machined this:
http://www.x-eng.co.uk/images/forum/lighterplug.jpg (http://www.x-eng.co.uk/images/forum/lighterplug.jpg)
(Is there a way of embedding images on the forum?)

With a socket to match!  It would be much easier just to use a better connector, such as an Anderson however!

Si


Title: RE: current rating of automobile cigarette lighter plugs
Post by: N6AJR on March 25, 2013, 11:59:31 AM
I have 2 radios in the car and 5 in the truck.  in both cases I ran a heavy pair of of wires ( 8 or 10 gauge) from the battery to the radios. Well fussed and protected where it passes through the firewall.

  in the truck I actually have an 800 watt 110 volt inverter and I use the terminals on the back of it as my power take off point. from there i feed a power pole  gizmo that has several contacts on it to feed the radios.

I have a dedicated 900 mhz rig , a 2m dedicated rig, a 220 mhz radio, an ft 857 for all hf and some other bands too. and on the top of the stack is a kenwood 742 with 2m, 440, and 1.2 ghz. so I can monitor several 2 m frequencies, and most any band I want.  I have 8 antennas on the truck, 4 on NMO mounts through the roof and 4 on the bed rails, including 2 screwdrivers.

Any how do it right the first time. run a nice pair of heavy wire to feed the radios, ( you could even cannibalize a set of jumper cables), well fused and all radios and antennas with a good ground where appropriate

. I even added a separate 12 volt ciggy lighter plug for charging the cell phone and such. I also like the 110v on the truck as if you need to run the laptop or a coffee pot or a soldering gun, you have 110 volts and don't need a special 12 volt converter for each device.

Figure it out, allow for expansion in the future and do it right.  I really enjoy operating mobile.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: KF8SJ on March 26, 2013, 07:46:40 PM
if you have to replace the battery:
1.  get the highest rated capacity that will fit in the battery holder. won't cost much more and will probably
     last a lot longer-currently have 6 years in an 01 silverado.
2.  check clearances and see if you have room for a dual post battery-side and top terminals.use whichever 
     set is not connected to the vehicle for your radio connections-simplifies things and gives a more
     secure connection.

     happy mobiling   73  jim studer kf8sj  aka jimthegoatman
     


Title: RE: current rating of automobile cigarette lighter plugs
Post by: NO9E on March 27, 2013, 11:01:00 AM
I ran FT-100 from cigarette plugs. Could run full power on US cars but only reduced power from Honda or Toyota. Very useful on rental cars or where one does not want any permanent changes. Never a problem.

With voltage conditioner MFJ-4403 that uses supercapacitors,  any cigarette plug in any car would likely supply enough power for any 100W rig. This is because the conditioner replaces 20 A peaks with about 5A average.

Ignacy, NO9E 


Title: RE: current rating of automobile cigarette lighter plugs
Post by: W9MMS on March 27, 2013, 08:18:25 PM
I ran FT-100 from cigarette plugs. Could run full power on US cars but only reduced power from Honda or Toyota. Very useful on rental cars or where one does not want any permanent changes. Never a problem.

With voltage conditioner MFJ-4403 that uses supercapacitors,  any cigarette plug in any car would likely supply enough power for any 100W rig. This is because the conditioner replaces 20 A peaks with about 5A average.

Ignacy, NO9E 

Ignacy, the scary thing about what you just wrote, is you believe it!

Please go back and revisit the principles of "Time Constant" in regards to Capacitor.


(((7))) Milverton.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: N4CR on March 27, 2013, 09:33:57 PM
I ran FT-100 from cigarette plugs. Could run full power on US cars but only reduced power from Honda or Toyota. Very useful on rental cars or where one does not want any permanent changes. Never a problem.

With voltage conditioner MFJ-4403 that uses supercapacitors,  any cigarette plug in any car would likely supply enough power for any 100W rig. This is because the conditioner replaces 20 A peaks with about 5A average.

Ignacy, NO9E 

Ignacy, the scary thing about what you just wrote, is you believe it!

Please go back and revisit the principles of "Time Constant" in regards to Capacitor.


(((7))) Milverton.

And regardless of that, peak current isn't what melts wires. Average current is what melts wires and that's not mitigated by a supercap. It's made worse.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: KM3F on March 27, 2013, 09:48:18 PM
A 'capactor bank' at the radio will allow somewhat more power to be drawn on a mode such as SSB where the caps have a chance to recharge between audio drive signals but there is a limit to this.
This would be of little to no help on FM trying to extend the circuit's full current limit.
This is the same trick the auto audio high power boys do to feed the big amps when the lows are hit instead of trying to get it 'all' out of the battery and alternator but they use large gage wire.
Good luck.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: W9MMS on March 27, 2013, 10:40:23 PM
I ran FT-100 from cigarette plugs. Could run full power on US cars but only reduced power from Honda or Toyota. Very useful on rental cars or where one does not want any permanent changes. Never a problem.

With voltage conditioner MFJ-4403 that uses supercapacitors,  any cigarette plug in any car would likely supply enough power for any 100W rig. This is because the conditioner replaces 20 A peaks with about 5A average.

Ignacy, NO9E 
Ignacy, this is not mean to attack you as a person, however lets go back and re examine ( for the benefits of others) some very glaring statements.

1) "I ran FT-100 from cigarette plugs. Could run full power on US cars but only reduced power from Honda or Toyota." <snip>
  Most cars uses wire size of 12 swg or less to power their Cigarette lighters.
  The Amperage required for 100 watts PEP is around 20 Amperes.
   12 to 13 volts with a peak current of 20 Amperes through a 12 swg wire will encounter massive voltage drop, which leaves the question to be asked.
  Were you actually getting 100 watts PEP form that FT 100 using the cig lighter?
   I'll skip over the potential fire hazard that could have happened to the vehicle electrical system.

2) Using a " Super Capacitor " or any Capacitor for that matter, will only multiply the potential danger to the Electrical system.
    Once discharged to whatever percentage, the massive inrush of current required by the very nature of a capacitor will increased the fire danger 10 fold.
My point is simply  V = IR  has not change since Ohm's Law.

PS.   There are many young operators who uses this forum to further their knowledge of the Hobby, and sometimes do take whatever is written here as the
GOSPEL.
We all ( Myself included ) should be very thoughtful of what we print here on the forum.


((((73)))) Milverton.   


Title: RE: current rating of automobile cigarette lighter plugs
Post by: W8JX on March 28, 2013, 05:29:12 AM
  Most cars uses wire size of 12 swg or less to power their Cigarette lighters.
  The Amperage required for 100 watts PEP is around 20 Amperes.
   12 to 13 volts with a peak current of 20 Amperes through a 12 swg wire will encounter massive voltage drop, which leaves the question to be asked.
  Were you actually getting 100 watts PEP form that FT 100 using the cig lighter?

I love thins "massive voltage drop" theory. Assuming it is 12ga, 10 feet of it would drop a "massive" .3 volts at 20 amps and even 14 would only drop .5 volts. In realty the length of in a average car feeding lighter socket from main buss is less than 10 feet so voltage drop in wiring is not really a big issue at all.

   I'll skip over the potential fire hazard that could have happened to the vehicle electrical system.

Love this fire hazard thing.

2) Using a " Super Capacitor " or any Capacitor for that matter, will only multiply the potential danger to the Electrical system.  Once discharged to whatever percentage, the massive inrush of current required by the very nature of a capacitor will increased the fire danger 10 fold. My point is simply  V = IR  has not change since Ohm's Law.

Love this too. A capacitor will actually reduce average load on power lead during SSB operation. There will be a very brief surge draw 9less than a second) when a large capacitor is first charged from zero but then it will never as it feed radio for peak draws and recharges during low demand but can never discharge below voltage on power feed to it.  It is a great trick to use a large cap to stabilize voltage and reduce peak draw on a power feed. I have used it for many years. Again love the fire hazard claim

PS.   There are many young operators who uses this forum to further their knowledge of the Hobby, and sometimes do take whatever is written here as the
GOSPEL.
We all ( Myself included ) should be very thoughtful of what we print here on the forum.

I agree many seek knowledge here but also correct knowledge. One should try to base comments on direct knowledge of actual application rather than what they think might happened based on never have done it and a "theory". 

The weak link here is the plug in the socket not wiring in car. If it does not make excellent contact with socket, resistance can develop and plug can get hot and possible melt under prolonged very heavy loads. But as one poster stated based on his own experience when you use a large capacitor in circuit feed from socket the average draw on plug is reduced and it also runs cooler.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: N3QE on March 28, 2013, 06:35:44 AM
I might remind that the purpose of the original cigarette lighter plug is to get hot :-).

Tim.

resistance can develop and plug can get hot and possible melt under prolonged very heavy loads.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: N4CR on March 28, 2013, 10:48:37 AM
Love this too. A capacitor will actually reduce average load on power lead during SSB operation.

I'd love to see your proof of this. You have a load. You add a component and now the load draws less average power. This could be part of a perpetual motion machine if you could harness that magic component.

The rig draws x average current. Let's call that N electrons per second.

The capacitor draws only leakage current. Let's call the L electrons per second.

Now you tell us that L+N electrons per second is less than N electrons per second?


Title: RE: current rating of automobile cigarette lighter plugs
Post by: M0HCN on March 28, 2013, 12:26:09 PM
Don't forget that heating in the wiring is proportional to average of (current squared) so a short term 20A at say 10% duty cycle produces much more heat then 2A continuous would.

If we assumed say 0.1 ohms loop resistance then during that 20A pulse we are dropping 2V in the wiring and dissipating 40W in the cables (For 4W average dissipation at 10% duty), the steady state 2A is dropping 0.2V and dissipating 0.4W for the same average current in the load. 

Fitting significant local energy storage may help, but how much strongly depends on how much voltage drop you have under load, and what the power back off ratio for the modulation mode in use is in terms of the current envelope (quite different to the RF power envelope with most simple minded PA designs).

In any case, lighter sockets are notoriously poor, better to use almost anything else (Speakon loudspeaker connectors are nice).

Regards, Dan.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: KB1GTX on March 28, 2013, 12:35:48 PM
I tried to use one of those radio shack 2.5 amp power supplies on my hr 2510 and it would pop the breaker after a few seconds and the lights would dim on the radio, but with a 1F cap the radio runs perfect,, now this is on ssb only with just the alc compression that's in the radio that I speeded up a bit..  With the tests I ran it seems that you can "stretch" a power supply to 3to1 on an untouched ssb radio running normal limiting.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: W8JX on March 28, 2013, 01:41:59 PM
Love this too. A capacitor will actually reduce average load on power lead during SSB operation.

I'd love to see your proof of this. You have a load. You add a component and now the load draws less average power. This could be part of a perpetual motion machine if you could harness that magic component.

The rig draws x average current. Let's call that N electrons per second.

The capacitor draws only leakage current. Let's call the L electrons per second.

Now you tell us that L+N electrons per second is less than N electrons per second?

I meant to say reduce peak loads and maintain a more steady average draw on power feed and steadier voltage for rig. 


Title: RE: current rating of automobile cigarette lighter plugs
Post by: AD5X on March 28, 2013, 05:06:00 PM
Actually, the MJ-4403 works very well.  It works a lot like the Gamma HPS-1a power supply.  The Gamma uses a 5-amp 13.8V supply with a 5-farad capacitor bank across the output.  It does a good job of powering a 100 watt SSB radio, though I found that you needed to drop to about 80 watts on CW as the higher duty cycle on CW overwhelmed the 5-amp power supply at 100 watts CW. 

I ran a bunch of tests on the MFJ-4403 on the bench.  It places a large current limiting resistor in series with the capacitor bank (4.33 farads)  until the capacitor bank is nearly charged, then the resistor is shorted out by a relay - i.e. a step-start circuit.  That takes about 30 seconds or so.  Once that 4-farad capacitor bank is charged, it does a very good job of handling the current peaks for intermittent modes like CW and SSB at 100 watts.  Most of my on-the-air experience was with the MFJ-706 - always powered from the accessory socket in various cars.  The MFJ-706 is a package that includes a MFJ autotuner, a MFJ-4403 - and your IC-706.

Of course, wiring directly to the battery is cheaper and better.

Phil - AD5X


Title: RE: current rating of automobile cigarette lighter plugs
Post by: N4CR on March 28, 2013, 07:13:55 PM
Love this too. A capacitor will actually reduce average load on power lead during SSB operation.

I'd love to see your proof of this. You have a load. You add a component and now the load draws less average power. This could be part of a perpetual motion machine if you could harness that magic component.

The rig draws x average current. Let's call that N electrons per second.

The capacitor draws only leakage current. Let's call the L electrons per second.

Now you tell us that L+N electrons per second is less than N electrons per second?

I meant to say reduce peak loads and maintain a more steady average draw on power feed and steadier voltage for rig. 

There is no doubt of that.

The interesting thing that comes along with averaging the current is that it also averages the voltage. So the voltage is never as low without the supercap, but by the same token, it's also never as high. Since we know that lower voltage feeding a regulated circuit causes more current to flow, the small gains in reducing the current surges are paid back in the slightly higher average current because of the slightly lower average voltage.

There's no free lunch.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: W8JX on March 28, 2013, 07:29:18 PM

The interesting thing that comes along with averaging the current is that it also averages the voltage. So the voltage is never as low without the supercap, but by the same token, it's also never as high. Since we know that lower voltage feeding a regulated circuit causes more current to flow, the small gains in reducing the current surges are paid back in the slightly higher average current because of the slightly lower average voltage.

There's no free lunch.

This is somewhat true as far as voltage but a slightly lower peak voltage when transmitting is more than offset by it being more stable and not sagging during voice peaks delivering higher average output and cleaner signal too (in theory) due to more stable voltage so there is indeed a bit of free lunch.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: N4CR on March 28, 2013, 08:00:56 PM
This is somewhat true as far as voltage but a slightly lower peak voltage when transmitting is more than offset by it being more stable and not sagging during voice peaks delivering higher average output and cleaner signal too (in theory) due to more stable voltage so there is indeed a bit of fee lunch.

If it's a fixed load, then voltage drop is the key to less current flowing. (light bulbs are not fixed loads)

If it's a regulated load, if voltage drops, more current flows and the same wattage is dissipated within reason.

If you mean less voltage sags is your free lunch, then yes. But that won't make your cigarette lighter wiring not catch on fire from too high average current.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: W8JX on March 29, 2013, 06:58:24 AM
If you mean less voltage sags is your free lunch, then yes. But that won't make your cigarette lighter wiring not catch on fire from too high average current.

And just how many cars have had the lighter wiring catch fire?? Maybe if you bypassed fuse and shorted it out.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: NO9E on March 29, 2013, 07:13:24 AM
Quote
We all ( Myself included ) should be very thoughtful of what we print here on the forum.

Good that young people do not follow us blindly.

Excessive safety is sometimes more harmful than normal behavior. Usually devices contain enough safeguards not to be destroyed before a fuse pops up. If they do, perhaps our experience is worth more than the damage.

W8JI has a story about people trying to treat 3-500z lightly. Then, the tube is not gettered enough self-destroys.  

Fairy tale below.

One guy wanted a really strong antenna. He used very heavy wire.  Then 1) a lightning stroke and destroyed his shack, or 2) copperweld wire rusted and "improved" operating bandwidth while reducing the efficiency by 50%, or 3)  very heavy attachments to trees destroyed the trees, and the wire while being removed kinked causing injury, requiring a trip to the emergency room.  

Another guy used a thin tire. He tolerated 2% drop in efficiency compared to a thicker wire. After 5 years, 1) lightning vaporized his wire causing no damage to the shack, or 2) the wire was broken in heavy winds but the tree has survived; he discarded the wire and invested $10 in new wire.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: N4CR on March 29, 2013, 08:23:48 AM
If you mean less voltage sags is your free lunch, then yes. But that won't make your cigarette lighter wiring not catch on fire from too high average current.

And just how many cars have had the lighter wiring catch fire?? Maybe if you bypassed fuse and shorted it out.

It's a metaphor.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: KM3F on March 29, 2013, 04:06:49 PM
Fuse values in cars and truck are engineered to fail long before wire overheats unless some fool put in higher capacity fuses.
He then deserves to get what he gets from doing so.
No mfger would want the liability of losing a vehicle in the owners hands from a proven over fused circuit as part of it's normal speced design.
Trucks often are designed and wired for a bit larger current.
In a Ford F150, The Cigar lighter is fused at 20 amps. It's socket is not the same as  a standard power port.
The power port along side of it, is also rated at 20 amps.
In these trucks there are two fuse panels. One in the engine bay and one in the dash.
Normally power port appliance plugs are not rated above 10 amps and very often have their own fuse inside the plug at no more than 10 amps if that..
One must look at the power port rating for fuse size in any vehicle to be sure before using it for other than a normal appliance use.
Good luck.


Title: RE: current rating of automobile cigarette lighter plugs
Post by: W7HBP on April 08, 2013, 11:48:12 AM
Anyone have any idea how much current you can draw from the cigarette lighter plug in most automobiles? I want to push ~ 400 watts mobile but not sure if this is too much current draw.

Lane
Ku7i

Most are on a 15 amp circuit. But the wire is so small to the acc socket anymore, I suspect 7.5 amps. Some have a thermal protector in them too. If its overloaded, this thermal protector will open and shut the circuit down. Here is what I'd do and did. As a Toyota dealer tech, I liked the idea of the switch socket. But I ran a power source right to a terminal block, full 12V using 12AWG wire right from the battery with a 15A auto fuse right near the power rource. Then at after the terminal block, I installed a Bosch type relay to turn the power on and off using the cigarette lighter socket to power up the relay only, no radio load on the small acc socket circuit.