Rear outlet (power)

[AJ]

How much 12 volt power (amps) can the rear power outlet on a '04 Liberty handle?
I have a 12 volt cooler that I have plugged in but the plug-in (male and female) both get very hot.
The draw is about 4 amps so I'm wondering if that's the limit or possibly the connections are not good.
What have you used on that outlet?
AJ

 

[sleeve]

In my KJ, the rear is fused for 20Amps. HOWEVER, when the plugs heat up, the plastic connector on the back of them can melt and cause the outlet to go non-functional on you. Even when you are under the 20Amp current draw of the fuse. I would really only use that power point for items less than 2Amps.

 

[kj924]

Wonder if that has been a Recall in the past? Good to know before hand....I use it for a 12V air compressor. Come to think of it, I have never used my rear outlet yet. kopkrab.gif

 

[ridenby]

Havn't used mine,way it looks never has been.

 

[oddball]

I used my rear outlet once to air up a tire without any negative issues.

 

[kb0nly]

A good rule of thumb on those is 5-10 amps max, and that depends on the vehicle. I have taken them apart on a few vehicles to see what gauge of wire is in there, most of the time its not much heavier than 18 awg, if your lucky it might be 16 or 14 instead.

Why they fuse them at 20 amps? Well there is a few reasons i guess but i don't agree with any of them. A lot of the times its because the fuse is actually powering more than just that outlet, i don't know for sure if its this way on the KJ as i haven't looked at the service manual, but i know on our PT Cruiser there is a 20 amp fuse and that provides power to both the front and rear power outlet as when i pull that fuse they both go dead.

My usual habit is to pull the 20 amp fuse and put in a 10 amp fuse for greater safety, i want the fuse to go before wires start melting if there is an accident.

I was told once by a service manager that they put a 20 amp fuse in that circuit to handle large turn on current surges, for things like those coolers and warmers, etc. They have a large current draw for a few seconds that can be around 10-15 amps, but once they are running the only pull 5-10 amps continuous.

 

[Powerslave]

I was told once by a service manager that they put a 20 amp fuse in that circuit to handle large turn on current surges, for things like those coolers and warmers, etc. They have a large current draw for a few seconds that can be around 10-15 amps, but once they are running the only pull 5-10 amps continuous.

That's why they're rated at 20, that is a PEAK draw. Anything with a motor, also, has a higher start-up current.

 

[sleeve]

It's not the peak current that kills the outlets though. It's the heat that is generated when large powerdraws force a lot of current through that tiny 18ga (?) wire. That heats up the back side of the power point and melts them...

I would say in an emergancy it's fine - but for constant use I would still be hesitant to use anything with a high current draw on that outlet.

 

[AJ]

I checked the wires that go to the power point and they are definitely 16 or 18 ga.
It looks like the lead (to the power point) is a "pig-tail" from, perhaps, the tail or brake light. That might be the reason for the 20 amp fuse if it's the brakes light circuit.
Whatever, I changed the 20 to a 15 amp fuse and no apparent problems with the brake light. Yet.
Checked the back of the power point connecter and found no melting so will still use the cooler but will check for excessive heat.
Thanks for the info.
AJ

 

[AJ]

I checked the wires that go to the power point and they are definitely 16 or 18 ga.
It looks like the lead (to the power point) is a "pig-tail" from, perhaps, the tail or brake light. That might be the reason for the 20 amp fuse if it's the brakes light circuit.
Whatever, I changed the 20 to a 15 amp fuse and no apparent problems with the brake light. Yet.
Checked the back of the power point connecter and found no melting so will still use the cooler but will check for excessive heat.
Thanks for the info.
AJ

 

[kb0nly]

It doesn't appear to share with any of the lighting, but it does come from the rear end harness.

When in installed my hitch and trailer wiring the inline powered converter from Hopkins, model 42475 i think it was, that plugs inline with that large rear end wiring harness plug and takes power from the rear power outlet circuit. I know this because when i pull the fuse for the rear outlet my trailer lights no longer work but everything else does.

 

[jnaut]

Your cigarette lighter (now called a power outlet) can handle a fair amount of heat. I have a small 12v cooler which runs in my cargo area and yes, the 12v plug gets pretty hot. Remember, those cigarette lighter outlets used to house...wait for it... a cigarette lighter which was designed to get glowing red hot. Now, I'm not suggesting that you should have something in there that hot for a sustained period of time, but like I said, I run a Wagan 12v cooler which gets pretty hot (almost too hot to touch if you unplug it) and the only bad thing I've ever done with it was run down my battery.

 

[Powerslave]

It's not the peak current that kills the outlets though. It's the heat that is generated when large powerdraws force a lot of current through that tiny 18ga (?) wire. That heats up the back side of the power point and melts them...

I would say in an emergancy it's fine - but for constant use I would still be hesitant to use anything with a high current draw on that outlet.

I never indicated anything about peak and heat, only what the max rating for the plug is, and why.

You would not want to keep drawing 20AMPS as a continual flow for hours on end, it would eventually damage the plug and/or wires. 20 Amps is the MAX it can provide, at peak level. Peak menaing, it can spike there for a few minutes, seconds, whatever, not a continual draw.

 

[sleeve]

Right, we are saying the same thing..

I wasn't correcting you, I was only reitterating the failure mode for these things.

 

[Ry' N Jen]

We run a large electric cooler off of the rear power outlet all day and night.
At night I have used 2 55 watt Quartz Halogen work lights off of the
rear power outlet for half an hour until the propane lantern is fired up without any heat or problems.

 

[LibertyFever]

I don't think it would be that difficult to run a new fused 14 gauge power line to the rear of your Libby (and ground from the chassis). I ran one under my passenger's side front seat for a 400W 110VAC inverter.

Here's a question for everybody, if the gauge of the wiring to the factory rear outlet is too small would it be possible for the voltage at the outlet to drop possibly damaging the 12V cooler? My inverter likes to have the engine running to be happy.

 

[jnaut]

I don't think it would be that difficult to run a new fused 14 gauge power line to the rear of your Libby (and ground from the chassis). I ran one under my passenger's side front seat for a 400W 110VAC inverter.

Here's a question for everybody, if the gauge of the wiring to the factory rear outlet is too small would it be possible for the voltage at the outlet to drop possibly damaging the 12V cooler? My inverter likes to have the engine running to be happy.

What kind of 12v cooler is it? Is it a real compressor type cooler or a peltier circuit type cooler? If it's a peltier type, no, you shouldn't have any problems. If it's a normal compressor type cooler, running the compressor at low voltage may be a problem.

But I'm reading between the lines on your message. Are you running your coller off your inverter? If your inverter can't pull enough dc voltage to maintain the AC side, it should probably start beeping or shut down. I know my 350watt inverter would do that if it became overloaded on the AC side.

 

[sleeve]

Here's a question for everybody, if the gauge of the wiring to the factory rear outlet is too small would it be possible for the voltage at the outlet to drop possibly damaging the 12V cooler?

Most definently there will be voltage drop across the wire for the rear power outlet. However, it varies based on the current load that you are pulling out of the wire.

VD [Voltage Drop] = I [electrical load / draw] x R [resistance]

Here is a nice write-up on VD