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2006 Forester
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Discussion Starter #1 (Edited)
The last time we went camping, I needed an AC outlet to charge my new video camera's battery, so I purchased a Wagen Tech 175W AC Inverter with 12V cigarette lighter plug to stash in my Fos. Because the car's cigarette lighters only work when the key is turned in the ignition, I'd like to rewire the rear compartment lighter to be always-on so I can use the inverter and not have to have the keys in the ignition.

Well, because of the discussion in the following posts below, I ended up running a 12-gauge wire from the rear compartment 12V outlet to the battery having a switch near the outlet to turn the power on/off.

To do this I purchased an assortment of beefy materials...
Red Glow 20A Rocker Switch
24A #12 wire ATM Fuse Holder
15A ATM fuses
12-gauge Female Disconnects
25' 12-gauge Wire
Battery Post Ring Terminal with 3 12-gauge spaded
Quick Splices
12-gauge 1/4" ring terminal (ground)

Here's a picture of the back of the rear compartment's sidewall storage cubbyhole...errrr...whatever you call it. I had to remove the rear compartment floor to pull the side interior and window trim up enough to get at this area. The picture shows the wiring from the outlet to the switch using 12 gauge quick connects. I used a meter and tested the OEM power harness to the outlet to figure out which outlet spade was was hot and ground. I used masking tape to outline the rectangle I needed to cut for the switch, then used a knife to carefully score the rectangle prior to final cutting...I wanted a perfect fit. I ran the ground wire to a nearby bolt and used a quick connect to splice/ground both the outlet and the switch.


I ran the power wire to the front passenger-side footwell with the other hidden wires under the door/floor trim, then across to the rubber firewall grommet in the driver's side footwell. With the scraps left over, I figure I used 22-23 feet of the 12-gauge wire. I bought a battery post ring terminal with 3 spades to tap battery power from with the female disconnects, and put a 15A fuse inline just off the battery.

Here's a picture of it all together. The switch's red lamp indicates if the power to the outlet is on or not. I decided to put the switch in the upper back corner of that cubbyhole and near the outlet...I figured the switch will be the most out of the way in that location.


This turned out to be a great little project. Thanks to all for all the discussion and advice.
 

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2008 XS 4EAT
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2006 Forester XT
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The 'no load' draw is with nothing connected to it.

What use would that be?

As soon as you plug anything in, the fuse will blow.

An inverter that size will flatten the battery in less than an hour, unless the engine is running.

S
 

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2006 Forester
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Discussion Starter #5
Mmmmm...that good info to know StealthTL, I should've known about that no load draw what with 175W .:crazy: And thanks for the links good dog.

The inverter will pretty much be used to charge re-chargeable batteries, but I got an inverter with just enough balls to run larger items (lights, fan, radio, etc.) if necessary.
 

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2006 Forester
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Discussion Starter #7
Another good link Ferret, that looks like the easiest mod to get the job done.

From reading the threads, it appears that Subaru made a reasonable decision to wire the lighters always-off when the car is not running so the battery doesn't drain. I guess running the inverter to charge anything more than a cell phone would drain the battery if the car isn't running, therefore the auxiliary battery setup that frogstar noted sure sounds like the best option to run an inverter when the car is off.

Maybe when I need to use the rear cigarette lighter when the car is off I should simply get my lazy butt to turn the power on with the ignition key. :shake: Regardless, I'm going to do the mod from ferret's link.

All in all, this has been very informative.
 

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2007 Forester Sports XT 4EAT
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Something to keep in mind. The conversion of Watts to Amps is governed by the equation Amps = Watts/Volts. 175W/12V=14.6A! This is something they don't spell out on the inverter specifications. You will overload the 12V outlet! :icon_eek:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

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2007 Forester Sports XT 4EAT
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After more research, the watts can't be used to get the 12V amps, since they're really not the same, as in 175W/AC & not 175W/DC (12V). What I do see is that they are very careful not to say what the 12V input current is. A cue is the 12V input fuse, which on this unit is 15A. My guess is that the 12V input current is less than 15A, but will still be pretty high. :frown:

Here's a link to the inverter User's Manual. The 12V input fuse is on page 4. They recommend not running the inverter more than 2-3 hours before recharging the battery by running the vehicle for 10-20 minutes. :wink:

Bobby...
 

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Discussion Starter #10 (Edited)
Wow, you're right, Bobby, the car fuse is a 15A for the 12V outlet. And thanks for interpreting the inverter electrical info. I checked to make sure it was the correct fuse by plugging in my GPS to the rear cigarette lighter and pulling out the fuse, and the GPS lost power. I also checked the inverter fuse in the male plug which is 20A/250V.:icon_eek:

So I need to watch what I use the inverter for and try not to get near the 175W, eh? Should I swap the inverter fuse to one of lower amps (than the car fuse) just in case?

Oh yeah, the rear accessory power relay in my Fos is on the left of the fuse box and sandwiched between it and power wires and support beam. I unlocked the round plastic holding clip but could not pull the relay because I could not get in there to get a good grip on it. Just no room to work. Then it was a PITA re-clipping the relay holding clip. I may leave well enough alone wrt the jumper wire mod.
 

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I've been in the wiring for the rear 12V outlet, which you can view on my post here & the wiring is very light, not much more than 18 gauge, maybe 16 gauge & it's a long ways to the battery. I don't think I'd want to pull too much current (amps) those those wimpy wires! :icon_eek:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 

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Discussion Starter #12
Thanks for your input, Bobby, you really got me thinking. Makes me wish I paid more attention during the electricity portion of my physics class. :icon_confused:

I've been searching the internet to determine the max amp load I should run with the OEM wire to the cigarette lighter so as not to overload it. I'm going with the conservative assumption that the wire is 18-gauge, copper, a run of 20 feet with < 3% voltage drop, a continuous load, for 12V. To make a long story short, there sure are alot of sites to read with many equations to chose from, and the more I read the more confused I get.

My one conclusion is that if I want to take advantage of the inverter's potential and run it at it's max, I should upgrade the wire to the cigarette lighter port, hard wire it with fuse directly to the battery, and possibly install an on/off switch nearby...and have the motor running when using the inverter for large loads. :icon_wink:
 

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2018 2.5i Premium CVT
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Yes! I've seen wattage ratings for inverters that would suck the battery dry in minutes. Kilowatts! Currents that would require massive gauge wiring. They never mention any of that. And these are all ratings of output wattage. So if you simply compute amps = watts/volts to size your fuse and your wiring, you are assuming 100% efficiency of the inverter. Which ain't so!

Subaru wiring is notoriously flimsy, and power wasted in the wiring goes up as the square of the current. We lose over 2 volts in the headlight circuitry, which represents a back and forth journey of maybe 15 feet max.
 

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Discussion Starter #15 (Edited)
Well...I upgraded the 12V outlet wiring, but I edited the writeup and posted it in my first post.:raspberry:

But after a few days of flicking the switch, the bulb in the switch burnt out already.:icon_mad:
 

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2012 2.5X Premium Standard
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The last time we went camping, I needed an AC outlet to charge my new video camera's battery, so I purchased a Wagen Tech 175W AC Inverter with 12V cigarette lighter plug to stash in my Fos. Because the car's cigarette lighters only work when the key is turned in the ignition, I'd like to rewire the rear compartment lighter to be always-on so I can use the inverter and not have to have the keys in the ignition.

Well, because of the discussion in the following posts below, I ended up running a 12-gauge wire from the rear compartment 12V outlet to the battery having a switch near the outlet to turn the power on/off.

To do this I purchased an assortment of beefy materials...
Red Glow 20A Rocker Switch
24A #12 wire ATM Fuse Holder
15A ATM fuses
12-gauge Female Disconnects
25' 12-gauge Wire
Battery Post Ring Terminal with 3 12-gauge spaded
Quick Splices
12-gauge 1/4" ring terminal (ground)

Here's a picture of the back of the rear compartment's sidewall storage cubbyhole...errrr...whatever you call it. I had to remove the rear compartment floor to pull the side interior and window trim up enough to get at this area. The picture shows the wiring from the outlet to the switch using 12 gauge quick connects. I used a meter and tested the OEM power harness to the outlet to figure out which outlet spade was was hot and ground. I used masking tape to outline the rectangle I needed to cut for the switch, then used a knife to carefully score the rectangle prior to final cutting...I wanted a perfect fit. I ran the ground wire to a nearby bolt and used a quick connect to splice/ground both the outlet and the switch.


I ran the power wire to the front passenger-side footwell with the other hidden wires under the door/floor trim, then across to the rubber firewall grommet in the driver's side footwell. With the scraps left over, I figure I used 22-23 feet of the 12-gauge wire. I bought a battery post ring terminal with 3 spades to tap battery power from with the female disconnects, and put a 15A fuse inline just off the battery.

Here's a picture of it all together. The switch's red lamp indicates if the power to the outlet is on or not. I decided to put the switch in the upper back corner of that cubbyhole and near the outlet...I figured the switch will be the most out of the way in that location.


This turned out to be a great little project. Thanks to all for all the discussion and advice.

Resurrecting an older thread, yes.

OP, would you mind reposting those photos for us, if you still have them?
 

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2006 Forester
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Discussion Starter #19
Not sure what happened to the pics. Bu here ya go...


Here's a picture of the back of the rear compartment's sidewall storage cubbyhole...errrr...whatever you call it. I had to remove the rear compartment floor to pull the side interior and window trim up enough to get at this area. The picture shows the wiring from the outlet to the switch using 12 gauge quick connects. I used a meter and tested the OEM power harness to the outlet to figure out which outlet spade was was hot and ground. I used masking tape to outline the rectangle I needed to cut for the switch, then used a knife to carefully score the rectangle prior to final cutting...I wanted a perfect fit. I ran the ground wire to a nearby bolt and used a quick connect to splice/ground both the outlet and the switch.

I ran the power wire to the front passenger-side footwell with the other hidden wires under the door/floor trim, then across to the rubber firewall grommet in the driver's side footwell. With the scraps left over, I figure I used 22-23 feet of the 12-gauge wire. I bought a battery post ring terminal with 3 spades to tap battery power from with the female disconnects, and put a 15A fuse inline just off the battery.


Here's a picture of it all together. The switch's red lamp indicates if the power to the outlet is on or not. I decided to put the switch in the upper back corner of that cubbyhole and near the outlet...I figured the switch will be the most out of the way in that location.
 
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