Inverter Wattage for 12V (120W) cigaraette lighter socket

[phizy]

Hi.

I have a 2011 Pilot, EX-L, no touring, no DVD player, just the straight EX-L.

I noticed on the cigarette lighter port it says 12V, 120W max.

I want to get one of the inverters that plug into the port. Does this mean I have to get one that is under 120 Watt AC output? I had bought one from Sears that was 140 W AC output and I was afraid of blowing the fuse so I returned it.

Thanks,
Paul

[RSQ Pilot]

Originally Posted by phizy

Hi.

I have a 2011 Pilot, EX-L, no touring, no DVD player, just the straight EX-L.

I noticed on the cigarette lighter port it says 12V, 120W max.

I want to get one of the inverters that plug into the port. Does this mean I have to get one that is under 120 Watt AC output? I had bought one from Sears that was 140 W AC output and I was afraid of blowing the fuse so I returned it.

Thanks,
Paul

Fuse and wire gauge will only safely support 120 watt (10 amp) max draw on the 12 volt system. If the inverter is rated at under 10 amps under full load you should be OK. Some of the smaller 12V DC power inverters will work in a cigarette lighter/accessory plug as long as the draw doesn't exceed 10 amps. If it does it will blow the vehicle's lower rated fuse and could harm the wiring. That's why you will see most over 180W have alligator clips and heavier guage wire to hook it directly to the battery.

[phizy]

So, does that mean 140W output AC would be drawing 11.7 Amp from the DC side? In other words, assuming 100 % efficiency, is the output AC wattage on an inverter equal to the input DC wattage? If so, and then assuming 90 % efficiency, then the maximum wattage inverter I should get is 108 W, or 100 W (for those that are actually sold).

Is this a correct assumption?

Originally Posted by RSQ Pilot

Fuse and wire gauge will only safely support 120 watt (10 amp) max draw on the 12 volt system.

[RSQ Pilot]

Originally Posted by phizy

So, does that mean 140W output AC would be drawing 11.7 Amp from the DC side? In other words, assuming 100 % efficiency, is the output AC wattage on an inverter equal to the input DC wattage? If so, and then assuming 90 % efficiency, then the maximum wattage inverter I should get is 108 W, or 100 W (for those that are actually sold).

Is this a correct assumption?

115V Output does not directly relate to 12VDC input or draw. It also depends upon the device itself, the load and the vehicle 12V system.
Power Inverter FAQ
You could use a higher rated inverter as long as you don't over load it with the AC draw of your device(s). Surge loads may also pull the maximum wattage while continuous load may not.
The Touring has an OEM inverter rated a 150 watts but it has a safety shutdown if surge load or demand exceeds the 150W AC.

[N_Jay]

I have had no problems using 300 and 400 Watt rated inverters.

The loads are usually in the 70 to 100 watt range. PC, TV, etc.

The 10A lighter socket is fused at 15 or 20 amps to handle some surges.

Just keep an extra fuse around in case you have a problem.

[phizy]

So, essentially, the 120W DC limits the safe current to 10A. I need to make sure the inverter I get operates with an input current of no more than 10A. The problem I found, is I can't often find the input current listed with an inverter.

[rocky]

The box may not have it, but input and output voltage/ amp/ watt should be shown on the unit itself.

[N_Jay]

Originally Posted by phizy

So, essentially, the 120W DC limits the safe current to 10A. I need to make sure the inverter I get operates with an input current of no more than 10A. The problem I found, is I can't often find the input current listed with an inverter.

The input current is a function of the output current.

If what you are plugging in will work with a 120 watt inverter it will work fine with a larger inverter.

I would not go crazy, as a 1000 watt unit might blow the fuse during start up (Many inverters can draw a very short surge when first plugged in and/or turned on. This is more related to the design and size than the plugged in load)

[phizy]

I guess I'm still a little confused; I'm not sure what a safe inverter would be to avoid blowing the fuse. I understand the relationship between amp, volt, watt, and the draw on the AC end. What I don't understand is what is happening on the DC end to get to the AC. So, if the AC end draws, and I'll go extreme here, 700 watts, does that mean the inverter is going to be drawing near 700 watts to supply that amount of power, or, does it depend on the inverter? It seems to me that the current flow out of the inverter will need to be fueled by the input current unless there is some rather high charge capacity on the inverter.

But, to get a safe one, where I don't risk blowing the fuse, I need to make sure the surge draw on the DC end of the inverter is below 10A right?

If I'm driving and that fuse goes, what do I lose?

Thanks.

[N_Jay]

The total power out MUST equal the total power in.
So the power out, plus the power lost in heat (yes the inverters get a little warm), plus the power to turn the fan (if it has one), plus the power to light the little lights will EXACTLY equal when it draws.

So if it is putting out 100 watts to run your laptop, it is taking in something just north of 100 watts.

The rating of the inverter makes no difference. (The design does a little because some are less efficient than others in that they lose more energy as heat. This is especially true of older units.).

Second the 120 watt rating is conservative as the fuse is 15A, (15A at 13.8V = 207 watts) but also carries the load for some other accessories.

Now, there is one thing to consider with bigger inverters. They tend to take a surge when you first turn them on or plug them in. This surge is bigger on bigger inverters. (and tends to be worse on older designs.). I did have a 600 watt unit that very occasionally would blow the fuse when first plugged in. (It since died, so maybe it had a "problem" all along).
I have also used 100, 150, 300, 400 and 700 watt inverters in both my Pilot and my CRV with no issues.

Hope this all helps.

[phizy]

Thanks this does help. What accessories are on that fuse in the 2011 Pilot? What would happen if it popped while driving?

[N_Jay]

Originally Posted by phizy

Thanks this does help. What accessories are on that fuse in the 2011 Pilot? What would happen if it popped while driving?

It i all accessory stuff, if I recall.

Look in your owners manual at the fuse listing.
I have an 2003 and it is probably different.

[whizmo]

The service manual shows this fuse, in addition to the accessory circuits, has the noise canceling system (if equipped), keyless entry system, the "gauge control module" and the shift lock relay. Not sure if this means you'd lose your instrument gauges, but I doubt any of this stuff is mission-critical if you do happen to pop the fuse.

I don't think this is too complicated - if the socket is rated fro 120W, then make sure whatever device you hook to the inverter uses somewhat less than 120W. The "somewhat" depends on the efficiency of the inverter and whether there are any startup demands of the device that exceed the constant current. There's probably a little headroom in the circuit as well to handle small overloads. If you're close to the limit, I think you trial/error this sort of thing - try it and see how it goes. If you're popping fuses, you've got an issue. Fuses are cheap and easy to replace. But I wouldn't uprate the fuse to a higher value.

- Mark