Adding 20A circuit for inverter, what can I power, and batteries?

[mnewxcv]

So three things I want to discuss: adding a 20A circuit for a small inverter, what that circuit can power, and possibly talk about adding an aux battery to my vehicle. My vehicle is a Lexus rx400h, you can read about it here:

Overland/cross country vehicle: Lexus RX400h Hybrid

I've always had an interest in the overland scene, and have been a lurker on the forum for many years now. I bought a 2000 Jeep Cherokee about 6 years ago and I still have it, and it has taught me quite a bit about wrenching on your rig. That being said, it has come to the point where I would...

expeditionportal.com

First, I have a 400w pure sine wave inverter that I want to hook up full time to a 20A circuit (I know absolute max will be 240w not accounting for loss or inverter draw). It will be used mainly for powering my laptop, which is currently using a cigarette lighter on a shared circuit. The reason I am choosing 20A and not higher is because I would like to tap into an existing circuit in the vehicle. My vehicle was not equipped with a power inverter, but it was a factory option. While I am not yet certain the wiring for it is present, I believe All I need is a switch and a relay to activate the circuit and provide power to my inverter in my rear cargo area (location of my inverter and location of the factory inverter if equipped). Here is a diagram of the factory circuit I want to utilize.



as you can see, the switch gets power with ignition, activates the relay which is on a 20A fuse, and goes to the inverter via the black wire. The red and brown AC wires are because the power outlet was in a different location than the inverter, and will not be used (if present). So what I am planning is to add the factory switch as well as the factory relay, and extend the black and white/black wires from the inverter harness to my inverter (1-2ft away from factory location). Does anyone see any issue with this?


Second, what are some things that are able to be powered by 200w AC that might be useful on the road or while camping?


Lastly, I have seen 20A DC-DC chargers for charging AUX batteries. Would it be possible to alternatively put an aux battery in my cargo area (under floor storage area) to power a larger (~1000w) inverter, and when that battery gets low, use the DC-DC charger via the circuit listed above? I know AGM is recommended and in this case, deep cycle, but how are people venting these if used in an in cabin cargo area of an SUV?


Thanks for reading!

 

[hour]

Since you already have the smaller inverter, you could use that for now and easily upgrade to your 20a DC-DC idea later if you need to. Venting shouldn't be a concern with AGM, and you might need an AGM anyway if you're trying to stash it beneath something (ability to lay AGMs on their side).

 

[mnewxcv]

thanks for the response. I will give it a go and see what happens. I'm having some doubts about whether or not all the wiring is present, but I will look into that tomorrow. Here you can see the area I have free if I go the battery route:

 

[hour]

Might want to take a tape measure out and check the depth of that compartment, but I'm sure some AGM offering could fit on its side, or maybe even standing upright if you got one with screw terminals on top/side and no posts.

I just googled the factory rx400h 115v inverter and found a thread mentioning it was 100w. Then additional snippets from what I guess was the owners manual, stating to not exceed 120w on the entire circuit all outlets combined. I guess it's possible that it's the same circuit as your cigarette lighters elsewhere in the vehicle? If the fuse is 20, you'd think that the wiring would be adequate for at least that much. You could possibly verify the gauge if its printed on the wires. Also some post mentioned there was a switch for the inverter up front. If you don't have that, it'd be a huge bummer to find the wire only to discover it not active. If you want to at least warm up to the idea of running dedicated wiring, I'm sure someone's done a step by step aftermarket sub install for your vehicle.

You could charge a laptop, watch tv, inflate air mattresses, charge power tool batteries, run a whole bunch of LED lighting, run a couple of heated blankets... on 200w. Of course you can do most of that with DC, a lot of the stuff I mentioned actually operates on DC anyway.

 

[mnewxcv]

Might want to take a tape measure out and check the depth of that compartment, but I'm sure some AGM offering could fit on its side, or maybe even standing upright if you got one with screw terminals on top/side and no posts.

I just googled the factory rx400h 115v inverter and found a thread mentioning it was 100w. Then additional snippets from what I guess was the owners manual, stating to not exceed 120w on the entire circuit all outlets combined. I guess it's possible that it's the same circuit as your cigarette lighters elsewhere in the vehicle? If the fuse is 20, you'd think that the wiring would be adequate for at least that much. You could possibly verify the gauge if its printed on the wires. Also some post mentioned there was a switch for the inverter up front. If you don't have that, it'd be a huge bummer to find the wire only to discover it not active. If you want to at least warm up to the idea of running dedicated wiring, I'm sure someone's done a step by step aftermarket sub install for your vehicle.

You could charge a laptop, watch tv, inflate air mattresses, charge power tool batteries, run a whole bunch of LED lighting, run a couple of heated blankets... on 200w. Of course you can do most of that with DC, a lot of the stuff I mentioned actually operates on DC anyway.

good eye. I have noticed the 100/120w limitation listed, but I can only guess that is due to the inverters limits/losses. The circuit is on a 20A fuse, so the entire circuit must be able to handle 20A. In my original post I posted the diagram, but I cut it down to isolate the inverter circuit. Here is the full version showing the power outlet #1 circuit as well, which is separate from power outlet #2 circuit (inverter). Power outlet #1 circuit is for the front and rear 12v outlets:



and also, here is the CIG circuit:



they are independent of one another. I will do some digging today and see what I can find. I did pick up the relay I needed at the junk yard yesterday, so if the wiring is present, all I need is a switch.

 

[dreadlocks]

circuits shouldn't be ran at full capacity, if its on a 20A fuse you should not hook up loads more than ~15A or else expect to pop that fuse constantly.

 

[mnewxcv]

circuits shouldn't be ran at full capacity, if its on a 20A fuse you should not hook up loads more than ~15A or else expect to pop that fuse constantly.

Thanks! Yes, I agree. I stated wanting to use about 200w, which with the vehicle running, should be just under 15A.

 

[dreadlocks]

kinda, as you put load on a wire the voltage is going to drop.. the voltage at the inverter wont be same under load as idle.. my 1kw inverter pulls my Lipo battery down from ~13.8v to 11.5v.. so instead of pulling 72A like you'd calculate at resting input voltage it actually pulls >86A IRL

even though its a small inverter, the wiring is factory and likely going to choke voltage and increase amperage.. I'd guess if you go much over 180W you could be blowing fuses.

 

[mnewxcv]

kinda, as you put load on a wire the voltage is going to drop.. the voltage at the inverter wont be same under load as idle.. my 1kw inverter pulls my Lipo battery down from ~13.8v to 11.5v.. so instead of pulling 72A like you'd calculate at resting input voltage it actually pulls >86A IRL

even though its a small inverter, the wiring is factory and likely going to choke voltage and increase amperage.. I'd guess if you go much over 180W you could be blowing fuses.

Good point on the voltage drop. I will see what I find for wiring. If anything, I can run a thicker wire from the drivers foot well to the rear cargo area, once I find the circuit in the vehicle.

 

[luthj]

Here is the blow curve for blue sea atc fuses. Note that it can carry is rated current indefinitely.

 

[Buddha.]

It will be used mainly for powering my laptop

Do 12v laptop chargers exist?

 

[DaveInDenver]

Venting shouldn't be a concern with AGM, and you might need an AGM anyway if you're trying to stash it beneath something (ability to lay AGMs on their side).

Sealed lead acid (AGM, gel) do not normally vent while charging but they can still if they overheat. They are safer but not absolutely safe. They have a valve that will pop open if the pressure builds up in the battery, usually because the charger is too aggressive, there's not enough air circulating to cool the battery or your charger regulation or temperature compensation has failed.

In normal use the amount of hydrogen that vents should be small and normal air movement usually disperses it, so it more something with which to be aware. Its still never bad to have a vent if you put the battery in an enclosed space (for example I see the OP is considering in that cargo space) that may not adequately turn over the air, especially one that may have ignition sources, e.g. switch and relays that create a small arc when operating.

http://www.dekabatteries.com/assets/base/0139.pdf

 

[dreadlocks]

Do 12v laptop chargers exist?

Usually they do, or you can read spec sheet of your AC power brick and make your own that provides same voltage and wattage as it.. gets expensive quick after a few generations of laptops though, more than an inverter cost wise but otherwise its more efficient to convert DC->DC than DC->AC->DC, at laptop charging wattages its really nothing to worry about honestly.. but if your working from camp or full timing it and running laptop all the time the efficiency gains of a direct 12v charger start adding up in the long run.

Glad my latest laptops all use USB-C, its made life alot better to have one outlet that charges two phones and two laptops and a handheld game console

 

[dreadlocks]

Here is the blow curve for blue sea atc fuses. Note that it can carry is rated current indefinitely.

View attachment 512497

of course they will but inverters and batteries are variable, they support inrush currents and while wattage remains amps will rise as battery drains.. a 180w inverter could support 360w for a time longer than it takes to pop a fuse.. a ~35A fuse would never trip under any normal operation but a short, and would trip before the wiring started a fire.. a 20A fuse for a 200W inverter seems like a recipe for nuisance trips IMO.

Murphy's law says that operating a device on a circuit fused below its capability is eventually going to result in a blown fuse, and likely at the worst possible time.