Simple MH Power questions

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Tiercel

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I have a simple two receptacle 400-watt inverter that plugs into the cigarette lighter of my 2000 Chevy Express chassis. It can also be directly hooked to the battery. I have two cigarette lighters that are hot with the ignition on and off. One has a 20 amp fuse and is clearly identified as "cigarette lighter" in the chassis fuse panel. I have not identified what circuit the other cigarette lighter is on yet. I assume that I can plug the 400-watt inverter in and just keep the draw under 20 amps.

It supplies a clean-power picture to my TV which I think pulls less than 1 amp.

Is it safe/legal/advisable to run the generator while the MH is moving?

I am guessing my heater blower and freshwater pump both run on DC power but I have not confirmed that yet.
 

Isaac-1

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Don't confuse amps AC with amps DC, a modern mid size flat panel TV might draw 25-30 watts (I bought a 24 inch smartTV last year which is rated at 25 watts max power draw, 10 years ago the same size non-smart TV would have been 60+ watts). As a rule of thumb 1 AC amp = 10 DC amps for inverter power draw. In this case 25 watt draw is going to be about 2 amps DC. A 400 watt max draw for the inverter would be around 35 amps DC which would blow the fuse on your lighter socket (or likely cause enough voltage sag due to the smaller wires going to the lighter socket that the inverter would shut down before the fuse blew).

p.s. running the generator while you are in motion is ok as long as you are not in some restricted situation like some tunnels, on a ferry, etc.
 

Ex-Calif

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I avoid plugging devices into a socket when they are known to have a potential higher draw. I would avoid plugging a 400W inverter into a 20 amp fused circuit.

I also don't like powering devices like an inverter from a cigarette type plug. I would figure out how to hardwire it in using appropriate sized wires.

I run my generator underway frequently to allow the cabin AC to be on and for riders to run the microwave to make snacks.

In addition to restrictions Isaac notes I also shut it down at fuel stops although it would likely do no harm.
 

Larry N.

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Is it safe/legal/advisable to run the generator while the MH is moving?
It definitely is. We (and many others) often run the genny in the summer so we can run the A/C to keep the coach cool.

I also don't like powering devices like an inverter from a cigarette type plug. I would figure out how to hardwire it in using appropriate sized wires.
I'd agree with that 100% -- too much chance of overloading the lightweight wiring they generally have. And those sockets aren't really designed for a lot of power anyway.
 

Mark_K5LXP

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The max current spec of a "standard" cigarette lighter plug is 10A. Some are now called "power ports" and may be a bit more robust than that, but that would be a case by case basis. In my own experience I've had one plug/socket melt with a 6A draw. I bought some "marine" locking 12V sockets to put in my RV this year and they're all "loose" with most plugs I have. Overall, cigarette lighter plugs bite as far as high power connections due to the wide variations of socket and plug sizes, contact area, spring tension and supply wiring. At a minimum I would test the one you have by connecting a load and measuring both the wiring drop and connection drop. It doesn't take a lot of watts to make things warm when it's a continuous load. The check the box solution is to install a high power connector like a powerpole and save the cigarette lighter for more pedestrian power use like phones or GPS.

Generators are typically OK to use while in motion. Since most things in an RV run on 12V and the engine supplies 12V to the house loads while underway, the only thing the generator would typically power would be the rooftop A/C. I've done it a few times, when temps are over 100 the dash A/C just doesn't have the capacity to cool the whole RV.

Mark B.
Albuquerque, NM
 

Isaac-1

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As an alternative to hardwiring the inverter, most of these have a DC fuse on inverter itself, either a screw off tip on the 12V plug with a glass fuse inside, or a blade fuse mounted on the body of the inverter. You might want to change this out with a lower rated fuse, so it will blow before the fuse panel fuse for the 12V lighter socket. Perhaps say a 10 or 12.5 amp fuse, that way if it blows it will be easier to reach than the main fuse panel. Here is a quick rough guideline to power draw for some recent model flat panel tv's


p.s. my general rule of thumb says don't draw over 75-100 watts continuous from a 12V lighter socket
 

Henry J Fate

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Cigarette plugs are terrible. It's been a standard power source in vehicles only because all vehicles came with a cigarette lighter and it all started from there. If you could go back in time and design a standard accessory power source in vehicles, it would certainly not be a cigarette style plug. Not a chance.

The biggest problem with cigarette style plugs is that many times the plug does not stay in the socket properly. This is a big problem with inverters as the integrity of the connection is very important.

Using the cigarette plug is fine for a temporary solution but if it is going to be a permanent power source, always best to hard wire the inverter.
 
Last edited:

Gary RV_Wizard

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Strongly agree with the others - trying to use a typical 12v lighter/utility outlet to power an inverter is very likely to result in a meltdown or socket or wiring. Rarely are they capable of continuous use at even 7A-10A (DC), and hopefully that 20A fuse will blow before the crappy wire to the socket burns through. Even the best 12v power outlets are usually 15A and that's peak rather than continuous. Hook that inverter to the battery or a primary 12v distribution point.

Feel free to use the generator anytime - that's what it is for. If a tunnel or area has a usage restriction, it will be posted.

Yes, the water pump and furnace fan use 12vdc. So do the circuit boards that control furnace, water heater and an RV-type fridge. This is true even when the RV is plugged to shore power or the generator is running.
 

Tiercel

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I found 2 potential places to hook up a 12v inverter.

The first is under the dinning table bench. This positive and negative (harder to see) come straight off the battery. The battery compartment is directly under the table.

This looks like an easy hook up. I can connect to the positive without even a splice.
 

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DonTom

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Cigarette plugs are terrible.
The European style 12V outlets and plugs work great. They are not the slightest bit flakey.

Where possible, I change to them. I have some now to install in my new RV. Easy to convert to the flakey USA type down the line, with a simple adapter cable, if the flakey USA style is really needed, but I like to start with the European style and convert the plugs as well. They are commonly used on European motorcycles.

-Don- Reno, NV
 

JayArr

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This positive and negative (harder to see) come straight off the battery. The battery compartment is directly under the table.

Looks like a good location but don't forget to add an inline fuse. Calculate the fuse value based on the guage of wire it is coming off of. In a short circuit event the fuse must blow before the wire catches fire. The load, or how much you plan to draw is NOT how you choose a fuse, fuses protect wiring not devices.
 

Ex-Calif

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Here's a DC wiring size chart you may find helpful. For an invertor I would shoot for 3% V-drop sizing. I use mostly 12 as it will carry 99% of any loads I would have on an RV.

However - choose the wire for the distance/load and the fuse to protect the load/wire.

Marine-Wire-2.jpgMarine-Wire-1.jpg
Marine-Wire-3.jpg
 

Isaac-1

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Looks like a good location but don't forget to add an inline fuse. Calculate the fuse value based on the guage of wire it is coming off of. In a short circuit event the fuse must blow before the wire catches fire. The load, or how much you plan to draw is NOT how you choose a fuse, fuses protect wiring not devices.
As long as there is an upstream fuse protecting the wiring, there is no reason not to lower the value of the fuse at the inverter, which will have the side effect of lowering the inverters max output before the fuse blows,but in this case the inverter is likely 4 to 10 times larger than needed to power the TV.
 

Tiercel

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It seems if I have an above adequate wire to the inverter and lower than rated knife fuses in the inverter that an inline fuse is not necessary. The inverter currently has two 20 amp knife fuses. I also cannot see myself plugging much into this inverter except a TV bought within the last 3 years that has a very low draw (As I recall about 35 watts). What other likely things would I use a 400-watt inverter for?
 

Tiercel

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It also seems I could connect to the direct feed coming into the right side of the 12VDC panel.
 

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DonTom

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What other likely things would I use a 400-watt inverter for?
For any item that draws less than 3.33 amps at 120 VAC (or less than 400 watts). All 120 VAC items should say the current draw (amps) or wattage on them near where the AC cord enters to equipment.

IMO, 400 watts isn't much, but will be handy for some small items.

-Don- Reno, NV
 

Tiercel

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Yep, I am very familiar with the UL label designating AMPS or WATTs. I agree that 400 WATTS is not much (this inverter was in the RV when I bought it) but on the other hand, it is surprising how efficient electronic devices have become. Clearly, I won't be running a toaster unless I want to wrap the supply wire around the bread and then sprinkle cinnamon on it to kill the taste of burned insulation. :)
 

John From Detroit

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When figuring the draw of an inverter use 10 as the battery voltage. Yes I know this is not precise but there are several factors that make it way closer to 12 or 14. So a 400 watt inverter can suck 40 amps.. or at least 39.. and on a 20 amp fused outlet both poppa fuse and melt-a-plug

Recommend direct connect.
 

JayArr

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It doesn't matter what you have plugged into the inverter, the fuse isn't for that. The fuse is to keep the wiring from catching fire if the power transistors in the inverter short out. It sounds like the knife fuses will protect from that, the only thing unprotected will be the wiring from the main line to the inverter, if it should chafe or short or the connection comes loose and arcs, and that line you found is connected directly to the battery, then you could have a fire.

Personally I'd be OK with that since I trust my wiring abilities, you have to decide for yourself.
 

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