12V appliances and 12V outlets

Searched the forum, and didn't find anything recent talking about this, so here goes

  We're just starting to take trips w/ our "new to us" 22' 4winds Class C, and I've been thinking of all that 12V juice going to waste while I drive (and don't want to run the generator for hours on end while driving). 

  After 6 years of cross-country roadtrips (us+4kids) in a minivan, we're used to using a portable cig lighter inverter that puts out <=400watts, to run a portable DVD player (2 screens) laptop, camera + phone chargers, etc.  I plan on using this same inverter to run a DVD player (~50 watts) and 32"lcd (<=110watts) while we're driving, plus laptop, phone&camera chargers, so I don't need to run the generator all day long.  When I tried out the TV installation on it's maiden voyage, I learned not to try to power the TV from the inverter while idling.  Now driver's side cig lighter won't work (gotta find that fuse)

  I don't have any 12v outlets other than the 2 cig lighters in the cab, which surprises me.  A lot of items I use can be powered either way, and I figure, why invert & rectify from DC-->A/C-->DC?  So...

Has anyone out there added 12v outlets to their rig? 

Anyone using 12v appliances?  What works well, what doesn't?  I understand I need to add up wattages and stay under the amount my inverter can safely maintain... here are some 12V things that are native DC, I plan to use from cig lighter outlets, or something better I may rig up:

Both cell phone chargers
kids Gameboy charger
1 of our DVD players
laptop power (yes, most have a cig lighter adaptors you can order that removes the need for the DC-->A/C-->D/C conversion game)
any small home appliance that has a "wall-wart" rectifier that will accept 9-15V DC in, can be jury rigged to use a cig lighter, provided it uses few enough watts
of course, my trusty portable 400W inverter we used to use in our minivan

I'm surprised you have a 400 watt inverter that will plug into a cigarette lighter.  The socket supplied by the chassis manufacturer is usually rated at less power than that - either 120 watts (10 amps) or 240 watts (20 amps).

Pull more power than that and yes, you'll pop a fuse.  Don't put in a bigger fuse or you'll overheat the wiring.

The other issue is the cab outlets, if they're the stock ones provided by the chassis manufacturer, draw power from your starting battery, so you have to be careful how you use them when the engine is not running.

The problem with the inverter shutting down while the engine is idling is from low input voltage.  When you try to pull heavy current through a small wire, you lose voltage.  At idle, the alternator is putting out less voltage and when you combine that with the voltage lost through the wire, the inverter thinks the battery is drained and shuts itself off.

The solution is to add a dedicated inverter outlet with short, thick wiring running directly to your house battery.  It's best to put the inverter within a short distance of the battery (to minimize the wire losses) but with that relatively small inverter you might be able to get by putting it next to your house DC fuse panel.  Then extend the 120 volt side to where you need it.

Most 12 volt appliances suffer from the limited power available through the cigarette lighter plug.  The socket itself is limited to a maximum of 240 watts, and as you found out some are even lower than that.  Anything that produces heat will have severely limited performance.  A typical 120 volt frying pan or portable electric oven uses about 1200 watts, for example.  Same for electric hair dryers.  The 12 volt versions just can't deliver enough power to be effective.

Yeah, I definitely need to start up the generator for larger appliances, like the A/C & microwave already, but this handy 400W inverter has really kept on tickin!  I've used it for 15 years in 4 vehicles, some one gave it to me who got it for free and didn't need it anymore.  I usually used it at 100w or less on long roadtrips.  I need to get a KillaWat and measure my 32" LCD at top white output and make sure.  I won't try it again off the highway tho.  I don't want to run the generator for a 2 hour movie while we're on the highway.

I have a 400 watt inverter and I have it connected directly to the batteries and it is located as close to the batteries as possible, less than two feet away.
You should not try and run the TV from a 400 watt inverter plugged into the cigarette lighter and run a DVD player and other items. That is drawing too much current and it will and did blow a fuse. 

You will need to install the inverter close to the batteries and keep the 12 volt wires as short as possible. Then you can use longer 110 volt wires to run to your devices.

Yes, Lou, my 400 watt inverter came with both a plug for the cigarette lighter and with wires to hook it up directly to the battery that were too small. I went and got heavier gauge wires and connectors and hooked it up properly.

No argument from me, Tom.  Hooking it directly to the battery is the way to go.

I just wanted to point out that it can also work wired to the rig's power panel.  Not as well as a direct battery hookup, but maybe good enough to run the TV and VCR.  At least that's what I've been doing for the past few months.  I know, it's just laziness on my part. :

That 12v really isn't free power either. Every amp you pull from the alternator increases the alternator's horsepower needs and the engine has to work harder. There is no free lunch.

true, but when you're driving at a steady 65 all day, it's a LOT cheaper coming from your alternator than running your generator at min draw all day.

In my rig I have 12v power adapters for both laptops and the phones.  I have a little cig lighter inverter that we use to run a curling iron (90w) and the electric beater.  Next time I get a cordless drill I'm going to get a 12v charger for that too.

Those are the only electrical devices we have that aren't built in, except for a 1500w heater we use in the winter.

but when you're driving at a steady 65 all day, it's a LOT cheaper coming from your alternator than running your generator at min draw all day.

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Are you sure?  My 7.5kw genset uses 0.13 gal/hr with little or no load, and a couple hundred watts is "no load" on a generator that size. Could you even tell if your engine was using an extra 0.1 gal/hr of fuel? I think not.  Most people just assume that the generator uses a lot of fuel and the engine only a little, but the known facts indicate otherwise.

Gary RV Roamer said:

Most people just assume that the generator uses a lot of fuel and the engine only a little, but the known facts indicate otherwise.

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That was me I had no idea an RV generator could use so little.  Your's is gasoline, as I assume, not deisel?  I have another generator (not for RVs) I used after Hurricane Ike that was 3.6 kw, but I was pouring a half-gallon an hour into that thing.  'course, it was running a lot, too.

Mine is diesel, but gas gennys don't use a lot more. For motorhome mounted gensets, 0.5 gal/hr @ 50% load is a fair estimate, whether gas or diesel, large or small. At less than 10% load, 0.1-0.2 gal/hr is typical.

My guess is your Hurrican power needs were at  least 50% load and maybe higher.

Our older motorhomes usually had one15 amp "Cigarette Lighter" outlet that could handle a heavier load butour current "power" outlets usually will not carry that kind of load.

I had to run a dedicated wire from the chassis bus just below the driver's seat to power an inverter for my laptop.