Voltage conversion for RVs

I have never seen such a thing... I have seen more systems that use inverters to crank the 12V accessory power up to 120VAC and use 120V accessories both on the road and on shore power. But there's no reason not to build such a thing.

Power is always conserved, and power is current times voltage. So if you take a 30A 120V circuit, step it down and rectify it, you should be able to get 300A at 12V, if there are no losses. This being the real world, 250A is all you can reasonably expect. But that is a hell of a lot of power.

--scott

You are correct, if you limit your phrase "accessory circuit" to the RV furnishing -- house lights, water pump, furnace blower, etc. -- and not to the 12v system normally used with the engine and chassis.

GB in NC

Most RVs have one. The converter takes the 120 VAC and converts it to

12 VDC for the 12 volt house circuits (lights, fans, furnace, water pump, etc.) and usually includes a charger for the on board 12 volt batteries.

Alex

What they mean is that they will convert 120 vac to 12 vdc up to 55 amps.It draws about 6 amps of ac power to do this. I don't think you'll ever have to convert all 30 amps of ac power to dc that would require something the size of stick welder, it would make close to 300 amps.

Tinker

The 55 amp would relate to the 12v output. Thusly, you'd have about 5.5amp on the 120v input side.

s

Never been around RV's, have ya?

So - This is a correct assumption.

As another posted, you will not convert all of a 120V 30A feed to 12VDC with anything smaller than a welder. You can count on getting what ever the converter is rated to do.

It is not lost (expect a small part as heat), but you will only get what the system can use.

AC power is voltage times current times the cosine of the phase angle between the voltage and current.

By adding a capacitor to the load in your house it is possible to make the power meter read zero and still power your house.

Yep, when you have a phase difference between current and voltage ( a reactive rather than pure resistive circuit), power is not what would be expected by the resistive example (Ohms law).

I am told that, at least in the early days, the old style power meter could also register incorrectly excessive consumption of power for the same reason. I dont know whether the meters are now better able to reflect a true value, or not.

volts times amps equals watts. Output watts equals input watts times efficiency. Apply some seventh grade algebra: Aout = Ain (Vout/Vin) * Efficiency.

120V * 30A = 3600W. w/ 75% efficiency, expect 2700 watts out. That's 12V @ 225 A.

This is correct but basically irrelevant to the subject at hand where we can basically assume everything is real power.

This seems like a good way to get a massive surcharge in your bill for having a reactive load (which the power company WILL do).

--scott

Apparently the new meters are quite sophisticated. Here's a device for sale that reduces power factor and your utility bill:

The old meters could only read real power not reactive and could be tricked.

There are still ways to get AC power into your RV for free. One could wind a large coil on the perimeter of the roof and park close (but asymetrically) to power lines and couple in power that way.

A friend of mine had a set of copper ground rods driven in under high tension lines and another set several hundred feet away from the lines. He could pull quite a bit of power from it, enough to light a shed and some lawn lights.

In a typical house, there is no such thing as 120 volts 30 amps. the biggest breaker in my power box for 120 volts is 15 amps. There might be a a 30 or 40 amp breaker at 240 volts for the stove dryer or air conditioner. If you need 12 volts when you are out camping then a battery charger should keep a 12 volt auxilary battery charged up. I have even seen some people use a solar panel to keep the extra battery charged when camping.

A neighbor across the street from me has five solar lights along each side of his sidewalk.Each one of the lights has a solar cell on top of the lights.During the day light hours the solar cells keep the batteries charged up and during the night time hours the lights are shining all night long.I am thinking the next time I go to the store, I will buy two or three solar lights.I think they would make good emergency lights to use in my house if the power goes out.

My brother in law owns a Pace Arrow motorhome.I am sure he knows more about motorhomes than I do. cuhulin

Go to the breaker aisle at home depot or lowes and LOOK at the breakers. The only reason there is no such thing as 120V 30A in your house is nobody needed a circuit of that rating. I have several in my house, not the least of which is the one my RV plugs into!

I thought RORT got bad sometimes but, Alt.RV makes it look positively sane. Biggest collection on morons I have ever seen!

HD Matt wrote in news:311020071334271895% snipped-for-privacy@multiprintinc.comnospam:

Hmmm - your unit must not be wired for 50A @ 240V like mine is...

For that matter, you must not do much heavy welding or machine [lathe, mill, etc.] work either...

Since a 30A @ 240V breaker is actually 2 30A @ 120V breakers that are "twinned", take a closer look at those used for Central Air Conditioning systems. (Some of these are wired for as much as 100A - especially those in "all-electric" houses that use Electric Central Heating. [BTDT])

Only lately - since the TROLLs moved in - but, for the most part, this NG has, usually, been more polite.

Killfile the TROLLs and things get a lot quieter.