autoformers for dummies (me)

I suspect that one reason RV parks say NO is that there is information that says NEC says no.

Here is a link

http://www.codebookcity.com/codearticles/nec/necarticle551-1.htm

Note the line You cannot use autotransformers with RVs 551.20(E).

so it may have nothing to do with "power stealing" at all.

Whats not clear is if this applies to the park side or the RV side.

Also, one thing to be aware of with an autotransformer is there is NO isolation provided by the transformer. the input and output sides share a common neutral, unlike a more conventional transfomer with primary and secondarys isolated.

pianotuna wrote:
100 volts X 12 amps = 1200 watts

Output from the autoformer

120 volts x 10 amps = 1200 watts

Your assumption here is basically correct except that the current from the pedestal has actually increased by almost 50 percent from 8.33 amps to 12 amps. and the power consumption has increased from about 833 watts to 1200 watts.

Basic Ohms law states that volts = current times resistance or current = volts divided by resistance. Ohms law has to do with DC voltage but generally remains true for AC circuits as well though there is small differences in the case of inductive and capacitive loads such as an air conditioner.

If your A/C is using 100 volts , then the amperage would be lower than if it was using 120 volts because the resistance of the load will basically stay the same. The amps used is dependent upon the volts applied to the device, even though it is an inductive load instead of a purely resistive one. So if your A/C would normally use 120 volts at 10 amps (1200 watts), the AC resistance of the unit is 12 ohms. If you only apply 100 volts to that 12 ohm device, it would be pulling 8.33 amps (100 volts divided by 12 ohms) not 10 (120 volts divided by 12 ohms).

So assuming pure efficiency and no loss across the autoformer. If you have the A/C running pulling 8.33 amps at 100 volts (100 volts divided by 12 ohms), you are also pulling 8.33 amps from the power pole (833 watts in and out of the autoformer). If your autoformer increases the output voltage to 120 volts on the output, the A/C will now pull the 10 amps it likes and use 1200 watts of power. Since the power pole can only supply 100 volts that means it has to pull 12 amps to supply the 1200 watts to the output, increasing the current from the pole by 3.67 amps.

I wouldn't call that stealing power, just trying to get what you are paying for. However, the increased current draw of the autoformer to achieve the 120 volts just exacerbates the power problem of the campground. The more current drawn across the distribution system, the lower the voltage for everyone on that system, the more the autoformer has to increase input current to achieve output voltage. Since the system can only supply so much power, if everyone was using an autoformer, it would most likely blow the main distribution breakers due to the perpetually increasing current draw.

So to restate your assumptions:

Output needs 120 volts x 10 amps = 1200 watts
Input to autoformer needs 100 volts times 12 amps = 1200 watts
Increase in input current is = 12 amps - 8.33 amps = 3.67 amps

TUNA TUNA
WHERE DID TUNA GO???!!!!!
ARE YOU SITTING BY THE POOL GIGGLING???

TUUUUNNNNNAAAAAA!!!!!!!!!!

:)

Hi rjxj,

Pretty much all campgrounds are 30 amps. That means energy at the source is 3600 watts. That is what I am paying for.

Using at extra 48 watts on 1200 watts out of a possible total of 3600 watts would not make much if any difference to the campground. Nor should it inconvenience anyone even if every RV had and autoformer.

rjxj wrote:
Not being a smart a-- but let me ask this, could everyone in the campground run an auto former at the same time? I'm not real worried about it and not going to use one but it is interesting because there is only so much energy available at the source. Not that you would ever see everyone doing it but just in theory. I dont care if you use one or not and I believe I have even joked with you about it before. I do agree that if we are paying for X we should be getting X.

Yet in another way the whole issue doesn't surprise me, I mean the RV is cheesy as heck so why would where it connects to be any different. :)

Naio wrote:
Ok, so it is costing the cg $80 per day. Divided by 500 sites, that is 16 cents per site. If they truly can't afford that overhead, I am pretty sure Mr Tuna would not mind paying the extra 16 cents.

:R

So..

You ARE saying that you would not mind your next door neighbor and their next door neighbor and next one and next one and so on to connect an extension cord to YOUR home and "borrow" some power and YOU pay for them to live scott free????

THAT IS WHAT YOU ARE SAYING :h

Obviously you have never been in the position of owning or operating a business..

A business MUST make some sort of "profit" in order to continue and that goes for campgrounds.. Electricity in campgrounds is not "free" to the campground. They MUST pay for it and at COMMERCIAL RATES and as I mentioned, commercial power rates ARE more expensive than residential (in the USA, can't say about Canada but I would expect similar).

"borrowing" a few extra watts to you might seem trivial but in the end of the day that $80 extra they pay WILL affect the EMPLOYEES, the SERVICES the campground provides to YOU and others.

Sometimes I am extremely embarrassed owning a RV knowing just how selfish MOST CAMPERS are and this forum seems to bring out some of the most selfishness that I have ever seen.

It is the reason why some campgrounds METER their lots and the ones that don't meter, raise the rates.. Then folks come here and whine about how expensive the campgrounds have gotten :S

You do also realize the more power drawn, the lower the voltages get for everyone??? Yep, makes a bad thing even worse when you are selfish..

Hi Triker33,

My comfort level for running the roof air is 108 volts. The cut out on the Progressive industries is 104 and the Surge Guard is even worse at 102 volts, so those devices are essentially useless to me.

I'm using a Mexican autoformer called a "Sola Basic". For voltage it has three levels of boost and one level of buck 110-->121, 100-->121, and 90-->109 volts. Buck is 135-->125 volts.

Testing on the bench showed it performed as advertised.

Real life testing showed similar boosting with between 1300 and 2995 watts of load.

Because of the way I wired the Sola unit, I can more than double the surge protection of the PI and SG units. I'm currently at 2400 joules and 40,000 amps.

Triker33 wrote:
A autoformer won't boost you from 110 to 120V most don't have that much boost.
If you have a surge protector with the low & high cutoff you won't be running your roof AC on lower power then it can handle.

I have had a Hughes(OK), Frank's(Junk) and now no longer available the best of them all a Power Master(very,very good)autoformers all 30AMP.

Power Master Autoformer it has 12% boost.

Hi Gdetrailer,

The campground always has the option to install meters. If they don't then on a thirty amp service I'm paying for 3600 watts. So long as I don't exceed that I'm not inconveniencing anyone, nor stealing anything.

I don't think campground owners understand the difference between the 30 amp and 50 amp too well. One of the local campgrounds charges an extra $2 per day for 50 amp. 3600 watts vs 12000 watts. I think they'er nuts to shoot themselves in the foot that way, but no one is "forcing" that on them.

BTW privilege????, I'm the customer? They offer me service for which I pay for. They should deliver.

Gdetrailer wrote:


See the area I outlined in bold.

Folks that say autoformers are "stealing" or "cheating" the campgrounds power ARE technically correct.

Since a autoformer is not lossless there is 48W MORE power being drawn from the input than what you get from the output..

Put it this way, IF the campground had a power meter on your site YOU would be paying for 1248W but only getting 1200W worth of energy to use..

Now multiply that 48W x the amount of camping spots and it will be pretty apparent that the campground WILL have even a larger loss in costs..

For instance say the campground has 500 spots and EVERYONE decided to use a autoformer, the campground will pay for an additional 24Kw of power per hr use.. for 24 hrs that would be 576 Kwhrs per day the campground would have to pay for!!

My home electric cost me about $.07 per Kwhr (some places pay $.11 per Kwhr) at a residential rate.. That would be a $40.32 per day loss for the campground..

HOWEVER, with electric power you do need to understand that BUSINESSES do not pay residential rates.. They pay at COMMERCIAL RATES which ARE MUCH HIGHER.. Typically commercial power will cost about DOUBLE RESIDENTIAL RATES!

That would mean that my example would now be about $80 PER DAY the campground would pay..

It is for that reason some campgrounds have rules about autoformers..

Put yourself into the shoes of a business owner.. You would not be happy with having your business costs go up.. You would have to take action somewhere to trim costs OR RAISE CAMPING RATES..

Use only what you need.. Don't waste power, water, ect by abusing privileges..

Hi road-runner,

Unfortunately 120 volt AC motors draw more and more amps as voltage drops. It damages the motor and the damage is cumulative. So that part of the "stealing" is incorrect.

I'm drawing more amps--but less than the 30 amps I've paid for. Personally, I limit my load to 24 amps because that is all that a 30 amp connection is supposed to do on a 30 amp line.

road-runner wrote:


Argument in favor of "stealing": Because of low voltage, every rig will draw fewer amps that they would if the voltage were higher. With the autoformer you've created an unfair advantage for yourself compared to the other campers, and you're drawing more amps than you would without the autoformer.

If you chose the stealing argument, then you have to say that somebody who runs their water heater or fridge on electric is also stealing from those who run it on propane, or somebody who chooses to run the air conditioner is stealing from somebody who doesn't. All IMO of course.

Hi Bumproad,

Yes, they do. However, I believe that is because the camp owners are terribly ill informed about their electrical systems.

I've even been to one park that forbid the use of air conditioners.

Bumpyroad wrote:
I have read here that some campgrounds forbid their use.
bumpy

Hi ktmrfs,

Thanks for the code link. It does define an RV as "temporary" living quarters. I'm full time, so I guess, technically, this regulation doesn't apply to me.

As to there being no isolation from an autoformer, are you saying there IS isolation when I simply plug into the pedestal? That seems a bit of a "red herring" to me.

ktmrfs wrote:
I suspect that one reason RV parks say NO is that there is information that says NEC says no.

Here is a link

http://www.codebookcity.com/codearticles/nec/necarticle551-1.htm

Note the line You cannot use autotransformers with RVs 551.20(E).

so it may have nothing to do with "power stealing" at all.

Whats not clear is if this applies to the park side or the RV side.

Also, one thing to be aware of with an autotransformer is there is NO isolation provided by the transformer. the input and output sides share a common neutral, unlike a more conventional transfomer with primary and secondarys isolated.