autoformers for dummies (me)

Gdetrailer, you seem to have missed the part of my post where I advocated PAYING FOR the extra 16 cents worth of electricity.

Why does that not surprise me?

Hi accsys,

Unfortunately motors draw more and more amps as voltage drops. I do monitor wattage and have seen the roof air draw 1900 watts (partly because of lousy voltage at the campground). So your argument for lower amps at lower voltage for motors is dead wrong.

If I am paying for 30 amps (3600 watts) and using 12.43 amps (1243 watts) I am not overloading or inconveniencing anyone in the campground.

I don't understand how you are getting from 8.33 amps to 12 amps.

8.33 amps @ 120 volts would only be 999.6 watts not the 1200 that the roof air starts out at.

accsys wrote:
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

pianotuna wrote:
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.

as far as isolation, normally that is not an issue since the transformer supplying the pedistal has isolated primaries and secondaries.

The caution was aimed at people who think a autotransformer is also an isolation transformer. It can be a big suprise! Again, for RV use I don't think it posses any issues.

pianotuna wrote:
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.

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..

Have you ever thought about "informing" the campground owners that you are having issues with extremely low voltages?

And that those extremely low voltages can and will destroy your electrical equipment??

And that the campground owners CAN contact their electric provider for FREE assistance to determine if the problem is the electric co side OR the campground wiring??

I know myself when I first moved into to my home, I upgraded my electrical system from 60A to a 200A service entrance..

Then had a whole house A/C put in..

Then every time the A/C turned on my Sat receiver would shut down and reboot..

Called the Electric co, they sent out a Linesman who checked the voltage at my new 200A panel, then the voltage at the pole pig..

Came back and told me the problem WAS on the electric co end.. The voltage was sagging on the electric co lines feeding the pole pig that served my home. The lines had never been upgraded and over the years many more homes had been built and connected to those lines.

Two weeks later, the power company installed three HUGE booster pole pigs about 4 miles away from my home..

ONE phone call from ONE home owner (me) solved a major low voltage issue for at least 1,000 customers and a few businesses past the boosters.

Using an autoformer may "fix" your problem but in the end it makes it worse for everyone else.

The problem may not be all the campgrounds fault, it could be the electric co fault.. The electric co WILL attempt to correct the problem IF they are aware of the problem AND it is their equipment casuing the problem.

Put in a AC volt/amp meter into my TT for this year.. The campground we like had a rock steady 121V-122V, and that was with blazing hot temps this year hovering right under 100 F..

Granted the campground was only half full when we were there but I can say for the many years we have been there, never had a brown out or loss of power.

Stopped at my cousins home.. 111V-116V.. Campground voltage WAS better regulated than a residential outlet.

If YOU are not part of the solution, then you ARE part of the problem..

One more thought has occurred to me.

The national electric code requires campgrounds to have at least 41% of the total capacity of any loop. That means for a 3600 watt connection (30 amps) everyone can draw 1476 watts. As I'm only planning on 1248 watts, I'm well below that number of watts.

The other side of that coin is the 24 amp limitation that I impose upon myself. That takes the number down to 1180 watts assuming the 41% number is calculated in. However, the Magnum hybrid inverter/charger will pick up those extra watts from the battery bank if need be.

My solar system, before I had the autoformer, when I was forcing the Magnum to do not just load support, but voltage support, was contributing most of the extra wattage needed.

I think we pay dearly for renting a tiny space. I'd far rather boondock.

Gdetrailer wrote:

pianotuna wrote:
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.

Gdetrailer wrote:


..

Have you ever thought about "informing" the campground owners that you are having issues with extremely low voltages?

And that those extremely low voltages can and will destroy your electrical equipment??

And that the campground owners CAN contact their electric provider for FREE assistance to determine if the problem is the electric co side OR the campground wiring??

I know myself when I first moved into to my home, I upgraded my electrical system from 60A to a 200A service entrance..

Then had a whole house A/C put in..

Then every time the A/C turned on my Sat receiver would shut down and reboot..

Called the Electric co, they sent out a Linesman who checked the voltage at my new 200A panel, then the voltage at the pole pig..

Came back and told me the problem WAS on the electric co end.. The voltage was sagging on the electric co lines feeding the pole pig that served my home. The lines had never been upgraded and over the years many more homes had been built and connected to those lines.

Two weeks later, the power company installed three HUGE booster pole pigs about 4 miles away from my home..

ONE phone call from ONE home owner (me) solved a major low voltage issue for at least 1,000 customers and a few businesses past the boosters.

Using an autoformer may "fix" your problem but in the end it makes it worse for everyone else.

The problem may not be all the campgrounds fault, it could be the electric co fault.. The electric co WILL attempt to correct the problem IF they are aware of the problem AND it is their equipment casuing the problem.

Put in a AC volt/amp meter into my TT for this year.. The campground we like had a rock steady 121V-122V, and that was with blazing hot temps this year hovering right under 100 F..

Granted the campground was only half full when we were there but I can say for the many years we have been there, never had a brown out or loss of power.

Stopped at my cousins home.. 111V-116V.. Campground voltage WAS better regulated than a residential outlet.

If YOU are not part of the solution, then you ARE part of the problem..

And on the other hand, I have called my local power company three times about our power problem, it hasn't been resolved and I've never heard back from them. The power will flash on an off a couple of times. Then all of the yard motion lights light turn on and stay on until I physically turn them off. This happens a couple times per month.

Because of no action or interest from the power company, I've been changing the motion lights from the old 150W bulb units to new LED lights so that when they stay on for weeks on end while I'm traveling, they don't burn so much power. I think you just got lucky.

Bill

Hi Naio,

In June I was at a campground and did not yet have the autoformer. It was hot and there was the usual voltage sag (103 with only the roof air running). I used the Magnum hybrid inverter/charger load support feature and found that I could "force" it to do voltage support. It generally took about 200 watts from the battery bank to do this. My solar system was replacing those watts. So, in a sense, I should have been billing the campground for about 1.2 kwh's of "my" energy. Or about......16 cents!

I do not plan on advertising the fact that I'm using an autoformer--just as I did not advertise that I had to use the hybrid feature of the Magnum to support their "code minimum" wiring.

Naio wrote:
Gdetrailer, you seem to have missed the part of my post where I advocated PAYING FOR the extra 16 cents worth of electricity.

Why does that not surprise me?

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.

NOT completely true
there are autoformers that are isolation transformers
just because a $400 Hughes is not Isolation , does not mean they don't exist

Sola makes them so do others

48watt loss, so watt? pun in intended
the loss is on the output side of the pedistel , that the camper is paying for
the camper paid for his site, he still can't use any more power, than any body else, hes getting the same volts at the same amps, and if the breaker trips, he has to turn something off to reduce his load
all he is doing is protecting his A/C and appliances from the low voltage
and giving up a few watts of power to external heat , instead of inside power use
I never ran an absorption fridge on electric, unless i ran out of propane,
it was always LP even if plugged in someplace with full hookups, and i very seldom ran out of LP
there are many people here that run the RV absorption fridge on electric 300+watts plus your HW and the A/C and you want throw stones at somebody that uses an autoformer to protect his Appliances ?
i know some of you have residential fridge, like me
are you going to say you DONT want to protect that fridge from low voltage ?
my fridge is ALWAYS protected from low voltage, its on an inverter,
it the converter and A/C that will suffer IF i camp where there is low voltage (and before somebody pipes in , my inverter does not have 'pass thru', i do have an external TS i added so my generator will power the fridge when running, but on the few times i use shore power, that TS is NOT in use)
I don't use hook ups very often, but IMO somebody with an autoformer is NOT stealing anything
110v 30amps = 3300va, 100v 30amps 3000va
when the voltage goes low your available power goes low, you cannot get anymore than 30, and actually a little bit less
resistance heat devices will use less power, AKA fridge heating element and water heater, you might not notice the difference in your shower, but you sure will in your fridge, and you are going to wish you had an autoformer, unless you switch the fridge to lp so the beer stayed cold and the ice cream hard

this power stealing debate is almost as useless as the dodge chevy ford truck debate

pianotuna wrote:
Hi accsys,

Unfortunately motors draw more and more amps as voltage drops. I do monitor wattage and have seen the roof air draw 1900 watts (partly because of lousy voltage at the campground). So your argument for lower amps at lower voltage for motors is dead wrong.

I cannot agree here. The motor may try to pull more amps but if it isn't available from the pole it will not succeed, hence the problems with running A/Cs on low voltage. How are you monitoring wattage?

If I am paying for 30 amps (3600 watts) and using 12.43 amps (1243 watts) I am not overloading or inconveniencing anyone in the campground.

What you are paying for bears no relationship with what happens to the rest of the campground

I don't understand how you are getting from 8.33 amps to 12 amps.

I explained that in my original post - perhaps you didn't read it with an open mind? Put an ammeter in line with the input power and you will see the current rise as you increase the voltage on the output of the autoformer

8.33 amps @ 120 volts would only be 999.6 watts not the 1200 that the roof air starts out at.

If you are starting out at 100V, your A/C is not starting out at 1200 watts, no matter how hard it may try

Bottom line is that an autoformer will cause higher currents drawn from the pedestal than would be drawn otherwise - the additional power has to come from somewhere.

pianotuna wrote:
Hi Naio,

In June I was at a campground and did not yet have the autoformer. It was hot and there was the usual voltage sag (103 with only the roof air running). I used the Magnum hybrid inverter/charger load support feature and found that I could "force" it to do voltage support. It generally took about 200 watts from the battery bank to do this. My solar system was replacing those watts. So, in a sense, I should have been billing the campground for about 1.2 kwh's of "my" energy. Or about......16 cents!

I do not plan on advertising the fact that I'm using an autoformer--just as I did not advertise that I had to use the hybrid feature of the Magnum to support their "code minimum" wiring.

Naio wrote:
Gdetrailer, you seem to have missed the part of my post where I advocated PAYING FOR the extra 16 cents worth of electricity.

Why does that not surprise me?

Sounds fine to me. As I said on the prev page, every rig uses cg services differently. Some use showers, some use AC, some use dump station... I personally feel confident that your 16 cents is not going to put anyone out of business when they are on the losing end, nor keep them solvent when they are on the receiving end.