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RV-Dreams.com Home -> RV-Dreams Community Forum -> RV Accessories -> autoformers
Post Info TOPIC: autoformers
BiggarView


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I have read recently that rules  or regulations are in the works for banning the use of autoformers.

The logic given seems reasonable, while an autoformer will help protect the user's household or Rv circuitry, it does so pulling pulling amps from the same circuit that others are drawing power from thus cascading the power issue until it becomes catastrophic down the line.

I've also read tha that some CGs are already banning the use of them.  It seems high demand in CGs especially on hot days when A/Cs are running full tilt is more than CG wiring can withstand when you now add in more and more residential fridges in RV and other power hungry appliances that did not really exist in the RV world only a couple of decades ago when many of these CGs were built and have not been subsequently upgraded  to meet higher demands. 

The question is therefore, given the above.... any thoughts on the use of autoformers from actual users?



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Dutch


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The NEC section 551 on RV's and RV parks has a one sentence entry about autoformers (autotransformers) in the "Combined Electrical Systems" section, 551.20(E), that simply states: "Autotransformers shall not be used."

No explanation is given...

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bjoyce


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I have heard that regulations are coming for at least 20 years and so far, nothing. We have had one since around 2003. My experience is that few RVers have autoformers, so talking about a group of RVers causing a catastrophic failure doesn't make sense to me. Plus the problem is mostly with older campgrounds with only 30AMP service. Realize that many newer campgrounds have transformers with autoformers built-in, it is old World War 2 technology and on the DC side is used all the time, including MPPT solar charge controllers. We have seen campground voltage climb over 130 volts in some places due to their transformers autoforming.

There are a very few campgrounds that mention autoformers in their rules and my experience is these are places to avoid, since they have substandard wiring. My experience is most 50AMP has adequate voltage, but about 25% of 30AMP only campgrounds have voltage issues at least some of the time.

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bjoyce


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Dutch wrote:

The NEC section 551 on RV's and RV parks has a one sentence entry about autoformers (autotransformers) in the "Combined Electrical Systems" section, 551.20(E), that simply states: "Autotransformers shall not be used."

No explanation is given...

 Interesting.  Realize that this is for the RV park wiring, not the RVs themselves.  Since I have been at RV parks that use autotransformers, either they are not to code (which is much more common than you might imagine) or were put in when the code was different.  I can be quite obvious when the boost kicks in if you have a voltage meter visible.  I have also seen the campground "electrician" adjusting a transformer, so it might not be an autotransformer, just a person doing the same thing.



-- Edited by bjoyce on Friday 31st of January 2020 08:57:32 AM

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arcaguy


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I think this autoformer ban is a red herring. How much amperage can you draw from a 30 or 50 amp circuit? 30 or 50 amps if it is protected by the properly sized breaker/fuse. Does the circuit breaker care if the power is being used by your microwave, A/C, refrigerator or an autoformer? I'm thinking no, but I may be wrong.

While I realize that an autoformer will draw some power just to operate in standby/monitoring mode I don't think that it is substantial. In my book, the real problem is insufficient power being supplied by the park or their upstream utility. An autoformer does not cause this problem, it solves it for me. The solution to the problem is likely within the park's power, but maybe not their budget. I don't think it's reasonable for a park, or a utility for that matter, to ask me to risk my appliances due to their lack of sufficient electrical power. Just my thinking on this subject, and I may be wrong.

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bjoyce


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Another thing, confirmed by a couple RV techs, is that an air conditioner will use more watts of power (watts is volt times amps) when on low voltage than on normal voltage. So a RV using an autoformer will use less electricity, less watts, to run their air conditioner than their neighbor not using an autoformer on low voltage. Plus the air conditioner should last longer due to not being stressed as much. This mostly applies to air conditioners, but low voltage can cause many electrical devices to behave badly and/or fail prematurely.

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Journal at http://www.sacnoth.com
Full-timing since July 2003
RonC


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I am a small sample size, but we’ve been full time since 2016. We’ve stayed in many RV parks ... maybe 100 or so ... all over the country including Canada. We’ve used a Hughes Autoformer since day one. I have never encountered a park that prohibits autoformers, or even mentions them. I would bet that most do not even know what an autoformer is, or what it does. Just my $0.02 FWIW.



-- Edited by RonC on Friday 31st of January 2020 12:06:59 PM

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LarryW21


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Let’s understand what some in the RV Park business are saying...we have electric sites but if you decide to pay extra for an electric site you may receive electricity that could harm your RV...LOW voltage...and you can’t do anything about it such as attaching an autoformer and we won’t repair your RV or refund any of your money.



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Dutch


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bjoyce wrote:
Dutch wrote:

The NEC section 551 on RV's and RV parks has a one sentence entry about autoformers (autotransformers) in the "Combined Electrical Systems" section, 551.20(E), that simply states: "Autotransformers shall not be used."

No explanation is given...

 Interesting.  Realize that this is for the RV park wiring, not the RVs themselves.  Since I have been at RV parks that use autotransformers, either they are not to code (which is much more common than you might imagine) or were put in when the code was different.  I can be quite obvious when the boost kicks in if you have a voltage meter visible.  I have also seen the campground "electrician" adjusting a transformer, so it might not be an autotransformer, just a person doing the same thing.


-- Edited by bjoyce on Friday 31st of January 2020 08:57:32 AM

The specific section I quoted refers to the combined voltage requirements of RV's where both 12-volt and 120-volt systems coexist as shown in 551.20(A) quoted below.

551.20 Combination Electrical Systems.

(A) General. Vehicle wiring suitable for connection to a battery or dc supply source shall be permitted to be connected to a 120-volt source, provided the entire wiring system and equipment are rated and installed in full conformity with Parts I, II, III, IV, and V requirements of this article covering 120-volt electrical systems. Circuits fed from ac transformers shall not supply dc appliances.

(B)...

(C)...

(D)...

(E) Autotransformers. Autotransformers shall not be used.

(F)...



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Dutch

34' 2001 GBM Landau Class A

2011 Toyota RAV4 4-down toad
bjoyce


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Dutch: Since MPPT solar charge controllers are autotransformers, I guess a lot of people are in violation.

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Bill Joyce,
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Journal at http://www.sacnoth.com
Full-timing since July 2003
BiggarView


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The only way an autoformer cound supply power to a DC appliance is for it to be DC autoformer. Since an autoformer we are talking about here is an AC device supplying AC power to a charger(or a converter) or inverter/charge that passes it converted to DC to a DC bus, it seems to me that this definition does not apply. Somewhere in the line from AC source to DC output to a DC device, some kind of transformation from AC to regulated DC seems to require a device that massages the power to be consistent or "autoformed" or nothing would work reliably or so it would seem to me. Just trying to understand the use and function of an autoformer for RV applications.



-- Edited by BiggarView on Saturday 1st of February 2020 09:19:05 AM

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Brian, Cindi & Josie (our fur baby)
2017 RAM 3500 Laramie 4x4 CCLB, CTD, Aisin, B&W hitch, dually
2020 Keystone Montana Legacy 3813MS w/FBP ,MORryde 8k IS, Kodiak disc brakes, no solar  YET!
Dutch


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bjoyce wrote:

Dutch: Since MPPT solar charge controllers are autotransformers, I guess a lot of people are in violation.

 I suppose they are if it's applied to the low voltage system. I'm not advocating for either side of the issue, just stating what the NEC says about it. I have been in parks that used it as a justification for banning their use though. 



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Dutch

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2011 Toyota RAV4 4-down toad
LarryW21


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Guilty as sin, Bill. What’s the fine?

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