Autoformers

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tndal

tndal

Member
Joined
Jul 3, 2011
Posts
12
Location
Smyrna,TN
Anyone using an Autoformer?  thinking of getting one due to low voltage issues at local state parks, thoughts???
 
I have a 30A autoformer that I use when necessary.  It was a particular park that we were at for several months which necessitated the purchase.  It has rarely been used since.

Don't listen to those who claim that somehow autoformers let you "steal" power from other campers.  The autoformer doesn't change the fact that the breaker on your pedestal will only allow 30A or 50A to go through it.  The autoformer can't "make" the breaker give you any more power than it is rated at.
 
tndal said:
Anyone using an Autoformer?  thinking of getting one due to low voltage issues at local state parks, thoughts???
Click to expand...

I use a Hughes 50 amp.. Following observations:

Some campgrounds have it in the rules "NO AUTOFORMERS" This includes the one I'm parked at as I type this though I've seen them and no complaints from management.

I have one site I spent half a summer on and my wife told me I'd be unhappy with the power cause the voltmeter on a neighbor was in the red (True) mine was nice and Green as the unit worked as designed.

Mine is installed. Hidden, I know where it's at but unless you know where to look you won't find it.

Two (soon to be 3 I hope) reasons.. 1: I never forget it (Since it is always there).
2: Park management does not know it is there (Since they do not see it)

third reason is another device I will put in the line.... Using the same install kit.
 
John, at some point I?m considering an autoformer as well, and I?ve thought about mounting it in the electric bay but am concerned about ventilation, how did you address this or is it not a concern?
 
Some parks prohibit autoformers (auto transformers) because they believe the myth that they "steal" power, but others prohibit them because they are aware the NEC prohibits their use.

 

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That's relevant for the permanently installed parts of the electrical system, i.e. using an auto transformer to boost voltage to a string of outlets at the far reaches of the park can create problems with neutral rise and ground loops to those outlets.

But these concerns aren't relevant when auto transformers are used after the park outlet to feed a single RV through the short length of the RV's shore power cord.
 
Lou, that section only pertains to the wiring/equipment used for the RV's electrical system, not the park wiring. If you have a reasonably current NEC available, it's in Chapter 5, Section 551, Part II, 551.20 "Combination Electrical Systems" (E) of the 2017 edition, just as it has been for a number of editions back. As far as I can tell, the prohibition has likely been there in some form since the first NEC edition that included RV's and RV parks.
 
I have a 30 amp Hughes autoformer.

Mine is mounted permanently  in a compartment that is about 3x2x1 feet where the power cord is stored.

The case temperature has never got hot.  Case is comfortable to touch after running for several hours and boosting about 5 volts.

I have an older one that has I believe three step voltages.

 
Autoformers are nice, but rather expensive. The feature that drives up the cost is their ability to adjust the amount of voltage increase that they provide. In many applications, that feature may not be required. If you are in a location where the voltage is virtually always low, there is a much less expensive option.

Buck-boost transformers will increase (or decrease) the voltage by a constant amount. The most common have a 12 volt boost, but others are available. Some models offer the ability to change the constant voltage boost by switching taps.

A typical 12V booster at 30A will be in the vicinity of $100 A 50A version will be around $140.

Joel
 
I misspoke. The amount of voltage boost is fixed, but is not exactly constant. These transformers work by connecting the primary and secondary windings in series, so the voltages add.

In a common design, the primary:secondary ratio is 10:1. Thus with a 110V input, the output will be 110+110/10, or 121V, a 11V boost. With a 100V input, the output will be 100+100/10, or 110V, only a 10V boost.

Joel
 
Great Horned Owl said:
Buck-boost transformers will increase (or decrease) the voltage by a constant amount. The most common have a 12 volt boost, but others are available. Some models offer the ability to change the constant voltage boost by switching taps.

A typical 12V booster at 30A will be in the vicinity of $100 A 50A version will be around $140.
Click to expand...


Very interesting. I did a little poking around but couldn?t immediately identify a 50A version; do you have a link?
 
Sun2Retire said:
John, at some point I?m considering an autoformer as well, and I?ve thought about mounting it in the electric bay but am concerned about ventilation, how did you address this or is it not a concern?
Click to expand...

With a circular saw of course (how I addressed it)

So you understand

My RV is a bath and a half model.. Imagine my surprise when I had a problem with the Auto Transfer Switch and I found it in the most logical spot.. Which as it happens is under the counter in the half bath.... I opened the cabined and there is a shelf and a compartment that is more or less blocked off (Slots on either side of the block off plate) Remove two screws and the panel and there is the ATS.. and a lot of space.. Just enough for the auto former.

And that is where I put it.

I then cut slots in the cabinet doors to add additional air gaps. (The saw) cut straight and it does not look like the chop job it truly is  but that's how I did it.

The plans are to move my Surge Protector to between the Auto-Former and the ATS (If I could program the blasted low voltage cut off I'd leave it at the park outlet)  and with the autoformer "Installed" this means I add cords to the Surge Guard and pull and plug a couple of plugs  No actuall rewire needed save for changing the cords on the surge guard to pigtails.
 
Have you actually observed low voltage at the parks you use, or is this precautionary thing?  And how low is low?  Most parks, even public ones, have decent power these days. But "most" is nowhere near "all".
 
Gary RV_Wizard said:
Have you actually observed low voltage at the parks you use, or is this precautionary thing?  And how low is low?  Most parks, even public ones, have decent power these days. But "most" is nowhere near "all".
Click to expand...

I bought my autotransformer because we were spending the summer at a small park on Prince Edward Island that had really erratic power.  It's bad enough that the far corners of the island have somewhat variable voltage but this park's wiring was outdated and added to the problem.  Inside the MH we observed voltages as low as ~105V and I was concerned that those might cause my Progessive Power Management system to cut off power (it actually did once or twice).  So I bought a 30A Hughes to deal with the situation since all we had was a 30A hookup anyway.  The Hughes bucked the power up by 10V which kept the Progressive happy and eased my concerns about what the low voltage was doing to my A/C's and other motorized devices.

I have to admit that I've not needed it since then, but I carry it around since who knows when the need might arise?
 
Gary RV_Wizard said:
Have you actually observed low voltage at the parks you use, or is this precautionary thing?  And how low is low?  Most parks, even public ones, have decent power these days. But "most" is nowhere near "all".
Click to expand...


Likewise we have a state park we like that has poor power - it routinely drops to the 105 range with even a modest load. When we?re there I run both hot water and fridge on gas and it?s still too low. A 12v 50A buck-boost would be great, if I could figure out which one and how to wire it.
 
Gary RV_Wizard said:
Have you actually observed low voltage at the parks you use, or is this precautionary thing?  And how low is low?  Most parks, even public ones, have decent power these days. But "most" is nowhere near "all".
Click to expand...

Yes we have been in a couple of parks that at peak load times the voltage has dropped below 104 volts at the pedestal. At one recently the problem was on one phase only, ie: 103 volts on L1 and 119 volts on L2. So considering a autoformer to help prevent brownouts and the EMS from cutting the power off.
 
[quote author=docj]Is that a request for a volunteer to complete it?[/quote]

If that turns you on, go for it.
 
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