What is an Autotransformer?

David472 · 09-06-2011, 10:33 AM

At the risk of posting something which can be found elsewhere......
A couple people here on the JOF have mentioned Autotransformers for their shore power. For this device name, Auto does not mean automatic, but rather a single winding in a transformer. They can be made to function in an automatic manner though. Some RVer's use them to boost a low pedistal voltage up to a more useable level. Typically, for the products sold to RVer's, a fixed boost of 10% is either switched into play or out of play (bypass). Here is a link which describes Autotransformers in general;

http://en.wikipedia.org/wiki/Autotransformer

And here is a link which shows one made by Surge Guard for RVer's;

http://tweetys.com/surge-guard-30-am...r-booster.aspx

At some campgrounds, there seems to be mis-understanding about what impact an Autotransformer would have on the CG electrical supply system. As with all transformers, the electrical power (watts) into it will equal the electrical power out of it. There will be a small amout of Eddie Current loss in the transformer, but that is minor in this context. With a low pedistal voltage of say 100 volts, the pedistal circuit breaker will still have a 30A limit (or maybe 50A), so, the power formula being current times voltage, 100x30 is 3,000 watts. If the pedistal delivered a healthy 120v at 30A, then you would in theory have 3,600 watts available. So you see, a low pedistal voltage being fed into an Autotransformer, does not increase the electrical power drawn from the pedistal. In fact, there is less power available before the circuit breaker trips. I hope you found this post informative and helpful.

Terry · 09-06-2011, 12:35 PM

Thanks David - good explanation.

Murphie · 09-07-2011, 02:37 AM

David, what would you recommend for protecting a trailer with a 30 amp service? Would a person be better off buying a EMS devise that seems to be popular here or would going with a line conditioner be a better choice?

Lady Fitzgerald · 09-07-2011, 08:39 AM

I'm not David but I would strongly recommend an EMS unit (not just a surge protector). All an autoformer does is boost low voltage, up to a point. If the voltage drops low enough, it will revert to bypass mode. The newer Hughes Autoformers do have surge protection but can't be user serviced if the MOVs are damaged by a really large surge por spike. The autoformer has no excessvely low or high voltage protection whereas an EMS unit will shut off the power if it goes too low or too high.

One would think using an EMS after an autoformer would give better protection than just the EMS or autoformer alone but reports I've read on other forums say that, in practice, the better EMS units (such as the Progressives) will shut down before the autoformers can react to a low voltage situation. My choice would be to use the EMS unit to ensure my electronics and other electric appliance don't fry and if chronic low voltage becomes a problem, move.

David472 · 09-07-2011, 11:52 AM

Murphie,
My preference is to have an EMS unit, for much the same reasons stated by Lady Fitzgerald. The wife and I travel when we camp, and so don't stay more than several days at any one CG. Typically, I measure the line voltage, and the lowest I have seen under load so far is 110 volts, which is just adequate and not a worry. For us, an autotransformer would not be of much benefit, but an EMS type device would provide protection for those sudden events which may come along. There is no way a person could react as fast as an EMS. A few weeks ago, at a CG in Mich, during the evening our interior lights suddenly went bright for 5 or 6 minutes. I measured the voltage, and it was about 7% higher than normal. Not likely enough to trigger any EMS (although there could have been a small spike first), but it demonstrates how suddenly and unexpectedly something can happen. At present, we have only a surge protection device, and my manual voltage monitoring. In the future we may be looking at getting an EMS device, for the hi-low voltage protection they offer over what we currently have.

P.S. - You asked if a line conditioner would be a good choice. Please know that an Autotransformer is not a line voltage conditioner. Those are typically made for industrial applications, are quite complex and expensive, like $3,000 range and up.

Murphie · 09-07-2011, 04:35 PM

David, thanks for your input, I will budget for an EMS next year.

Lady, your info has not gone unnoticed and is appreciated.

Seann45 · 09-08-2011, 07:18 AM

Measuring the voltage at the post is next to useless... what happens 10 min after you measure it? When 30 people flip on their A/C units? That is why I have the surge guard. It constantly measures line voltage and polarity. If anything happens to the voltage (over or under) it cuts off power to the RV. I Cannot say enough good things about this device.
Seann

Terry · 09-08-2011, 07:54 AM

Quote:

Originally Posted by Seann45

Measuring the voltage at the post is next to useless... what happens 10 min after you measure it? When 30 people flip on their A/C units? That is why I have the surge guard. It constantly measures line voltage and polarity. If anything happens to the voltage (over or under) it cuts off power to the RV. I Cannot say enough good things about this device.
Seann

Well not only the 30 people - but when the pedestal is static and no current is being pulled by you, it will probably register just fine. Have a bad connection inside and as soon as you crank up the AC or the Micro - bam - sparks fly. Ask me how I know? lol....after that experience I researched and purchased one.

David472 · 09-08-2011, 08:49 AM

Quote:

Originally Posted by tafische

Well not only the 30 people - but when the pedestal is static and no current is being pulled by you, it will probably register just fine. Have a bad connection inside and as soon as you crank up the AC or the Micro - bam - sparks fly. Ask me how I know? lol....after that experience I researched and purchased one.

Notice, I said UNDER LOAD.

Seann45 · 09-08-2011, 09:20 AM

Since you are on a common line other RV's effect your voltage.

Since we are talking about this and I am a HUGE believer in them .. I noticed that camping world has Surge Guards on sale right now...
http://www.campingworld.com/browse/p...=61711&rewrote

David472 · 09-08-2011, 09:58 AM

Quote:

Originally Posted by Seann45

Since you are on a common line other RV's effect your voltage.

Since we are talking about this and I am a HUGE believer in them .. I noticed that camping world has Surge Guards on sale right now...
http://www.campingworld.com/browse/p...=61711&rewrote

Seann45,
Besides GST and PST, how much customs duty and shipping do you pay on top of the sale price? Or, maybe you just wait until you're south of the border? The regular price of $311 turns into $499 here in Canada.

Terry · 09-08-2011, 10:14 AM

Quote:

Originally Posted by David472

Notice, I said UNDER LOAD.

Yep! I think we have all beat this poor dead horse to death! I think we all agree - GET ONE...lol....

David472 · 09-08-2011, 10:33 AM

Quote:

Originally Posted by tafische

Yep! I think we have all beat this poor dead horse to death! I think we all agree - GET ONE...lol....

I think I'm going to talk with our local dealer, and see if he can source one at a better price. I will show him Tweetys price and see if he can come close. I hate paying $85 shipping plus customs duty. I like your set-up tafische.

Lady Fitzgerald · 09-08-2011, 10:48 AM

Quote:

Originally Posted by Seann45

Measuring the voltage at the post is next to useless... what happens 10 min after you measure it? When 30 people flip on their A/C units? That is why I have the surge guard. It constantly measures line voltage and polarity. If anything happens to the voltage (over or under) it cuts off power to the RV. I Cannot say enough good things about this device.
Seann

A surge guard protects only against surges and spikes by shunting them to ground. There is a limit to how much they can do. An EMS will also shut off the power in case the voltage runs too high or low. They also will protect against improperly wired services (just because a pedestal is wired correctly doesn't mean some yahoo can't make stupid changes upstream later on; I've seen it happen). Based on what you said, I suspect you were referring to having an EMS. I agree one cannot say good enough things about them.

However, I disagree about measuring voltage at the post being next to useless. Doing so before pulling in could save a bunch of hassle since you could discovered it was wired wrong or even dead. It's much easier to check several pedestals than to move an RV from space to space. If several pedestals have problems, it's nice to know before you commit yourself.

As you said, conditions can change within minutes after you measure so an EMS is still needed for full protection but it takes so little time to precheck the pedestal, it makes sense to do so.

Terry · 09-08-2011, 01:35 PM

Quote:

However, I disagree about measuring voltage at the post being next to useless. Doing so before pulling in could save a bunch of hassle since you could discovered it was wired wrong or even dead. It's much easier to check several pedestals than to move an RV from space to space. If several pedestals have problems, it's nice to know before you commit yourself.

I have to disagree with you disagreeing...lol...but thats ok - we all have different ways we like to do things....

I actually back into the spot, pull the cord, and let the EMS do its things before I start any setup. It is actually quicker than pulling out my tester and I get the added benefit of putting some load on it as well. I have yet to find a pedestal that the simple voltage/polarity check has not shows is good - but I have found 2 that failed under load.

I think if I did find a bad pedestal at my camp site, I would then take my meter and check the other sites before I moved --- but the odds are in my favor it will be good.

David472 · 09-08-2011, 03:44 PM

Quote:

Originally Posted by tafische

Snip..... - but I have found 2 that failed under load......Snip

Tafische,
please enlighten us. Your PI-EMS would have told you what the 2 pedistals failed for. So, can you tell us?

Terry · 09-08-2011, 05:28 PM

Sorry if I was not clear. The two failures I referred to happen before I got the EMS.

The first issue I had was an old pedestal that I don't think was making a good connection inside. The voltage went low and the plug got very hot and partially melted. The low voltage detection should have shut it down.

The second failure was more dramatic. I hooked up and was all happy pulling just a few amps. My DW turned on the micro and everything went haywire - lights flickered, Micro went nuts and I heard this arching noise. I ran outside and the pedestal was making all kinds of noises. I tried to hit the breaker and it basically popped out of place and arched even worse inside. I was able to hit the main to the pedestal and get it shut off. Turns out the breaker had come loose and was barley making contact. In this instance it would have helped both from the voltage drop and the delay when it looses power.

It was after that incident that I got the EMS. I can't say for sure, but 8 months later my Micro quit. i don't use it that much, so I can't say for sure it caused it - but it sure could not have helped it.

So there you go - two significant problems within 12 months - hopefully with the EMS these will not repeat themselves. In both of these instances the pedestal read as being just fine with the meter.

David472 · 09-08-2011, 07:14 PM

Okay tafische, thanks for the descriptions. You have had your share of grief with pedistals. I'm sure you feel more safe with the PI-EMS in line. One thing I've seen a few RVers do when they arrive....they flip the pedistal breaker off then back on. I thought that was rather interesting. The switching action would tend to "wipe" the contacts of the breaker. That wouldn't prevent your two cases though, and also one could argue that too much flipping of any one breaker would wear it out prematurely. On the other hand, maybe your second problem example was preceeded by too many off-on flipping of the breaker? In case you're wondering, I don't routinely switch breakers off and on. Only for cases like you experienced where there clearly is a problem.

Seann45 · 09-09-2011, 08:15 AM

Quote:

Originally Posted by David472

Seann45,
Besides GST and PST, how much customs duty and shipping do you pay on top of the sale price? Or, maybe you just wait until you're south of the border? The regular price of $311 turns into $499 here in Canada.

Unfortunatly Camping World demands to ship UPS (Unreliable Pathetic and Shi**y) I buy my stuff when I am in the US and the DECLARE it at the boarder. Most often I get it free then under my personal exemption.

Seann45 · 09-09-2011, 08:20 AM

Quote:

Originally Posted by Lady Fitzgerald

A surge guard protects only against surges and spikes by shunting them to ground. There is a limit to how much they can do. An EMS will also shut off the power in case the voltage runs too high or low. They also will protect against improperly wired services (just because a pedestal is wired correctly doesn't mean some yahoo can't make stupid changes upstream later on; I've seen it happen). Based on what you said, I suspect you were referring to having an EMS. I agree one cannot say good enough things about them.

However, I disagree about measuring voltage at the post being next to useless. Doing so before pulling in could save a bunch of hassle since you could discovered it was wired wrong or even dead. It's much easier to check several pedestals than to move an RV from space to space. If several pedestals have problems, it's nice to know before you commit yourself.

As you said, conditions can change within minutes after you measure so an EMS is still needed for full protection but it takes so little time to precheck the pedestal, it makes sense to do so.

Jeannie you are thinking of a surge PROTECTOR.. Surge Guard is the name of a product... and it works GREAT to protect the RV ... it cuts off all power to the RV if it senses high or low voltage conditions.. protects from surges and does a 2 min polarity check every time you plug in the RV... if the plug head is miss-wired it will not allow power through to the RV
Seann

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