Autotransformer

[gus]

Back in April Nick posted this;

   
Re: Surge- Circuit protector - 50 amp - is this new?
« Reply #12 on: April 04, 2007, 10:09:45 PM »
   Reply with quote
I'm wondering if the Hughes Autoformer is worth the investment?

Model #VC-50
The VC-50 is a dual transformer controller for those RVs with a 50 Amp power requirement. The VC-50 has the same outstanding control and surge features found in the VC-30.

FEATURES
· 50 Amp / 12,000 Watt capacity
· Fully automatic boost up to 12%
· Boost indicator lamps for each circuit (2)
· Spike and surge protection to 3,580 Joules
· Weatherproof
· U.L. listed transformer
· Dimensions: 9 " W x 5" D x 12" H
· Weight: 40 lbs.
· Two year limited warranty
· Made in U.S.A.

www.rvperformanceproducts.com

Nick-

however, nobody answered??


I still have the same question, surely there is an electrical whiz here who knows? Jerry?

My reaction to this thing is that it appears to create power but, of course, a transformer can't do that - it can only change (transform) power. When it increases voltage it has to decrease amps (v x a=v x a) and also will have a small transformation loss. So, not only can it not increase power it actually loses power.

I can see that a decrease in amps is better than a decrease in volts (brownout) but how do they get away with calling this thing a power booster? It doesn't actually say that in Nick's post but I've seen magazine ads that say that. Maybe the loss in amps is so small it isn't significant since it appears they can only boost volts up to 12%.

It appears to me they are playing loose with the word power since they say "50 Amp power requirement" , but amps isn't power?

I just read an article in MotorHome magazine that said it "consumes a lot of current" and that if everyone in the RV park had one it would probably blow the whole RV park power supply!

Does anyone have any actual experience with the Autoformer?

[Nusa]

With all those devices, I'm sure the 50A advertised refers to the service the park claims to provide, not the electrical specs of the device itself. In any case, the blurb also says 12,000 Watt capacity, which IS a power measurement (Watts = Voltage * Amps, or in this case 12000 = 50 * 240). Odds are that's evenly split between the two 120V circuits mentioned. And yes, there are always losses (in the form of heat) any time you convert voltages. And yes, any time you lower the voltage the current has to go up to get the same power. If park voltage is low, you may not be able to get the full voltage-adjusted 50A before blowing the park breakers, but you may get 45A.

I don't know either product, but both appear to be similar in nature. They either provide park power to the RV, or park power + 12%, based on if the supply voltage is too low. If the park voltage is way low (under 100V per leg), you're still screwed. If the park voltage is too high, neither device is going to fix that. And yes, if everyone pulled all the current they're allowed, many parks couldn't support it. But it's not the devices fault, it's the park electrical design that's at fault, or a park management decision to bet on enough people not using all the power they paid for.

[Kristinsgrandpa]

Nusa, good post.

I've used autotransformers on two occasions at work and they do keep the voltage drop to a minimum. Low voltage is the cause of failure of a lot of appliances. I personally like the idea.

It causes headaches to park owners that aren't up to snuff on their power supply.

They are against the law according to the National Electric Code, which is effect in almost all states. There is like only 5 or 6 that haven't adopted it.

If you get one be sure and keep it hid from park owners/operators and mums the word.

Ed

[HighTechRedneck]

It causes headaches to park owners that aren't up to snuff on their power supply.

They are against the law according to the National Electric Code, which is effect in almost all states. There is like only 5 or 6 that haven't adopted it.

I am just curious.  What is the reason for the problem and the laws.  It's not like they draw full power all the time whether it is being used or not.  Power consumption (input) will always be equal to the load (output) plus the loss factor (which shouldn't be that extreme).

[Jerry Liebler]

I sure wouldn't invest over $500 in one.  From the description I read it's output voltage  is either exactly the input or 110% of the input.  When it is 110% obviously the input current is 110% of the output current.  So in the voltage step up situation it would be possible to trip the park's breakers if the load really was 50 amps.
I've see very few situations where a 10% boost would rescue a low voltage situation.  If it's too low I'll just run my generator.
Regards
Jerry 4107 1120

[H3Jim]

I will attempt an explanation, and hopefully I get it right.  I'm sure the really smart people will correct me if I'm wrong.

Normally with a low voltage situation, as the voltage drops, the electric motors in an appliance will still draw the same wattage, but that increases the amperage.  Its this increase in amperage that burns out the appliance, as its wires are gauged for the lower current that the standard voltage provides.  Light bulbs simply get dimmer.

Enter the transformer. When your RV is plugged into a low line voltage situation, it keeps the voltage where it should be, but it draws higher amperage from the source to do so, increasing the current on the supply lines to a level potentially higher than they were designed for.  Read it can overheat the wires and cause a fire.  It also further lowers the voltage available for everyone else, exacerbating the problem, and likely causing the appliances in others RV's that are not protected by a transformer to now fail.

[Nusa]

Except that wires are protected by breakers, which really do measure current rather than voltage. Degrading the quality of your neighbors power has merit, however, but doesn't excuse the substandard power quality in the first place.

But doesn't the NEC pretty much end at the outlet, so far as the law is concerned? Does it apply to RV's at all, in the eyes of the law?

[gus]

Jim,

You seem to have it right as far as I know.

I doubt that a park with a big bunch of outlets would be affected much by one transformer because of the very small percentage of power one outlet will draw. That is probably the reason for the statement in the article I read that a large number of transformers could cause a problem.

I have never noticed a problem with low power but my power usage is modest. I think that any voltage decrease would be immediately noticed in dimming lights and slower AC fan speed. Of course this could be a problem if you had the AC on and were absent, but I never do that.

I just don't think it is worth $400-600 for me. It might be for one of the monster buses or MHs.

[Sean]

OK, let's clear up some legal confusion here:

What the NEC forbids in RV's are "autotransformers."  Like everything in the NEC, the prohibition is for safety reasons -- the NEC wants you to use a full, isolating-type transformer.

Note that the prohibition has nothing at all to do with whether or not you step up park voltage.  For all the NEC cares, you can take park input voltage of 120 volts and step it up to 240, if that's what you need.  They just want the transformer's primary and secondary windings to be electrically isolated.

And, yes, the NEC applies to all RV's, and yes, the NEC rules apply past the "outlet" -- for example the NEC also regulates the construction of plugs, extension cords, certain appliances, etc.

Hughes sidesteps the NEC because they don't build the RV, and the RV manufacturer is not building the RV with an autotransformer included.  It is designed, billed, and sold as a "portable" accessory.

As for whether or not anyone needs one of these contraptions:  If you are going to be staying in parks with consistently low voltage, and you plan on running motors (such as air conditioners or a household fridge), then, yes, one of these can help.  But in three and a half years on the road full time, the only time I wished for one was when we were in Mexico, where park voltage tended to swing wildly from less than 80 volts up to to 105 or so.  It was a real challenge keeping the air conditioning running under those circumstances.

To be honest, we normally have our LVCO set at 96 volts, and I just don't worry about running the AC on any voltage down to that point.  YMMV.

-Sean
http://ourodyssey.blogspot.com

[Nick Badame Refrig/ACC]

Thanks Sean,

Thats what I was waiting to hear..

Your setting on your LVCO may be a little too low at 98v. I had my RS3000 set at 98V and when I had a low

voltage ordeal on my last outting, my Frigidaire Side-by-Side's board locked up and everything melted inside before

I had a chance to notice it. My inverter panel warned me and shut everything down at 98v but, aparently the refriges

board couldn't withstand it and locked out. A simple reset [unplugging the board for a few seconds] corrected the problem.

So, now i have rethought the 98v and now have the cut off set at 102v just to satisfy the refrig...

Nick-

[rv_safetyman]

I too am glad that this subject came up again. 

We attend a lot of FMCA rallies and often connect to the power service that is provided.  In some cases, the power is from rented trailer mounted generators.  In other cases is is from some very old fairground wiring that is distributed via long cables and some very questionable distribution boxes.  We were just at Indio and I started to plug into one of the connections.  I always check the connection with my Good Governor (http://www.campingworld.com/browse/skus/index.cfm?skunum=16036) and an adapter for 50/30/15amp connections.  When I plugged it in it read 148 volts.  Another fellow grabbed his digital meter and said I must have read it wrong, as he got 70 volts.  I went back very quickly and my meter agreed with his.  Bottom line that box was really messed up.  When we were in Charlotte a couple of years ago, we were on an obviously marginal power supply generator.  Apparently one leg was marginal (often around 100 volts or less), but my leg seemed to be OK.

Before I continue, mentioning the Good Governor brought to mind a thread that is related and has some good discussion about checking the wiring at the post.  However, others have really hammered home the fact that bad power is often transient and Murphy would dictate that it would be good when we checked it   That thread is worth reading if you are interested in this thread:  http://www.busconversions.com/bbs/index.php?topic=3209.15

Back to this thread.  I am of the school that I don't think the Autoformer is worth the money, or will do the job.  What I do want is something that will shut off the power when there is a problem.  I have been looking at the products offered by:  http://progressiveindustries.net/

This seems to be a very straight forward system that will shut the power off if it gets out of range.  I am told that the system will restore the connection if the power comes back into range (would be a good option if the problem was only a isolated condition - pun intended).  I think it will also not permit connection if there is an open ground or some other wiring issue.  We went to the tent today in Quartzsite and I think it is in the $250-300 range for the hard wired version.  Seems to me to be a good insurance policy.

Hopefully Sean and others will offer some insight.

Jim

[Nick Badame Refrig/ACC]

Hi Jim,

That is what my Xantrax RS3000 does. it shuts down the system and set off an alarm at the panel when the electric exceeds

my programed parameters.

Nick-

[rv_safetyman]

Hi Nick.  My Trace does the same thing, but I have several things that are not in the "pass through" circuits that the Trace protects.  For example, my roof airs would not be protected by the Trace, nor the washer and dryer.  My AquaHot heating element would probably not be an issue.  I do occasionally run my 110V air compressor and that would not be protected.

The system I mentioned would protect everything in the bus from what I can see.

I have the best Trace, but I wonder how well it protects itself from huge swings in voltage or wiring issues . 

Jim

[Nick Badame Refrig/ACC]

Hi Jim,

I see what you mean. I have everything running through the RS so I'm covered.

Nick-

[rv_safetyman]

One more thought.  There have been some very strong warnings to always shut off bus breaker for the post power (you all have one right at the input of the power cord, right? - it is code) before you plug into 50 amp service (maybe 30 amp as well).  The thought being that you could plug in the male connection in at an angle and connect to the hot legs before the ground and/or neutral make their connection (that is why the round RV/Marine connections are preferred as I understand it - they always connect the ground and neutral before the hots are connected).

In any case, I think the system I am talking about would shut off the power if that occurred and  you forgot the shut off the breakers.

Jim