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Old 09-06-2012, 10:36 PM   #11
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The Powermaster guy says they're not autotransformers but rather voltage boosters.

Sounds like calling an automobile a car in my opinion.
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Old 09-07-2012, 09:42 AM   #12
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The big difference is isolation in case of a failure in the windings.
There is no galvanic isolation in an autotransformer.


Quote:
Originally Posted by herk7769 View Post
Autotransformer - Wikipedia, the free encyclopedia

This does explain it quite well.
An autotransformer IS a step up/down transformer.
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Old 09-07-2012, 10:50 AM   #13
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Quote:
Originally Posted by wfmdfm View Post
I thought an Auto Transformer changed the output voltage as a result of the current being drawn thru the coil. A step up transformer is fixed and can only be adjusted by physically changing taps on the transformer. Sounds fishy. My code book is at my office but I will look up the chapter.
Wally
Autotransformers are actually most often used to step down voltage usually for a short period. They are wound with a single core of laminated iron, with a single winding which may be hundreds of turns of wire. The supply power to the winding and and using the same common at the bottom of the winding, they can "tap" the same winding at multiple points and take off lower voltages right on up to 15% higher voltage as the supply. They are "auto" only because its fabricated of one winding not two. When used for short voltage drops it can used to start large motors which need a lower starting voltage to prevent overloading the power supplys.
Transformers have two windings and up to 3X more ďironĒ laminations, are normally used to step up or down voltages for continuous use. They are considerably heavier and costlier than these RV type step ups. The quote above was playing games with terms, I don't think the average RV'er could lift and stow a standard transformer of these ratings.

Autotransformers with built in VR for up to 3 taps do it with electronics, the input voltage controls the output by switching taps. All this luxury costs power to provide. The xfer itself has not only resistive load but also plenty of reactive load (apparent power) which are a direct load on the 30 supply, something you are trying to preserve. Transformers are not the most efficient sources of electrical transmission esp the auto style. Maybe this is why the mfgrs donít publish the losses.

I would not discount or rule out the NEC guides to banning them. That was published for a good reason and should be discovered. Personally I donít carry one, My theory is if the campground has low voltage time to refund and check out. I have a triple meter 2DC and AC meter at the door of my RV and can tell at glance if power is NG. Normally I donít find low voltage in the camps I frequent, admittedly have not done state parts in quite some time. If you are paying 35 to 50 a night you should have sufficient power.

I have seen myself the failure of two autotransformers used in motor starting. The problem is when they fail, they can self ignite the varnish/epoxy insulation before the breaker can trip. They then continued to burn feeding on liquid insulation causing smoking hot localized fire. Perhaps this is why NEC banned them, donít really have firm answer though.

Just food for thought.
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Old 09-09-2012, 08:29 PM   #14
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Long talk with Frank yesterday.

Long story (no kidding) short; the RV autotransformers are not UL rated.
They want 10,000 bucks per unit rated.
He is not aware of any units being sold that have the rating.

If you "install" the unit while retaining the socket and plug connections it is not considered "permanent" according to the code.

Update on Powermaster.

He stole his designs from Hughes mostly and two circuits from Frank.
He was not sued by Hughes or Frank because he was convicted and sentenced for stealing and selling satellite TV service.
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Old 09-09-2012, 10:06 PM   #15
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So is PowerMaster out of business?
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Old 09-10-2012, 04:23 PM   #16
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So is PowerMaster out of business?
Supposedly. Who knows what he is doing and with whose stuff.
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Old 09-10-2012, 04:48 PM   #17
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Supposedly. Who knows what he is doing and with whose stuff.
I thought he was only the distributor not the manufacture.
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Old 09-10-2012, 05:06 PM   #18
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It's hard to tell since his website is still active. But...Burro travel trailers site is still up so I guess that doesn't tell us much.
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Old 09-11-2012, 10:50 AM   #19
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Found out he worked in sales for Hughes Autoformer and was terminated. He took circuit design info when he left. He also took apart an early Franks unit and tried to reverse engineer an Autotransformer that used the best of both. Apparently his bashed design did not have enough from each to make a case for either. While Hughes and Frank's were in talks to combine forces, Todd (Powermaster) was arrested and convicted for stealing and selling satellite service boxes.

If he is still selling his Autotransformer, it was news to Frank at Frank's Electronics.
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Old 03-21-2013, 08:58 AM   #20
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FYI, read in another forum of someone ordering a PowerMaster directly from Todd yesterday. He's still in business.
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