We lost our shore power

John,

Unless I'm misreading your message, there appears to be a contradiction ...

....below that point current in the motors increased greatly

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I read numerous posts on the other forum and did some searching. Seems like they have similar conflicting "here's the scoop" posts without any valid technical explanations or empirical data. I'd appreciate a link to the post you mentioned if you're able to find it. I was getting lost among all their ads. There are zero ads in our forum messages.

BTW I plan to gather the empirical data if/when I ever buy an autoformer. I have the necessary equipment to allow me to do that, but don't know if I want to spring for the price of an autoformer.

BTW did you ever receive the small package I mailed you? Sorry it took me 2 years to stumble across it.

"An autotransformer is an electrical transformer with only one winding."

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Tom,
Not exactly correct. Autoformer and autotransformer are used interchangeably, but are different. An autoformer really has two windings, but they are wound on the same core and share a common connection between the primary part of the winding and the secondary part. This makes them inherently more dangerous than a true autotransformer, because there is no isolation between them. An autotransformer, on the other hand, has separate, insulated windings that provide isolation from the primary current source.

I mentioned phase shift (where current either leads or lags voltage; depending on whether it's a capacitive or inductive load) in an earlier post, but it probably wasn't too clear just how important this is. To better understand why these devices are somewhat detrimental to all who are connected to the same feeder transformer, people may want to look at the explanation of Power Factor. Manufacturing companies in particular, because of the number and size of the motors they use, pay the electric utility dearly for a low power factor, to the point where many have found it less expensive to install large banks of capacitors to bring their PF up to near unity.

Thanks Karl.

An autotransformer, on the other hand, has separate, insulated windings that provide isolation from the primary current source.

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I guess that we took a different class when it came to autotransformers. This is close to what I remember, but that was a very long time ago. Maybe it was the Welsh accent coming through in my messages  ;D

Understand the power factor issue, but I guess I ignored the fact that an AF is a large inductive load. I think of motors as having a low PF, but hadn't given any thought to a transformer.

Tom,
Over the years, various devices have been called by different names - autotransformer being one. What Wiki describes is what I used to (and still do) call a Variac. For the purposes of our discussion, everybody's right! There is another type which uses a self-adjusting movable core to, in effect, change the permeability of itself, resulting in a (somewhat) constant voltage regardless of input variations. 

The problem with running air conditioning and other induction motors at reduced voltages is fairly simple: You may notice that induction motors are most commonly rated at a speed of either 1725 rpm or 3450 rpm, when you may have expected it to be some number divided equally by the frequency of the applied voltage - 60Hz in our case. Well, it doesn't quite work that way. The rotor is always somewhat slower than the rotating magnetic field of the field coil, so it is always playing a game of "catch-up", which it never quite achieves. At normal voltages and provided that the voltage and current are in phase, it will always run at that speed (1725 or 3450) and will draw the least amount of current for the given load. If either of those two things change, it needs to draw more current to keep the speed constant. Therein lies the problem. With low line voltage, or current that is out of phase with the voltage, the increased current draw needed to maintain that speed can and will cause increased heat to be generated, leading to possible failure of the motor - as some people, sadly, have first-hand knowledge of.

Tom, your recall of the Autotransformer (And WiKi's) also happens to be how I recall them  And I've used more than one over the years.  Single winding tapped

Thanks Karl & John. Time for me to retreat to my article writing before someone suggests we're disagreeing.