Day Brown wrote in a message to Roy J. Tellason:
 DB>  On 11-19-97 Roy J. Tellason wrote to all... 
 RJ> I was browsing this catalog offering inverters,  and saw 
 RJ> mention in there that some stuff will run on just about any 
 RJ> type,  some stuff wants a modified sine wave at least,  and 
 RJ> some wants a "pure" sine wave.  I can't find the reference in 
 RJ> that catalog at the moment.
 RJ> Can somebody run down what sort of stuff is fussy about its 
 RJ> power,  and perhaps why?  Some of the things on that list were 
 RJ> rather surprising...
 DB> Lemmee know whatcha find Roy.  I had a brand new BJ cannon that 
 DB> immediately *fried* when run on a sin wave inverter. seven 
 DB> weeks later, the replacement fried just as fast. 
That's odd,  because this literature seemed to imply that sinewave inverters 
were okay with fussy stuff like that,  and that they'd have trouble with 
modified sine and other types of inverters.  Or at least that's the way I 
read it,  maybe I oughta find that bit and read it over,  to make sure I've 
got it straight.
 DB> Researching the cause, I found an article in Electronic 
 DB> Engineering Times from some German researchers about disasters 
 DB> with PFC computer power supplies.  It seems that the PFCs 
 DB> sample the AC sign wave in the same manner that sin wave 
 DB> inverters and switch mode power supply designs used in 
 DB> printers, and god nose what else.
 DB> When several PFC devices are on a given AC bus, each will pick 
 DB> up on a random spike in the line, and in each trying to damp 
 DB> it, all at the same time, the feedback over-responds, and 
 DB> catastrophic surges have been bounced back to the nearest 
 DB> transformer, which shorts out, and the Germans found a lotta 
 DB> fires.
 DB> What is more, neither the utility equipment manufacturers would 
 DB> admit to any culpability, nor would any of the PFC 
 DB> manufacturers.  Naturally, the law suits would be considerable. 
 DB> ;}  And, any new design changes would be evidence of original 
 DB> defect.
 DB> So, such a list as you propose, would not be a popular item 
 DB> with the electronic equipment manufacturers and vendors.
 DB> SO: I for one, would not use any inverter at all on any device 
 DB> with a switch mode power supply; the feedback overload may not 
 DB> appear initially, nor soon, but *can* at any time.  Lacking a 
 DB> choice, If I had to use one, I would employ an isolation 
 DB> transformer, the bigger the better, hoping the hysteresis would 
 DB> be sufficient to damp the resonant harmonics that otherwise 
 DB> break into feedback,  much as a high school gym PA breaks into 
 DB> a squeeeeel. 
That sorta seems to say that a lot of stuff I want to run off-grid ain't 
gonna happen...      :-(
email: roy.j.tellason%tanstaaf@frackit.com 
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