Path: utzoo!mnetor!uunet!steinmetz!beowulf!bownesrm
From: bownesrm@beowulf.UUCP ( Stowaway aboard the Long Shot)
Newsgroups: sci.electronics
Subject: Re: Running 120V AC equipment off 240V AC.
Message-ID: <1119@beowulf.UUCP>
Date: 11 Feb 88 05:45:25 GMT
References: <204@unh.UUCP>
Organization: Function Consulting, Albany New York
Lines: 51
Keywords: step-down transformer, resistive/inductive loads
Summary: Nope, it has to due with Xformers & SCRs
	 (square vs sine waves)

In article <204@unh.UUCP>, abc@unh.UUCP (Avinash B Chopde) writes:
> 
> A question about stepping down voltage.
> 
> I went into a Radio Shack shop to get a transformer (primary 240V,
> secondary 120V) so that 120V equipment can be run off 240V AC supply.
> 
> Does this have something to do with resistive/inductive loads ?
> Anybody have a simple answer (non-technical! - am an electronics ignoramus!),
> or, (better still) a refutation of the salesman's talk ?
> 
	Mostly the 240-120 converters (at leasst the one I bought
from RS a few years back) work by using an SCR to hack the wave up.
This results in some squarish waves instead of a nice smooth sine. When
you run this high delta Voltage through a transformer (like an AC motor)
it tends to produce some really nifty destructive spikes. The rule is,
"When in doubt, use an isolation transformer."
	When we moved to N. Ireland, we had a set of circuits in the house
wired to a 2.5 KvA transformer. Solved all our problems.
	(Incidentally, most hair driers have DC motors. This chopped up
wave won't cause a problem there.)


> A specific question : will there be any burnouts if I use a 1000W convertor
> specified to be used for hair-dryers for audio equipment instead ?
> 

	It depends on what it is. I ran a stereo cassete deck off an
SCR type converter but I looked at the schematics first to make sure
the ac went straight to a rectifier.


> Thanks in advance for any replies.
> -- 

	No problem. I have LOTS of experience dealing with this. If
any of the aforementioned techno-babble was confusing, send
me mail.




Bob Bownes, aka iii, aka captain comrade bob    | Since I AM my employer,
Function Consulting,	Albany, New York, 12203 | I guess these opinions are
(518)-482-8798 voice (518)-482-9228 (anon uucp) | those of my employer 
 bownesrm@beowulf.uucp				| my houseplants, and my TR-6.
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