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Re: SRSG phasing part 2
Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>
In a message dated 4/6/01 3:00:36 PM Eastern Daylight Time, tesla-at-pupman-dot-com
writes:
Scot, all,
It is absolutely essential that you select the proper value of capacitor
which gives only a small resonant rise across the motor. You wan't
maybe a 5 to 10 volt rise or less. It's even OK with no rise at all, if
the motor stays locked throughout the variac's range, or most of
the range. Your capacitor value is too large. Try something half
the size, and go from there, using trial and error selection until
you get the proper safe amount of reso-rise. Oh, no motor is in
the circuit !!!!! The motor *has to be* in the circuit to dampen the
resonant rise !!!!!!!!!!!!!! Why run it without the motor? !!!! I
guess
you didn't have the protective fuse in place or it probably would have
blown and stopped the dangerous reso-rise.
John Freau
>
> Hi All.... especially John...
>
> I went to a web page of Johns and built the circuit shown on the page for
> phase control of
> SRSG motors.
>
> After building it, I decided to test the circuit for voltage and smoke...
> what I found was
> as I turned the variac up ( no motor in the circuit) the voltage increased
> rapidly ( resonate
> rise? 120V -at- 0 on the variac dial and increasing to 200V -at- 40% on the
> variac (( i quit there
> to avoid cap damage )) ) and the cap seemed to humm quite a bit more than
> I thought was
> comfortable.
>
> the motor is a 1/4 hp inductive 120V, I'm using 50K ohm worth of
> resistance ( 20W) a 260V
> 32uF cap and a variac rated for 240V 10A ( using terminals 3 ((wiper) and 4
> ) fuse is rated
> for 10A. the "hot" lead is run thru the variac.
>
> my question is... is this circuit supposed to increase the voltage to the
> motor to change
> the phase or what?? I'm lost on this one. What am I supposed to be looking
> for?
>
> Scot D