By the way, be very careful when working with a CT. If the secondary ever goes open circuit (ie: the burden resistor is disconnected) the voltage will skyrocket! Bob Ammerman RAm Systems ----- Original Message ----- From: "Ian McLean" To: Sent: Friday, February 20, 2004 7:08 AM Subject: Re: [EE:] Current Transformers > Thanks Edward, > > That clears things up nicely. I am sure I can get this to work now ;-) > > Thanks to everyone else who responded as well, and for the links to CT > suppliers. > > Rgs > Ian > > > -----Original Message----- > > From: pic microcontroller discussion list > > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Edward Gisske > > Sent: Friday, 20 February 2004 6:01 pm > > To: PICLIST@MITVMA.MIT.EDU > > Subject: Re: [EE:] Current Transformers > > > > > > Ian, > > > > Typically, you run the current carrying wire through the core of the > > transformer one time (sometimes a few turns). That is the > > primary. The wires > > coming off the CT toroid are the secondary. > > > > You are correct about the TVS (also known as a "Bi-Zener"). > > Please pardon my > > acronyms. The voltage rating is selected to be low enough so > > you don't blow > > up whatever is downstream of the CT. A 1.5KExxx part will > > soak up 1.5KW > > surges without blowing up. It is unlikely you will have to > > dissipate any > > more than that under transient conditions, so it should > > work,. The TVS is > > only in action in starting or overload conditions. It is an > > open circuit > > under normal conditions. Think of it as two Zener diodes > > wired back-to-back > > that limit AC waveforms to the breakdown voltage of the TVS. > > > > MOV's usually don't have a low enough turn-on voltage to be > > effective for > > PIC-style circuits (under 5V) so the TVS works better. > > > > Just put it in parallel with the burden resistor, which is in > > parallel with > > the CT secondary. It is a belt-and-suspenders sort of back-up > > to protect the > > rest of the circuit under fault conditions. > > > > Regards, > > Edward Gisske, P.E. > > Gisske Engineering > > 608-523-1900 > > gisske@offex.com > > > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu