A little background first. I am testing single phase commercial soft serve ice cream machine similar to what you might find at a fast food restaurant or a local ice cream vendor. The unit normally draws less than 1A of current until the compressor and motors turn on, at that point the current draw is about 14A. This happens about every 10 minutes if product is not being drawn from the machine. If ice cream cones and shakes are being drawn at a rate of 1-2 a minute all of the motors will run continuously. So, with that said I have been running the machine in the "idol" state with no product being drawn as this would be the typical mode during the slow times in the normal installed location.
With this type of machine I have been referring to A.14 of IEC 61000-3-3 for the test criteria. There are a couple of items in A.14 that don't seem to be very clear. First, the 3rd dashed item under a) says to measure dmax 24 times in accordance with Annex B, but if the 1st measurement is > +/- 10% of the dmax referenced in Clause 5 then only 1 measurement is required. If the result is higher than that of Clause 5 isn't it a failure? Second, the last note in A.14 says that Pst and Plt are to be determined analytically. As I have done the calculations don't seem to be very different from the measured values (as long as the source is stiff enough to handle the inrush.) It does not seem to adjust the limits at all. Am I seeing this correctly? Third, the equation (5) in Clause 4.2.3.1 calls for the dmax value. Since dmax is a percentage should the value be entered as 4 or 0.04 if the dmax value is 4%? In all of this it seems that A.14 gives the impression that there is some understanding that EUT's with compressors will have difficulties complying with the standard but it doesn't appear that there is any slack given in the limits, only that you have a modified route to show compliance. Is there something that I am missing here?? Also, I did try using the method described in b) of A.14, it gave worse results. Locked rotor current for compressors is extremely high, for the one I calculated the locked rotor current is 60A and I used an assumed PF of 0.8. All comments are appreciated, I have been struggling through this one for a little while now. Regards, Josh - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
