Wayne Dohnal wrote:
Minimum current when switching the load on at peak voltage? Makes me feel like I'm in the twilight zone. This defies simple logic, which is probably why I went into digital electronics instead of this analog, inductive, reactive hocus-pocus that defies understanding. Reminds me of the horrors of Mr. Maxwell and field theory. End of rant.
For a serious question, the soft start on page 10 of the ST app note doesn't have anything in common with the RV air conditioner soft start capacitors, does it?
Wayne,
I'm not sure what soft start capacitors are. Truthfully, I have only known the term to be simply applied as "soft start".
While I grew up in an analog world and taught primarily analog electronics, I am not and was never anything close to an expert on all the technologies related to electric motors - be they AC, DC, single phase, three phase or what ever. I was introduced to SCR's and Triac's back in the early 70's as a method of theater lighting control that replaced auto-transformers and resistor coils and then slowly began to assimilate them into other analog projects I was working on where fast acting triggers and switches were needed along with motor speed controls.
I have not seen a detailed schematic diagram for the soft start control board used in some of the newer RV air conditioners, but I would not be at all surprised to find that the process described on page 10 of the ST application is indeed closely related to what is being done. I have also been under the impression that the term soft start was being universally applied to scroll refrigeration compressors vs. conventional head-on piston & crankshaft compressors. The scroll or screw compressor of course starting with minimum head pressure that slowly increases as motor speed begins to rise.
Then we find the term soft start technology or SST being used as part of battery to AC inverter technology which, once again, brings us back to the application presented on the referenced page 10. This implies that we can easily include soft start circuity on either the delivery or receiving end - which again makes perfect sense to me.
Maybe someone with more experience in motor controls and starting circuits is reading that will chime in? For me, it's time to go to bed - good night :Z
