Crydom SSRs - tips?
in [Basics]
|
Prev: AC and meter movements
Next: Help: Making Project boxes
From: Paul E. Schoen on 14 Apr 2010 02:00 "Ecnerwal" <MyNameForward(a)ReplaceWithMyVices.Com.invalid> wrote in message news:MyNameForward-613D64.17264813042010(a)news.eternal-september.org... > In article > <MyNameForward-295C88.17205213042010(a)news.eternal-september.org>, > Ecnerwal <MyNameForward(a)ReplaceWithMyVices.Com.invalid> wrote: > >> Without going to the bother of simulating it > > This is primarily the bother of getting simulation set up on my computer > - something I've had in the copious spare time project list for a long > time. Copious is ironic in that description. > > Otherwise I'd be quite happy to settle it - but it might be easier to do > with with an oscilloscope and a motor, around here - but then I'd need > one of those DC powered random turn-on SSRs to see how it varied in real > life. You are correct that a motor is not purely inductive, and in fact if it is capacitor start the current may actually lead the voltage for a while and then it becomes a dynamic load which may be mostly resistive as it is doing work. The turn-off of an inductive load with a SSR actually occurs when the current reaches zero, but a motor load acts as a generator as it coasts to a stop. And I think the starting capacitor may kick back in when the centrifugal switch closes and it may act as a dynamic brake to some extent. You may want to add an R-C snubber across the motor and/or the SSR. Some SSRs have overvoltage protection which actually turns them back on to avoid catastrophic breakdown. You probably won't have any problems using your oversized SSR. But there is a huge body of knowledge about various types of motors and their characteristics and the best ways to control them. I am partial to 3 phase induction motors and I have played around with variable frequency PWM motor drives, and I even rewound an old 1/2 HP single phase pump motor to run on three phase at about 8-12 VAC from a SLA battery. Paul |