Charged capacitors and inrush current in an appliance

Question

Here is a circuit of electronic fan speed controller:

Speed of the fan can be controlled by the following logic levels on various pins:

This circuit is meant to be used with a 220 VAC power line and a ceiling fan which looks like this:

Typical wattage is 60-80 watts for these fans.

I want to optimize the circuit and I feel that I can get rid of R7, R8, R17 and R19. R7 and R8 appear to be inrush current limiting resistors (am I right?) whereas R17 and R19 are discharge resistors for the capacitors.

I tested the concept and it worked fine without those resistors. However I am not sure about the long term effects.

My concerns and questions are follows:

1) Can I remove R7 and R8 without having an adverse effect on life of the circuit and the fan connected to it?

2) With 200K discharge resistor in place, the capacitor discharges from 220 VAC to under 5 VAC within 2 seconds. Without those resistors, it takes around 8 seconds. Complete circuit will be inside a plastic casing. Is this discharge time acceptable? Are there any safety regulations related to this? Will removing those discharge capacitors have any adverse effect?

Answer 1

1. You'd have to do long-term testing to find out. You won't save any money if you skimp a few cents on resistors, but then have a rush of warranty claims in a few months time because the semiconductors keep blowing.
2. This is a safety-related component. Touching a charged capacitor while standing on a step latter to fault-find a bit of kit (which probably has a blown semiconductor), and touching a capacitor charged to 300V DC could be nasty. When measuring the remaining voltage, are you allowing for the resistance of the voltmeter?

Answer 2

A capacitor working in an AC circuit will hold the charge that the AC waveform is at the exact moment of disconnection. When there is a 220V AC sine, the instanteanous voltage will peak from a -311V to +311V, crossing 0 in between. Just imagine you left one of the capacitors still charged at -311V from a previous operation, and the triac in the cricuit is going to switch on at the moment the sine is peaking at +311V, the inrush current will be instantaneously very high, probably not blowing up anything at the moment but may degrade performance of the semiconductor over time. So, yes, I'd keep the resistors to discharge the capacitors when not in use.