Hi, stumbled across this forum when trying to research a solution to my problem, and got nagged by the pop-ups to register Looks a useful and interesting community. Hopefully I can give something back in time.
I'm building a microprocessor (Raspberry Pi) controller to monitor humidity in a loft (we have a condensation problem) and then switch on extractor fans. The switch is an opto-coupler Songle 10A 250VAC SRD-05VDC-SL-C as used by many Raspberry Pi projects. http://www.ebay.co.uk/itm/5V-1-2-4-...no-Raspberry-Pi-ARM-AVR-DSP-PIC-/252051910091 Many example projects say a Snubber should be inserted across the contacts and invariably state one at 100nF and 100Ω but then say "dependent on load".
The extractor fan is Envirovent SILENT 100 running at 240V 50Hz 8W. No other information provided. These typically run off the lighting circuit. I calculate 8W as 0.03A but have read one should multiply by a factor of 10 for the start up load (back EMF?). But that is still only 0.3A.
I came across a previous thread on RC Snubber Values http://forum.allaboutcircuits.com/threads/rc-snubber-values.78661/#post-555959 and read the reference document and down loaded the spreadsheet:
http://www.hiquel.com/fileadmin/userfiles/AppNotes/Englisch/HIQUEL_Snubber_AppNote_EN_0100.pdf
http://www.hiquel.com/fileadmin/use.../HIQUEL_SnubberCalculator_AppNote_EN_0100.xls
I entered:
Line frequency [Hz] 50 Hz
Supply voltage [V RMS] 240 V
Nominal load current [A RMS] 0.03 A
Damping factor 0.23
Preset: 0.01
Maximum relay inrush current 0.3 A
The results are:
Capacitance Cs [nF] 5 nF
Resistance Rs [Ω] 33720 Ω
I set the chosen Capacitance value at 6.8nF (row 65) but the maximum chosen Resistance (row 70) allowed is 3300Ω - way below the above figure of 34KΩ. These values generate lots of warnings (orange) and one "error": Damping factor 0.022.
The reference document states: "If the snubber circuit is over-sized the leakage current would rise and the protection circuit would loose its efficiency".
Something doesn't feel right with these values. Most RC Snubbers (RC Networks) seem to be 100Ω or 120Ω. E.g. RC NETWORK, 250V, 0.01UF, 120R, PCB MPN: XE12001 ROXBURGH (wattage not stated).
Guidance much appreciated.
Many thanks
Alan
I'm building a microprocessor (Raspberry Pi) controller to monitor humidity in a loft (we have a condensation problem) and then switch on extractor fans. The switch is an opto-coupler Songle 10A 250VAC SRD-05VDC-SL-C as used by many Raspberry Pi projects. http://www.ebay.co.uk/itm/5V-1-2-4-...no-Raspberry-Pi-ARM-AVR-DSP-PIC-/252051910091 Many example projects say a Snubber should be inserted across the contacts and invariably state one at 100nF and 100Ω but then say "dependent on load".
The extractor fan is Envirovent SILENT 100 running at 240V 50Hz 8W. No other information provided. These typically run off the lighting circuit. I calculate 8W as 0.03A but have read one should multiply by a factor of 10 for the start up load (back EMF?). But that is still only 0.3A.
I came across a previous thread on RC Snubber Values http://forum.allaboutcircuits.com/threads/rc-snubber-values.78661/#post-555959 and read the reference document and down loaded the spreadsheet:
http://www.hiquel.com/fileadmin/userfiles/AppNotes/Englisch/HIQUEL_Snubber_AppNote_EN_0100.pdf
http://www.hiquel.com/fileadmin/use.../HIQUEL_SnubberCalculator_AppNote_EN_0100.xls
I entered:
Line frequency [Hz] 50 Hz
Supply voltage [V RMS] 240 V
Nominal load current [A RMS] 0.03 A
Damping factor 0.23
Preset: 0.01
Maximum relay inrush current 0.3 A
The results are:
Capacitance Cs [nF] 5 nF
Resistance Rs [Ω] 33720 Ω
I set the chosen Capacitance value at 6.8nF (row 65) but the maximum chosen Resistance (row 70) allowed is 3300Ω - way below the above figure of 34KΩ. These values generate lots of warnings (orange) and one "error": Damping factor 0.022.
The reference document states: "If the snubber circuit is over-sized the leakage current would rise and the protection circuit would loose its efficiency".
Something doesn't feel right with these values. Most RC Snubbers (RC Networks) seem to be 100Ω or 120Ω. E.g. RC NETWORK, 250V, 0.01UF, 120R, PCB MPN: XE12001 ROXBURGH (wattage not stated).
Guidance much appreciated.
Many thanks
Alan