1
\$\begingroup\$

I have a phase regulator and I'm using it for regulating the RPM of a fan - centrifugal blower. The motor is a shaded pole induction motor (220VAC, 28W).

The regulator is working fine, but if the RC Snubber (R8+C8) is disconnected (due to the failure of C8 or R8), the voltage and current are getting out of phase and false triggering / turn off of the triac occurs, which leads very quickly to overheating and failure of the coil of the induction motor.

  • What type of capacitor should I use to minimize the chance of its failure (I’m using this regulator for 8 hours a day)?

  • Or is there a way to add additional circuit for protection, if such failure occurs?

I’m currently using Polypropylene capacitor rated for 250VAC/400VDC (Wima MKP 10 - https://www.wima.de/wp-content/uploads/media/e_WIMA_MKP_10.pdf). For the resistor I’m using 1W/Metal Film.

schematic diagram

\$\endgroup\$
4
  • 1
    \$\begingroup\$ You have a snuber, but it is disconnected, you ask what snubber you should put and you already have it. I don't get it???!!! \$\endgroup\$ – Marko Buršič Aug 3 '19 at 17:31
  • \$\begingroup\$ @MarkoBuršič As I think, Kadel is asking about a suitable capacitor type for C8. If C8 fail , motor will damage. \$\endgroup\$ – user_fs10 Aug 3 '19 at 17:53
  • 1
    \$\begingroup\$ @MarkoBuršič Yes user_fs10 is correct. The RC Snubber is always connected of course, but in case C8 fail (or if R8 fail) the snubber will be respectively disconnected. And i know that without this snubber the motor will be damaged quite fast (i already tested it). \$\endgroup\$ – Kadel Aug 3 '19 at 18:04
  • \$\begingroup\$ The cap type seems correct, but the voltage rating is too low. You are snubbing inductive spikes, so you need to have a higher rating than the mains voltage. If cost wasn't a big concern, I would use a 2 kV cap. \$\endgroup\$ – Mattman944 Aug 3 '19 at 21:08
1
\$\begingroup\$

The edited question is clear, now. The capacitor is correct WIMA MKP 250VAC is the correct choice. The resistor could be under rated, also it seems a little bit too low 360 ohm to me.

Have a look here: RC snubber circuit design for TRIACs - STMicroelectronics , there is a calculation for 26W pump and the calculated sbubber is 10nF and minimum resistance of 620 ohm. I wouldn't change the capacitor you've got, it's really high quality and for this specific task.

Choose a capacitor for higher voltage, like WIMA MKP 630V

Also, BTA-16 is somehow too big for the required load, if you can change it use a smaller one like BTA-06.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.