# Calculating the current of a household appliance

Discussion in 'General Electronics Chat' started by electrophile, May 28, 2016.

1. ### electrophile Thread Starter Member

Aug 30, 2013
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I'm trying to build a ceiling fan regulator which incorporates a triac. I was trying to figure out the current rating for this and I was hoping someone would let me know if this is the right way to do it. Here goes:

The ceiling fan is rated for 75W. For 220VAC and a power factor of about 0.85 (from my research on the web but feel free to correct me) would the current be:

75/(220 x 0.85) = 0.4 A?

If this is correct, can I use a 1A (constant on-state) rated triac?

2. ### Alec_t AAC Fanatic!

Sep 17, 2013
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I'd use a higher current version. Not much difference in price, greater safety margin.

Jul 18, 2013
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I agree, with triac's there is not a lot of point sizing them tight.
Max.

4. ### be80be Senior Member

Jul 5, 2008
432
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Ceiling fans dont last long if you wanting to use this for speed control too.
Plus it will start humming loud

Mar 4, 2014
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6. ### be80be Senior Member

Jul 5, 2008
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I replace about 50 to 75 fans a year that people put on a dimmer they use capacitors to change speed and don't like dimmers at all

Jul 18, 2013
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I have had mine for 25 yrs, buzzes a little at low rpm but not a problem.
Max.

8. ### be80be Senior Member

Jul 5, 2008
432
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That's cool but most new ones are lucky to make it a year before you can't stand to be in the room with them and forget to turn it up to full speed to start the fan and your just cooking the wires in it. I'm a electrician 35 years I've seen most anything that can go bad happen there are dimmable fans but most are not made to use dimmer

GopherT likes this.

Mar 4, 2014
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10. ### electrophile Thread Starter Member

Aug 30, 2013
100
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@Alec_t and @MaxHeadRoom Thanks. I however, have a space constraint and the 1A ones fit in quite nicely. I saw a few 4A in DPAK cases which could also work.

Thanks. What would you recommend for fan speed control?

Mar 4, 2014
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12. ### electrophile Thread Starter Member

Aug 30, 2013
100
1
Thanks. I'm however, not looking at getting a commercial control unit. I'm building one that can be controlled through an MCU. Power control is just one of the things that the MCU does.