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From: Ian Stirling
Subject: Re: Higher loads on triac light dimmer ???
Date: Thu, 19 Sep 2002 16:11:55 +0000 (UTC)
References: <3D88B55D.7E72FBC2@nospam.com> <3D88C107.CDF46D67@texas.net> <3D88D6D0.750B841D@texas.net> <3D88ED75.6BBD801D@texas.net>
NNTP-Posting-Date: Thu, 19 Sep 2002 16:11:55 +0000 (UTC)
User-Agent: tin/1.5.6-20000803 ("Dust") (UNIX) (Linux/2.4.18 (i686))
John Woodgate wrote:
> I read in sci.electronics.design that Kevin McMurtrie
> wrote (in onic.net>) about 'Higher loads on triac light dimmer ???', on Thu, 19
> Sep 2002:
>>The problem is that having a small duty cycle means the peak voltage
>>must be higher. That also means the peak current is _much_ higher.
>>That's what's going to be a problem for the house wiring and nearby
> What a curious notion! The idea is to reduce the power in a resistive
> load by applying a sliced sine voltage waveform. To reduce the power,
> the peak voltage has to be *reduced* and this *reduces* the current.
It reduces the current from the value it would have had if the heater
was connected to twice it's design voltage.
But it increases the peak current from that that would occur if
it was connected to it's design voltage of sine-wave.
Taking the above case.
1300W heater with 110V sine-wave.
RMS current = 11.8A
Resistance = 9.3 ohms
Peak current = 16.63A
Peak voltage = 155V
Now, if you chop a 220V sine wave so that the RMS power through the heater
is the same (at about 40 degrees after the peak):
1300W heater with chopped 220V sine-wave.
RMS current = 11.8A
Resistance = 9.3 ohms.
Peak current = 25.4A
Peak voltage 237V
http://inquisitor.i.am/ | mailto:email@example.com | Ian Stirling.
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