Re: Motion detector


"Sylvia Else" <sylvia@xxxxxxxxxxxxxxxxxxx> wrote in message
news:00ade816$0$1485$c3e8da3@xxxxxxxxxxxxxxxxxxxx
Trevor Wilson wrote:
"Sylvia Else" <sylvia@xxxxxxxxxxxxxxxxxxx> wrote in message
news:00b04b29$0$12969$c3e8da3@xxxxxxxxxxxxxxxxxxxx
Trevor Wilson wrote:
Sylvia Else wrote:
Trevor Wilson wrote:
"Sylvia Else" <sylvia@xxxxxxxxxxxxxxxxxxx> wrote in message
news:0011d0d7$0$2124$c3e8da3@xxxxxxxxxxxxxxxxxxxx
Trevor Wilson wrote:
"Phil Allison" <phil_a@xxxxxxxxxx> wrote in message
news:7pfv32FkduU1@xxxxxxxxxxxxxxxxxxxxx
"Trevor Wilson"
"Phil Allison"
**Complete bollocks. A TRIAC has miniscule leakage. Less
leakage current, in fact, than the suppression capacitor
across the relay contacts. MUCH less.
** The leakage current flowing in such a suppression cap
produces no heat and consumes no power.

Cos the PF is zero.
**Indeed it is, unless it the relay contacts happens to be in
series with a resistive load (like an incadescent lamp).

** Huh ????

Cold lamps have typical resistances under 100ohms

The AC current from a 47nF cap at 240 volts is 3.5 mA

Do the math.

I get a PF of 0.0014

Over to you.....
**Misunderstanding and poor wording by me. I do not dispute the
PF. I was making the point that the current through a typical
suppression cap exceeds the leakage current through a typical
TRIAC. It was for Sylvia's benefit, since you already knew that.


It didn't, and doesn't, seem relevant though, given that my point
related to power consumption.
**It is very relevant. The leakage current through a typical
suppression cap across a relay is in the order of milliamps. The
leakage across a tyical TRIAC is in the order of microamps. The use
of a relay in such an application does not guarantee zero power
consumption when non-operational.
As Phil has pointed out, and you have conceded, the PFs are different,
and I was clearly focussing on power, not current.
**As was I. The POWER consumed by the device using a relay will probaby
be significantly higher than if it uses a TRIAC. The reason is that the
current flowing through the load will be much higher with a relay.


It might be, but it's not the power consumed by the load that is the
main concern.

**Yes, it is.

It is the power consumed by the switching element, since
it is where most of the voltage drop occurs.

**Change of discussion, duly noted. There will be a Voltage drop across
any semiconductor, whilst there will be essentially zero drop across
relay contacts. THAT, however, is not your original contention.

The TRIAC is essentially
resistive, so it is consuming real power.

**Wrong. The TRIAC is essentially a solid state switch. It does, however,
dissipate some power, due to the valtage drop across the device. A relay
(usually) exhibits a far lower Voltage drop.

Remember, we're talking about the off state. The voltage drop across the
device is the input voltage, near enough.

**Correct. Since the off state of a TRIAC exhibits a leakage current in the
order of a few microAmps, it is several orders of magnitude less than the
current flow through a typical suppression cap across relay contacts.



The relay, with a capacitor
across its contacts, is only consuming reactive power, for which there
is no charge to a retail customer.

**WRONG! The capacitor across the contacts allows a small current to flow
into the load at all times. This power will certainly be charged to the
consumer. A TRIAC, OTOH, will usually allow a much smaller current to
flow into the load. Thus, the consumer will pay less.



Your ignoring the power dissipated in the TRIAC.

**Well, no, I'm not. The Pdiss is miniscule in the off state.

That's most of the
power consumption of the combined system in the off state.

**Yes, it is. It is also far less than the Pdiss of the load, when using a
relay. The TOTAL power consumption of a TRIAC device (when connected to the
load) is generally lower than a relay device.


--
Trevor Wilson
www.rageaudio.com.au


.

Relevant Pages

  • Re: Motion detector
    ... produces no heat and consumes no power. ... suppression cap exceeds the leakage current through a typical ... suppression cap across a relay is in the order of milliamps. ... consumption when non-operational. ...
    (sci.electronics.repair)
  • Re: Motion detector
    ... produces no heat and consumes no power. ... suppression cap across a relay is in the order of milliamps. ... leakage across a tyical TRIAC is in the order of microamps. ... consumption when non-operational. ...
    (sci.electronics.repair)
  • Re: Motion detector
    ... produces no heat and consumes no power. ... suppression cap across a relay is in the order of milliamps. ... leakage across a tyical TRIAC is in the order of microamps. ... consumption when non-operational. ...
    (sci.electronics.repair)
  • Re: Motion detector
    ... produces no heat and consumes no power. ... suppression cap across a relay is in the order of milliamps. ... leakage across a tyical TRIAC is in the order of microamps. ... consumption when non-operational. ...
    (sci.electronics.repair)
  • Re: Triac or relay to switch AC power?
    ... > Triac or relay to switch AC power? ... the controller has to keep sending the signal for an ...
    (sci.electronics.design)