| Author |
Message |
Chris
Guest
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 Posted:
Sat Sep 24, 2005 12:35 am Post subject:
Triac Switch Inductive Loads |
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http://www.chrisncarol.com/switch.jpg
I'm looking to use a moc3032 zero crossing couple and a triac to swich
an ac motor on, now my understanding is that because it's a zero
crossing it will only turn on at the base of the wave and not in mid
wave, now using a microcontroller can i pwm this signal and chop off the
ends of the wave for a "dimmer" like effect?
Thanks
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Genome
Guest
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| Posted:
Sat Sep 24, 2005 12:35 am Post subject:
Re: Triac Switch Inductive Loads |
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"Chris" <chrispol@videotron.ca> wrote in message
news:ye%Ye.2331$US5.35715@wagner.videotron.net...
| Quote: | http://www.chrisncarol.com/switch.jpg
I'm looking to use a moc3032 zero crossing couple and a triac to swich
an ac motor on, now my understanding is that because it's a zero
crossing it will only turn on at the base of the wave and not in mid
wave, now using a microcontroller can i pwm this signal and chop off the
ends of the wave for a "dimmer" like effect?
Thanks
|
Is there something wrong with your software that prevents you from drawing
nice circuit diagrams.
Like, if you don't care...... why should I give a fuck?
How do you think Carol might feel?
DNA |
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Chris
Guest
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| Posted:
Sat Sep 24, 2005 12:35 am Post subject:
Re: Triac Switch Inductive Loads |
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Hummm someone must have problem's, don't like it don't look at it....
Nice and constructive input than you very much.
Especially from someone that doesn't post their name or email.
Genome wrote:
| Quote: | "Chris" <chrispol@videotron.ca> wrote in message
news:ye%Ye.2331$US5.35715@wagner.videotron.net...
http://www.chrisncarol.com/switch.jpg
I'm looking to use a moc3032 zero crossing couple and a triac to swich
an ac motor on, now my understanding is that because it's a zero
crossing it will only turn on at the base of the wave and not in mid
wave, now using a microcontroller can i pwm this signal and chop off the
ends of the wave for a "dimmer" like effect?
Thanks
Is there something wrong with your software that prevents you from drawing
nice circuit diagrams.
Like, if you don't care...... why should I give a fuck?
How do you think Carol might feel?
DNA
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Rich Webb
Guest
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| Posted:
Sat Sep 24, 2005 5:47 am Post subject:
Re: Triac Switch Inductive Loads |
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On Fri, 23 Sep 2005 19:21:18 -0400, Chris <chrispol@videotron.ca> wrote:
| Quote: | Hummm someone must have problem's, don't like it don't look at it....
Nice and constructive input than you very much.
Especially from someone that doesn't post their name or email.
|
Just put him in your killfile. I did, a long time ago; helps the signal
to noise ratio quite a bit.
The short answer to your original question (if I understand it
correctly) is "not really." Triacs, once triggered, stay on until the
trigger is removed AND the current through it drops to zero. You could
probably get a PWM-ish effect by selecting 1-of-N half cycles but I
doubt that the motor would be entirely happy.
Good info at
<http://www.st.com/sitesearch/consult5/index.php?mid=29e7ebcb9fde302ae47c8901d3f0a269&l=en&q=triac>
particularly
<http://www.st.com/stonline/products/literature/an/3566.htm>
--
Rich Webb Norfolk, VA |
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Chris
Guest
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| Posted:
Sun Sep 25, 2005 8:35 am Post subject:
Re: Triac Switch Inductive Loads |
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Chris wrote:
| Quote: | Hummm someone must have problem's, don't like it don't look at it....
Nice and constructive input than you very much.
Especially from someone that doesn't post their name or email.
Genome wrote:
"Chris" <chrispol@videotron.ca> wrote in message
news:ye%Ye.2331$US5.35715@wagner.videotron.net...
http://www.chrisncarol.com/switch.jpg
I'm looking to use a moc3032 zero crossing couple and a triac to swich
an ac motor on, now my understanding is that because it's a zero
crossing it will only turn on at the base of the wave and not in mid
wave, now using a microcontroller can i pwm this signal and chop off the
ends of the wave for a "dimmer" like effect?
Thanks
Is there something wrong with your software that prevents you from drawing
nice circuit diagrams.
Like, if you don't care...... why should I give a fuck?
How do you think Carol might feel?
DNA
|
Hi, Chris. Don't mind Genome -- he's a regular contributor to s.e.d.
and has a lot of competence in SMPS, as well as high current-high
voltage switching and analog designs in general. I guess you just
caught him on his rare bad day. But picking on the significant other
is usually bad form. We all have our own allotted portion in this vale
of tears (note the logical progression -- engagement ring, wedding
ring, suffering). And your .jpg file is OK -- just a standard
opto-triac setup.
If you're switching an inductive load, you're going to have problems
with triacs. They will switch off at zero voltage/zero current, but
will tend to stay on for inductive loads because zero current and zero
voltage occur at different times in the line cycle.
Also, your zero-crossing opto triac trigger isn't going to cut it for
speed control. You can't turn on in the middle of an AC half-cycle at
all. Using the MOC3032 for voltage control would work for something
like a heater or soldering iron, where the thermal time constant is
very long in relation to an AC half cycle. Your motor will probably
cog like crazy with this kind of speed control, though. It won't be
pretty.
If you want to do something like this, and assuming phase control will
work for your AC motor, you're going to first have to replace the
zero-crossing opto triac trigger with something like the MOC3011, which
will have random phase turn-on. Also, the classic way to overcome the
inductive load problem is to use back-to-back SCRs instead of a triac,
but that would involve some extensive redesign of your circuit. If you
want to keep everything else in place, you might want to look at
replacing the triac in your circuit with one of the Teccor
"Alternistors", which have many of the characteristics of back-to-back
SCRs, but also only have one trigger input. They can be turned on in
QI and QIII, and may work for your application. Try the Q60165L6
(TO-220 package, rated for 15A and 600V). It's pin-for-pin drop-in
compatible with the standard triac pinout, and will definitely work a
lot better than a triac.
Good luck
Chris |
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Jasen Betts
Guest
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| Posted:
Sun Sep 25, 2005 8:35 am Post subject:
Re: Triac Switch Inductive Loads |
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On 2005-09-23, Chris <chrispol@videotron.ca> wrote:
| Quote: | http://www.chrisncarol.com/switch.jpg
I'm looking to use a moc3032 zero crossing couple and a triac to swich
an ac motor on, now my understanding is that because it's a zero
crossing it will only turn on at the base of the wave and not in mid
wave, now using a microcontroller can i pwm this signal and chop off the
ends of the wave for a "dimmer" like effect?
|
no.
when a triac turns on it doesn't turn off until the current through it drops
to zero,
if it turns on at zero crossing it'll remain on until the end of the
half-cycle, (or slighly longer with an inductive load)
if you're wanting to do a dimmer by feeding partial cycles to the motor
use a regular (non-zero-crossing) triac drive optocoupler like moc3012
you'll also want a zero-crossing detector to give you a starting point for
your count...
--
Bye.
Jasen |
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Chris
Guest
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| Posted:
Sun Sep 25, 2005 4:35 pm Post subject:
Re: Triac Switch Inductive Loads |
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Thanks all, is a moc3022 ok? thats all that is available locally i
already did the zero detect.
Chris
Chris wrote:
| Quote: | Chris wrote:
Hummm someone must have problem's, don't like it don't look at it....
Nice and constructive input than you very much.
Especially from someone that doesn't post their name or email.
Genome wrote:
"Chris" <chrispol@videotron.ca> wrote in message
news:ye%Ye.2331$US5.35715@wagner.videotron.net...
http://www.chrisncarol.com/switch.jpg
I'm looking to use a moc3032 zero crossing couple and a triac to swich
an ac motor on, now my understanding is that because it's a zero
crossing it will only turn on at the base of the wave and not in mid
wave, now using a microcontroller can i pwm this signal and chop off the
ends of the wave for a "dimmer" like effect?
Thanks
Is there something wrong with your software that prevents you from drawing
nice circuit diagrams.
Like, if you don't care...... why should I give a fuck?
How do you think Carol might feel?
DNA
Hi, Chris. Don't mind Genome -- he's a regular contributor to s.e.d.
and has a lot of competence in SMPS, as well as high current-high
voltage switching and analog designs in general. I guess you just
caught him on his rare bad day. But picking on the significant other
is usually bad form. We all have our own allotted portion in this vale
of tears (note the logical progression -- engagement ring, wedding
ring, suffering). And your .jpg file is OK -- just a standard
opto-triac setup.
If you're switching an inductive load, you're going to have problems
with triacs. They will switch off at zero voltage/zero current, but
will tend to stay on for inductive loads because zero current and zero
voltage occur at different times in the line cycle.
Also, your zero-crossing opto triac trigger isn't going to cut it for
speed control. You can't turn on in the middle of an AC half-cycle at
all. Using the MOC3032 for voltage control would work for something
like a heater or soldering iron, where the thermal time constant is
very long in relation to an AC half cycle. Your motor will probably
cog like crazy with this kind of speed control, though. It won't be
pretty.
If you want to do something like this, and assuming phase control will
work for your AC motor, you're going to first have to replace the
zero-crossing opto triac trigger with something like the MOC3011, which
will have random phase turn-on. Also, the classic way to overcome the
inductive load problem is to use back-to-back SCRs instead of a triac,
but that would involve some extensive redesign of your circuit. If you
want to keep everything else in place, you might want to look at
replacing the triac in your circuit with one of the Teccor
"Alternistors", which have many of the characteristics of back-to-back
SCRs, but also only have one trigger input. They can be turned on in
QI and QIII, and may work for your application. Try the Q60165L6
(TO-220 package, rated for 15A and 600V). It's pin-for-pin drop-in
compatible with the standard triac pinout, and will definitely work a
lot better than a triac.
Good luck
Chris
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Chris
Guest
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| Posted:
Sun Sep 25, 2005 4:35 pm Post subject:
Re: Triac Switch Inductive Loads |
|
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Chris wrote:
| Quote: | Thanks all, is a moc3022 ok? thats all that is available locally i
already did the zero detect.
Chris
|
Hi, Chris. The MOC3022 is alright -- it's actually an upgrade, because
the output is rated for 400V instead of 250V. The MOC3022 will work on
240VAC control circuits as well as 120VAC.
If you're wondering, the alternistor is available from Mouser and
Digi-Key.
If you run into problems driving the motor, feel free to post again.
Please include some information on the motor if you do.
Good luck
Chris |
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Harold Ryan
Guest
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| Posted:
Sat Nov 05, 2005 8:52 am Post subject:
Re: Triac Switch Inductive Loads |
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Yes you can pwm. However, you will most likely turn on 50 cycle half cycles
in some repeating sequence. IF you don't then the motor will manifest a beat
frequency. To eliminate the speed variations, you need to monitor the ac
cycles to synchronize the controls that you are trying to make. The feedback
circuit can be a simple opto coupler that turns on every other AC cycle.
Harold
"Chris" <chrispol@videotron.ca> wrote in message
news:ye%Ye.2331$US5.35715@wagner.videotron.net...
| Quote: | http://www.chrisncarol.com/switch.jpg
I'm looking to use a moc3032 zero crossing couple and a triac to swich
an ac motor on, now my understanding is that because it's a zero
crossing it will only turn on at the base of the wave and not in mid
wave, now using a microcontroller can i pwm this signal and chop off the
ends of the wave for a "dimmer" like effect?
Thanks |
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