I have a 10A solid state relay and a microcontroller or two sitting
around. I was curious if I could control the speed of the AC motor by
cycling the availability of the juice like I could with a DC motor.
IE: Hook the hot wire through the relay and cycle it on for 20ms, off
for 80ms for a 20% duty cycle or some such (with the ability to adjust
the duty cycle of course, 100% for 5 seconds at start, etc).
I don't know much about AC though and less about AC motors. Is this a
valid approach? Will it burn up the motor, catch the relay on fire,
destroy my karma, etc?
TIA!
-Kevin
On Jan 16, 12:36 am, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll>
wrote:
If you don't hold its hand all the way,
Google Groups does a really crappy job of posting to Usenet.
Long links in particular get smashed.
http://groups.google.com/group/sci.electronics.misc/msg/a988332e61a73ee0
If you will put each of those on a line of its own,
you have a better chance of them not getting screwed up.
In addition, if you use an email address as a username,
Google also fucks that up.
If you *sign up* for a group before posting to it
http://groups.google.com/groups/mysubs
and give yourself a username (without a domain in it),
you will look less goofy to other people using Google Groups
(aka The Usenet Archive).
>I have one of these (http://www.bestgrowlights.com/site/403863/page/
>941189) but the bugger blows way too much air and is very loud. So I
>bought one of these (http://www.plantlightinghydroponics.com/fantech-
>variable-speed-fan-control-p-1487.html) and that did slow things down
>a bit but not enough.
If you just bought the properly-sized device in the first place,
you wouldn't have to jump thru hoops.
http://google.com/froogle?q=muffin-fan+cfm&num=100&scoring=p&price=between&price1=1
So a transformer to bring the 120 down to 3 V peak-to-peak then boost
the baseline to 2v DC put that into the ADC input? Then when it gets
close to 4.5 or .5 then kill the motor and re-enable at the same
voltage on the other side of the peak/trough?
Or could you accomplish similar with op-amps?
If you just want to detect the zero-crossings of the AC supply, there's
an even easier way. Take the 120V AC, feed it through a large resistor
( > 1 MOhm ) directly into a microcontroller pin. The input protection
diodes will clamp the mains voltage to a nice square wave, and the
approx. 100 microamps that flows through the resistor is well within their
ability to handle --- check the data sheet.
However, I'm not sure that Kevin S's phase-control-dimmer-style speed control
is a good idea ... a motor is an inductive load, and treating it like a
simple resistive load is likely to burn out your switches, your motor,
or both...
--
Wim Lewis <wi...@hhhh.org>, Seattle, WA, USA. PGP keyID 27F772C1
"We learn from history that we do not learn from history." -Hegel