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In lugnet.robotics, Philippe Hurbain wrote:
> This is clearly outside of my own SOA there!
I've been operating outside my personal SOA for years now :)
> Are you sure that duty cycle modulation works with this kind of
> AC motor?
It's actually not a motor - it's a small electric hot water heater element. When
plugged in it produces 1300W, but if I want less than that I need to figure out
some way to reduce the current, or the voltage... or, alternatively, cycle it on
and off very rapidly. 1300W on for 1 sec and then off for one sec should
simulate a power output of 650W, for example. But if the cycle time starts
drifting up above 1 sec, it will induce thermal oscillations in the system I
don't want... so switching something like this off/on rapidly seems to be a good
option.
> ...to keep it simple and safe - you might try to control the
> dial of a powerful light gradator with a NXT motor?
That was actually my first thought (in fact using a "dimmer switch" manually
would be good enough... I really just need a way to set the power output, no
absolute need for NXT control). The problem is nobody needs to "dim" 1300W light
sources, and worse, most of these dimmers work by dissipating and dropping the
power in the dimmer, not the light... meaning in this case you don't save power,
and the dimmer gets... really warm.
What I've got now is a wall switch in a small wooden box, with a LEGO framework
pinned to it with an NXT motor. The motor is used to simply throw the switch
back and forth at the desired rate. This should work... but it's really noisy,
and limits the cycle time to around a second (hard to throw the switch faster
than that under NXT control). I saw your control circuitry, and starting
thinking of ways to do it completely solid-state (well, or solid + relay state,
if that makes sense).
--
Brian Davis
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Message has 1 Reply:
 | | Re: Motors comparison page updated
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| (...) Good thing, the load is not inductive. (...) OK, with a 1 second cycle time, and pure on/off, it is simpler. All you need is a solid state relay. (...) Looks like some people do: (URL) and worse, most of these dimmers work by dissipating and (...) (14 years ago, 13-Jan-11, to lugnet.robotics, lugnet.org.us.smart)
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Message is in Reply To:
| | Re: Motors comparison page updated
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| Hi Brian, (...) I was surprised too. I suspect a relatively high internal resistance of the windings, rather than mechanical friction, as the source of losses. No, (shame on me!) I didn't checked yet with an ohmmeter. (...) This is clearly outside (...) (14 years ago, 13-Jan-11, to lugnet.robotics, lugnet.org.us.smart)
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