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Posted by Existential Angst on December 5, 2009, 2:15 pm
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Awl --
How to do?
TRIACs? http://en.wikipedia.org/wiki/TRIAC
In that article they mention "alternistor". Useful? Never heard of it.
How bout PWM? http://en.wikipedia.org/wiki/Pulse-width_modulation good
article, overview, incl. rheostats and variacs. Not clear, tho, if pwm acts
to change the effective input frequency.
I'm guessing that, in general, speed control of 1 ph induction motors is
not so swift, given that people here are swapping out 1 ph induction for 3ph
+ VFDs.
But if it IS doable on smaller motors, it would be a big help.
The blower motor at hand (kitchen hood) is surely no more than 2-3 A, and
I'll bet about 1.5 . I've used a variac on this motor, with very middling
results.
If 1 ph induction is freq dependent, why can't a VFD be used on a 1 ph (220
V) induction motor?
If I need to go 3ph+VFD, Dealerselectric.com has fractional hp 3 ph motors,
down to 1/4 hp, prices not on web.
Graingers has no 3 ph motors under 1 hp, and none of those under $250...
wow....
--
EA, PV'd
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Posted by Existential Angst on December 5, 2009, 2:30 pm
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> Awl --
>
> How to do?
>
> TRIACs? http://en.wikipedia.org/wiki/TRIAC
> In that article they mention "alternistor". Useful? Never heard of it.
>
> How bout PWM? http://en.wikipedia.org/wiki/Pulse-width_modulation good
> article, overview, incl. rheostats and variacs. Not clear, tho, if pwm
> acts to change the effective input frequency.
>
> I'm guessing that, in general, speed control of 1 ph induction motors is
> not so swift, given that people here are swapping out 1 ph induction for
> 3ph + VFDs.
>
> But if it IS doable on smaller motors, it would be a big help.
> The blower motor at hand (kitchen hood) is surely no more than 2-3 A, and
> I'll bet about 1.5 . I've used a variac on this motor, with very middling
> results.
>
> If 1 ph induction is freq dependent, why can't a VFD be used on a 1 ph
> (220 V) induction motor?
>
> If I need to go 3ph+VFD, Dealerselectric.com has fractional hp 3 ph
> motors, down to 1/4 hp, prices not on web.
> Graingers has no 3 ph motors under 1 hp, and none of those under $250...
> wow....
Would
http://www.grainger.com/Grainger/items/5JJ60?cm_mmc=Google%20Base-_-Motors-_-Motor%20Supplies-_-5JJ60
work? $36. What type of controller is this?
Higher amp controllers:
http://www.grainger.com/Grainger/ac-speed-controls/motor-supplies/motors/ecatalog/N-9yj?op=search
Also higher priced -- $200 range.
--
EA
>
> --
> EA, PV'd
>
>
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Posted by Existential Angst on December 5, 2009, 3:45 pm
Please log in for more thread options
> Awl --
>
> How to do?
>
> TRIACs? http://en.wikipedia.org/wiki/TRIAC
> In that article they mention "alternistor". Useful? Never heard of it.
>
> How bout PWM? http://en.wikipedia.org/wiki/Pulse-width_modulation good
> article, overview, incl. rheostats and variacs. Not clear, tho, if pwm
> acts to change the effective input frequency.
>
> I'm guessing that, in general, speed control of 1 ph induction motors is
> not so swift, given that people here are swapping out 1 ph induction for
> 3ph + VFDs.
>
> But if it IS doable on smaller motors, it would be a big help.
> The blower motor at hand (kitchen hood) is surely no more than 2-3 A, and
> I'll bet about 1.5 . I've used a variac on this motor, with very middling
> results.
Heh.... just looked at the plate.... 1/20 hp!! mebbe 1/2 A??
Hellified 1/20 hp blower.... wow.....
With oil cups. :)
--
EA
>
> If 1 ph induction is freq dependent, why can't a VFD be used on a 1 ph
> (220 V) induction motor?
>
> If I need to go 3ph+VFD, Dealerselectric.com has fractional hp 3 ph
> motors, down to 1/4 hp, prices not on web.
> Graingers has no 3 ph motors under 1 hp, and none of those under $250...
> wow....
>
> --
> EA, PV'd
>
>
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Posted by whit3rd on December 5, 2009, 8:10 pm
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wrote:
[speed control of 1ph induction motors]
> How to do?
A stepped pulley on the motor, and another stepped pulley on the
load, with provision for changing the belt position...
That example is THE most difficult type of motor to speed-control.
With 3ph, you at least can rectify the input to get DC power (but
with 1ph, your DC power is pulsed; you have to filter it to begin
with).
> TRIACs?
... are a kind of switch that are easily turned ON, hard to turn OFF;
not right
for this problem.
> How bout PWM? =A0
... requires DC input power and a controllable ON/OFF switch; yes,
this
can work, but usually it's done with DC motors for simplicity. For AC
you need to solve the problem twice...
> But if it IS doable on smaller motors, it would be a big help.
The small induction motors that DO work with speed controls (chem
lab stirrer, some multispeed fans) are very low power because
they're inefficient and would burn up if scaled to 1/8 hp or larger.
Universal motors (with brushes) can be speed-controlled with a triac
or SCR, with some care; that's how the variable-speed Dremel works.
Most such motors are designed for intermittent duty, the power
efficiency
is not usually high. You lose torque as well as speed at low
drive levels (the stepped pulleys are better in this regard).
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Posted by Existential Angst on December 6, 2009, 12:11 pm
Please log in for more thread options
wrote:
[speed control of 1ph induction motors]
> How to do?
A stepped pulley on the motor, and another stepped pulley on the
load, with provision for changing the belt position...
That example is THE most difficult type of motor to speed-control.
With 3ph, you at least can rectify the input to get DC power (but
with 1ph, your DC power is pulsed; you have to filter it to begin
with).
> TRIACs?
... are a kind of switch that are easily turned ON, hard to turn OFF;
not right
for this problem.
> How bout PWM?
... requires DC input power and a controllable ON/OFF switch; yes,
this
can work, but usually it's done with DC motors for simplicity. For AC
you need to solve the problem twice...
> But if it IS doable on smaller motors, it would be a big help.
The small induction motors that DO work with speed controls (chem
lab stirrer, some multispeed fans) are very low power because
they're inefficient and would burn up if scaled to 1/8 hp or larger.
Universal motors (with brushes) can be speed-controlled with a triac
or SCR, with some care; that's how the variable-speed Dremel works.
Most such motors are designed for intermittent duty, the power
efficiency
is not usually high. You lose torque as well as speed at low
drive levels (the stepped pulleys are better in this regard).
=================================================
What do you think of the Dart controller in the graingers link?
What method does it use? It's sposedly good up to 2.5 A, which on paper is
about 1/3 hp.
I put the variac back on this blower, on my bench.
The variac actually does an OK job, but speed regulation is not very stable,
as the motor tries to get in synch with the 60 Hz, and thus it's full rpm.
Once at full rpm, more V does not increase speed, just increases the hum!
Probably more load would call for more voltage.
The Q is: will a Variac at 60 V or so make the motor hotter than usual, at
reduced rpm? Not enough back-EMF to limit current?
--
EA, PV'd
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>
> How to do?
>
> TRIACs? http://en.wikipedia.org/wiki/TRIAC
> In that article they mention "alternistor". Useful? Never heard of it.
>
> How bout PWM? http://en.wikipedia.org/wiki/Pulse-width_modulation good
> article, overview, incl. rheostats and variacs. Not clear, tho, if pwm
> acts to change the effective input frequency.
>
> I'm guessing that, in general, speed control of 1 ph induction motors is
> not so swift, given that people here are swapping out 1 ph induction for
> 3ph + VFDs.
>
> But if it IS doable on smaller motors, it would be a big help.
> The blower motor at hand (kitchen hood) is surely no more than 2-3 A, and
> I'll bet about 1.5 . I've used a variac on this motor, with very middling
> results.
>
> If 1 ph induction is freq dependent, why can't a VFD be used on a 1 ph
> (220 V) induction motor?
>
> If I need to go 3ph+VFD, Dealerselectric.com has fractional hp 3 ph
> motors, down to 1/4 hp, prices not on web.
> Graingers has no 3 ph motors under 1 hp, and none of those under $250...
> wow....