Small single-phase VFD for 120V?

On Wednesday, October 13, 2021 at 2:16:03 PM UTC-7, palli...@gmail.com wrote:
> whit3rd - <vituperation extirpated> wrote: 

> > > A Variac is all he needs for speed control. 
> > 
> > That's not speed control for induction motors,
> ** Yes it is you fucking, know nothing twat.. 

Most induction motors are thermally protected, because they will burn up
if stalled.   Running slower than synchronous warms the rotors, and running a
lot slower burns them.   You cannot speed them higher
than the synchronous speed with higher voltages, and ought not
deliberately let them go much slower.

One can let the rotors slip and get lower speed, but few induction motors
are designed to survive that.   

> Standard home fans can be speed controlled over the *full range* using one - way better than with the built in speed switch. 

Only very low performance fans.   A multispeed blender, however, generally 
needs brushes.   Better power per lb, and better energy efficiency.

On 14/10/2021 02:07, whit3rd wrote:
> Most induction motors are thermally protected, because they will burn up
> if stalled.   Running slower than synchronous warms the rotors, and running a
> lot slower burns them.   You cannot speed them higher
> than the synchronous speed with higher voltages, and ought not
> deliberately let them go much slower.
> 
> One can let the rotors slip and get lower speed, but few induction motors
> are designed to survive that.
> 

Perhaps, but to burn the motor takes a lot of power and surely running 
the motor from a variac at reduced voltage reduces the liklihood of heat 
damage?

The load on a fan does not rapidly fluctuate - I'd have thought a variac 
transformer would work just fine, even if not the "officially approved" 
method?

piglet

whit3rd= Demented Psychopath  wrote:

=======================
 
> 
> > > > A Variac is all he needs for speed control. 
> > > 
> > > That's not speed control for induction motors, 
>>
> > ** Yes it is you fucking, know nothing twat..
>
> Most induction motors are thermally protected,

** Not the ones in small fans  -   you asinine fuckhead.

( snip fake quote from Google) 


> > Standard home fans can be speed controlled over the *full range* using one
>>  - way better than with the built in speed switch.

> Only very low performance fans.

**  Read what I wrote  -   cunt boy. 

 piglet wrote:
===========
>
> Perhaps, but to burn the motor takes a lot of power and surely running 
> the motor from a variac at reduced voltage reduces the liklihood of heat 
> damage? 

** Motor current drops in line with applied AC voltage.

   So  I squared R losses drop even faster. 

> The load on a fan does not rapidly fluctuate - I'd have thought a variac 
> transformer would work just fine, even if not the "officially approved" 
> method? 

** But is is  -  just a tad expensive for lost cost fans. 


.....   Phil

On Wednesday, October 13, 2021 at 11:40:10 PM UTC-7, palli...@gmail.com wrote:
> piglet wrote: 
> ===========
> > 
> > Perhaps, but to burn the motor takes a lot of power and surely running 
> > the motor from a variac at reduced voltage reduces the liklihood of heat 
> > damage?
> ** Motor current drops in line with applied AC voltage. 

No, of course it doesn't; it drops in line with applied AC voltage minus the
back-EMF of the motor.   That back-EMF is missing if the motor isn't
rotating at the intended (circa 1800 RPM in 60 Hz land) rate.

A nominal 1720 RPM induction motor at 1/4 HP is developing that 1/4 HP with
a 'slip' of 80 RPM; at higher loads, it goes below 1720 RPM, and
burns up.

 whit3rd =  INSANEa Google Monkey wrote:
=============================
 piglet wrote: 
 =========== 
> > > 
> > > Perhaps, but to burn the motor takes a lot of power and surely running 
> > > the motor from a variac at reduced voltage reduces the liklihood of heat 
> > > damage? 
>
>
> > ** Motor current drops in line with applied AC voltage.

> No, of course it doesn't; 

**   FFS   is their no end to  the vile lunatic Google troll.

 Read this: 

 FOAD you pile of stinking autistic shit. 

 

.....  Phil 

On Thursday, October 14, 2021 at 7:09:55 PM UTC+11, palli...@gmail.com wrote:
> whit3rd  wrote: 
> =============================
> piglet wrote: 
> =========== 
> > > > 
> > > > Perhaps, but to burn the motor takes a lot of power and surely running 
> > > > the motor from a variac at reduced voltage reduces the liklihood of heat 
> > > > damage? 
> > 
> > 
> > > ** Motor current drops in line with applied AC voltage. 
> 
> > No, of course it doesn't;
>
> ** FFS is their no end to the vile lunatic Google troll. 

Phil seems to be the vile lunatic troll here. He doesn't seem to understand how AC motors work, and he does get very upset when this pointed out.

-- 
Bill Sloman, Sydney

Cunthead, know nothing arsehole Bill  Slowman bullshitted .
===============================================
>> > 
> > > > > Perhaps, but to burn the motor takes a lot of power and surely running 
> > > > > the motor from a variac at reduced voltage reduces the liklihood of heat 
> > > > > damage? 
> > > 
> > > > ** Motor current drops in line with applied AC voltage. 
> > 
> > > No, of course it doesn't; 
> > 
> > ** FFS is their no end to the vile lunatic Google troll.
>
> Phil seems to be the vile lunatic troll here.

**  Lets just see about that. 

> He doesn't seem to understand how AC motors work,

** Think I know how fan motors perform, very well. 
     Deal with the fuckers often enough. 

> and he does get very upset when this pointed out. 

**  I see no " pointing out" going on here -  what so fucking ever. 

Just more of the usual wild, unsupported, barking mad assertions from the same old fucking idiots. 
Like cunthead Bill Slowman. 

FYI to all: 

I have a common 40W pedestal fan with a 13 inch dia fan blade. 
Tested a few minutes ago: 

At  240VAC  rms current is 163mA. 
at  200VAC   it became 144. 
at  100VAC  it become  76.
at   50VAC    it become 33. 

by which time the blade was no longer turning. 
Not far off linear, you *must* agree. 

But sanity never certain when dealing with totally psycho, ASD fucked arseholes.


.......  Phil 

On Thursday, October 14, 2021 at 8:29:18 PM UTC+11, palli...@gmail.com wrote:
> Cunthead, know nothing arsehole Bill Slowman bullshitted . 
> ===============================================
> >> > 
> > > > > > Perhaps, but to burn the motor takes a lot of power and surely running 
> > > > > > the motor from a variac at reduced voltage reduces the liklihood of heat 
> > > > > > damage? 
> > > > 
> > > > > ** Motor current drops in line with applied AC voltage. 
> > > 
> > > > No, of course it doesn't;  it drops in line with applied AC voltage minus the
back-EMF of the motor. That back-EMF is missing if the motor isn't
rotating at the intended (circa 1800 RPM in 60 Hz land) rate. 

- I've added the back the stuff Whit3rd posted and Phil snipped, probably because he couldn't make sense of it.

> > > ** FFS is their no end to the vile lunatic Google troll. 
> > 
> > Phil seems to be the vile lunatic troll here.
>
> ** Lets just see about that.
>
> > He doesn't seem to understand how AC motors work,
>
> ** Think I know how fan motors perform, very well. 

Well enough that you don't blow them up all that often, but simple models of what they are doing, and how they are doing it, don't have to be all that accurate or well-founded.

> Deal with the fuckers often enough.

In a fairly standardi situation. always doing much the same job.

> > and he does get very upset when this pointed out.

> ** I see no " pointing out" going on here - what so fucking ever. 

<snip>

Of course you don't.  You snipped the "pointing out" that whit3rd posted, presumably because you couldn't understand it 
 
> Just more of the usual wild, unsupported, barking mad assertions from the same old fucking idiots. 
> 
> FYI to all: 
> 
> I have a common 40W pedestal fan with a 13 inch dia fan blade. 
> Tested a few minutes ago: 
> 
> At 240VAC rms current is 163mA. 
> at 200VAC it became 144. 
> at 100VAC it become 76. 
> at 50VAC it become 33. 
> 
> by which time the blade was no longer turning. 
> Not far off linear, you *must* agree. 

Far enough off to make it perfectly clear that you haven't got a clue about what was actually going on. When the fan is no longer turning, there isn't any back EMF, so the motor windings are just inductors - and not very good inductors, particularly when the magnetic path through the iron gets warm. as it does when the fan isn't rotating.

> But sanity never certain when dealing with totally psycho, ASD fucked arseholes. 

And you are the prize local example of that species. When you do know what you are talking about you can make a lot of sense, but this isn't one of those occasions.

-- 
Bill Sloman, Sydney

Cunthead, know nothing FUCKING  arsehole Bill Slowman bullshitted . 
========================================================= 
>
> > > > > > > Perhaps, but to burn the motor takes a lot of power and surely running 
> > > > > > > the motor from a variac at reduced voltage reduces the liklihood of heat 
> > > > > > > damage? 
> > > > > 
> > > > > > ** Motor current drops in line with applied AC voltage. 
> > > >
> > > > > No, of course it doesn't;

**  Fraid it actually *does* with fan motors.
     ------------------------------------------------------

> 
> > > Phil seems to be the vile lunatic troll here. 
> > 
> > ** Lets just see about that. 
> > 
> > > He doesn't seem to understand how AC motors work, 
> > 
> > ** Think I know how fan motors perform, very well.
> >    Deal with the fuckers often enough.
>
> In a fairly standard situation.

** As is exactly the case in question here. 
   =========================---====
 

> > ** I see no " pointing out" going on here - what so fucking ever.
> 
> Of course you don't.

**   Cos there actually isn't any. 

> > Just more of the usual wild, unsupported, barking mad assertions from the same old fucking idiots. 
> >
> > FYI to all: 
> > 
> > I have a common 40W pedestal fan with a 13 inch dia fan blade. 
> > Tested a few minutes ago: 
> > 
> > At 240VAC rms current is 163mA. 
> > at 200VAC it became 144. 
> > at 100VAC it become 76. 
> > at 50VAC it become 33. 
> > 
> > by which time the blade was no longer turning. 
> > Not far off linear, you *must* agree.
>
> Far enough off to make it perfectly clear that you haven't got a clue about what was actually going on. 

**  That is not supported by the facts -  not one tiny bit.
    ========================================= 

> > But sanity never certain when dealing with totally psycho, ASD fucked arseholes.
>
> And you are the prize local example of that species.
>

**  Not according the the very clear, obvious facts. 

    Slowman is a vile, narcissistic moron with rampant dementia. 

    He exists ONLY to cause harm to the truth and the innocent. 
    ==============================================

    Someone needs to put a stop to him. 



......  Phil