Variac capacity

[Bob Engelhardt]

I have a Ward-Leonard variac that was originally used, I think, for
theatrical lighting. It is labeled "20A resistive, 14A otherwise". I
suppose "otherwise" means motors, but motors aren't usually run off
variacs. What else could "otherwise" be?

Also, why only 14A?

 

[pfjw@aol.com]

On Monday, November 4, 2019 at 10:19:00 AM UTC-5, Bob Engelhardt wrote:

I have a Ward-Leonard variac that was originally used, I think, for
theatrical lighting. It is labeled "20A resistive, 14A otherwise". I
suppose "otherwise" means motors, but motors aren't usually run off
variacs. What else could "otherwise" be?

Also, why only 14A?

"Otherwise" would be non-resistive loads - which would be reactive (capacitance) loads, or inductive (Motors and such) loads.

From another website, put simply:

When electricity flows through a circuit, there are points on the circuit, called loads, where energy is drawn away. Loads, in essence, are objects that use electricity--such as light bulbs. There are a variety of classification systems, but one way you can divide loads is into resistive, capacative, inductive or a combination of these types.

So:

A Variac "sees" a resistive load as a constant, whereas reactive and inductive loads will vary, so the amount of current the variac "sees" may be greater than the constant load at onset, shutdown, or when the load varies. Hence the derating.

Peter Wieck
Melrose Park, PA

 

[Bob Engelhardt]

On 11/4/2019 10:32 AM, pfjw@aol.com wrote:
> "Otherwise" would be non-resistive loads - which would be reactive (capacitance) loads, or inductive (Motors and such) loads. ...

Right ... I should have been more specific: what DEVICES would be
reactive? Motors, but motors really don't like being run on variacs.
Even universal motors are terrible at less than rated voltage. Assuming
theatrical stage use makes it more mysterious as to what devices might
be "otherwise".

> A Variac "sees" a resistive load as a constant, whereas reactive and inductive loads will vary, so the amount of current the variac "sees" may be greater than the constant load at onset, shutdown, or when the load varies. Hence the derating.

But even resistive loads, especially theatrical lights, have in-rush
much higher that steady state. And a variac has a huge thermal sink to
handle transients (this variac weighs 20lbs).

Maybe it's the high voltage kick on inductive turn-off that's the
problem. The kick would be proportional to current, wouldn't it (more
energy to dissipate)? Do motors show inductive kick on turn-off?

Another thought - Ward-Leonard's main business was motor controllers,
So the theatrical use assumption may be wrong.

 

[John Robertson]

On 2019/11/04 8:46 a.m., Bob Engelhardt wrote:

On 11/4/2019 10:32 AM, pfjw@aol.com wrote:
"Otherwise" would be non-resistive loads - which would be reactive
(capacitance) loads, or inductive (Motors and such) loads. ...

Right ... I should have been more specific: what DEVICES would be
reactive?  Motors, but motors really don't like being run on variacs.
Even universal motors are terrible at less than rated voltage.  Assuming
theatrical stage use makes it more mysterious as to what devices might
be "otherwise".

A Variac "sees" a resistive load as a constant, whereas reactive and
inductive loads will vary, so the amount of current the variac "sees"
may be greater than the constant load at onset, shutdown, or when the
load varies. Hence the derating.

But even resistive loads, especially theatrical lights, have in-rush
much higher that steady state.  And a variac has a huge thermal sink to
handle transients (this variac weighs 20lbs).

...

When I was one of the geeks working the theatre lighting at our high
school in Toronto (Northern Secondary School - mid to late 60s) we used
the large lever variac style dimmers to bring the lights up. The school
had (as I recall) 2500 students and a huge auditorium with a great many
row and spot lights for productions.

So the idea was you were supposed to bring the lights up, not in a
switched on rush, but as fast as you would raise the lever - a second or
two - which allowed for the filament to heat up a bit slower and saved
replacement bulbs. There may even have been a minimum setting to act as
a 'keep-alive' to preheat the filaments of the big spots - I just don't
recall...

John :-#)#

 

[pfjw@aol.com]

On Monday, November 4, 2019 at 11:47:31 AM UTC-5, Bob Engelhardt wrote:

Another thought - Ward-Leonard's main business was motor controllers,
So the theatrical use assumption may be wrong.

Keep in mind that the Kleig Light (Carbon-arc) and mercury-vapor lamps, some of which are dimmable to a point, are reactive loads. And, the Kleig light as stage lighting persisted into the 1970s on movie sets (with proper filtering against dangerous actinic wavelengths) and mercury-vapor devices are still used in some lighting designs. So, if a lighting device required a strike function, and repetitive in some cases, that would certainly de-rate the Variac as compared to a simple incandescent/resistive load.

Note also that brush-type AC motors may have variable speed controls - such as on your corded hand-drill. I can think of any number of devices that would use such a motor and also allow for the use of a large Variac. A theatrical variable wind machine comes immediately to mind.


Peter Wieck
Melrose Park, PA

 

[Phil Allison]

pf...@aol.com wrote:

-------------------

"Otherwise" would be non-resistive loads - which would be reactive (capacitance) loads, or inductive (Motors and such) loads.

From another website, put simply:

When electricity flows through a circuit, there are points on the circuit, called loads, where energy is drawn away. Loads, in essence, are objects that use electricity--such as light bulbs. There are a variety of classification systems, but one way you can divide loads is into resistive, capacative, inductive or a combination of these types.

So:

A Variac "sees" a resistive load as a constant, whereas reactive and inductive loads will vary, so the amount of current the variac "sees" may be greater than the constant load at onset, shutdown, or when the load varies. Hence the derating.

** ROTFL

The Weaky criminal fuckwit really needs to see a doctor.

His chronic verbal diarrhoea is getting very serious.

The above is all complete DRIVEL.

Peter Wieck

** Wot a know noting, fucking idiot.

> Melrose Park, PA

** Must stink up the whole neighbourhood.


...... Phil

 

[Phil Allison]

Bob Engelhardt wrote:

----------------------

I have a Ward-Leonard variac that was originally used, I think, for
theatrical lighting. It is labeled "20A resistive, 14A otherwise".

I suppose "otherwise" means motors, but motors aren't usually run off
variacs. What else could "otherwise" be?

Also, why only 14A?

** The variac itself has no concern about the load other than the RMS current value. Cos that is what heats the windings.

Is there a switch on the unit ?

That part may be rated at 14A inductive due to potential arcing at switch off.


..... Phil

 

[Phil Allison]

Bob Engelhardt wrote:

-----------------------

Right ... I should have been more specific: what DEVICES would be
reactive? Motors, but motors really don't like being run on variacs.
Even universal motors are terrible at less than rated voltage.

** What bullshit.

AC/DC brush motors respond beautifully to Variac control.

So do the motors in regular fans.

Go try it yourself sometime.



..... Phil

 

[John Robertson]

On 2019/11/04 3:43 p.m., Phil Allison wrote:

pf...@aol.com wrote:

-------------------

"Otherwise" would be non-resistive loads - which would be reactive (capacitance) loads, or inductive (Motors and such) loads.

From another website, put simply:

When electricity flows through a circuit, there are points on the circuit, called loads, where energy is drawn away. Loads, in essence, are objects that use electricity--such as light bulbs. There are a variety of classification systems, but one way you can divide loads is into resistive, capacative, inductive or a combination of these types.

So:

A Variac "sees" a resistive load as a constant, whereas reactive and inductive loads will vary, so the amount of current the variac "sees" may be greater than the constant load at onset, shutdown, or when the load varies. Hence the derating.


** ROTFL

....

If Mr. Wieck is incorrect why not point out his errors instead of simply
insulting him?

We all make mistakes, but only adults know how to correct, admit to, and
deal with errors.

Peter Wieck


** Wot a know noting, f...

Let's get personal, eh? That works so well in a discussion.

Melrose Park, PA

** Must stink up the whole neighbourhood.


...... Phil

Sheesh...

John :-#(#

 

[Phil Allison]

John Robertson wrote:

----------------------

"Otherwise" would be non-resistive loads - which would be reactive (capacitance) loads, or inductive (Motors and such) loads.

From another website, put simply:

When electricity flows through a circuit, there are points on the circuit, called loads, where energy is drawn away. Loads, in essence, are objects that use electricity--such as light bulbs. There are a variety of classification systems, but one way you can divide loads is into resistive, capacative, inductive or a combination of these types.

So:

A Variac "sees" a resistive load as a constant, whereas reactive and inductive loads will vary, so the amount of current the variac "sees" may be greater than the constant load at onset, shutdown, or when the load varies.. Hence the derating.


** ROTFL


If Mr. Wieck is incorrect why not point out his errors instead of simply
insulting him?

** What he posted is way beyond mere correction.

The guy is a deranged old cunt with a vile attitude.

He only ever responds to correction with malicious jibes at me.


> We all make mistakes,

** Some folk make nothing but mistakes.

Known usually as "bullshit artists".

Weaky is a monstrous example.

Be fighting with him for almost 20 years.

Peter Wieck


** Wot a know noting, f...

Let's get personal, eh?

** I want the asshole gone - ASAP.

His bad advice ruins other's attempts to post good advice.

Melrose Park, PA

** Must stink up the whole neighbourhood.


...... Phil


Sheesh...

** You are one grade A, narcissistic dope - pal.


...... Phil

 

[Bob Engelhardt]

On 11/4/2019 12:20 PM, John Robertson wrote:
....

So the idea was you were supposed to bring the lights up, not in a
switched on rush, but as fast as you would raise the lever - a second or
two - which allowed for the filament to heat up a bit slower and saved
replacement bulbs. ...

That makes sense, thanks.

 

[Bob Engelhardt]

On 11/4/2019 12:33 PM, pfjw@aol.com wrote:
> Keep in mind that the Kleig Light (Carbon-arc) and mercury-vapor lamps, some of which are dimmable to a point, are reactive loads. And, the Kleig light as stage lighting persisted into the 1970s on movie sets (with proper filtering against dangerous actinic wavelengths) and mercury-vapor devices are still used in some lighting designs. So, if a lighting device required a strike function, and repetitive in some cases, that would certainly de-rate the Variac as compared to a simple incandescent/resistive load.

I never would have thought of them as reactive, but it's interesting.

> Note also that brush-type AC motors may have variable speed controls - such as on your corded hand-drill. I can think of any number of devices that would use such a motor and also allow for the use of a large Variac. A theatrical variable wind machine comes immediately to mind.

My limited experience with single-speed universal (brushed) motors is
that reducing the voltage reduced the speed, but also the torque. To an
extent that it was not useful.

 

[Phil Allison]

Bob Engelhardt wrote:

--------------------

My limited experience with single-speed universal (brushed) motors is
that reducing the voltage reduced the speed, but also the torque. To an
extent that it was not useful.

** No so.

Torque is proportional to current draw, which depends in turn on the load applied. Brush motors have a max current limit beyond which the com begins to burn.

So the applied voltage can be well below the rating and the torque available remain the same, but at a lower rpm.

A triac controller does a good job too and SCR ones have back emf ( ie speed ) feedback that is very useful.

Induction fans can be varied from full to just ticking over with Variac.

The usual speed controls use series switched inductors or capacitors to drop voltage.


....... Phil

 

On Tuesday, 5 November 2019 00:04:02 UTC, Phil Allison wrote:

> ** You are one grade A, narcissistic dope - pal.

I doubt you have any pals here.

 

On Monday, 4 November 2019 15:19:00 UTC, Bob Engelhardt wrote:

I have a Ward-Leonard variac that was originally used, I think, for
theatrical lighting. It is labeled "20A resistive, 14A otherwise". I
suppose "otherwise" means motors, but motors aren't usually run off
variacs. What else could "otherwise" be?

Also, why only 14A?

Fluorescent lighting was also pf not 1. We had a lot of fl lighting on a big variac. It had standard electromagnetic ballasts, and contrary to oft stated opinion it did dim well enough - we knew to not keep it running dimmed, and it blacked out at a low light level, it wasn't perfect but certainly good enough.

Discharge light sources were always pf not 1 in the pre-electronic days, whether fluorescent, carbon arc or mercury vapour. i was never proportional to v with them, and in most cases the ballasts were inductive not resistive. And of course projector carbon arcs ran through mercury rectifiers to give asymmetric electrode heating to minimise the light source size.


NT

 

[Phil Allison]

Some moronic Psychopath tabb...@gmail.com wrote:

-----------------------------------------

Phil Allison wrote:

** You are one grade A, narcissistic dope - pal.

I doubt you have any pals here.

** I bet even your dog cannot stand a vile pig like you.


....... Phil

 

[Phil Allison]

Some complete MOLRON called tabb...@gmail.com wrote:

---------------------------------------------------------

Also, why only 14A?

Fluorescent lighting was also pf not 1.

** Irrelevant to the RMS current draw.


> Discharge light sources were always pf not 1 in the pre-electronic days, whether fluorescent, carbon arc or mercury vapour.

** Irrelevant to the RMS current draw.

The lying fuckwit dose not even understand " I squared R" heating.


.... Phil

 

On Tuesday, 5 November 2019 05:55:12 UTC, Phil Allison wrote:

Some moronic Psychopath tabby wrote:

-----------------------------------------

Phil Allison wrote:

** You are one grade A, narcissistic dope - pal.

I doubt you have any pals here.


** I bet even your dog cannot stand a vile pig like you.


...... Phil

So you're a failure at betting too eh. Also no understanding of species or psych 101.

 

[Phil Allison]

Some complete MORON called tabby wrote:

--------------------------------------------------------


** Irrelevant to the RMS current draw.

It's not, and I didn't claim it was, but hey.

** Three deliberate lies in one short sentence.

Might be a bullshit record.



...... Phil

The lying fuckwit dose not even understand " I squared R" heating.


... Phil

that makes you the lying fool.

I see you've not learnt to spell moron yet. And at the risk of stating the obvious, we don't have any morons (or 'molrons') on this group. Maybe you should look the word up some time.


NT

 

On Tuesday, 5 November 2019 20:31:27 UTC, Phil Allison wrote:

Some complete MORON called tabby wrote:

** Irrelevant to the RMS current draw.

It's not, and I didn't claim it was, but hey.


** Three deliberate lies in one short sentence.

Might be a bullshit record.



..... Phil

you've outstupided yourself.