Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old November 4th 19, 04:18 PM posted to sci.electronics.repair
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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?

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Old November 4th 19, 04:32 PM posted to sci.electronics.repair
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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
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Old November 4th 19, 06:20 PM posted to sci.electronics.repair
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Default Variac capacity

On 2019/11/04 8:46 a.m., Bob Engelhardt wrote:
On 11/4/2019 10:32 AM, 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 :-#)#

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Old November 4th 19, 06:33 PM posted to sci.electronics.repair
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Default Variac capacity

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


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Old November 5th 19, 12:43 AM posted to sci.electronics.repair
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Default Variac capacity

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 ****wit 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, ****ing idiot.

Melrose Park, PA


** Must stink up the whole neighbourhood.


...... Phil
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Old November 5th 19, 12:47 AM posted to sci.electronics.repair
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Default Variac capacity

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



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Old November 5th 19, 12:52 AM posted to sci.electronics.repair
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Default Variac capacity



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 bull****.

AC/DC brush motors respond beautifully to Variac control.

So do the motors in regular fans.

Go try it yourself sometime.



..... Phil




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Old November 5th 19, 12:52 AM posted to sci.electronics.repair
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Default Variac capacity

On 2019/11/04 3:43 p.m., Phil Allison wrote:
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 :-#(#
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Old November 5th 19, 01:03 AM posted to sci.electronics.repair
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Default Variac capacity

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 **** 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 "bull**** 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








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