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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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#1
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Variac capacity
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? |
#2
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Variac capacity
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 |
#3
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Variac capacity
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#5
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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 |
#6
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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 |
#7
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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 |
#8
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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 |
#9
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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 :-#(# |
#10
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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 |
#11
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Variac capacity
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. |
#12
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Variac capacity
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#13
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Variac capacity
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 |
#14
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Variac capacity
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. |
#15
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Variac capacity
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 |
#16
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Variac capacity
Some moronic Psychopath 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 |
#17
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Variac capacity
Some complete MOLRON called 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 ****wit dose not even understand " I squared R" heating. .... Phil |
#18
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Variac capacity
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. |
#19
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Variac capacity
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 bull**** record. ...... Phil The lying ****wit 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 |
#20
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Variac capacity
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 bull**** record. ..... Phil you've outstupided yourself. |
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