[Amps] HV transformer and Variac

[donroden at hiwaay.net]

I agree with Ros.

I've never heard of a pole-pig or an  autoformer get more that just  
above warm running a pair of 4-1000s yellow-orange.   If you have it  
.... use it.

Don W4DNR


Quoting Ros <ros at netbox.com>:

> First, the Variac is not a transformer in the classical sense, it is  
> an autoformer or auto-trans-former.  It will not lose efficiency.  
> Here is a schematic of one and perhaps you can see why it won't lose  
> efficiency.
>
> A common transformer has less efficiency than an autoformer due to  
> core loses, eddy currents, hysteresis, more heat (I2R losses), etc.
>
>
>
> Ros, W5BRY
>
>
>
>
> On 7/22/2015 8:28 PM, Steve Bookout wrote:
>> Hello all,
>>
>> Thanks to everyone for the informative responses.  Although I've  
>> now got more info to use in order to figure out what I am going to  
>> do, I'm not sure what that will be.
>>
>> It's really just a bit 'hot' for my needs and if I turn it down  
>> with a variac, regulation may suffer.  I do have a stack of two  
>> variacs on a common shaft, and although they are large, I don't  
>> know what their actual specs are.  Something for me to check.
>>
>> 73 de Steve, NR4M
>>
>> On 7/21/2015 03:03 , Steve Bookout wrote:
>>> Hello all.
>>>
>>> Question for the experts.
>>>
>>> How does using a Variac to control the output of a HV transformer  
>>> affect things like efficiency?
>>>
>>> I think it would be reasonable to think that a transformer  
>>> operated at less than rated input voltage would be less efficient  
>>> than one run at full primary voltage.  I mean, it cost 'something'  
>>> just to make a transformer act like a transformer.
>>>
>>> I ask because I have a perfectly fine 'pole pig' transformer rated  
>>> at 5 KVA.  7200 AC volts on the output (reversed) is a bit much  
>>> for my needs, so was wondering what the trade-off would be if it  
>>> were run at considerably less than 220 input.
>>>
>>> I can see this is a better xformer for a 4cx10000, than anything I  
>>> would be using, but I have what I have.
>>>
>>> 73 de Steve, NR4M
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>>
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