[Amps] HV transformer and Variac

[Ros]

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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