Hi Ros, to split hairs here, one would say the autotransformer would loose
very little efficiency. As you know, when there is copper wire and there is
current, there will be a loss of current squared times resistance.
The majority of the current would be in the turns of the autotransformer
between the input and output terminals so the loss would be related to the
input to output voltage ratio.
That is my personal understanding and subject to correction.
73,
Gerald K5GW
In a message dated 7/23/2015 8:26:29 A.M. Central Daylight Time,
ros@netbox.com writes:
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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