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Re: [Amps] HV transformer and Variac

To: amps@contesting.com
Subject: Re: [Amps] HV transformer and Variac
From: donroden@hiwaay.net
Date: Thu, 23 Jul 2015 08:46:03 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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@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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