[Amps] Paralleling plate xfmrs.

[Michael Tope]

Hi Jim,

Hmm, ignoring the impact of primary resistance, a 19.09 ohms secondary 
resistance could (in theory) lead to a current imbalance of 0.96 amps 
with an 18.4 volt difference in secondary voltage. That is to say, the 
transformer with the 5318.4 Volt secondary would source 0.48 amps more 
than it otherwise would if the transformers were perfectly balanced and 
the transformer with the 5300.0 Volt secondary would source 0.48 amps 
less. That is worst case. However, I suspect you can't ignore the 
primary resistance. It will be much lower compared to the secondary, of 
course, but the current in the primary will be much higher, so the 
impact of the primary resistance in terms of current balance could be 
just as large. If that is the case, the secondary imbalance would drop 
by a factor of two (the 5318V transformer would sourcing +240mA and the 
5300V one would be -240mA from a perfect balance).

The resistance of copper goes up with temperature, so the transformer 
with the higher share of the current would run somewhat hotter which 
would tend to reduce the current imbalance compared to what you would 
get if the copper in the two transformers stayed at the same temperature 
(negative feedback). Also, I am ignoring the effects of core B-H curve 
non-linearity. Offhand, I don't know if that comes into play with a 
typical plate transformer. That might be just a function of the 
self-inductance of the windings (i.e. magnetizing current), but I would 
have to crack open a textbook on that question to be sure.

Do you know the primary winding resistance of the subject transformers?

73, Mike W4EF................



On 10/27/2025 1:12 PM, jim.thom jim.thom at telus.net wrote:
>> Jim, do you have data for the winding resistance of the 5300V transformers?
>> 73, Mike W4EF....
> 19.09 ohms on each secondary.
>
> Jim   VE7RF
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