Differences between power transformers

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
106
Hello. I have 2 transformers:
1. Toroidal transformer, primary 230V, secondary 2x15Vac connected in series to have 30V and 100VA total power
2. E+I sheets transformer, same primary, but with only one 30Vac secondary, and 120VA power.

The problem is when powering a load, for example when using the transformer for a variable power supply, the E+I transformer output goes down to 29Vac, and the output of a rectifier and filter, made by a 8A bridge rectifier and 3X2200uF/63V and one 4700uF/80V in parallel is 33Vdc, when powering an 1.6A load.
When using the toroidal transformer to power the same variable power supply with the same rectifier and filter as described above, which is powering the same 1.6A load, the output of the toroidal transformer is 30Vac and the voltage after filtering is 37-38Vdc.
While no load, the output of the 2 transformers are:
1. 31.72Vac
2. 30.51Vac
With 1.8A load the output of E+I transformer is 29.6Vac, and with the same load, the output of the toroidal transformer is 30.2Vac.

My misunderstanding is why the rectified and filtered voltage is lower when using the transformer at point 2, despite its more VA ?
 

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
106
Ok... that's good to know, but... the efficiency of the transformer can make the rectified and filtered voltage be lower if the rectifier input voltage is about the same (1-1.5Vac difference) ?
I will mention that in load, the difference between the 2 transformers is 1-1.5Vac...
 

schmitt trigger

Joined Jul 12, 2010
475
Measure the DC resistance of the windings.
I could tell you with almost 100% certainty that the toroid’s windings will be significantly lower.
Why? Because of the shorter mean-turn length.
 

LowQCab

Joined Nov 6, 2012
1,372
The extra efficiency of the Toroidal Transformer translates in to
better "Voltage Regulation", ( this is an actual Transformer Specification ),
meaning less Voltage "sag" under load.
Generally the only way to tell if a Toroidal Transformer is over-loaded is
to check its actual operating-temperature against its specified temperature range.
.
.
.
 

MaxHeadRoom

Joined Jul 18, 2013
23,951
From my experience with adding/reducing turns/winding's on both types is IE are around 5.5 turns/volt, toroidal 2.5 turns/v, maximum.
 

Thread Starter

mike_the_begginer

Joined Dec 7, 2019
106
I measured the DC resistance of the secondary windings: toroidal = 0.7 ohms, the other transformer = 0.6 ohms, the primary windings: toroidal = 15.1 ohms, the other transformer = 12.8 ohms.
 
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