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Selectronic Rcore transformer
Selectronic Rcore transformer
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Old 5th December 2015, 07:32 AM   #1
AndrewT is offline AndrewT  Scotland
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Default Selectronic Rcore transformer

The three transformers have matching wiring colour codes.
Each limb of the Rcore has a half primary and half of the secondaries on it.
i.e. the half primary is close coupled to the half secondary. This is the correct way to build an Ccore and an Rcore.

The two labeled transformers show:
30VA
Primaire: 117Vx2 Bleu / Noir
Secondaires: 18Vx2 Bleu / Jaune
. . . . . . . . . 18Vx2 Rouge / Blanc
Ecran electro-statique: Masse Noir

One primary is wire coded Blue/White, the other primary is wire coded Blue/White
For conventional wiring to 110/120Vac one would connect the two Blue wires to Mains Live/Hot and connect the two White wires to Neutral/Cold
and
for 220/240Vac one would connect Blue of one primary to the White of the other primary. Then connect the Blue wire to Mains Live/Hot and connect the White wire to Neutral/Cold
NO !!!!!
the blue and white do not indicate the phasing of the windings. All three transformers are colour exactly the same way, so it's not a building error.

For 220/240Vac the two white wires are connected.
Then the Mains Live goes to one Blue and the Mains Neutral goes to the other Blue.


The same phasing error occurs on the secondaries.
One limb has two windings Blue/Yellow and Red/Black. Connect Yellow to Red for a series connection (in this case 36Vac) and then Blue and Black are the output.

Repeat for the other limb with it's pair of secondaries.

Now for a dual polarity supply where the windings are series connected, one needs to connect the two Black wires.
The 72Vac output is from the two Blue wires.

This is the same for all three Rcores from selectronic.

The 120VA Rcore came without any labeling. Fortunately the colour coding is identical to the 30VA

I cannot understand why the manufacturer, Shilchar, has coded the two limbs differently for phase.
I cannot understand why Selectronic does not state that one limb (both primary and secondaries) are out of phase with the other limb.

Have any of you found the same, or was the phasing correctly coded on your Selectronic/Shilchar Rcores?

Use a Mains Bulb Tester to check the primary wiring. A Variac does not prevent damage with this wire coding error.
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Last edited by AndrewT; 5th December 2015 at 07:46 AM.
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Old 5th December 2015, 07:36 AM   #2
AndrewT is offline AndrewT  Scotland
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The regulation when checked with 234Vac applied to the series connected dual primaries is:
30VA 25.5% transformer regulation,
Primary winding resistance 152.5r
Secondary winding resistance 18.4r

120VA 15.1% transformer regulation.
Primary winding resistance 18.14r
Secondary winding resistance 2.49r

At full power the copper losses would be 6.9W for the 30VA indicating a maximum efficiency of ~81.3%
the 120VA has a maximum efficiency of ~90.4% and copper losses are 11.7W

As confirmed by another Thread, I don't know how to work out the iron losses when the transformers are delivering full power into a resistive load.
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Last edited by AndrewT; 5th December 2015 at 07:44 AM.
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Old 5th December 2015, 08:06 AM   #3
TonyTecson is offline TonyTecson  Philippines
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Selectronic Rcore transformer
small traffos will have lower efficiency than the bigger ones...
otherwise they look normal, just use them...
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Old 5th December 2015, 08:34 AM   #4
Elvee is offline Elvee  Belgium
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The phasing conventions of transformers are wildly different dependent on the tastes and culture of the manufacturer.
Never take anything for granted.

Quote:
Originally Posted by AndrewT View Post
As confirmed by another Thread, I don't know how to work out the iron losses when the transformers are delivering full power into a resistive load.
The iron losses are practically unchanged between zero and full load (they decrease slightly when loaded).
You can measure them open circuit, using a real wattmeter (I think I showed an example of such an instrument).
For very small transformer, there will be a second order interaction between iron and copper: the magnetizing current is so high that it becomes sufficient to generate non-negligible copper losses.
You can correct the iron losses value by subtracting the Im²R from the global open circuit losses.
For large, properly designed transformers, this is not necessary
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Old 5th December 2015, 08:36 AM   #5
AndrewT is offline AndrewT  Scotland
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I know that small transformers have lower efficiency and larger transformers have higher efficiency.
I know that EI and toroid have different efficiencies.

I am giving some Rcore data that may be useful to others. These are the first Rcore transformer I have had the chance to see/measure.

There was talk on another Thread that Rcore was more efficient than toroid. I asked the author for some data. He had misused the word as a result of translation, he meant something other than efficiency.
So far I have never seen comparison of Rcore to toroid transformer efficiencies.
I suspect that Rcore may have a slightly lower efficiency than Toroid, if both are designed to similar parameters/brief.
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Last edited by AndrewT; 5th December 2015 at 08:51 AM.
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Old 5th December 2015, 08:40 AM   #6
TonyTecson is offline TonyTecson  Philippines
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Selectronic Rcore transformer
rcores will be smaller and weighs less than a comparable EI of the same rating...
though to be honest i have not used any of them in my project, just saw them in some gears that came my way..
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Old 11th August 2017, 09:15 PM   #7
scoobis is offline scoobis
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Quote:
Originally Posted by AndrewT View Post
The regulation when checked with 234Vac applied to the series connected dual primaries is:
30VA 25.5% transformer regulation,
Primary winding resistance 152.5r
Secondary winding resistance 18.4r
Do they rate the voltage at full load?

Does that mean your getting 22.5v with no load?
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Old 12th August 2017, 09:00 AM   #8
AndrewT is offline AndrewT  Scotland
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Transformers are rated at full rated load.
The label on the 30VA transformer states primaries are rated @ 117Vac
Using that information I tested at that voltage.
The output without any load was 22.6Vac.
That indicates a transformer regulation of 25.5%

I can only report what I could measure.

I suspect these Shilcar manufactured transformers are being labeled incorrectly.
But I have no way to determine the real VA rating, nor the maximum operating temperature.
Selectronic have stopped selling these transformers.
I wonder why?
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Old 12th August 2017, 09:02 AM   #9
TonyTecson is offline TonyTecson  Philippines
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Selectronic Rcore transformer
yes, so expect the unloaded voltages on the secondary to be higher....
it will drop to rated spec when rated current is drawn...
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Old 12th August 2017, 09:55 PM   #10
scoobis is offline scoobis
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i contacted one of the Chinese suppliers of r-core transformers off ebay and just got the replies today. This one i inquired on is dual 15v transformer 30VA r-core. The brand of r-core was called Zero Zone (I never used them and not vouching for them at all)

They stated ther transformer voltages were rated at a 50% load 115v in, and there 15v transformer outputs ~16.5 at no load. i believe this correlates to about a ~20% regulation assuming the regulation is linear, which, if i understand the theory right it should be. or 10% if you derated down to 15VA

This also this would mean at my local 120v - no load voltage would be closer to ~17.2v and id have to calculate off that.

But it really brings up something important. that the voltage ratings are not necessarily at 100% load, depending on the manufacturer.

Caveat Emptor - always ask or find the details of any ratings.
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