R Core Transformers

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#22
jimmyd53 said:
Santoru and JPS,
What is the ballpark price on 115v/300va/18v+18v R Core from your respective sources? Thanks. James
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300VA R core, 18+18 V secondary with shielding would be around $140 (Yen is strong now) from Phoenix in Japan. Quantity discount is 30% off for ordering 10 of same specification. Shipping will be added but shipping multiple transformers together saves a lot there, too.

Satoru
 
#25
I have looked at a number of vendors mentioned in this thread as well as eBay. As someone mentioned, almost all appear to be made in China no matter where you purchase them. I have not been able to determine whether any of these transormers are built to appropriate safety standards, i.e., UL, CSA, or any of the various European "alphabet soup" of regulatory agencies. Given the horror stories about the lack of quality and quality control in Chinese manufacturing, I'm extremely concerned about the very real possibility of one of these transformers burning my house down after some amount of time. Even the apparently reputable Selectronic company in France gives no indication of agency approval for these transformers.
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Hi Brian,

Could this be helpful for you?

http://www.lenco-elect.com/r_core_transformers.htm

Does anyone know if an R-Core transformer will show the same kind of attenuation of HF as an Ei-core trafo?

Karsten
 
#26
I believe they are constucted like a C-Core with the primary on one side and the secondary on the other, so they have better isolation than a EI and don't suffer losses from the gap of the C-Core or the possible miss alignment of the 2 sections.


Ragards
James
 
#27
I'm wondering about this, too. I would guess, from the claim that stray fields are arranged to cancel, there should be 1/2 pri and 1/2 sec on each leg, hopefully well seperated (split bobbins for low coupling capacitance). To be a perfect tranny there would also be a need for a electrostatic screen layer encapsulating the primary to reduce capacitive coupling. I suspect R-cores to be very sensitive to DC, which is a disadvantage.

For the german speaking folks, here is a reseller in switzerland who seems to have some types available:
http://www.hifituning.ch/transfor.htm

- Klaus
 
#28
Karsten, not exactly helpful. While they have a few words on the left side of the screen, there is no other information. I believe that someone checked with this Lenco outfit and found that they can't supply transformers.

JPS, just because UL and CSA have offices in China is no indication that any Chinese transformer you purchase is UL certified. I repeat my comment. I have found no web vendor from whom I can actually purchase an R-core transformer that indicates that their transformer is UL (or CSA, etc.) certified. Just because some Chinese or Indian factory makes "good" transformers for some customers does not mean that the ones that make it out to hobbyists is the same thing. Ask Mattel what happened to the quality lead-free paint that they shipped to their Chinese contract manufacturer.

I will check out this Lenco company and see if they really make their own USA-made transformers and what their certifications are.

Just for reference, even some of the respected toroid vendors have models that are not UL listed as I found when attempting to source one for a product I was designing.
 
#29
BrianL said:
Just for reference, even some of the respected toroid vendors have models that are not UL listed as I found when attempting to source one for a product I was designing.
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This is normal practice, because it depends on the region of market which certificate(s) a product will have/need. No need for north-american standards (as per UL) for a xformer with only 230V primaries. So IF a transformer has at least any certificate (and be it CCC, for the chinese market) it's certainly safe enough, as those standards don't differ dramatically. UL isn't the only one for your region, it just happens to be the most respected.

WRT transformes, I know of many european manufacturers which have full approvals for local and specific target markets, but not UL (and North-America isn't a target, therefore). Although this can be usually had as an option, at extra cost, and is normally combined with a power derating for the transformer (which might indicate that the UL approval is more strict in thermal issues).

- Klaus
 
#32
What is the differences between an O-Core and a normal Toroid transformer?
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Standard toroid has square cross section. O core or
R-toroid as we call it has round cross section.

Standard C core has square cross section and is in two halves. R-core has round corss section and is a single piece made with silicon steel strip.
 
#34
Hi again BrianL - and others!

BrianL
JPS, just because UL and CSA have offices in China is no indication that any Chinese transformer you purchase is UL certified
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Sorry if I made a little mistake. However, I have found a chinese producer of (high quality?) R-Core transformers. This company states (under "Construction and safety"):

The entire production process, no matter whether materials, manufacturing, or survey and inspection, is under strict control. Our products are certified to meet the international safety standards of different countries, such as UL, TUV, VDE and CE, etc.
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http://www.rn-core.com/english/products/sort285.asp

Hope that this helps and that I didn´t make another little mistake ;-)

Kind regards

Karsten
 
#36
side note:

THLAudio in Thailand listed a few dozen dual 42V secondary 280VA R-core transformers they removed from Proton amps, for $15 each.
With added P&H costs, pretty interesting for the Ozyania blokes.
Unfortunately, Dutch customs would fry my heiney if i ordered a couple.

(for the weak of mind: Proton is a Thai audio gear manufacturer, the (NAD designed) D-1200 from 1987 was pretty much the numero-1 power amp with R-core transformers inside.)


Edit-to :Link

PS : James, TY for the Nikko info, no doubt Mr Tsunemoto would agree that i should be flogged in public by a bunch of leather motorcycle dykes for my ignorance. (if only)
 
#37
BrianL

Karsten,

Interesting,

But now we're back to "where can you purchase them"...
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Hi Brian,

Don´t be afraid to drop the company an email or give them a phone call (email-addresses and phone numbers are shown).

Modern chinese companys have employees who speak very good english. If you are strictly looking for shops where to buy R-Core trafos locally I might, unfortunately, not be able to help you.

I do not know about the prices from the chinese factory, but maybe a group buy could be interesting???

The primary reason for me to show the link was due to the question about different international approvals. At least in the picure their R-Core trafos are good looking 🙂

Kind regards

Karsten
 
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