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Old 12th March 2008, 03:55 PM   #21
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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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Old 13th March 2008, 12:53 AM   #22
satoru is offline satoru  United States
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Quote:
Originally posted by jimmyd53
Santoru and JPS,
What is the ballpark price on 115v/300va/18v+18v R Core from your respective sources? Thanks. James
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
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Old 13th March 2008, 04:39 AM   #23
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Satoru. Thank you for your prompt response. I was afraid that the price was going to be high given the weakness of the US dollar. $280 for a pair plus shipping is more than I want to spend. Take care. James
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Old 13th March 2008, 09:13 AM   #24
JPS is offline JPS  India
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Quote:
Santoru and JPS, What is the ballpark price on 115v/300va/18v+18v R Core from your respective sources? Thanks. James
Price sent by email. pdf file showing sizes is attached here.
regards
Attached Files
File Type: pdf rcore-va.pdf (70.4 KB, 251 views)
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Old 13th March 2008, 09:59 AM   #25
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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.
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
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Old 13th March 2008, 10:04 PM   #26
tvi is offline tvi  Australia
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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.


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Old 13th March 2008, 10:39 PM   #27
KSTR is offline KSTR  Germany
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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
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Old 14th March 2008, 05:06 AM   #28
BrianL is offline BrianL  United States
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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.
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Old 14th March 2008, 05:45 PM   #29
KSTR is offline KSTR  Germany
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Quote:
Originally posted by BrianL
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.
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
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Old 15th March 2008, 05:10 AM   #30
BrianL is offline BrianL  United States
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Actually it was a transformer by a European/American company and was meant to sell in the USA.
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