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Old 5th September 2007, 09:54 AM   #1
CJ900RR is offline CJ900RR  Sweden
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Default Searching for toroid, 2x70V seccondary...

I need a toroid with primary winding 220V and seccondary winding of 2x70V, to reach 100V DC. VA-rating should be >800VA. Any ideas where to look?

The closest I have found is 65V and 110V, nothing inbetween.

Alternative I could need some guidance how to reduce voltage from 155V DC to 100V DC using passive components or step-down regulators.

Best regards, Calle....
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Old 5th September 2007, 11:32 AM   #2
paulb is offline paulb  Canada
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You could get a custom one. Why not just use the 2x65V?
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Old 5th September 2007, 11:56 AM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
have you considered adding extra turns to generate the extra 5Vac in each winding?

The wire in a 800VA 65Vac will be sized to pass 6.15Aac continuously.
If you add extra turns using the same diameter wire then you get 70Vac @ 6.15Aac, well not quite, becasue that would imply a higher VA of 861VA. It would be reasonable to assume that the modified winding could safely achieve a VA rating about half way in between say about 830VA.

It's relatively easy to remove the outer insulation and add the couple of dozen turns required. Then carefully rewrap the insulation.

BTW,
what is the mains voltage specification for your chosen transformers? are they really 220Vac or 230Vac?
What is your normal mains supply voltage? How much does it vary hour to hour or season to season?
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Old 6th September 2007, 05:04 AM   #4
CJ900RR is offline CJ900RR  Sweden
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Quote:
Originally posted by paulb
You could get a custom one. Why not just use the 2x65V?
Yes there is allways custom ones, but my guess is that it would be even more expensive....

Quote:
Originally posted by AndrewT
Hi,
have you considered adding extra turns to generate the extra 5Vac in each winding?

The wire in a 800VA 65Vac will be sized to pass 6.15Aac continuously.
If you add extra turns using the same diameter wire then you get 70Vac @ 6.15Aac, well not quite, becasue that would imply a higher VA of 861VA. It would be reasonable to assume that the modified winding could safely achieve a VA rating about half way in between say about 830VA.

It's relatively easy to remove the outer insulation and add the couple of dozen turns required. Then carefully rewrap the insulation.

BTW,
what is the mains voltage specification for your chosen transformers? are they really 220Vac or 230Vac?
What is your normal mains supply voltage? How much does it vary hour to hour or season to season?
It could be a solution to modify a excisting one. But it would be more easy to buya premade one

The mains in Sweden is nowdays 230Vac but I, and allmost everyone else still say 220Vac from old habbit. The voltage usually stays near 230Vac with a +- of about 5Vac.
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Old 6th September 2007, 08:29 AM   #5
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I'd go with the 65-0-65. I very much doubt that you'll notice the difference from 70-0-70.
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Old 6th September 2007, 11:35 AM   #6
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You could use two 25-0-35 torroids stacked. These are readily available.
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Old 6th September 2007, 11:47 AM   #7
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try the site below, if you think Indian quality is ok. i think they will make it for you. it won't be very costly.

http://www.toroidal.com/service.html
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Old 6th September 2007, 11:50 AM   #8
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http://www.toroidal.com/t_toroidal.html
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Old 6th September 2007, 02:55 PM   #9
K-amps is offline K-amps  United States
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Antek on ebay sells 67-0-67 but 110mains... I think they may have dual prims, in whch case hook em in series...
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Old 6th September 2007, 06:12 PM   #10
y8s is offline y8s  United States
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http://www.toroid-transformer.com/

they have 2x68V
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