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Old 8th March 2014, 08:42 AM   #571
AndrewT is offline AndrewT  Scotland
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AJT,
do you use a different flux for the different thicknesses and types?
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Old 8th March 2014, 09:21 AM   #572
AJT is offline AJT  Philippines
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Quote:
Originally Posted by AndrewT View Post
AJT,
do you use a different flux for the different thicknesses and types?
yes, if the core material is M6 quality i use 1T,
if low quality i use down to 0.6T
if i do not know where the core came from, i assume it as low quality...
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Old 4th April 2014, 06:50 AM   #573
rawbas is offline rawbas  Philippines
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Hi Tony,

Nice to see this thread. I would like to ask for some help. I have a toroid trafo, and I wanted to rewind it but I am not sure what is the VA rating. Here is the dimension,
(od= 4.5 inches, id= 2.5 inches, h= 2 inches).

Thanks
Ren
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Old 4th April 2014, 09:25 AM   #574
AJT is offline AJT  Philippines
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Quote:
Originally Posted by rawbas View Post
Hi Tony,

Nice to see this thread. I would like to ask for some help. I have a toroid trafo, and I wanted to rewind it but I am not sure what is the VA rating. Here is the dimension,
(od= 4.5 inches, id= 2.5 inches, h= 2 inches).

Thanks
Ren
VA is about 300 to 350...assuming that your dimensions are bare core...
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Old 4th April 2014, 09:25 AM   #575
AndrewT is offline AndrewT  Scotland
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Are those the iron core dimensions, or the overall size with the windings intact?
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Old 5th April 2014, 05:54 PM   #576
rawbas is offline rawbas  Philippines
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yes, it is bare core..

Thanks Tony.
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Old 6th April 2014, 01:18 AM   #577
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no, that core is good for a lot more than 300 va.

you should be able to wind the primary with 230-245 turns of 15 awg wire, for 1.6-1.5T

about .5 ohms primary resistance.. 5 amps works out to 12 watts of primary copper loss at 720 watt load.
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Old 6th April 2014, 01:23 AM   #578
AJT is offline AJT  Philippines
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i tend to be conservative in my traffo builds...for EI i seldom went beyond 1T, since EI cores available here in Manila are low quality ones, i operate them at 0.6T average...

i suppose you can get more out of that torroid, but question is at what temperature rise?

if you live in an area where ambient temperatures are in the low 20*C you can operate the traffo more aggressively
, otherwise in our place where ambient temperatures can go as high as 40*C, then you would tend to be conservative....
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Old 6th April 2014, 01:29 AM   #579
AJT is offline AJT  Philippines
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Quote:
you should be able to wind the primary with 230-245 turns of 15 awg wire, for 1.6-1.5T
this assumes 120 volt primary?

in our country 230volt is common...
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Old 6th April 2014, 04:54 AM   #580
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small transformers typically run copper losses at 2-10 fold the no load core loss.

since copper loss follows the inverse of flux squared assuming constant copper volume, well, you can find your own optimal operating point yourself.

but cutting the flux down to 1T to save 2 watts of no load loss, when you're going to burn 15? times that in the copper isn't really smart.

of course leakage flux is a problem, so don't try and run it at 1.8T...
yes, of course its for 120vac. double the turns and add 20% for 50 hz, 18 awg would be more appropriate

Last edited by johansen; 6th April 2014 at 05:03 AM.
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