Adding Another Secondary to a Toroid

SRMcGee · 31st March 2009, 12:54 AM

Folks:

I have an Antek 3225 toroid (two 25 V secondaries, 300 VA) which will be used in a Gainclone project for my daughter. The chassis we will use is small (an 80mm tall HiFi2000 Galaxy Maggiorato) and we need to conserve space, so I'd like to wind some additional wire around the toroid and create another 10 to 12 volt secondary to power things like relays (for the source selector) and LEDS for the front panel. Here's the question: what gauge wire should we use? We aren't going to need much current but I don't want to undersize anything and create a safety hazard.

Suggestions?

Thank you,
Scott

sawreyrw · 31st March 2009, 01:38 AM

A rough rule of thumb is 450 amps/cm^2 of copper. So, if you know the RMS current you can calculate the necessary cross sectional area. This, in turn, can be used to determine the wire gauge. For example, 20 gauge magnet wire has a cross sectional area of .00517 cm^2 and can handle 2.32 amps.

SRMcGee · 31st March 2009, 04:45 PM

sawreyrw:

Thank you! Is there a good reason to use magnet wire instead of regular single conductor insulated wire? Radio Shack apparently sells magnet wire but I have single conductor stuff on hand. As noted, my requirements are minimal (probably under 100 mA).

Regards,
Scott

AndrewT · 31st March 2009, 05:17 PM

Hi,
0.6mm diam copper can give upto 800mA. The continuous DC current available will be 400mAdc. 0.5mm <=300mAdc

Insulation simply wastes space. Do ensure it stays cool. Enamel is available in 130degC and higher, the thermoplastic insulations generally available will fail below 100degC.

tinitus · 4th April 2009, 09:57 PM

Hi

It may be different, or may not

I just finished rewinding a toroid with double windings, intended to be used fore speaker xo

Its 5mH and 0.5mH

Coupled in series "the right way" it gives 9mH

But if I reverse one winding I get a low 2mH

Which indicates to me that there is some sort of phasing going on

Maybe you also have to consider the right orientation of the new winding ?

Just realised how to measure the orientation of a power supply toroid, to avoid wrong phase

Am I right on this issue ?

jrenkin · 17th April 2010, 05:22 PM

Quote:

Originally Posted by sawreyrw

A rough rule of thumb is 450 amps/cm^2 of copper. So, if you know the RMS current you can calculate the necessary cross sectional area. This, in turn, can be used to determine the wire gauge. For example, 20 gauge magnet wire has a cross sectional area of .00517 cm^2 and can handle 2.32 amps.

I thought this might be helpful:
American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies

31st March 2009, 12:54 AM	#1
SRMcGee diyAudio Member Join Date: May 2004 Location: Wynnewood, PA	Adding Another Secondary to a Toroid Folks: I have an Antek 3225 toroid (two 25 V secondaries, 300 VA) which will be used in a Gainclone project for my daughter. The chassis we will use is small (an 80mm tall HiFi2000 Galaxy Maggiorato) and we need to conserve space, so I'd like to wind some additional wire around the toroid and create another 10 to 12 volt secondary to power things like relays (for the source selector) and LEDS for the front panel. Here's the question: what gauge wire should we use? We aren't going to need much current but I don't want to undersize anything and create a safety hazard. Suggestions? Thank you, Scott

31st March 2009, 05:17 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, 0.6mm diam copper can give upto 800mA. The continuous DC current available will be 400mAdc. 0.5mm <=300mAdc Insulation simply wastes space. Do ensure it stays cool. Enamel is available in 130degC and higher, the thermoplastic insulations generally available will fail below 100degC. __________________ regards Andrew T.

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31st March 2009, 01:38 AM	#2
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	A rough rule of thumb is 450 amps/cm^2 of copper. So, if you know the RMS current you can calculate the necessary cross sectional area. This, in turn, can be used to determine the wire gauge. For example, 20 gauge magnet wire has a cross sectional area of .00517 cm^2 and can handle 2.32 amps.

31st March 2009, 04:45 PM	#3
SRMcGee diyAudio Member Join Date: May 2004 Location: Wynnewood, PA	sawreyrw: Thank you! Is there a good reason to use magnet wire instead of regular single conductor insulated wire? Radio Shack apparently sells magnet wire but I have single conductor stuff on hand. As noted, my requirements are minimal (probably under 100 mA). Regards, Scott

4th April 2009, 09:57 PM	#5
tinitus diyAudio Moderator Join Date: Nov 2005	Hi It may be different, or may not I just finished rewinding a toroid with double windings, intended to be used fore speaker xo Its 5mH and 0.5mH Coupled in series "the right way" it gives 9mH But if I reverse one winding I get a low 2mH Which indicates to me that there is some sort of phasing going on Maybe you also have to consider the right orientation of the new winding ? Just realised how to measure the orientation of a power supply toroid, to avoid wrong phase Am I right on this issue ?

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