2 transformers instead of "dual secondary" ?

neutron7 · 6th November 2005, 10:19 PM

parts express has these little torroids for sale for $5. they are 14v CT. i guerss they are they are approx 60 - 80va by comparing the weight to hammond ones.

anyways i was wondering if it would be safe to use 2 of them as a 28 + 28 by wiring them in parrallel on the primary side. what about the phase of the secondaries, does that have any effect? please see attached image

i was thinking of 2 per channel, and a fifth one for the preamp, thats $25

doh they are out of stock anyways

bogicp · 6th November 2005, 11:28 PM

Quote:

Originally posted by neutron7
parts express has these little torroids for sale for $5. they are 14v CT. i guerss they are they are approx 60 - 80va by comparing the weight to hammond ones.

anyways i was wondering if it would be safe to use 2 of them as a 28 + 28 by wiring them in parrallel on the primary side. what about the phase of the secondaries, does that have any effect? please see attached image

i was thinking of 2 per channel, and a fifth one for the preamp, thats $25

doh they are out of stock anyways

Anyway, your wiring schematic is OK.

best regards

-boggy

planet10 · 7th November 2005, 12:45 AM

Should be no problem.... i've a whack of projects i'm going to do this in (ie 6 trafos for a VBIGC) but 28 V ? Do you mean you have 28V CT trafos? 14 VCT would also be called 7-0-7.(ie 14-0-14)

Tweeker · 7th November 2005, 04:08 AM

If you get phase wrong its 0V. They actually have dual secondaries rather than 7-0-7, or at least the 14-0-14 ones did. I just tied them together for 28VCT. You could use four to give dual 28V secondaries. The primaries would need to be series connected. The insulation would need to be up for this.

peranders · 7th November 2005, 04:52 AM

Do you have 120 VAC mains? What voltage rating have the transformers? Check once more your connection of the primary side.

If your transformers are 120 V, the windings must be in parallel of cource.

planet10 · 7th November 2005, 04:53 AM

Quote:

Originally posted by Tweeker
2 14VCT/dual 7V secondary transformers giving a single 28V secondary.

Is this right? Err its wrong. Knew I was forgetting something.

I think you have the primaries wrong. If those are 7-0 + 0-7 trafos, you still only have 7-0-7. (55 VAC in 3.5-0-3.5 across each trafo)

If the primaris were wired in parallel you would have 14-0-14.

dave

Tweeker · 7th November 2005, 05:34 AM

Er whoops, your right, primaries parallel. Other project on my mind confused me. (where two 120V xfmrs were run off 240V). Edit clock ran out on first post, then decided to actually make circuit to see what I was missing.

Tweeker · 7th November 2005, 04:33 PM

I have some of the old PE 120V primary dual 14V (advertised as 28VCT) secondary unused for sale at my cost if anyone needs a few. 80VA each seems about right. Using a pair to supply a chipamp works just fine.

7th November 2005, 12:45 AM	#3
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	Should be no problem.... i've a whack of projects i'm going to do this in (ie 6 trafos for a VBIGC) but 28 V ? Do you mean you have 28V CT trafos? 14 VCT would also be called 7-0-7.(ie 14-0-14) __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

7th November 2005, 04:52 AM	#5
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Do you have 120 VAC mains? What voltage rating have the transformers? Check once more your connection of the primary side. If your transformers are 120 V, the windings must be in parallel of cource. __________________ /Per-Anders (my first name) or P-A as my friends call me

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7th November 2005, 04:08 AM	#4
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	If you get phase wrong its 0V. They actually have dual secondaries rather than 7-0-7, or at least the 14-0-14 ones did. I just tied them together for 28VCT. You could use four to give dual 28V secondaries. The primaries would need to be series connected. The insulation would need to be up for this.

7th November 2005, 05:34 AM	#7
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	Er whoops, your right, primaries parallel. Other project on my mind confused me. (where two 120V xfmrs were run off 240V). Edit clock ran out on first post, then decided to actually make circuit to see what I was missing.

7th November 2005, 04:33 PM	#8
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	I have some of the old PE 120V primary dual 14V (advertised as 28VCT) secondary unused for sale at my cost if anyone needs a few. 80VA each seems about right. Using a pair to supply a chipamp works just fine.

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