I'm re-using transformers...

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... from old audio gear. I just want to check something as I'm not planning  
on dying this week.

If the voltages I'm getting from the secondaries aren't what I want is it ok  
to use the '120v' primary windings to get different voltages on the  
secondaries?

Thanks,
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: I'm re-using transformers...
~misfit~ wrote:
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No, it's not okay to connect a 120v primary to 240v directly.  What were  
you hoping to do?

Depending on the rating of the transformer, and what kind of power  
you're trying to draw, you might be able to use a mains-rated capacitor  
in series with the primary to drop the voltage down from 240v to 120v,  
but that only gives you the rated secondary voltage output, and I'm  
guessing that's not what you want.

A transformer designed for 60hz might also run a bit hotter on 50hz.

Peter




Re: I'm re-using transformers...


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Not the best idea - if you accidentally hit series resonance, things start  
to happen.................................  


Re: I'm re-using transformers...
 ~misfit~ wrote:

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** If this is a mains power transformer, the operating frequency need to be double if you do that. 100Hz instead of 50Hz.  

If not, then the primary current will be massive as the iron core is driven hard into saturation. The tranny will smoke and fuses blow.

So in general - no way.  



....  Phil

Re: I'm re-using transformers...
On 08/06/17 15:56, Phil Allison wrote:
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If the transformer has a 220V winding, he might be ok using that...
or not?


Re: I'm re-using transformers...
Clifford Heath wrote:

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Phil Allison wrote:
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** Like Schrodinger's cat, only trying it out will prove the point.  

It might run hot or make a lot of buzzing noise or both.

Beware if it is a toroidal type.


....  Phil  

Re: I'm re-using transformers...
On 8/06/2017 5:29 PM, Phil Allison wrote:
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What should I beware of with toroidal types? I only ask because I have  
one, 240V primary, 24V 0 24V secondary in a home built bench psu. It  
seems to be working okay.

Re: I'm re-using transformers...

Peter wrote:

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** But if you had one with a 220 V primary .....  

The difference is the toroidal cores are different - there are air gaps at all to soften saturation AND the core goes sharply and HARD into saturation.  

A toroidal designed for 60Hz operation is very often unusable at 50Hz.  

Massive off load current draw - more than the full VA rating.  



....  Phil  
  

Re: I'm re-using transformers...
On 8/06/2017 8:59 PM, Phil Allison wrote:
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Mine is running within the specs stated on the sticker so it should be  
okay then. Many thanks for the advice.


Re: I'm re-using transformers...
Once upon a time on usenet Phil Allison wrote:
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Thanks Phil. It seems I need to read an 'into to transformers' type  
tutorial.
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: I'm re-using transformers...
 ~misfit~ wrote:

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 ** You could do a lot worse than start here:  

http://sound.whsites.net/xfmr.htm



.....  Phil  




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Re: I'm re-using transformers...
Once upon a time on usenet Phil Allison wrote:
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Excellent, thanks. I've bookmarked it and will read it as I am able. :)
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: I'm re-using transformers...
Once upon a time on usenet ~misfit~ wrote:
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Just FYI the reason I've been testing my salvaged transformers is because  
I'm in need of a reasonable pre-amp as I've recently changed from using  
integrated amps due to the decent speakers I now have that sound better and  
better the more power they get. (Even at low volume. Powering them with a  
~150w amp they sound much more detailed and image much better than powering  
them with a 60w amp.)

However I can't afford the ~$1.5K a new preamp costs and despite watching  
online auctions for a year haven't found anything suitable. (I need a  
remote. Being an invalid it ruins my enjoyment of music if I have to keep  
getting up to get the volume just right.) Funds are very very tight.

So, after trying various cheaper units from AliExpress which were  
dissapointing I ordered one of these;
https://www.aliexpress.com/item/PGA2311-Volume-Stereo-Pre-amplifier-Preamp-Board-with-LCD-and-Remote-control/1695574309.html
and figure that, if it sounds good when I have the funds I'll then get one  
of these to house it;
https://www.aliexpress.com/item/New-Version-aluminum-Case-for-PGA2311-CS3310-Preamp/32809522765.html

However on going through my collection of centre tapped transformers  
salvaged from various things the only 6v-0-6v transformer I was able to find  
was from an old digital alarm clock (and is actually 6.0 - 0 - 6.3v) but I  
reckon it's only capable fo supplying about 2 watts - which likely isn't  
enough. I have a bunch that are 12 - 0 -12 and a few from amplifiers going  
right up to 75 - 0 - 75.

Ultimately, after my first post inthis thread I ended up ordering one of  
these in 6 - 0 - 6 configuration;
https://www.aliexpress.com/item/1-10W-EI-Ferrite-Core-Input-220V-50Hz-Vertical-Mount-Electric-Power-Transformer-Leave-A/32799457326.html
for another ~NZ$20.

I'll assmeble it on a board when I get these two parts and see how it  
sounds. If it's good I'll then try to find the ~NZ$90 for the case.

However now I've had to buy a transformer I'm starting to think I should  
have just bit the bullet and bought the pre-built unit;
https://www.aliexpress.com/item/Finished-PGA2311-Remote-Pre-amplifier-Preamp/32809614146.html

Anyway fingers crossed, I've already wasted about $50 buying several cheaper  
pre-amps. I have one that sounds pretty damn good but it's not got a remote  
and is single input. Adding a motorised pot and control circuitry and  
switchable inputs to that might cost as much or more and still be a fail  
(with my limited skills).

Cheers,
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: I'm re-using transformers...
Once upon a time on usenet Phil Allison wrote:
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I've also saved all three parts to my HDD. I'm a slow learner (learning  
disability - I can only absorb so much at a time before getting hellacious  
headaches) and in the past I've gone to read a bookmarked site only to find  
it's no longer there. :-/

Thanks again.
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: I'm re-using transformers...
Once upon a time on usenet Phil Allison wrote:
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Phil quick question (as I can't readily find the answer right now).

Can I use a transformer with the primary side described as 'double 120v  
50/60Hz' on 240v by running the two primaries in series?

Cheers,
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: I'm re-using transformers...
~misfit~ wrote:

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 ** Errr - that is how it is meant to be used.  

 In parallel for 120VAC, in series for 240VAC.  

 You WILL need a to get the phasing right, hopefully the units are marked or you have an info sheet showing which wire colours to join.



....  Phil  

Re: I'm re-using transformers...
Once upon a time on usenet Phil Allison wrote:
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I thought so as it makes sense but I haven't read that anywhere and the site  
selling them doesn't say that.

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Makes sense.


Hopefully. I haven't ordered yet but AliExpress isn't known for giving out  
lots of info. :-/

Thanks for replying. :)
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: I'm re-using transformers...


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Series won't do anything if you get the phase wrong. Power up parallel with  
a light bulb in series to limit the current in case you got it wrong.  


Re: I'm re-using transformers...
Once upon a time on usenet Ian Field wrote:
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Thanks. I'll screw a batten fitting to a piece of wood, been meaning to do  
that for a while. I knew there was a reason to keep a few old incandescant  
bulbs...

I've got quite a few saved transformers and have been connecting up the ones  
that I know the primaries are 240v but am having trouble working out what's  
going on with secondaries where there are multiples. I'm getting AC volts  
readings between secondary wires that, when tested for resistance (not  
powered up) don't appear to be connected. I'm guessing capacitive coupling  
maybe? Was thinking putting a light bulb for a load might give me a better  
idea of what's going on.

I have a nice little (~50VA) toroidial that is obviously 'double 120v' as  
two primary wires are soldered together and have heatshrink over them. (I  
removed it and tested resistance and it reads like a centre-tapped winding.)  
However it's got four secondary wires and I'm damned if I can make sense of  
whats's going on just with the meter. (Tested for resistance unpowered then  
AC volts when powered up.) I'm hoping loading them will help.

Cheers,
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: I'm re-using transformers...


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In series - wrong phasing just doesn't work.

In parallel - wrong phasing lets the magic smoke out.  


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