I'm re-using transformers...

If the transformer has a 220V winding, he might be ok using that... or not?

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

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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

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Phil Allis>

** 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

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.

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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

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

..... Phil

Mine is running within the specs stated on the sticker so it should be okay then. Many thanks for the advice.

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  

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  

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;

and figure that, if it sounds good when I have the funds I'll then get one of these to house it;

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;

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;

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  

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

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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** 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

I thought so as it makes sense but I haven't read that anywhere and the site selling them doesn't say that.

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  

In series - wrong phasing just doesn't work.

In parallel - wrong phasing lets the magic smoke out.

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.

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** Nonsense, the situations are both the same. One half of the primary is trying to magnetise the core in the opposite direction to the other. So the core does not magnetise, there is no back emf - leaving only the resistance of the windings.

You are thinking of the situation with split *secondaries*.

..... Phil