Transformer Wiring Safety Question (pics included)

[sjaltenb]

Here is a photo of the transformer for my multfx project. It has 15 secondaries, for those intersted its:

9@ 12v,100ma
3@ 12v,200ma
1@ 24V,200ma CT
1@ 12v, 1amp
1@ 15v, 100ma

Anyway, I used the body of the transformer to anchor all the leads with a zip tie mount. They aren't going anywhere.The transformer came with solder lugs, which was really nice. I used Belden 22ga shielded wire for my secondary leads to the PSUs to ensure low noise. The little wires are leads to the shield of each wire that will be grounded later. The white is the transformer's shield.

Does anyone see any safety concerns here, as far as the anchoring to the chasis, etc? Each wire is heatshrunk individually around the lug, and then each pair is again heatshrunk. Should be pretty failsafe, but, comments, suggestions are welcome.

Thanks:

[andrew_k]

where did you get that crazy chunk of iron from??! 
how much?

[sjaltenb]

czech republic. $75. really darn nice work.

[Cliff Schecht]

Looks alright, but there's only one way to find out if it works. Ohm it out to check for shorts  then plug it in to a low power source (a function generator, for example) and crank up the amplitude. Measure voltage on all of the secondaries and make sure that everything is scaled properly.

[R.G.]

Ohm it out to check for shorts  then plug it in to a low power source (a function generator, for example) and crank up the amplitude. Measure voltage on all of the secondaries and make sure that everything is scaled properly.

I check them two ways. One is with the light bulb tester and a 25W bulb in it. The other is as you suggest, but with a 6.3V filament winding in another transformer as the source.

[sjaltenb]

so your saying use the lower voltage secondaries of another transformer as the primaries on this one, then check to see if each secondary is working properly?

does a transformer work as a ratio? So, if my inputs are normally 120v, and my output is 12v, this is a 1/10 ratio, so if i used 12v as a primary it should output 1.2v on the 12v secondaries?

I could be way off on this, some good reading may be in order.

[petemoore]

does a transformer work as a ratio? So, if my inputs are normally 120v, and my output is 12v, this is a 1/10 ratio, so if i used 12v as a primary it should output 1.2v on the 12v secondaries?
   Yepp a 1:10 .. ratio on this one?, looks to me like you've got it...
 

[earthtonesaudio]

But the reason to be careful is if you think you have the primary but you really have the secondary, and your 12V input turns into 120V.

[R.G.]

so your saying use the lower voltage secondaries of another transformer as the primaries on this one, then check to see if each secondary is working properly?

does a transformer work as a ratio? So, if my inputs are normally 120v, and my output is 12v, this is a 1/10 ratio, so if i used 12v as a primary it should output 1.2v on the 12v secondaries?

I could be way off on this, some good reading may be in order.

a) yes
b) Transformers ONLY work as ratios; that is what defines them. The voltage ratios are the same as the turns ratios in the windings. Your illustration is correct, as is earthtones' in that if you feed 12 in one place, the output is 1.2V. Feed 12V in the other way, get 120V. Works for all windings on the transformer, with some caveats. You must never drive a winding with a greater voltage than it's designed for, and the windings MUST be open circuited when you do this test. Loading throws off the results, and greater voltage can saturate the core.
c) reading is always in order, no matter what

[sjaltenb]

Thank you all!

I always feel bad posting these questions, but I learn so much when I do... not just how to do it,  but HOW IT WORKS, which is the much more important thing. Hopefully my posts help others as well, as I know I read them all on here and whether or not I respond or not, I am soaking up information.

Back to the bench.

[sjaltenb]

Hello all, I finally powered this bad boy up.

Firstly, and most importantly, I got a new multi-meter. its amazing how using one that is works properly can give you good readings, my other one apparently was fried.

Anyways, I first fed the main transformer with a smaller 12v transformer as the mains. It was actually feeding around 16V and the ratios out of the secondary were pretty close to what they should have been, but slightly over.

I then went ahead and plugged in the mains. I was getting 123.5 out of the wall which put my 12v secondaries at around 13.5. Not exact as far as ratios, but close enough I suppose.

I got the following readings:

Mains, Primaries: 123.5
12v secondary:  13.4
15V secondary:  16.8
24V secondary:  26.9

I am assuming that loading the transformer will effect the voltages too. However I am pleased the the readings are slightly over, as I was cutting it close on the power supply input voltages. I am glad that I left room for heat sinks, as it turns out that I may be regulating more power than I previously calculated.

The outputs seem to work however and all readings for the 12v outputs are consistant.