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Safety advices before experimenting with these circuits

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J_Nichols

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I am experimenting with electricity and I know it's dangerous.
I have some different questions that I will ask one by one.

I want to check if these tests are safe. Lets start.

I have a small transformer rated :
  • It doesn't matter how I connect the input? I mean if I want to connect the live wire. Can it be connected in the top left connection or top right connection?
 

MaxHeadRoom78

Well-Known Member
You would need to connect 12vac to the secondary to get 230vac out of the original primary, the efficiency is lower, however.
Max.
 

alec_t

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Can I connect the 230 V AC in the output to use the transformer as a step up transformer?
Definitely not :eek:. That would destroy at least the transformer.
 

audioguru

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2nd question
Can I connect the 230 V AC in the output to use the transformer as a step up transformer?
I would love to see a video of the transformer exploding or catching on fire! Why destroy the transformer by connecting it wrong?
 

dr pepper

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As alec says the transformer will blow up, it would try to generate thousands of volts which the insulation wouldnt withstand and most likely go up in smoke, possibly taking you with it.
 

KeepItSimpleStupid

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I think there's an interpretation problem here.

For the 230 side anything less than 230 V can be applied.
For the 12 V side, anything less than 12 v can be applied.

primary and secondaries can be reversed, there is a slight loss penalty to do so.
Lower frequencies require more iron, so you will see xformers rated for 50/60 Hz. Operating 60 Hz transformers at 50 Hz may or may not work.

Transformers, transform power so V1*I1=V2*I2 so don't exceed the designed rms currents.
The ratio of voltage transformation is 240/12.

In the US, both sides of the 240 V would be hot. We need to switch L1 and L2 since they are provided by a center-tapped 120-0-120 transformer where 0V is our Neutral.
We use the designations of (L1 L2 N and G) or (L and N) for single phase residential electricity.
 

dr pepper

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Yes if you put 12v 50-60hz on the secondary you'd get 240v on the primary, the regulation on a small trans would be poor, meaning the voltage would drop as soon as a load is connected, might be enough to drive a small fluorescent tube.
If you exceed the rated voltage primary or secondary the core would saturate, making the winding act more like a short circuit.
 

KeepItSimpleStupid

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I had no issues making a sort-of inverter to run a synchronous motor for a telescope. I was asked to design the circuit and someone else put it together and it worked fine.
 

audioguru

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A transformer has resistance in its windings so for it to transform 230VAC to 12VAC then it is made maybe 230V to 14VAC for this tiny transformer so that its resistance drops the output down to 12V at its rated load current.

If you use the "14V" transformer with only 12VAC then the high voltage will not be 230V, it will be 197VAC with no load and will be 169VAC at its rated current.
 

dr pepper

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Off topic I know, speaking of mains synchronous motors I have a small collection of vintage electric clocks, a couple I rewound for 12vac and now run of an accurate frequency source, the same inverter idea could run unmodded mains ones.
 

schmitt trigger

Well-Known Member
When one is experimenting with an unknown transformer I always do these things:

1) With a multimeter, find the highest resistance winding. This will most likely be the primary winding.

2) With a Variac, starting from zero and very slowly apply voltage on the primary, while simultaneously monitoring the secondary with a DMM.

3) Variacs almost always have a fused output. For this experiment, I replace the fuse with a low value one (1 amp). Something shorts, out, no big deal.
 

dr pepper

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I doubt the op has a variac, a bulb bopper would do though and is much cheaper, just a bulb in series with the mains in.
I bet there isnt many who remember the proper use for bulb boppers, maybe Nige does.
 

fezder

Well-Known Member
I doubt the op has a variac, a bulb bopper would do though and is much cheaper, just a bulb in series with the mains in.
Tis is handy and cheap device! I too have one with swicth for bypassing that bulb, as well as two different (e14 & e27) sockets for different ratings.
 

fezder

Well-Known Member
might be enough to drive a small fluorescent tube
I once did this, funny thing was that CFL left smoke out....wasn't mercury smoke, but didn't proceed with circuit to investigate further...
 

dr pepper

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I have 2 sockets on mine, handy for building & testing smps's.
Disposeable camera inverter boards make handy little cfl lighter uppers, everyones moved to leds now though.
 

fezder

Well-Known Member
everyones moved to leds now though.
LED's are efficient but CFL's are cool because high-voltage involved :p I have bunch of salvaged CFL "bulbs" (and ind.bulbs too) waiting for suitable application, hopefully not trashbin
 

Nigel Goodwin

Super Moderator
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LED's are efficient but CFL's are cool because high-voltage involved :p I have bunch of salvaged CFL "bulbs" (and ind.bulbs too) waiting for suitable application, hopefully not trashbin
Sorry, but CCFL's are absolutely crap :p - twice as expensive to run as LED, slow to warm up, and poor colour :(

I've binned all mine, and replaced them all with LED's - I didn't consider them worth keeping for anything.
 

dr pepper

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They have chokes in that can be repurposed, if you have time.
Not long back we were saying the same about incandescent, we'll be saying the same about current phosphor leds when quantum leds take over.
 
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