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markthespark

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Hi i was havin a conversation with some lads at work today about what would happen if you connected the 12v secondary side of the tranny to a 230v supply, would you get a really high voltage but low current out of the primary side, acting like a step up transformer??

i have very limited knowledge on transformers and would be interested to know?

Muchas grassy arse:)
 
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wayne

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  • #3
the kind of thing you do once if you are daft
 
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MacSparky

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  • #5
Why not? i thought primary and secondary windings were the same csa.
Regards
MacSparky:)
 
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Grae79

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  • #6
if i had one in the van i'd give it a go
 
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MacSparky

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  • #7
The thing is if it did work how would you test it as the voltage would be around 2760 volts ( i think):(.... wheres Tony when you need him.
Regards
MacSparky:)
 
T

treelectric

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  • #8
This would not work. Check the resistances of the pri and sec windings. You will find the are in the ratio of about 20 to 1, the sec about 1/20 of the primary, so connecting this to 240 would melt it.
Also 12 volt sec at 1 amp would mean the primary would only draw a current of 1/20 amp at 240 volts, so the primary dooes not need so much csa as the secondary for this transformer.
The VA rating of the transformer for 1 amp at 12 volts will be 12VA. Since the VA rating is the same for pri and sec windings, then for the primary at 240v, the current will be 12/240 which is 1/20th amp.
So for any transformer, VxA on one side will equal VxA on the other, so you can work it all out if you know one side.
 
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MacSparky

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  • #9
Nice bit of info treelectric;)
 
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Shakey

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  • #11
This would not work. Check the resistances of the pri and sec windings. You will find the are in the ratio of about 20 to 1, the sec about 1/20 of the primary, so connecting this to 240 would melt it.
Also 12 volt sec at 1 amp would mean the primary would only draw a current of 1/20 amp at 240 volts, so the primary dooes not need so much csa as the secondary for this transformer.
The VA rating of the transformer for 1 amp at 12 volts will be 12VA. Since the VA rating is the same for pri and sec windings, then for the primary at 240v, the current will be 12/240 which is 1/20th amp.
So for any transformer, VxA on one side will equal VxA on the other, so you can work it all out if you know one side.

Dont quite agree with the resistances side of things. Obviously we are talking about impedence rather than resistance

And Xl = 2 Pi FL

the L is fixed for the coil, and the frequency hasnt changed. Therefore the Xl of the coil is the same, regardless of which V we apply to it. Obviously the I drawn will relate to the V applied, and the Xl of the coil will mean it will draw whatever I it needs. The coil MAY be able to handle this, it may not, depending on the VA rating of the tranny

It isnt 'automatically' going to blow!!!;)
 
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Grae79

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  • #12
this is the reply I got back from Aurora's technical department with regards to their electronic transformers: "I suspect that if you were to put 230VAC into the output terminals of a transformer then nothing would happen that you can see. It would however blow the surge protection fuses within the transformer and probably burnout the terminals meaning that the transformer would be unusable"
 
S

Shakey

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  • #13
this is the reply I got back from Aurora's technical department with regards to their electronic transformers: "I suspect that if you were to put 230VAC into the output terminals of a transformer then nothing would happen that you can see. It would however blow the surge protection fuses within the transformer and probably burnout the terminals meaning that the transformer would be unusable"

Nah,,,,,,what do they know;)
 
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Grae79

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  • #15
i was thinking Trip to Trumpton
 
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alex

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  • #16
yep sorry it just blows i did it the other week when not concentrating.

sorry to dissapoint but no big bang or anything just didnt work.
 
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rumrunner

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  • #17
yeah ,it would depend on the secondry load,:p
 
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  • #18
Once (not so long ago in a place not to far away) i watched someone blow the Fudge out of a timed SELV fan controller! he was connecting it all up, but some how he managed to put the perminant live, and neutral in the 12v side, and he went to turn the power back on the test it, and it didnt like it (well much!!) you know why i know this, because it was me!! lol
 
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kippaxkid

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  • #19
Never tried it on a larger transformer but I'm sure it's only blowing the output fuse because it is now an input fuse.
I've (seen it)done it to smaller tx's using batteries and flipflops( no, not those) to "defend" property (ahem)
I tutted very loudly when I saw him (before the Disgusted of Dagenham brigade, let rip)

Bit like a cross between a cattle fence and a cattle prod. Not something you grabbed twice.
 
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MarkieSparkie

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  • #21
Dont quite agree with the resistances side of things. Obviously we are talking about impedence rather than resistance

And Xl = 2 Pi FL

the L is fixed for the coil, and the frequency hasnt changed. Therefore the Xl of the coil is the same, regardless of which V we apply to it. Obviously the I drawn will relate to the V applied, and the Xl of the coil will mean it will draw whatever I it needs. The coil MAY be able to handle this, it may not, depending on the VA rating of the tranny

It isnt 'automatically' going to blow!!!;)
This thread is over 3 years old, but just in case students or apprentice are reading this...
This is utter tosh, most transformers have two or more windings (unless it's an autotransformer), lets consider the case in question. One primary winding and one secondary winding, the impedance of the windings in this case are likely to be different, because the inductive reactance and the coil resistance are different for each winding as they are wound from wire of differing CSA and number of turns wound.
The insulation of both windings will be rated and flash tested appropriately for 230Vac namely at 2300Vdc. If the primary and secondary are swopped so the former 12Vac secondary is supplied as a 230Vac primary, the former 230Vac primary now tries to become a 4408Vac secondary but the winding insulation quickly fails destroying the winding and possibly the other winding and the former their both wound on, until the point where the circuit protection breaks the primary supply.
If the "transformer" (really a switched mode voltage converter) was of the type used often for ELV lighting and fans. With 230Vac applied to the former 12Vac output of the converter, the output circuit protection devices would fail instantaneously due to over-voltage, rendering the "transformer" dead scrap.
 
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K

Knobhead

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  • #22
In theory 4370V. But the 12V winding impedance would be so low that you’ll be struggling to see through the smoke to read your meter.
 
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telectrix

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Esteemed
simmilar happens when connecting a 12v halogen lamp to 230v. you can't see through the broken glass. maybe that's why manufacturers put a voltage rating on equipment.
 

ackbarthestar

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Old song from the 60's comes to mind

Get the fire brigade!:eek:
Wasn't it 'Get the fire brigade' and then 'Flowers in the rain' ..... by the Move?
Which is probably what would happen if you made contact with the secondary terminals !
 

ackbarthestar

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I suspect that the electronic switchers would disconnect before anything serious happened. But a toroidal or double wound transformer would certainly give you a belt.

For continuous use you would need to limit the current flow through the primary winding to stop it from overheating and catching fire.

I heard that once a transformer catches alight, you then have to bury it in sand or fill the room with halon gas because you can't put it out. Mind you, I knew a woman once who could fill the room with a gas that could put you to sleep permanently.
 

the pict

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Arms
Theres mushrooms in my garden too
Pict
 

robd

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Arms
Can confirm it doesn't last very long and does trip MCB, did it myself in a daft moment, the best bit was it was only accessible by a nice crawl through a gulley amongst some fibreglass. Needless to say I was pretty chuffed with myself :)
 

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