Transformer

[epilot]

hello there

i am new here in this forum so hope i am coicing the correct part for tallk about my problem.

i have a transformer with no mark on it, it is broken now and the coils in the 220V part are cut and damaged, so what i have is
V1=220V
R2=2 OHM ( resistance at reduced voltage part)

plese can some one direct me to find the V2 for this transformer to use from a replacement for the device?

is there any formula?
thanks for any help.

 

[chemelec]

Not Possible with the info given.

 

[instruite]

As you told the primary is connected to 220V
I guess it used for some power supply circuit
If you can provide some details about the rest of circuit like capacitor voltage rating (or any mark on it)
The best will be if there is any regulator IC in the circuit and you can provide any infor about that IC then it will be easy to determine the requirement for your secondary voltage

 

[audioguru]

Its size would be an indication of its power output.

 

[lord loh.]

Its size would be an indication of its power output.

I do not think so :?

My friends brought a transformer rated 1A. And brought a similar sized rated 300mA!!!

And I after lot of searches concluded that the resistance of teh secondary is no indication of the number of turns....

If one knows the SWG of the wire, one can get to know the resistivity of Cu and find the length by:

R=p l/A

p - "rho" Resistivity
l -length of wire
A - cross section area or wire.

It might be possible to consider the length of the wire proportional to the number of turns. And thus find the secondary voltage.

The trouble is to find the thickness of the wire and the restivity.

A Question from me : Does resistivity depend on the thickness? I had a derrivation in my class about strain guages where we considered dp/dS - change in resistivity due to change in strain. ???? :?:

 

[Someone Electro]

Since you have an huge amount of wire in the coil there are prety much factors and 0.01 mm in thicknes can make a respectable difrence is the resistance of the coil.Can you post the capacitor values of the PSU circuit and partnubmers of ICs in TO-20 packeges.

 

[audioguru]

My friends brought a transformer rated 1A. And brought a similar sized rated 300mA!!!

It shows the poor quality of the 1A transformer.
I betcha that the 1A transformer doubles or triples its output voltage without a load, while the 300mA one's output rises only about 1.5 times. :lol:

 

[Sebi]

i have a transformer with no mark on it, it is broken now and the coils in the 220V part are cut and damaged



Check the thermal fuse (if existiert, connected seriel with primary winding). Location: under the cover papier (or mylar folie).

 

[epilot]

hi all folks and thanks for the replays

the transformer is from a rechargeable lantern
and yes it is from the power supply of lantern

the power capacitor marked as 16V , 1000uF
i think the transformer should be an 1A transformer

really i hoped some one could direct me for a formulla for the transformers, i know one
V1/N1=V2/N2
but it cant help me really

 

[Someone Electro]

Dose that latern contanin a batery pack?

If yes then whats the baterypacks voltage? (this wod help a lot)

 

[epilot]

yes it has rechargeable battery and it is 6volt
but i am following a formulla yet

 

[Someone Electro]

The transformer is 7V secundary !

 

[epilot]

why?

i think there is 7.5V transormers for sell i never seen any 7v transformer?

 

[Someone Electro]

You cod use an 7,5 wallwart to replace your old charger.Its the easyest solution.

 

[monkeytree]

can you meassure transformer output voltage acurately by just connecting it up to a multimeter or does it needed to be connected up to something else?

 

[Someone Electro]

To do that you wod need to cenect it to mains but the primary coil is damaged

 

[epilot]

monkeytree,
i am not sure if i could understand you correctly.

anyway i'll go and get a 6 and a 7.v transformer and see which one is better for the lantern

thanks alot for all helps

 

[Laplink]

I wrote you a lengthy reply but now it is gone. I clicked 'submit' and it returned me a blank 'post a reply' !!!!!!!!!!!

The number of turns and the turns ratio are important. The resistance does change with the size of wire. The size of the wire determines current. The resistance is unimportant. You cannot measure it accurately with a multimeter unless you know what you are doing. Transformers will work backwards, put 5V a.c. in the output and measure your broken wires for 220V.
For 6volt d.c. out with a full wave bridge and no regulation:-
6(volt) X 0.707(RMS) = 4.242Volts a.c.output for the transformer.
If you have a linear type regulator allow atleast another volt.



http://www.dse.com.au/cgi-bin/dse.filereader?42d0b3f80714a43e2740c0a87f9c0728+EN/catalogs/SUP1000053

 

[Someone Electro]

A thick wire has lower resistance.Its like having more thin wires.

It wod be realy dificult to get the thurns.

 

[audioguru]

For 6volt d.c. out with a full wave bridge and no regulation:-
6(volt) X 0.707(RMS) = 4.242Volts a.c.output for the transformer.
If you have a linear type regulator allow atleast another volt.

Your calculation has the etxreme accuracy of 3 decimal points but forgets to include the nearly 2V forward voltage drop of the bridge rectifiers.
Therefore if you have 6VAC you would barely get 6VDC if the filter cap is big enough to reduce most ripple.

An ordinary linear regulator that is not designed to be "low dropout" operates poorly with only 2V extra across it, pretty well with 3V across it and is spec'd with 5V across it. Therefore I would use at least 9VAC to get a regulated 6VDC, which is more than double your calculation. :roll: