Discussion in 'Homework Help' started by muhsiul hassan, Aug 15, 2008.

1. ### muhsiul hassan Thread Starter New Member

Aug 15, 2008
3
0
we know that, the ratio of windings in primary and secondary is the ratio of input and output voltages. for example, for step down transformer, if 220V is to transform into 22 voltage then ratio of primary and secondary windings will be 10:1.
my question is, what will be the number of primary winding but not the ratio. i mean if i use 2000 windings in primary and 200 in secondary and if i use 200 and 20 in primary and secondary respectively will i get same result?? i just need the equation for the number of windings. and another thing...which wire should i use? i mean what will be the gauge number? is there another equation about the gauge number? please inform.

2. ### SgtWookie Expert

Jul 17, 2007
22,183
1,732
Just because it is urgent for you does not make it urgent for anyone else.

The more urgent the request, the more you may be subjected to ridicule for lack of planning.

Lack of planning on your part does not make for an emergency on my part.

Transformer calculations are far more complex than what you think. Try some searches on them.

3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
You can use this formula to find the number of turns:

N=V/(B*A*f*2*π)

where

N=number of turns
V=peak value of the sinusoidal voltage
B=peak value of the flux density
A=cross sectional area of the core
f=frequency

4. ### yubyub Member

Aug 13, 2008
19
6
on google search "maximum current through wire" or something like that. You want to pick wire that is getting fully saturated, or at least isn't overly effected by skin effect. Theres equations to determine the amount of cross sectional area vs saturated area. This should be over 50% saturated. (to minimise space that the wire uses).

if you'r using like 10 turns or something on a big transformer than just pick some thick wire. It's mostly a concern when you need like 100 turns on a transformer.

5. ### muhsiul hassan Thread Starter New Member

Aug 15, 2008
3
0
actually i am a novice student in practical electronics. can you please explain me how can i calculate the maximum flux density in that equation. as per i know there is an equation
E= 4.44fN$\phi$= emf of any coil(primary/secondary)

where f= freq.
N= no of turn
$\phi$= flux no
but i cant calculate the flux no.
can u please specify me how can i calculate the flux density(B) or flux no $\phi$?
thanks

Apr 26, 2005
3,412
1,251
7. ### familyguy New Member

Aug 18, 2008
2
0
To determine wire thickness you will need to know the current through the wire. eg if you want 22 volts at the secondary at say 1 amp then power in watts = va or 22 x 1 = 22 watts. The input power at the primary would be slightly higher to allow for losses in the core etc. So from this input amps is 24/240 = 0.1 amps. A good safe figure for current carrying capacity of copper wire is 4 amps/sq.mm. The 22v secondary would need wire with a cross sectional area of about 0.25 sq.mm and the 220v primary would need wire with a cross sectional area of about 0.025 sq.mm There is a fair bit of latitude here anything from 3 to 5 amps per sq. mm is safe for 100% duty. Do a google for copper wire tables, look up the cross sectional area and of the various sizes and you will have your wire diameter.