Toroidal Transformer design

[harii74]

Hello all
I need to know the toroidal transformer design calculation.

How to find core area?
How to find turn per volts? and etc.
Please give me a direction in this.

 

[mtwieg]

It's not really different from any other core geometry (except that it usually doesn't have a gap). The core material will determine most of the design. As for the core geometry, you only really need to know the effective path length and effective core area. Unless you want to be really precise, then you can probably just use the mean path length and core crossectional area for those.

 

[chuckey]

The manufacturer of the core will give you this data.
Frank

 

[ravslanka]

hi mtwieg,

i dont use effective mean length in designing my ei transformer
and i use the formula npri=vinx10^8/4.44xfxbxac.never made a toroid but have
searching for very long time found nothing special. how you do that can you
explain with some example and procedure.

thanks in advance

ravs

be a vegeterian.....

 

[mtwieg]

hi mtwieg,

i dont use effective mean length in designing my ei transformer
and i use the formula npri=vinx10^8/4.44xfxbxac.

I'm assuming that this is a ripple calculation? I usually phrase it as V*t=Ac*N*ΔB. But applying this formula will require knowing your application, and the properties of the core (desired ripple field/current and core area).

never made a toroid but have
searching for very long time found nothing special. how you do that can you
explain with some example and procedure.

Explain the application more specifically and I should be able to help. Is this for a SMPS? What topology?

 

[harii74]

Thanks to mtwieg and ravslanka
I use the formula for finding CA (core area) and TPV (Turns per volts) for designing EI transformer
as
CA= 1.151 sqrt(volts and ampere).
TPA= 10^8/4.44xFxBxCA
Should i change the constant instead of 1.151 in CA?
SHould i put different value for B?
Please clarify in this.

 

[ravslanka]

I'm assuming that this is a ripple calculation? I usually phrase it as V*t=Ac*N*ΔB. But applying this formula will require knowing your application, and the properties of the core (desired ripple field/current and core area).




Explain the application more specifically and I should be able to help. Is this for a SMPS? What topology?

hi mtwieg,

these are mains transformer connected to 220 volt ac.usually use in audio amplifiers.yes bmax and cross sectio area should be known for a given mateial.

i was referring to iron core eg cgno/crgno m6 material.i was trying to make a toroidal transformer for an amplifier.80-0-80 10 ampere each.i didnt found anything on the net.i made an ei transformer it is very big and heavy around 22kg.i

suppose i have toroidal core outer dia= 175mm , inner dia=75mm height=40mm
ac=20cm^2,bmax=1.7t i think for m6 ,frequency=50hz.how would you calculate
for 80-0-80 10 ampere or 1600va mains transformer for turns of primary/sec
and also for wire selection.

for smps transformer formulala is same for all cores ie etd,ee,ei and troidal.does that same
implies to these iron cores.

regards

ravs

be a vegeterian....





---------- Post added at 22:04 ---------- Previous post was at 22:02 ----------

Thanks to mtwieg and ravslanka
I use the formula for finding CA (core area) and TPV (Turns per volts) for designing EI transformer
as
CA= 1.151 sqrt(volts and ampere).
TPA= 10^8/4.44xFxBxCA
Should i change the constant instead of 1.151 in CA?
SHould i put different value for B?
Please clarify in this.

hi harii74

for effective core area of toroidal

height of core x width of the tape wound stack

cant say for your ca constant as i use product of wa and ac but but you have to change bmax value for different materials.

regards

ravs

be a vegeterian

 

[ravslanka]

hi mtwieg

waiting fo your answer

ravs

be a vegeterian....

 

[mtwieg]

Thanks to mtwieg and ravslanka
I use the formula for finding CA (core area) and TPV (Turns per volts) for designing EI transformer
as
CA= 1.151 sqrt(volts and ampere).

So wait, is core area a parameter you have control over? What specifications do you have, and what are your limitations? Are you trying to design for a specific material or core geometry? To do this properly you have to start from there.

---------- Post added at 11:23 ---------- Previous post was at 09:58 ----------

hi mtwieg,

these are mains transformer connected to 220 volt ac.usually use in audio amplifiers.yes bmax and cross sectio area should be known for a given mateial.

i was referring to iron core eg cgno/crgno m6 material.i was trying to make a toroidal transformer for an amplifier.80-0-80 10 ampere each.i didnt found anything on the net.i made an ei transformer it is very big and heavy around 22kg.i

suppose i have toroidal core outer dia= 175mm , inner dia=75mm height=40mm
ac=20cm^2,bmax=1.7t i think for m6 ,frequency=50hz.

Okay this should be enough info to get started. Effective core area will probably be around 18.8cm^2, or 0.00188m^2. 220V at 50Hz means your core needs to tolerate a volt time product of 1.4Vs without its magnetizing B reaching 1.7T. V*t=N*A*B, so 1.4=N*0.0018*1.7, and N=458. So you need a minimum of 438 turns on your primary.

how would you calculate for 80-0-80 10 ampere or 1600va mains transformer

Not sure what 80-0-80 10 amp means. But in any case, all you really have left to choose is your wire gauge, and that's a more trial and error thing. The most surefire way would be to just use your window area to find the largest size wire that you can put the needed amount of turns around.

 

[ravslanka]

hi mtwieg,

thanks a ton.i haven't seen datasheets publishing volt-time product for tape wound cores.
so how did you calculated v/t product.

secondary
80-0-80 10 amp

0-80 0-80 two windings providing 10 amperes of current each

primary current will depend on the efficiency say 85%

input power=pout/eff

=1600x85/100

=1360 watts

average input current=pin/vin nom=1360/220= 6.18 ampere.

correct me if iam wrong.if this is correct we have to choose wire according to current rating
of wire.

did you included effective path length of toroid. in calculation

thanks again

ravs

be a vegeterian.....

 

[mtwieg]

hi mtwieg,

thanks a ton.i haven't seen datasheets publishing volt-time product for tape wound cores.
so how did you calculated v/t product.

volt time product won't be specified in the documentation. It depends on the number of turns (as in the equation).

The formula can be derived by starting with two basic inductance formulas:
L=N*dΦ/dI, where Φ is flux
and
V=L*dI/dt
we also know that Φ=B*A (flux is flux density multiplied by area)
so the first equation becomes L=N*dB*A/dI
substitute that in for L in the second formula and we get
V=(N*dB*A/dI)*(dI/dt)
rearrange to get
V*dt=N*dB*A or more simply V*t=N*B*A

secondary
80-0-80 10 amp

0-80 0-80 two windings providing 10 amperes of current each

primary current will depend on the efficiency say 85%

input power=pout/eff

=1600x85/100

=1360 watts

average input current=pin/vin nom=1360/220= 6.18 ampere.

Actually your input power will be 1882W, so you need 8.56A of primary current.

correct me if iam wrong.if this is correct we have to choose wire according to current rating
of wire.

Pretty much, yeah. Or just the largest wire that will fit in the core window.

did you included effective path length of toroid. in calculation

Path length actually plays no part in the calculations so far. Magnetizing flux swing doesn't depend on it; only on core area, number of turns, and V*t. What more path length gets you is just a bigger core which allows you to use larger wire and get more current through. So what you really want is window area.

 

[shajpb]

hi mtwieg,

How can I calculate the VA ( volt*Ampere) Capacity of a given toroid. Is there any equation for that.

Core size can be same as outer dia= 175mm , inner dia=75mm height=40mm

It is still confusing me. In the example here, it is not mentioned about the power which this particular toroid can handle safely. Can you please explain little more.

SHAJI

 

[mtwieg]

Calculating the capacity of a transformer is much different from the calculations above, which are mainly related to core saturation. Power handling is much less straightforward, and usually it's not feasible to come up with an accurate prediction by math alone.

For an estimate, you need to first find the maximum volt-time product allowed on the core which avoids saturation. The V*t=N*B*A formula will get you this number, provided you know your line frequency, number of turns, core area, and core material.

Finding the maximum current is the harder part. The limit on current is mostly defined by heating in the transformer, which is basically infeasible to predict. Your best bet is to just run current through it and measure the temperature rise of the windings and core. A good stopping point is 40 degrees C above ambient.

 

[shajpb]

hi mtwieg,

Let us think simple. For a normal EI transformer, we have an equation VA=31A^2, where A=Area of center limp
And we can reduce 20% loss to the worst case.

So Can you give such a simple to understand formula for VA calculation for toroid?
It is enough for a normal homebrewer, where critical calculation is not necessary.

Hope to hear you

SHAJI