Tony's latest traffo DIY build

[engel dela pena]

i already heard a clip of recorded music compairing a clip of both choke vs resistor
i personally in favor of choke coil,
(my personal taste,i also play guitar)

[AJT]

you can increase cap value to decrease ripple to say 470ufd instead...

[AJT]

sag is also due to the dc resistance of the power transformer used, not only the resistor....as you load the amp, voltage dips as a result of resistances in the power transformer....

[nazirdigi]

hi tony
i want to built a transformer for h900 amp. the voltage is 80,40,0,40,80 into 20ampere.
can u give me the bobbin size of the transformer and the ei core size primary and secondary windings wire gauge. so i can search.
my main voltage is 240ac.

thanks.

[AndrewT]

80+80*20 = 3.2kW
Using the formula VA ~30*(Core area)^2, re-arranged to Core area ~ sqrt(VA/30), you need ~10sqin
That is enormous.
Tony does your method give a similar result?

How does one determine what flux the core can operate at? Steel looks like steel to me.
How does flux affect that formula I quoted?
Finally how does one get from core flux & voltage to primary turns?

[AJT]

^3.2kw is secondary loading....power factor of 0.7 and you need a primary voltampere of 4.27kva

i use the formula from RDH3, VA= (5.58*A)^2;

A= 11.71 square inches,

you need a 2 in center leg x 5.5inch stack of core....
that weighs in at about 19kgs, you need about 3~4kgs of copper...

[engel dela pena]

this site is great and useful
thanks sir tony
GeeK ZonE - Winding Your Own Transformers

[AJT]

Originally Posted by nazirdigi

hi tony
i want to built a transformer for h900 amp. the voltage is 80,40,0,40,80 into 20ampere.
can u give me the bobbin size of the transformer and the ei core size primary and secondary windings wire gauge. so i can search.
my main voltage is 240ac.

thanks.

for a core 2in. center leg stacked to about 5.75inches you will need,

primary, 148 turns #13AWG copper wire,
secondary, 4coils quafillar wound 25turns #12AWG copper

note that i use american standard gauge, i know that in India, the British system is used, so make adjustment to suit your local conditions...

i based my computations on the assumption that you will be using the cheaper non grain oriented steel......

[pieter t]

Originally Posted by AndrewT

Yes, steel looks like steel, but checking my Waasner catalogue I see already 4 different grades of stamped laminations.
The better the grade, the higher the maximum flux density (and therefore power).
For example: for 3320 secondary VA an EI231b core is required in the best quality (M6-0,35mm). This core has a max flux density of 1,73T.
A lower grade EI231b core has 2700 secondary VA and max T of 1,49, and then there are two even lower grades for this core.
A good grade SE231b double-c-core (this range of c-cores is "equivalent" with EI cores so that the same bobbins can be used) has 3700 secondary VA with 1,75 T, to give you an idea of the higher efficiency of c-cores (one of their pros).

You can calculate flux for a given core and choose the required flux by one of the formulas. I use application sheets of Vacuumschmelze.
When choosing 1 - 1,2 T with a good quality core you will have a "cool" operating transformer with minimal stray fields, also more quiet.
The lower flux requires more primary windings (and therefore winding space) so often a more powerful core is required to get the low flux.

[jcatiwalaan]

I need a power transformer for H900 80-40-0-40-80 V / 15A to 20A. Boss Tony, is it possible for you to make 2 units for me? How much will it cost? PM me pls..

Thanks and God Bless

regards,
John L.