toroid for car amp smps

[sss]

OMG !!!
i think i made a critical mistake with my toroid

(post #94)

as u can see on the pic i didnt cover the toroid with anything before winding the primary !!
i used a special duct tape to isolate the primary from the secondary but forgot to isolate the core
is it that critical?

[tennisballg]

only if your wire insulation rubs off...

[Eva]

In theory, ferrite shows pretty high resistivity so windings are not likely to be shorted through the core

In the other hand, magnet wire isolation of adjacent turns may be scratched or damaged due to ferrite harshness during winding process and this may eventually cause shorts to appear in the long term. This is avoided by coating the ferrite with something soft enough in order to not damage the wire insulation

[ChocoHolic]

Great Thread!!!
I should have checked through all this earlier, but in fact the length of this thread threatened me....
Silly me.

@SSS
.... one point:
I would be carefull about the isoaltion properties of ferrites.
It is strongly nonlinear. At low voltages it is somehow isolating.
At high voltages it turnes more or less conductive....
Unfortunately I do not have detailed values.
Damn.., should know such things better. But in my applications, I usually treat ferrites as a conductive material.....

Especially i terms of reliability I would not feel comfortable with the
windings of this SMPS directly on the core.
Normally the varnish of the transformer wire should do the isolation
for such low voltages, but during winding it on the ferrite you really have had a lot of good chances to damage the isolation.
Also vibrations during operation will "work" on this.
If you only want to use that transformer for first checks on the workbench, than you can dare it that way. But if you want to use it
in your car for the next years... ??
...hope this is not frustrating you, sorry...
But I think its is the smaller drawback to rework the transformer, than facing issues later on.

Good Luck
Markus

[sss]

thanx for the replies everybody
i guess i will use it for testing only

here's some toroids from wilco corp
i'm looking at model ITL100
now can someone tell me plz how those parameters are fit into equation(s)
what is saturation DC Amp etc....?

[Eva]

Are you looking for transformer applications for inductor applications?

This table shows a range of high current pre-wound inductors including some data : saturation currents, inductance values and actual thermal current rating of the windings. They are probably made with iron-powder cores [maybe also gapped ferrite cores or air cored]

[sss]

oh i see , thanx Eva

i allready got all the parts needed to test my core , i guess i should play with the frequency untill the output voltage is maximal right?

[Alcaid]

The ITL501 is made of ferrite and has been tested in a SMPS by Rod Elliott on http://www.sound.westhost.com/project89.htm

[sss]

today i've checked the transformer and there some things that need to be fixed :

first the ringing
the transformer is making a high freq sound , i know it should be tightly wound and it is !!! but it still ringing , while testing i have increased the freq untill i couldnt hear it

the second problem is that the output voltage is higher then expected by approx 13V , i guess those are voltage spikes and they should be eliminated .

i assume that if the primary side will have a clean square wave then the output will be clean too is that right ??

i saw rods circuit and he got resistor capacitor network connected in paralell witt the primary

what if i will just connect a fast diode like this ??

[sss]

ca n anybody tell me if the diode will work plz