Power design is not my strong suit. But I would like help identifying what is the function of the toroid "T3". Also inductors have a tremendous amount of applications and I would like to know by looking at a torroid in schematic how can you immediately tell if it is being used a s a filter or a transformer?

I attached a portion of the schematic that shows the the toroid.

The overall operation of this section of the schematic illustrates (from right to left) a power input source(9-32V) going to a 20 A fuse, then the toroid, some other signal protection and signalling circuitry and then to a DC/DC converter that outputs 15V.

So again I would like to know:

1) What is the torroid doing? filtering? what frequencies is it passing, blocking? how much power is being lost?
2) how can i determine if a toroid is being used as a filter or a transformer?
3) how do you determine how many windings are required? links are ok but please let it be specific info not general info.

 

So again I would like to know:

1) What is the torroid doing? filtering? what frequencies is it passing, blocking? how much power is being lost?
2) how can i determine if a toroid is being used as a filter or a transformer?
3) how do you determine how many windings are required? links are ok but please let it be specific info not general info.

How are we supposed to tell when you show only one connection to the rest of the circuit? How about posting the whole schematic, or the whole left side of that paper, instead of mostly irrelevant parts?

 

How are we supposed to tell when you show only one connection to the rest of the circuit? How about posting the whole schematic, or the whole left side of that paper, instead of mostly irrelevant parts?

I didnt know the entire page was needed to determine if the torroid is a transformer or filter. Is this better. What is not shown toward the right of the schematic page is the DC to DC converter which outputs 15V. Not shown to the left is a 10 pos connector to pins go to the fuse.

 

From what I can see it is definitely a filter.
1)The actual cutoff frequency depeds on the inductance of the filter and the capacitor next to it, but generaly I would say 100-200khz is the range where it starts cutting off. As for the power lost in the filter, that depends on the DC resistance of the wires inside.
2) You can tell by two things, first a transformer would never have DC voltage right across a winding. Then, you can see that if it were a transformer, the left side of the schematic would connect to one winding and the right side to the other, but in this schematic the "transformer" is what you could describe as in series with the supply, so it doesn´t transform anything and just blocks high frequencies.
3) the windings depend on the cutoff frequency you want and what core material you have available. Then you look into it´s datasheet and see how many turns you need to get there. And based on your wire thickness you see if you can fit it or you need a larger core.