Toroid Transformer questions

Thread Starter


Joined Aug 15, 2008
While running around the net reading as much as i can, one thing i noticed is not a lot on toroid, and transformers. in terms of winding and making your own for whatever projects (even if only curiosity).

i don't really want to hash out stuff i can look up (or others can)
but i tried and couldn't find a place that would get the principal.

how far can you step up voltage in a small space?

can you wind 2:20 ratio on a tiny toroid and then chain 5 of them to get a
1:10k jump (at really really tiny amperage with losses)?

I do know that disposable flash cameras get this kind of jump, but theirs looks like one coil with just a high ratio of very fine wire. i have more 32 AWG and 43 AWG Essex wire than i know what to do with.

so i am just trying to learn given that kind of opportunity..

on another issue, can you use a toroid to make a 1:1 isolation transformer?
how would you go about knowing what frequencies it would impede and what range it would let go through?

i would be happy with a link if its way too much to explain, i do realize that each area has its own art behind it and just cause its passive in no way means its really simple. (ie i am realistic)

and lastly.. one project i have on my board is making a simple sine wave oscillator at around 1k H at a known ac voltage. the point is that i want to somehow figure out what the transformers i have are as far as turn ratios.

not perfect, but if someone has a better idea for me figuring the ratio, that would be awesome. resistance isn't good enough when the wire gauges are not the same... (though i guess if same wire gauge resistance would be proportional to length which would be related to turns... so somewhere there is an answer i am missing... no?)

[i have one that is just way to nice not to find some project for]

sorry if these seem like silly questions...

on the FUN side:
anybody have ideas for what you can do with a whole lot of wire, and a whole bunch of toroid s besides learn more about transformers, and high frequency filters :D (got lots and lots of magnets too) :) i even ended up with a handful of spark gaps... :cool: (came with a 47uf capacitor the size of a small loaf of bread... its discharged (and i have wired a resistor across the terminals as it has no use right now) i live in an apartment so, no large huge bolts of electricity and fire :p


Joined Mar 24, 2008
The subject can be quite complex, but the basics are simple. Where it is complex is flux densities and magnetic fields, they affect how much power can be transferred. While I am aware of the subject, I don't have it down by any means.

Where it gets simple is the formula for how much voltage is transferred. Both torrids and transformers use the same formula.

from Wikipedia said:
If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary (NS) to the number of turns in the primary (NP) as follows:

Thread Starter


Joined Aug 15, 2008
well yes i get that.

say you have a supply which can provide 10 amps at 1 volt.
if i put that through a transformer with a 10:1 ratio, i will end up with 10 volts at 1 amp.

however, the idea of chaining them is what i am curious
and how to find the frequencies they will pass.

most people describe toroid as throw them on.
and while that might be OK for certain things
knowing and selecting would be better.

but i do thank you for your time in going all the way over to wiki to cut and paste a reply, its greatly appreciated, and i hope you don't think otherwise.

for instance, i have three toroid and i have wound them the same.
each has 2 turns of 32AWG, and 200 turns of 43AWG.
using them in the voltage up arrangement
1 volt at 1 amp (AC of course), would output 10 volts .1 amps
if that is fed into the second same arrangement. you get 100 volts, .01 amps and third time, you get 1000 volts at .001 amps.

now i know we didn't account for the different wire gauges, and we didn't account for the frequency of the AC. wrong frequency and nothing will come out the other end of that chain.

now its interesting that the jewel thief circuit actually produces a voltage over 100 volts from a 1.5 volt or so source...

by the way, if you can find it FEMM 4.0 is good for basic magnetic field analysis. easy to use, and powerful enough that a hobbyist could change a design slightly and get a much better improvement.

as an example.. i did a coil project... and so i modeled what difference a threaded piece of metal and a smooth piece of metal would have. even though i couldn't model the exact metal i learned a whole lot in overall things to avoid and that would be favorable. in this case, the edges of the grooves of the bolt caused all kinds of complicated changes in the fields, and so that implied (to me) that i would lose a lot more energy to heat and other effects than i would with a smooth metal bar as a core which had much cleaner orderly magnetic field lines. all the ferric metals are the same as far as the way fields act, its just the magnitudes and properties in relation to each other that changes. so even if you don't have the right metal, having a close shape is enough to give you an idea of whats going on, when before you had no idea at all.

thanks!!! :)


Joined Jul 17, 2007
Like Bill says, transformers are really kind of a specialized field.

You can make calculations all day, using manufacturer's specifications and all that happy stuff, and when you finally wind and test the thing you'll find that you need to add or remove a dozen turns from one side or the other.

A transformer specialist I am not!

However, you can find a lot of good basic information on Ronald Dekker's page:

And to help you along with your toroidal core calculations, the Mini Ring Core Calculator is a very handy freeware tool:

Magnetics has a freeware Current Transformer Design software package, designed for use with their cores (naturally) but with the aid of the Mini Ring Core Calculator you might adapt the results to other company's (or even unknown) toroids.

Here's a useful page for transformer design:

Many links to freeware, hints & tips, etc.

Thread Starter


Joined Aug 15, 2008
Excellent! that will give me some reading.

as to chaining them? i guess it works as long as the frequency you use can pass through all of them... which is why they probably use more windings than chaining.. (not to mention noise)

and could a toroid with a few windings be used as an isolation transformer (if of course the frequency is correct... would have to be pretty high, no?)



Joined Jul 17, 2007
Well, transformers are pretty efficient - but still, you wind up with losses every time you go through a transformer.

I'm over-simplifying here, but the higher the frequency, the smaller the toroid can be used. However, at some point you'll run into things like core saturation, permeability problems, core heating and resultant instabilities, etc.

You'll note that a PC power supply is pretty compact for the amount of power it puts out.

If you went the traditional "mains transformer" route, you would have a very large and heavy transformer to get the same amount of power output. They use small toroids excited with high frequency instead.


Joined Jul 17, 2007
Yes, but read slup124.pdf as well. You have to get familiar with the various parameters and characteristics of magnetic cores.


Joined Dec 5, 2009
Are you chaining them inductively? or are you wiring them in series?

For instance, Are you using a larger primary, then a secondary winding, then a tertiary winding, ect?
Or are you taking a transformers secondary and connecting it to another transformers primary input via wire?