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Old 03-17-2012, 07:58 AM   #1
Evil Lurker
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Default A little guide to scavenging toroids, inductors, transformers, and magnet wire.

I thought I would do a little guide geared towards identifying and scavenging the magnetic components commonly found in electronics. This is because eventually if a person tinkers with electronics long enough to start doing a bit of prototyping... whether it be for a switching converter or joule thief, they will eventually need some magnetic components. The good news is that it is easy as heck to scavenge toroids and transformers essentially for free from any well stocked junk box. The hard part most of the time is simply figuring out how to re-purpose whatever it is to what ever it needs to be.

Take your basic toroid for instance. They are in all sorts of things, power supplies, TV inverter boards, even computer motherboards. The thing with toroids though is that they can be made from various formulations of powdered iron, ferrite, phenolic, or some rolled up brittle metal stuff and/or even be encapsulated in plastic. The reason behind all of the different materials is that each core composition has been specifically formulated to operate at maximum efficiency based upon intended application and specific frequency range.

Take these random toroids I have scavenged for example:

Notice how many of the toroids are colored and some are not. Generally a colored toroid is an indication that it is of the powdered iron type. However there is no firm set industry standard color coding for toroid inductors... a prime example is the large grey ferrite toroid on the left whereas the two slightly smaller toroids next to it are actually powdered iron/metal types.

If you are wondering exactly what is the difference between a ferrite toroid and a powdered iron type it more or less has to do with magnetic permeability and energy storage characteristics. Oversimplified, ferrite types are more suited towards high frequency transformer applications where there is very little holdup of energy in between on/off cycles (such as with the joule thief circuit) and for filtering of high frequency EMI. Powdered iron types are more suited towards lower frequency applications... the powdered metal more or less acts as it's own air gap and helps the core resist going into saturation. These are generally used for PSU output filtering and also find use in continuous mode DC boost coverter circuits. In fact just about all the green/blue and yellow/white toroids for the picture were snagged from the secondary side of various ATX PSUs.

The website below has a lot of great information about ferrite/iron properties. Judging by the application where the toroids were found, that website, and several other references I believe one can safely assume any yellow/white colored toroid consists of type-26 material and a green/blue toroid is type 52. The nice thing about knowing what material a toroid consists of is there are online calculators and programs floating about the internet that allow you to enter in the core size, material, and desired inductance and it will crap out an estimated number of turns of wire needed to achieve a particular inductance... and at the same time some will also do the reverse and let you estimate the inductance of an unknown scavenged toroid based on the number of turns it has.

Also a couple other ways to tell the difference between a ferrite toroid and powdered iron type is that they each have slightly different sizes and weights, ferrite being lighter. For a general idea of what is what, going from left to right the big grey toroid is a FT-140A, the next two are T-130's, the pi filter and two toroids below it are T-106's, then you a T-80,T-68,T-50 so on and so forth. The best list I have seen of standard toroid sizes is also at the same website I mentioned earlier.

Before I wrap the toroid part of my guide up there are just a few more things I feel should be mentioned. On the bottom part of the picture there are three groups of toroids. Going from left to right are a couple of those weird brittle foil plastic encapsulated type toroids. The group next to it consists of toroids wound as common mode chokes. These were snagged from ATX PSUs from the primary side input filtering part. The white plastic encapsulated ferrite ones were specifically snagged from various Bestec ATX-250-xx's and to be honest i can't recollect where the green ones came from, nor do I know what material they are constructed of. The last group are ferrites are a bunch mainly snagged from power cord filters and what not. Again I don't know too much about them and I'm more or less stuck without a LC meter.

Moving on to transformers, wire, and other inductors...

Toroids are wonderfully efficient with low losses. However if you have to wind more than a few turns on one it quickly becomes a royal pain in the ass without a 5 digit price tag automated winding machine like this:

Luckily there are also other types of inductors that can be more easily put to use and more or less just as easily scavenged. This also includes SMPS transformers which basically for all purposes are nothing more than inductors with multiple windings. The absolute dead simplest to work with are the bobbin wound types shown below and including the green/yellow thing in the picture below. These can be found easier than cow piles in a pasture littering the main circuit boards of CRT TV's and computer monitors. Usually the inductance is printed somewhere on the inductor and it can be lowered simply by removing turns or even completely changed by swapping wire sizes and adding even more turns. Converting one of the bobbin type inductors to a flyback transformer is also just as simple as wrapping a few turns of wire around the outside of the coil.

If one wants to really go all out then just snag a transformer. These take quite a bit of work to recycle but as can be seen I have several of them pictured to show it can indeed be done. Best way to do it is to heat them up in the oven to around 300F for the shortest time possible... just long enough to get the glue holding the ferrite cores together weak enough to gently gently gently pry them apart. And yes it has to be done while the transformer is still 300F. Grab it with a heavy towel, grab each half of the ferrite core with your thumb and index finger and gently gently gently torque the halves in opposite directions while simultaneously pulling them apart. It takes a bit of practice, but as can be seen even a small 5vsb transformer can be taken apart without damage (the bobbins on these things are ridiculously fragile... the pin header rows love to snap off with the slightest excess of pressure). Don't worry about heat damage to the transformer core and bobbin... the plastic used on some of these things can take temperatures well in excess of 500F and as long as the ferrite cores are not exposed to temps above their Curie temperature (like 400F or so) its all good.

Its important that the tape and windings also be removed while the transformer is still hot otherwise the tape is a complete and total bitch to get off. I swear it would not surprise me at all if I were to discover that the tape was at one time considered a candidate for use in bulletproof vests... yes its that tough. Like packing tape on steroids. But with the transformer still hot the adhesive is weakened and it comes off without too much hassle. I prefer to use a rubber hose pick or dental explorer type tool to get the tape started and snip off the wires going to the windings right above the header pins. When all the tape/wire has been removed just take a soldering iron to where the wire is wrapped around the pins and rake it off. Again if one tries to do it any other way they risk breaking off a header pin row... and yes I have snapped off quite a few of them before I finally started sticking transformers in the oven. When that happens the bobbin is ruined and the transformer might as well be tossed in the trash.

Also in the picture are two high voltage flyback transformer cores. I just got the square looking open frame one recently, I hope to get it wound pretty soon. It came out of an old circa 1970's television... they basically don't make them like that anymore. The other rectangular looking flyback core came out of a vintage 1990's set. In the middle of the picture there are two plastic looking thingies. These came off the yoke of a CRT I believe they have something to do with the horizontal deflection of the tube or whatever. The only thing I find interesting about these transformers is that they have a threaded ferrite core in the center of them... essentially a variable inductor. Also the square boxy looking things are SMD inductors... I really like these as I can get them easily from junk satellite reciever boxes I get for free at the local satellite installer/seller's business. They are easily adapted for use on a breadboard by soldering on a couple pins. The trick is to use an IDE header off an old junk motherboard... simply bend a couple of the pins and tack them on. The pins are sqare so they don't wobble around and are spaced exactly the same as the holes on a breadboard.
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