how to determine usage of Transformators - Page 1
Forum section: electronics / beginners

author: Axel1973
author_rank: Regular Contributor
timestamp: June 18, 2012, 09:18:37 pm
content: Hi Experts,in short:HOW TO DETERMINE TYPE OF TRANSFORMATORS AND/OR ITs USAGE?I mean, i know there are mains transf., LF transformers, HF transformers or filters, chokes, coils n what not. But how to tell what type of salvaged transformer/coil part you have or for what freq. its supposed to be used?Are there any rule of thumb or tips/scripts that i can follow to determine what type/use some transformer or coil is ? talking of things like type(material) of core, shape of core, thickness of wires, measured DC resistance or such...for example: some sort of transformer does have a winding/coil with a pretty low DC resistance of about 0.6Ohms or so. So as long i dont know more about the transformer i would consider connecting it to mains (or even floating 230V AC) could be a bad idea, since i dont know a thing about its AC resistance yet. 230V at 0.6 Ohms could result in a very high current, blowing "at least" fuses. So what should i do, test, measure to figure out in a safe manner what type of transformer i got and for what use it is?i hope i made my question clear since im not a native english speaker.Thanks for any feedback!greetsAxelAlways willing to learn.

author: joblessalex
author_rank: Contributor
timestamp: June 19, 2012, 12:29:21 am
content: A transformer is basically two coils of wire wrapped around a ferrite core. A few tips I know to tell what each one is used for:1. If it comes from an audio device, it is not always an audio transformer. The size of most audio transformers are very small, and are about the size of your thumbnail to as big as your thumb. That is general size. They usually have low resistances of 200 - 2 ohms. The core is usually solid black ferrite.2. Mains transformers are smaller and usually fit in your hand. The input is wound with very thin wire but a lot of it and should have a high resistance when measured. These use the I and E type ferrite core mostly.3. Switching type transformers can't be run off of direct mains and are pulsed. They have many output and input pins. I don't know much about them, so someone can fill in here.4. Finally, if it comes from something that requires high power/voltage, it will be way larger. Most high power ones are made with I and E pieces and can be run off of mains. Ex. battery chargers, microwaves, welders, ect. These will sometimes make a loud hum because of the amount of energy they use. They are very inefficient. Most run around 50-60Hz and use mains.The high voltage ones are used in CRT monitors and are usually encased in plastic and have a solid ferrite core sticking out on one side. These have lots of pins and coils to find out. The ones with least resistance are the input, usually a low voltage, and the wire on the top to another pin is out. This needs to be ran with high frequency input at around 20,000Hz or so. The output will arc across to the other pin if driven correctly.That's what I know. I am by no means an expert, that's just my experience.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 19, 2012, 04:57:30 am
content: Quote from: joblessalex on June 19, 2012, 12:29:21 amI think both you & the OP need to do some research.There are many sites on the Internet that can give you an insight into the characteristics & applications of transformers.

author: T4P
author_rank: Super Contributor
timestamp: June 19, 2012, 05:25:34 am
content: The type of E and I Laminations specifically used is made of silicon steelHere's a breakdown on transformers : EI laminated silicon steel transformers are lossy at high frequency due to it's inductanceFerrite cores are used for high frequencies because they have lower inductance (They are thus called toroids because of the shape) and lower lossesFerrite cores keep their regulation tighter then a EI lamination transformer because of the lack of a air gap, and also have lower EMI radiations

author: vk6zgo
author_rank: Super Contributor
timestamp: June 19, 2012, 08:52:38 am
content: Dave,we're both right on the lamination material!Most modern transformers use silicon steel.Historically,though,a lot of them used soft iron,& various steel alloys which offered some advantages.I have to disagree on ferrites,though.as they may be moulded to any shape desired.Laminated steel toroids are also made.,which have the same advantages you referred to except that they are limited in frequency of operation.For the OP:tryhttp://www.dave-cushman.net/elect/transformers.htmlor,http://www.site.uottawa.ca/~rhabash/ELG2331LN07.pdfAlso,there are several other threads on this forum with questions about transformers---please read them!

author: T4P
author_rank: Super Contributor
timestamp: June 19, 2012, 09:32:54 am
content: Yes indeed but it's typical sort of application you will findI have had a teardown on a 200W SMPS ( very old, older then i am ) and it uses laminated ferrite coresBut actually laminated ferrite is cheaper BUT yeah, it can't reach much higher then silicon steel anyway and lacks the ability like the toroidal ones doI do know there are "R" cores used by Atten in the ATF20B so ah well and "C" cores as well as "D" cores

author: M. András
author_rank: Super Contributor
timestamp: June 19, 2012, 02:11:35 pm
content: dont forget about iron powder cores, they are used in mains toroid transformers and some few khz transformers too

author: SeanB
author_rank: Super Contributor
timestamp: June 19, 2012, 03:48:03 pm
content: As well with monitors the transformer has a high voltage winding that is called diode split. It has multiple windings with a high voltage diode separating each section, to allow the generation of 30kV without internal arcing. Each section is a separate high voltage generator, with the capacitance of the winding to the inner well insulated shield providing a small capacitor to store the charge from the previouys section, allowing it to make a high voltage in a small volume. Focus and A1 voltage is tapped off of one of the lower sections, fed via a 10M resistor to 10M presets.Previously you had to use an external voltage tripler ( it actually would be either 3 or 5 sections of voltage multiplication, with a bleed resistor at the output that was a few gigaohms in value, and a tapping lower down used to drive the 2 presets built in for the focus and first anode voltages. The input would be from a single high voltage winding giving a 5 to 1a0kVAC input, which was about the most you could wind a winding with before it would arc over internally.the rectifiers used here are specialised, forward current of 30mA average and a reverse voltage of 15kV, in a casing the same size as a 1N4148. They have to be encapsulated unless you run them in either a vacuum or dielectric oil.

author: Axel1973
author_rank: Regular Contributor
timestamp: June 19, 2012, 07:43:12 pm
content: Quote from: vk6zgo on June 19, 2012, 08:52:38 amTo all: Thanks for all your replies and the Links! This gives he a nice kickstart into understanding types of transformers and usage. not yet done with reading, but started and these pages are definitly worth it! thanks.greetsAxel

author: Kremmen
author_rank: Super Contributor
timestamp: June 20, 2012, 12:42:11 pm
content: Quote from: Axel1973 on June 18, 2012, 09:18:37 pmThere are some explanations above but i feel they fall a bit short of the mark. If we are specifically discussing salvaged parts the identification can be a challenge. But let's divide and see if we can conquer.Firstly, you will not get very far by using resistance measurement alone. You do need an inductance meter to find out about coil inductances. Lacking that there is not much you can do. If you plan to reuse the components in a circuit, you absolutely must know the inductance values in the most cases. The values don't need to be measured with precision but you cannot be off by orders of magnitude. The inductances also give you the transformer winding ratios n1/n2 = sqrt ( L1 / L2 ).Secondly, you need to be aware that not all that looks like a transformer actually is one - in the strict sense of the word. Flyback converters use a "transformer" that is more appropriately characterized as a coupled inductor. The difference is important. One of those cannot successfully replace a true transformer due to differences in the design.Now then. If you salvage these parts yourself from an original circuit you have an advantage: you can identify the topology of the circuit. Roughly speaking, you tend to get transformer-like components only from circuits that do galvanic isolation. Non-isolating circuits like buck, boost, inverting and all their many derivatives generally contain an inductor for energy storage and release during the switch off time. Such inductors have an air gap to store the energy in the air gap flux. On the other hand a gap like this is not a feature of a true transformer. Transformers do not store energy in the flux. Note that powdered metal materials have a distributed air gap so you will not find a visible void or gap anywhere in the flux path of the core.If you have a transformer-like component then there is still the question whether it is a true transformer or a coupled inductor. If the component has a laminated iron core (of the E-I type or similar) then you are practically quaranteed to have a transformer if there is an identifiable primary and secondary coils. Line frequency inductors of the iron type tend to have just 1 coil.If the core material is ferrite or powdered iron or similar sintered material then it gets a lot harder. There is really no foolproof way to visually identify what kind of component you exctly have in your hands. If the transformer has an evenly split primary then it most probably is not a flyback inductor but a true transformer. However, the best chance to identify the component is to have the actual circuit in your hands before salvaging the part. Flybacks can be identified from a couple of key features - 1: there will be a single primary coil driven by a low side switch. The priomary may or may not have snubber components to reduce the kickback voltage. Also forward converters have this arrangement so you need to look at 2: A forward converter will have a flux reset coil on the primary side, with a diode in series (anode to GND). And then there are isolating Cuk and SEPIC converters that can be a bit hard to tell apart from those above... Ahh, it gets complicated.Once you have a certified transformer in your hands, you still have to find out what power and frequency it was supposed to handle. The power capacity can be estimated from the core volume and some indication regarding the current and frequency, by checking the coil wire gauge and type (regular magnet wire, litz, foil, single or multiple wire. Bear in mind that HF transformers regularly split the primary winding into bottom and top windings on the bobbin for flux distribution management.Finding out about the usable frequency and power can be done by measurement but then you need to be able to generate AC power at the frequencies and you need to be able to check the current and voltage waveforms to fing the core saturation points etc. I won't go into that since you would need the instruments and also the knowledge to recognize what you are looking at.But if you are the reading kind then let me suggest a couple of good sources that may help:http://www.amazon.com/Inductors-Transformers-Electronics-Vencislav-Valchev/dp/1574446797(maybe not quite worth the Amazon asking price but perhaps available cheaper elsewhere)http://www.amazon.com/Switch-Mode-Supplies-Simulations-Practical-Designs/dp/0071508589(this IMHO _is_ worth the asking price, high-ish though it be)

author: Psi
author_rank: Super Contributor
timestamp: June 20, 2012, 12:49:26 pm
content: I've often thought about making a transformer diagnostic tool.Something that can- Sweep from 50hz to 1mhz- Generate primary AC voltages at various currents and measure secondary voltage/load with auto ranging- Plot any combination of efficiency, frequency, current etc.And lots more.The issue is that it would be a very custom piece of test equipment, not something many people would use.I'm not sure it's really worth going to the effort to build it.

author: Kremmen
author_rank: Super Contributor
timestamp: June 20, 2012, 01:01:35 pm
content: Such an instrument would be interesting to proto shops for product verification and hobbyists for identification and testing, just as discussed above.I suspect that the market for the first group could be limited since all professional organizations already have a way to quality assure their products (if they mean to stay in business, that is).To be really useful, it would not be a simple thing to build such a tester. Nor would it be very cheap either, i suspect...

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: June 20, 2012, 01:11:18 pm
content: Psi , I would like to see that when your done ?My interest is RF , ham radio , I have been around a lot of surplus military , commercial , scrap and have picked up many with the intension of building power supplies for the shack and amps for RF - manly HF .Have not got any really big ones yet , the heaviest is maybe 30 lbs , some have been pulled from oscilloscopes , other test equipment , lots of multi-taps , some with as many as 40 some wires coming out .As I learn more about these , it will be time to go through and get rid of ones that do not fit any current future build , because space is limited

author: Neilm
author_rank: Super Contributor
timestamp: June 20, 2012, 06:50:32 pm
content: Quote from: Kremmen on June 20, 2012, 12:42:11 pmDepending on the application you would also have to test the material at many different frequencies. If you savage something and try to reuse it at a frequency it can't handle the core will probably get very hot.Quote from: Kremmen on June 20, 2012, 12:42:11 pmThe diodes might be replaced with transistors in high efficiency applications. The losses in a transistor are much less than a diode and a designer can easily knock a few percent off the losses.Also 3: resonant converters. These tend to have the primary and secondary separated to allow more stray inductance (used as part of the resonant tank). You can tell these as they more often than not use Litz wire (very high frequency) and have a capacitor in series with the transformer.Neil

author: Kremmen
author_rank: Super Contributor
timestamp: June 21, 2012, 01:34:58 pm
content: Quote from: Neilm on June 20, 2012, 06:50:32 pmYes, i think i briefly mentioned that but didn't really expand it. The material is of course key since the transformer won't work right with unsuitable core material.QuoteYep, forgot to mention that. When high efficiency is the target one gets lower forward losses with a transistor or FET vs diode. One will find the transistor in the same place a diode would occupy.Resonants are of course possible but you don't really see them that often, at least not in the "usual" salvage sources like PC power supplies, printers, scanners, copiers etc. But possible of course and an extra spice in the soup