hybridfree/eevblog-posts huggingface dataset:
Transformer Calculation App. - Page 1
Forum section: electronics / projects

author: jonathancunharj
author_rank: Newbie
timestamp: October 25, 2023, 12:42:05 am
content: Hello! I'm an electronics enthusiast, and in my free time, I'm a mobile developer. A while ago, I read the book "Transformers - Alfonso Martignoni," and it sparked the idea of creating a free and intuitive app to make it easier for power electronics enthusiasts to develop their projects in an intuitive and precise manner.Now, through the eevblog forum, which has been one of my primary sources of knowledge in various areas, I'm taking this opportunity to share my small effort in creating a tool to assist my fellow engineers and hobbyists.In the field of building precise transformers, specifically tailored to be your reliable resource for power transformer development, I present the link to the app!https://play.google.com/store/apps/details?id=com.jonathancunharj.transformercalcpro

author: jonpaul
author_rank: Super Contributor
timestamp: October 25, 2023, 06:40:25 am
content: Hello, bravo for the initiative. As user of iPhone, iPad, PCs, cannot use your app.It is Limited to 50/60 Hz mains power transformers?IOS app?Web app?"Transformers - Alfonso Martignoni " (Italinan?Brazilian?) is focused on mains power transformers.Many better texts exist that cover the entire field , see Hunt static electromagnetic devices and Magnetic components by Steve SmithNowadays most mains freq power trsf are readily avail commodities from many vendors.The need is in high freq SMPS trsf for power and bridge drivers.We used Intusoft Magnetic Designer for decades, fine PC app, covers most practical trsf designs.Bon chanceJon

author: RoGeorge
author_rank: Super Contributor
timestamp: October 25, 2023, 02:32:05 pm
content: Quote from: jonathancunharj on October 25, 2023, 12:42:05 amVery good idea, congrats!

author: themadhippy
author_rank: Super Contributor
timestamp: October 25, 2023, 02:36:45 pm
content: one minor point is your power section,it says va at the top in brackets but uses watts as the measurment unit,which is it?
Transformer core cross section and length of turn vs inductance. - Page 1
Forum section: electronics / projects

author: Circlotron
author_rank: Super Contributor
timestamp: May 30, 2017, 07:09:04 am
content: Let's say we have two transformers with identical core material. The one with the larger cross section needs 100mm of wire per turn. The smaller one needs 50mm per turn. Inductance depends on turns squared and also core cross section. For the same *length* of wire (assume single layer) would they have similar inductance?

author: MagicSmoker
author_rank: Super Contributor
timestamp: May 30, 2017, 10:27:24 am
content: Quote from: Circlotron on May 30, 2017, 07:09:04 amA tricky question... If two cores have different cross sectional areas but the same magnetic path length,le, permeability and are wound with the same length of wire then they will have the same inductanceprovided there is an integral number of turns in each case!
Transformer Design - Page 1
Forum section: electronics / projects

author: EEVaditya
author_rank: Regular Contributor
timestamp: May 28, 2018, 07:11:05 am
content: Hello,The attached document contains the Transformer Design specifications which I have given to Manufacturer.Do I need to provide any other data or is this data sufficient for manufacturer?Please guide.

author: BravoV
author_rank: Super Contributor
timestamp: May 28, 2018, 09:21:07 am
content: Quote from: EEVaditya on May 28, 2018, 07:11:05 amDid you really talk to the manufacturer ? I mean really talk before you order from them or pay them ?

author: chris_leyson
author_rank: Super Contributor
timestamp: May 28, 2018, 11:11:31 am
content: Looks like a design from Power Integrations, they really like using bifilar windings sometimes quadrifilarIt will be cheaper and easier if you don't use bifilar windings on the primary side and why is the bias winding 25AWG ? I'm sure most manufacturers won't have a problem except for the bifilar windings of course, they will put the cost up.

author: oldway
author_rank: Super Contributor
timestamp: May 30, 2018, 09:38:14 am
content: I have already manufactured 60Hz transformers (not ferrite) and I think there is a mistake in principle.As the project is not done by the manufacturer, how can it be made accountable for the value of the primary inductance of the windings?It should be asked a dozen prototypes without imposing the inductance, check if the value of the primary inductance resulting from the detailed manufacturing specifications is consistent with what is expected and only after that, specify the value of the primary inductance and the tolerance acceptable on this value.The manufacturer is not responsible for any errors in the client's project
Transformer driver topologies - Page 1
Forum section: electronics / projects

author: rubemjrx
author_rank: Newbie
timestamp: December 01, 2022, 07:51:57 am
content: I have been looking into a project where I want to drive a transformer to create a power output on the secondary winding. Not really any fixed specs or anything, I'm just seeing what's acheivable for now.I can figure out the frequencies and loads part of the problem. The thing is, I can't find find any real resources on how to actually drive the transformer from a DC supply. I have experience with controlling inverters to do field oriented AC motor control, so the first thing that comes to mind is using a full bridge, and PWM each half with opposite phase sine waves. Is this a reasonable approach? Do you have any resource recommendation so I can figure this out properly, like a textbook or a paper?Thank you!Rubem Bezerra.

author: Benta
author_rank: Super Contributor
timestamp: December 01, 2022, 11:03:25 am
content: DC or AC output?If it's AC output, a half- or a full bridge will do the job. Which one depends on your power levels.

author: rubemjrx
author_rank: Newbie
timestamp: December 01, 2022, 12:03:59 pm
content: AC output on the secondary. What would a DC output from a transformer look like?

author: Benta
author_rank: Super Contributor
timestamp: December 01, 2022, 07:55:18 pm
content: Sorry, my phrasing was perhaps unclear.With AC or DC I mean: do you need 50 or 60 Hz sinusoidal AC as the final output, or just DC. I'm not talking about the switching carrier frequency.
Transformer half wave rectifier inbalance in voltage - Page 1
Forum section: electronics / projects

author: ZeTeX
author_rank: Frequent Contributor
timestamp: June 18, 2016, 11:23:27 am
content: HiI have the following schematic on breadboard:Where V1 is 230/12V 3VA transformer, that outputs 15VAC RMS no load.C1/C2 are vishay 470uF 50V caps.D1/D2 are just jellybean diodesThe issue I'm having is that the voltage is not equal on the caps, for the positive cap (C1) I measure about 20V no load and with 240ohm load I measure about 14V, and for the negative cap (C2) I'm measuring about 7.50V no load and with 240ohm load I measure about 6V~.Why is it so?

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 18, 2016, 11:34:46 am
content: Swap the diodes.Does the problem move?Yes -> bad diode.No -> bad cap.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: June 18, 2016, 11:46:19 am
content: Quote from: PA0PBZ on June 18, 2016, 11:34:46 amFixed! Bad diodes.thanks!

author: Audioguru
author_rank: Super Contributor
timestamp: June 18, 2016, 02:49:07 pm
content: The extremely high unlimited inrush current blew up the little low power diodes. Why not use rectifier diodes made to do what you are doing? 1N4001.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: June 18, 2016, 03:42:20 pm
content: Quote from: Audioguru on June 18, 2016, 02:49:07 pmI'm using 1N4007 anyways, I might have shorted out something that killed the diodes, but it fixed now anyways.
Transformer Help - Page 1
Forum section: electronics / projects

author: PsychoMaster
author_rank: Regular Contributor
timestamp: May 22, 2015, 07:29:21 pm
content: Hi FolksI am building a 0-24v PSU that switches up in two stages using a relay and a 0-12-24 transformer.I do not have such a transformer but I do have separate 12v and 24v toroidal transformers. If I connect one secondary of each together and connect to either of the others through the relay to get 12 then 24 volts will this be OK? I am thinking about inrush current as a problem maybe. It would give the option of separate switches on each transformer if only using one voltage range.Would this be OK?
transformer modification - Page 1
Forum section: electronics / projects

author: justin66
author_rank: Regular Contributor
timestamp: July 28, 2015, 10:24:46 pm
content: i need to modify this transformer to supply lm3886t so i need split line 40Volt transformer. however its single line transformer. secondary has 100 turns and at 225v it outputs 18.2v what should i do to make it split line(with 4 wires) 40v transformer with a decent enough current to feed at least 1 lm3886t or possibly 2 of them? what should i do please how can i figure it out?http://www.part.lt/img/a2028855706d98a0ec5b38c5723ebd05750.jpghttp://www.part.lt/img/b61092cb4db331c6c59eaf7317e7a7bc973.jpg

author: tautech
author_rank: Super Contributor
timestamp: July 28, 2015, 10:43:00 pm
content: Here's a useful link:http://ludens.cl/Electron/trafos/trafos.html

author: Zero999
author_rank: Super Contributor
timestamp: July 29, 2015, 08:12:24 am
content: Use a voltage doubler circuit to give +/-48V.

author: justin66
author_rank: Regular Contributor
timestamp: July 29, 2015, 05:46:05 pm
content: Quote from: tautech on July 28, 2015, 10:43:00 pmthanksQuote from: Hero999 on July 29, 2015, 08:12:24 amthank you sooooo much i love you !!! you are my saviorhere is my setup configurationignore bottom note its fully working with 17v ac max input. change capacitors and resistors accordingly to input voltage
Need Help on Transformer Output Circuit Designs - Page 1
Forum section: electronics / projects

author: einsvanian
author_rank: Newbie
timestamp: December 26, 2012, 05:40:12 pm
content: I created a 120 VAC to 14VAC transformer with six 30 amp outputs. I am using six 40 amp bridge rectifiers to convert to pulsating DC. I would like these outputs to charge a battery bank of two 12VDC batteries in parallel. The issue I am having is figuring out the circuit that will regulate/control the battery charge. Since the output is Pulsating the charge controllers on the market now days don't like this type of input, unless I was misinformed; I asked most of the manufacturers if their devices can handle pulsating and they all said no. I would like to flatten out the ripple and control the charge. What type of circuit would be best? Can I buy it pre-made or build it myself?I would like to add a capacitor to the outputs to flatten out the ripple but need help on selectring the right model. I have no clue on how to control the charge though. I would like the system to stop charging when the batteries are full.Application: the transformer will be powered by house voltage of 120 VAC @ 60 Hz and supply 14 VAC to the bridge rectifiers to convert to pulsating DC then fed to a charge controller (home made or pre-built) which charges the batteries. The batteries will then power multiple inverters that according to calculations will require a maximum of 180 amps; hence the six outputs rated at 30 amps each a total of 180 amps. The system will never use the full 180 amps though.Edit: I forgot to ask... if the system is used continously will I even need to worry about controlling the charge. I am thinking the batteries will except what they need until full and the rest of the charge will continue to feed the inverters am I correct?Edit: Would the circuit be called a regulator instead of a charge controller?
Transformer power supply stuff - Page 1
Forum section: electronics / projects

author: sahko123
author_rank: Frequent Contributor
timestamp: June 15, 2020, 10:13:34 pm
content: I'm making a linear power supply for a project. I want to filter the mains in case the project is used in a place with shitty mains (like my home lab). Would the secondary voltage by a good representation of how the waveform would look at the primary side? I don't have a proper differential probe and cant really buy one to own yet so i want to somehow probe the mains without probing the mains.

author: Ian.M
author_rank: Super Contributor
timestamp: June 15, 2020, 10:32:37 pm
content: Maybe!It depends on what's wrong with the incoming mains waveform. Iron core transformers have limited bandwidth, so fast spikes, powerline communications databursts, much higher harmonics etc. will be severely attenuated on the secondary side, Also they will start to saturate if overvoltaged so the output may not be proportional to the input.OTOH if you don't have access to a CAT II or better isolated differential probe, its going to give you at least a rough idea if there is excessive waveform distortion without a significant risk of electrocution or blowing up your scope. Also, from the project's point of view, it doesn't really matter what the mains supply actually looks like as long as the secondary side waveform is reasonably clean near the peaks of the waveform, as that's the only part of the waveform that actually contributes to the ripple on unregulated DC rail.

author: David Hess
author_rank: Super Contributor
timestamp: June 16, 2020, 11:38:28 pm
content: For practical purposes, what you see on the secondary is all you have to deal with and a line frequency transformer filters its input pretty well. Line input filters are normally added to linear power supplies to prevent interference going in the other direction.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 17, 2020, 05:25:40 am
content: First I assume you have a scope and that it's grounded.You can make a 1:10 probe by putting 9 1M resistors in series, and putting a small capacitor over each.Make sure voltage ratings for both capacitors and resistors are adequate.Put some heat shrink tube over everything and put it in a plastic tube from for example a pen, and solder a needle to the hot end of the probe.Frequency compensation as normal for any 10:1 probe.You can quite safely poke around with this tip as long as the voltage is <1kV.Then do not use any additional GND connection of your scope, because your scope itself is (should be) grounded already.For the transformer option:Toroidal transformers tend to have a much higher bandwidth then E/I transformers.All mains rated transformers are usually close to saturation, but if you put the primaries of 2 (identical) transformers in series then each only sees half the mains voltage, and measurements will be more lineair.
Transformer primary testing / estimating? - Page 1
Forum section: electronics / projects

author: BiOzZ
author_rank: Regular Contributor
timestamp: July 16, 2013, 08:11:33 pm
content: i for the most part salvage everything from everything i take apart and as part of that i have a metric shit-ton of transformersnormally i just have a peak see at what windings are the thinnest to guess the primary side of the iron xfr but some of them are not made for 120v, some are tapped off and some are very high currentmy question is is there a generic rule of thumb for resistance or inductance (or both) of a primary transformer winding for a current range?i say this because today i plugged in what i thought was the primary winding to my testing ballast and it went up in a puff of smoke! (gotta get a smaller ballast) and it was the higher resistance side!

author: The Electrician
author_rank: Frequent Contributor
timestamp: July 16, 2013, 11:54:43 pm
content: Sounds like the transformer may have a shorted winding.
Transformer Ratio, Is it Linear? - Page 1
Forum section: electronics / projects

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: October 27, 2013, 12:43:54 pm
content: Going through some transformers for upcoming projects I decided to calculate the ratios as a 1/ value. For the most part my ratio calculations are just about spot on with the exception of some transformers seem to change their ratio with lower and higher input voltages. For example, I have lets say an 8-1, and I am using a Zpri(500) and a Zsec(15) with a sine wave and pulsed wave from 4 VAC to around 120 VAC. The ratio seems to stay very consistent over the range from about 25VAC to 120VAC but below that the ratio drops to about 6-1 and even lower when the voltages go down. Now, here is the real puzzler for me, not all the transformers do this. Some of the step up which are 1-1.5 and even 1-4 seem to stay consistent across the range, and even some step down do also. The only thing I can see that would possible change is the Z but checking that with my LCR at 60Hz, 120Hz, 1KHz and 100KHz I get just the opposite effect the Z which makes me believe that the ratio should go down when increasing V allowing Z to also increase. The AC supply may be the culprit also, it's not a filtered or regulated AC supply which may cause some changes in Z depending on the V level.Any thoughts or ideas as to why this is occurring? Why only some transformers doing this?

author: Neilm
author_rank: Super Contributor
timestamp: October 27, 2013, 03:58:38 pm
content: My first thought is that you are saturating the cores on those units that change the most

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: October 27, 2013, 06:53:25 pm
content: Quote from: Neilm on October 27, 2013, 03:58:38 pmThanks, I'll look at that.

author: JackOfVA
author_rank: Unknown
timestamp: October 28, 2013, 12:39:07 am
content: At low excitation voltage, transformers can become non-linear. If you look at the B-H curve for a typical power transformer you will see a linear region with non-linearity (saturation) at high levels of excitation and at low levels of excitation non-linearity due to a different effect. Stretching my memory, I recall the low excitation non-linearity being due to insufficient flux to cause all the magnetic domains to follow the flux -- some domains are "sticky" and require greater flux to reorient them. I'm sure that is not exactly correct but it's been a long time since I studied transformer theory.If you want to characterize the transformer core material, I suggest a B-H test setup. At powerline frequencies it can be simply done - a dual trace oscilloscope, variable AC supply and an RC integrator. Poke around Google and you'll find a number of articles on how to toss a B-H curve test setup together.

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: October 28, 2013, 12:51:27 am
content: Great advice JackOfVA. This makes a lot of sense. I will look up the info...
Transformer rewind - Page 1
Forum section: electronics / projects

author: spike1947
author_rank: Contributor
timestamp: September 28, 2021, 05:36:07 pm
content: HiI am going to rewind a small transformer, the size of the wire it had on was 0.06mm x 9 in a bunch, now I can't find that size anywere and if I did I would need 9 bobins of that size, I would lke to know what single core size wire I could use that would carry the same current !.cheersSpike

author: langwadt
author_rank: Super Contributor
timestamp: September 28, 2021, 07:25:57 pm
content: there's probably a reason it is made from multiple wires ...

author: andy3055
author_rank: Super Contributor
timestamp: September 28, 2021, 07:39:03 pm
content: .06 mm is thinner than a 40AWG wire. It might be that the transformer is for a specific purpose.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 28, 2021, 07:51:01 pm
content: Quote from: spike1947 on September 28, 2021, 05:36:07 pmIs each wire bare or insulated, as with enamel. If they are insulated, that could be Litz wire, which is usually used for high frequencies. You didn't say anything about the transformer. What type of core does it have?

author: JimRemington
author_rank: Regular Contributor
timestamp: September 28, 2021, 11:27:23 pm
content: What is the intended purpose of the rewound transformer?What voltage and current do you expect the new winding to carry?
Transformer spot welder logic. - Page 1
Forum section: electronics / projects

author: firewalker
author_rank: Super Contributor
timestamp: July 12, 2014, 03:34:33 pm
content: What is the logic behind a transformer spot welder (welding battery tabs type) controlled my an mcu?Zero cross detector -> Wait ~20 msec (50 Hz) -> Enable TRIAC (or any suitable device) -> Wait X*20 msec amount of time -> Turn off the TRIAC.To play with the power just allow more cycles (increase X)?Alexander.

author: tautech
author_rank: Super Contributor
timestamp: July 12, 2014, 04:14:34 pm
content: I think I would apply the KISS principle.Adjustable timer switching the Triac gate feed from a Triac controller.

author: jebcom
author_rank: Regular Contributor
timestamp: July 12, 2014, 06:07:00 pm
content: Yes, you're right to use zero-crossing detect and allow for a selectable number of cycles. If you have multiple taps on your transformer, you can also allow selection of taps to control heat. If you're doing a quantity of joints, the electrode tip will degrade, and you will need to either dress the tip or make adjustments in your number of cycles or voltage. Yes you do want to keep it simple, but you also need enough room for adjustment to get ideal welds in your range of working conditions.

author: eneuro
author_rank: Super Contributor
timestamp: July 12, 2014, 08:27:13 pm
content: Quote from: tautech on July 12, 2014, 04:14:34 pmI saw many spot welders with triacks and made myself one using this huge transformerHowever what about AC mosfets switch and current sensor to controll more tricky transformer primary?Just testing small optoisolated mosfets gate power supply to be able test those AC switches.I guess some kind of snubbers will be needed to this AC switch circuit.Did you tried drive transformers using such AC mosfet switches?

author: nctnico
author_rank: Super Contributor
timestamp: July 12, 2014, 09:05:10 pm
content: Usually only part of a 50Hz cycle is used. So wait until the zero crossing and then wait for the right firing angle to trigger the TRIAC.
Transformer Swap - Page 1
Forum section: electronics / projects

author: mundenez
author_rank: Newbie
timestamp: March 23, 2017, 09:14:42 am
content: Hey all. I'm new here so let me know if I've posted this in the wrong place, but:I've bought a sparkfun rework station and didn't realise it was 110v. Inside is the transformer in the pic. I was thinking about swapping it with something like this:https://www.aliexpress.com/item/Free-shipping-2PCS-30W-dual-9V-30W2-9V-transformer-power-transformer-Input-220V-50Hz-output-Two/32737943794.html?spm=2114.01010208.3.1.RuhbU9&ws_ab_test=searchweb0_0,searchweb201602_5_10065_10068_433_434_10136_10137_10138_10060_10062_10141_10056_126_10055_10054_10059_10531_10099_10530_10103_10102_10096_10052_10144_10053_10050_10107_10142_10051_10106_10143_10526_10529_10084_10083_10080_10082_10081_10110_10111_10112_10113_10114_10037_10078_10079_10077_10073_10070_10122_10123_10124-10531,searchweb201603_2,afswitch_1,ppcSwitch_5,single_sort_0_default&btsid=e3f5d050-ed8e-4314-9d34-c68b679ffc5e&algo_expid=b9cb994e-8fe6-44e8-a158-c150a7f6a7b4-0&algo_pvid=b9cb994e-8fe6-44e8-a158-c150a7f6a7b4Any reasons why this would not work?

author: amspire
author_rank: Super Contributor
timestamp: March 23, 2017, 09:31:08 am
content: Does the transformer you currently have have two 110V primary windings that can be in series or parallel?From the label, it looks like is does have two windings.

author: Anks
author_rank: Frequent Contributor
timestamp: March 23, 2017, 10:01:49 am
content: That transformer as amspire said can be wired for 115v or 230v AC

author: mundenez
author_rank: Newbie
timestamp: March 24, 2017, 12:17:09 am
content: I'll get a better photo. - Makes sense. So I connect the green from one coil into the red of the other and then treat the two remaining as the 220V primary supply?

author: amspire
author_rank: Super Contributor
timestamp: March 24, 2017, 01:36:28 am
content: Probably. You can check with multimeter to check which pairs belong to which winding. If each winding has a red and green wire, and if currently the two reds and the two greens are shorted, then connect a red from one winding to the green of the other.But sure the board that that connector plugs into doesn't have provision for selecting the voltage? A switch, or there are links on the board? That is what I would expect.Also if there is a fuse, you can change to half the current.
Transformer tap switching circuit? help please? - Page 1
Forum section: electronics / projects

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 27, 2013, 10:16:05 pm
content: Does anyone know of a simple circuit to trigger a 12volt relay, with the output voltage of an adjustable supply reaches a preset voltage.Basically, I have a centre tapped 9+9 volt transformer, and wish to use the first tap when the output voltage is below ~10volts, and switch to both taps in series above this.Thanks!

author: madires
author_rank: Super Contributor
timestamp: November 27, 2013, 10:20:16 pm
content: A simple comparator circuit will do the job, e.g. LM311.

author: Jon86
author_rank: Frequent Contributor
timestamp: November 27, 2013, 11:07:04 pm
content: Yep, comparator connected to a relay. Just setup a divider on one input of the comparator and connect the other to the output.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 27, 2013, 11:11:53 pm
content: I dont suppose anyone would know of any basic applications circuit diagrams?

author: madires
author_rank: Super Contributor
timestamp: November 27, 2013, 11:19:10 pm
content: Quote from: AmmoJammo on November 27, 2013, 11:11:53 pmYou should train your google fu :-)-http://www.physics.unlv.edu/~bill/PHYS483/comparators.pdf-http://home.cogeco.ca/~rpaisley4/Comparators.html
Transformer Teaser - Page 1
Forum section: electronics / projects

author: Rufus
author_rank: Super Contributor
timestamp: July 30, 2013, 07:16:54 pm
content: This had me scratching my head for a while but I think I understand now - what do you make of it?The circuit is a mains transformer secondary one side ground, a resistive load one side ground, a fast switch between the other end of both.In the attached traces yellow is the transformer side of the switch, pink the load side, blue an irrelevant control signal.The switch turns off at zero current and optionally on again shortly afterwards.Why does the transformer secondary voltage jump when a load carrying no current is disconnected and jump back when reconnected (with very little drive voltage available)?

author: IanB
author_rank: Super Contributor
timestamp: July 30, 2013, 07:58:37 pm
content: I can think of two possible candidates for a cause, but I don't know the answer.One possibility is that connecting the load changes the inductance of the coil by partially shorting it out. Since at the instant the inductance changes the stored magnetic energy in the core is the same, the voltage across the coil will change (much like a spinning ice skater speeding up when folding her arms).A second possibility is that even though the current is zero when the switch is operated, the system is not at steady state. There are non-zero dynamics present at that instant, and those dynamics react against the change in circuit topology to produce the observed effect.
Transformer unused taps, what to do? - Page 1
Forum section: electronics / projects

author: mrflibble
author_rank: Super Contributor
timestamp: March 02, 2015, 02:04:10 am
content: I've got a transformer with several taps on the primary side that will be unused. What's the best practice to do with the unused ones? I'm guessing just leaving them unconnected and cover with heat shrink, but best to ask first.In case the "primary side + multiple taps" creates confusion ... what would the answer be if the secondary side had multiple taps, with some unused?The primary windings in question are: two sets of 0 - 110 - 120 Volt windings. Only the 0 - 110 Volt tap of each will be used, and put in series for 220 Volt total on primary side. And as you may have guessed, the secondary is 220 Volt as well. To be used as an isolation transformer.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 02, 2015, 02:30:07 am
content: Yes, taped/shrinked off is fine. Or leave them on terminal blocks, in case someone ever wants to wire it for something else. (Unlikely I'm sure?)Tim

author: mrflibble
author_rank: Super Contributor
timestamp: March 02, 2015, 03:01:31 am
content: Thanks! Yeah, it's unlikely someone (that would be me) will want to use it for something else so no need for terminal blocks. The sole reason I bought this one is to use it as an isolation transformer.Unconnected + heat shrink it is.

author: Zero999
author_rank: Super Contributor
timestamp: March 02, 2015, 11:13:22 am
content: You could try using the secondary as the primary. Then you have a choice of different voltages.The only thing is the secondary normally has more volts/turn (to compensate for the losses) which means the output voltage will be slightly lower than expected but you've got two 0 to 120V windings which should compensate for this when connected in series.

author: mrflibble
author_rank: Super Contributor
timestamp: March 02, 2015, 12:52:53 pm
content: For a moment I did consider something like it. But that would mean adding a selection switch etc. Another option would be to use the leftover windings for 2x a lower auxiliary voltage. But best to restrain myself and keep it simple. Voltage in, same voltage out.Now if only I could find that double pole switch with indicator light that I'm sure I have ... somewhere.
Transformer utilisation with *BIG* choke input filter - Page 1
Forum section: electronics / projects

author: Circlotron
author_rank: Super Contributor
timestamp: August 03, 2020, 09:41:56 pm
content: Say we have a 100VA transformer feeding a bridge rectifier and then straight into a large filter capacitor. The power factor presented to our transformer will be about 0.6 and so we would be able to pull 60 watts DC from our 100VA transformer for it to be fully loaded.Then we put a big iron cored choke between the bridge rectifier and filter capacitor. And not just any old choke, but an ultra-choke (the dual of an ultracapacitor) Because of its huge inductance the current through the choke is essentially constant and so the current in the transformer secondary is a square wave.Seeing the transformer instantaneous current is now constant and not having gaps that need to be filled by current peaks with their consequent I2R losses, could we assume that the transformer losses are even lower than what they would be if the transformer was supplying a purely resistive load? Just how hard could we push the transformer if we used a ridiculous size inductor? What might be the maximum utilisation factor? This is obviously not a practical approach, just a thought experiment.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 04, 2020, 05:11:49 am
content: Hi,If the inductor is infinitely large so the current is a square wave and the diodes are ideal, no voltage drop.using the concept that PF = VA/WApparent Power/Real PowerThe Power Factor is 2 x SQRT(2) / Pi = 0.9This the ratio between the Average of a sine wave and the RMS of a sinewave.So you can get 90W from a 100VA transformer.You get a 100W if you use a PFC that is 100% efficient.Regards,Jay_Diddy_B

author: trobbins
author_rank: Frequent Contributor
timestamp: August 04, 2020, 05:40:35 am
content: Circlotron, it is also worth noting the additional transient stress this applies to secondary winding waveforms and diodes. The secondary winding current has to essentially flip in direction. The diode currents have to effectively start/stop instantaneously. Nothing happens instantaneously, and so you get dragged in to the underworld of stray/leakage/parasitic components that can't or shouldn't always be simply ignored.So the thought experiment should really start to look at secondary leakage inductance and how large that is, as it effectively lowers the utilisation time by introducing a transitional glitch twice each mains period. There are other secondary losses introduced also, like the cyclical charging/discharging of stray capacitances to the rectifier/choke node.
Transformer Varnish? - Page 1
Forum section: electronics / projects

author: AcHmed99
author_rank: Contributor
timestamp: January 21, 2015, 12:37:16 pm
content: I'm looking for an off the shelf, from a hardware store that can be used to coat windings on transformers and inductors. Something that will lock the windings in place and provide extra protection from moisture. I can get Super Corona Dope 4226 and other MG type coatings mail order but would prefer something suitable that I could just pick up at Lowes or home depot if possibble.Would an off the shelf polyurethane coating be suitable for example?

author: calexanian
author_rank: Super Contributor
timestamp: January 21, 2015, 04:51:10 pm
content: Depends on the insulation being used and the breakdown voltages you will require. You can just use a thinned down nitrocellulose dip. Clear nail polish works well. Thin it down a bit to penetrate. It is flammable so be careful. Q dope is a ploy styrene base product. Basically it's polystyrene dissolved in a solvent. Super flammable. You can use polyurethane, but it's not that good. I use a product from a company called Dolphs. It's a pretty standard transformer varnish. If you are only doing one however I would just go the brush on nail polish route. I would dilute perhaps an additional 30% or so to get it to penetrate.

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 21, 2015, 07:33:34 pm
content: I am using slow curing epoxy for small transformers (UHU Plus), but that is rather definitive! When you heat up the transformer thoroughly to 60 deg C (140 deg F) the epoxy becomes water thin and highly capillary. It creeps deeply into the windings. But the curing is also a lot faster than at room temperature, so you have to work fast!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 21, 2015, 08:33:29 pm
content: I've heard of plain old polyurethane being used... somehow I doubt that's going to be entirely an optimal coating though. I would at least suggest untinted gloss.For small things, I've been known to just tack them with superglue, or wrap with tape.Tim
Transformer's project?? - Page 1
Forum section: electronics / projects

author: paintball20205
author_rank: Newbie
timestamp: December 01, 2017, 12:10:28 am
content: I have two beautiful transformers!One from a microwave and the other one from an audio receiver. Any cool projects or ideas you guys could suggest to me? It's almost tempting to build an emp/ or a rail gun using the transformers with recycled laptop batteries and a bunch of high voltage capacitors. Im all ears!!!

author: jackbob
author_rank: Regular Contributor
timestamp: December 02, 2017, 06:58:06 am
content: Congrats! Those are what I started out with as a beginner. I will say they are extremely extremely dangerous and unforgiving if you make a mistake. I made lots of fun projects with them and I am still alive today because I recognized their danger and had enough basic electrical knowledge at the time to realize these transformers could toast me. I would not recommend even thinking about powering these transformers unless you recognize their danger and know a reasonable amount of electrical basics. They generally output somewhere between 1kV and 3kV and they are good for high voltage experiments such as Jacob's ladders and tesla coils. These would not be the transformers you would use with batteries or DC capacitors as you implied. This would not be the ideal transformer for a rail gun unless you tend to have a capacitor bank at thousands of volts which would be a very serious project more powerful than a high powered rifle. These transformers do not self-ballast meaning they will not regulate how much current they will draw (at least not within a reasonable amount) this makes them tricky to implement for any project including high voltage projects like Jacob's ladders as you need to ballast them with more inductance or some resistance or they will blow a 15/20 amp circuit breaker in a couple seconds and overheat within a minute or two of unballasted operation. More important than anything though, don't be overconfident. High voltage is very tricky and weird things start to happen when electricity no longer needs wires for current to flow
[SOLVED] Transformerless power supply - Page 1
Forum section: electronics / projects

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 15, 2017, 04:22:49 pm
content: hi All,Is a transformerless power supply a good idea for microcontrollers like in the circuit attached ? i was thinking of replacing the transformer to cut down cost with a schematic like thishttp://www.electroschematics.com/5678/capacitor-power-supply/Thanks in advance.

author: ataradov
author_rank: Super Contributor
timestamp: August 15, 2017, 04:35:15 pm
content: If you actually plan to use that FTDI while device is plugged into mains, then it is a horrible idea. You will end up killing USB ports, or yourself in the worst case.

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 15, 2017, 04:37:03 pm
content: Thanks alex.The reason would be because the power supply is grounded and......what else

author: ataradov
author_rank: Super Contributor
timestamp: August 15, 2017, 04:41:50 pm
content: You will have potentially live voltage with minimal to no isolation exposed on the USB connector. It is just a bad idea all around.You can use switching power supply, and small transformers are pretty cheap. You can probably even find complete sub-assembly at a decent price.Your other option would be to power all low-voltage part from USB +5V, if device is constantly plugged in.Or power FTDI from USB and use optocouplers to decouple it from the high-voltage part. Although this one also depends on what else on that board is accessible by the user. You don't want to have mains on encoder knobs either.

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 15, 2017, 04:56:47 pm
content: Quoteyea, i will just stick to the existing.

author: M4trix
author_rank: Frequent Contributor
timestamp: August 15, 2017, 05:34:14 pm
content: @anishkgt,regarding the TRIAC driving. From where you got that schematic ? What was the main purpose or what was the main load ?

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 15, 2017, 07:10:38 pm
content: The load is an MOT. The TRIAC driver schematic is in the data sheet of the driver itself. It's a dual SCR back to back.Sent from my iPhone using Tapatalk
Transformers and rectifiers.  - Page 1
Forum section: electronics / projects

author: afourtrackmind
author_rank: Contributor
timestamp: September 17, 2015, 09:41:51 pm
content: Hello EEVblog members!I'm about to try something without knowing what the result will be. Maybe I can call on your experience to predict what is going to happen and perhaps avoid releasing magic blue smoke.I have an amplifier with a very nice torrid transformer. I'd like to integrate a preamp inside that housing. My preamp PCB requires AC for a split supply that has the rest of the rectification and filtering on it's own, preamplifier PCB. My amplifier has another rectifier for itself. I want to know, can I connect the AC winnings of the secondary to both of those PSU/rectifiers?My mind sees it like this; Either one will only draw only what it needs so i think this should work, no problem. All of the my devices and caps have been upgraded to handle the voltage from the secondary. Am I making a mistake? Can anyone forsee any issues I'm going to create?Thanks for taking the time to read this, I hope you have an opinion and possibly some facts you can throw at me.Cheers,Aftm

author: Fank1
author_rank: Regular Contributor
timestamp: September 17, 2015, 10:06:13 pm
content: If the voltage on the transformer is correct and you don't over load it you will be fine.

author: afourtrackmind
author_rank: Contributor
timestamp: September 17, 2015, 10:21:32 pm
content: Thanks mate, going to start termination in the next hour or so.

author: singapol
author_rank: Frequent Contributor
timestamp: September 18, 2015, 03:09:21 am
content: I think it would be better if you add a small transformer to feed your preamp. This being audio you do not want extra noise from a big transformer and the higher voltage drop will strain the regulators in the preamp by dissipating excess voltage in the form of heat. There is the surge voltage and current that your preamp power supply will have to deal with everytime you turn on and off the main power supply although you have upspec the caps voltage ratings. It would be advisable to use surge protection devices like TVS diode, MOVs or NTC resistors if you want to tap from main transformer but take into account the pros and cons of using such surge devices. As they say garbage in, garbage out.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 18, 2015, 11:58:42 am
content: The voltage needs to match, at east resonably. Power audio amplifiers tened to have a rather high voltage.The voltage from an extra rectiifer will also have a connection to the supply of the amplifier - so you may get troube if you connect the preamp with the amplifier, as there is a gonnection through the supply. At best you have to take care of possible ground loops an hum from this.So a separate transformer is likely the easier way.
Transforming/translating circuit of some switching bipolar transistors to MOSFET - Page 1
Forum section: electronics / projects

author: abdulbadii
author_rank: Frequent Contributor
timestamp: April 04, 2023, 11:16:47 pm
content: How do we transform/translate circuit in which configuration of the bipolar transistors as switching used, to MOSFET ones?Such 12-24 DCV max 4 A load/motor in either of the BJT type H bridge circuit:sincere help is invaluable, thanks before

author: Whales
author_rank: Super Contributor
timestamp: April 04, 2023, 11:36:03 pm
content: Why do you want to change from BJT to FETs?For only 4 amps: an off-the-shelf "H-bridge" or "motor driver" might suit. Get one with simple "direction" and "enable" inputs and wire your switch to those.If you switch the BJTs with FETs directly then this circuit might work but will not run as well. On your second version (NPNs) the top two NPNs are being used in a common-collector configuration, so they will drop probably 2V or so. Most mosfets will probably drop more. These two top transistors will also get much hotter than the bottom two.Given that you are using a switch to operate the input: you can probably avoid this problem by using N-channel mosfets on the bottom and P-channel mosfets on the top. That way all transistors can run in a common-source (common-emitter) configuration, ie very small voltage drop and wasting very little power. This is usually not done because P mosfets cost more for the sample performance and driving the P mofset gates on top can be fiddly, but if you are using a simple switch and only controlling 4A@24V then it's easier.You will want to be wary of the maximum Vgs of mosfets (many are 15-20V). Some zeners and resistors on the gates may be necessary to avoid blowing them.N.B. it looks like your circuity has no "off" position. It's either running the motor forwards or backwards at all times.EDIT: Hmm, only one resistor? Surely this circuit won't work? I would have thought you need a separate resistor on each transistor base, as the top & bottom transistor base voltages will be very different.

author: Whales
author_rank: Super Contributor
timestamp: April 05, 2023, 10:17:54 am
content: Correcting what? I don't understand why you made those changes to the circuit. You have made it much more complicated, I can't work out what it does any more.Does this circuit already work? If not then I recommend trying it in real life on a breadboard (but at a lower voltage with a smaller motor).

author: Someone
author_rank: Super Contributor
timestamp: April 05, 2023, 10:20:51 am
content: Quote from: abdulbadii on April 05, 2023, 08:08:18 amNo

author: Someone
author_rank: Super Contributor
timestamp: April 05, 2023, 09:52:46 pm
content: Quote from: abdulbadii on April 05, 2023, 03:15:50 pmNope, you're still showing us short circuit conflating combustion apparatuses.How do you come up with these circuits?

author: Benta
author_rank: Super Contributor
timestamp: April 05, 2023, 10:07:22 pm
content: School homework.

author: Terry Bites
author_rank: Super Contributor
timestamp: April 05, 2023, 11:38:16 pm
content: Oh. I always thought you were older!You'll go far.
Transient generator for ISO 7367 and ISO 16750 - Page 1
Forum section: electronics / projects

author: rvalente
author_rank: Frequent Contributor
timestamp: September 15, 2020, 12:56:54 pm
content: Hello mates,did anyone ever made a transient generator for testing devices under ISO 7637 and 16750? (May be one for each pulse or standard)?I just want to have bench tests before bring the device to a certified lab, which is rather expensive.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 15, 2020, 01:06:46 pm
content: Quote from: rvalente on September 15, 2020, 12:56:54 pmHi rvalente,I have made transient generators ISO 7637 Pulse 2a (Load Dump), but this was only suitable for testing series regulator type devices, not transorb based shunt clamping circuits.The best approach is probably in simulation. Here is a link to an excellent article that includes the LTspice models:https://www.analog.com/en/technical-articles/ltspice-models-of-iso-7637-2-iso-16750-2-transients.htmlSome of the tests are easy to pass because the transients are high impedance.Regards,Jay_Diddy_B

author: rvalente
author_rank: Frequent Contributor
timestamp: September 15, 2020, 01:13:58 pm
content: Tks by your reply.I've seen this ltspice models, very very useful, but I'm not (yet, hopefully) a spice expert...This devices you've build, could you share a little more?Was your device made to test automotive equipment?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 15, 2020, 02:09:38 pm
content: Hi,I can share alittlemore.Block DiagramA 12V or 24V power supply is diode ORed with the transient generator.The amplifier is essentially the positive side of a high power 'Disco' amplifier using 6 large MOSFETs.An opamp circuit shapes the transient pulse.AssemblyThe transient generator was built on PCB about 5 x 8 inches.WaveformThe pink trace is the output from the transient generator. It is the ISO7637 type 2A pulse for a 24V vehicle 175V in amplitude 300ms duration, exponential decay.The green trace is the input from the pulse generator.The blue trace is the output from the LT4363 surge stopper (hard to see).As you can see, it is not trivial to make this pulse.Regards,Jay_Diddy_B

author: rvalente
author_rank: Frequent Contributor
timestamp: September 15, 2020, 07:51:21 pm
content: Great build! You made more and more curios to make my own, I've PM you.By the way, were you involved in this paper?https://www.analog.com/media/en/technical-documentation/tech-articles/lt-journal-article/LTJournal-V26N4-02-df-LTC4380-DanEddleman.pdf
Transient protecting a coax run - are gas gaps still 'the good stuff'? - Page 1
Forum section: electronics / projects

author: cvanc
author_rank: Frequent Contributor
timestamp: May 03, 2025, 12:09:12 pm
content: After a recent electrical storm I'm adding protection to the coax input of my cable modem. Gas gaps used to be considered state of the art, is that still the case?Feel free to pass along a specific make & model... TIA.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 03, 2025, 02:30:27 pm
content: The cable company added a box with the GDT along with a ground rod when they did the install. It did not save the modem which also had an internal GDT when we had an actual lightning strike.

author: Terry Bites
author_rank: Super Contributor
timestamp: May 03, 2025, 07:09:28 pm
content: Nothing protects from a lightning strike!GDTs wont strike below 50V other "gaps" are probably worse so you can kiss your LV circuits goodbye.You need to clamp the overvoltage and limit the clamp current or watch the clamp go up in smoke.Cable TV sometimes caries DC on top of the signal. That could be in the 30-100V range. Some investigation is needed.