hybridfree/eevblog-posts huggingface dataset:
transformer high voltage spike - Page 1
Forum section: electronics / beginners

author: Boschi
author_rank: Regular Contributor
timestamp: July 26, 2016, 09:33:16 pm
content: hi, it's mi first post here in the EEVBlog forumi bought my first scope ever just a week ago, and since then i have worked on a tracking pre-regulator PSU.i found this circuit:https://www.eevblog.com/forum/projects/very-low-noise-preregulator-for-benchtop-power-supply/after changing a bit the feedback using a optocupler,remove Q4 and change D3 to 5 volt i got a fully working tracking pre-regulator, but i also get some voltage spikes out of the transformer.now im using a 60VA 12Vac transformer, but i want to upgrade the transformer to 24Vac, so the spike will become dangerous to the MOSFET.is there something that i could do to minimize the spikes? Thanks!in the attached photos the blue wave is the scr gate control, the purple wave is the scr trigger and the light blue one is the rectified output of transformer
Transformer ID  - Page 1
Forum section: electronics / beginners

author: xenoxaos
author_rank: Contributor
timestamp: August 29, 2023, 01:59:43 am
content: If given an unknown transformer (or many), how does one determine the turns ratio, BSat, ideal frequency, voltamps, etc. And no, I'm not just gonna shove wires into the wall. Laminated steel is probably low freq, random ferrite/iron powder a bit higher.For worst case, you can always check the wire size, then grab the inductance on both sides. Open and at dead short. Chuck it in to find the reactance at 50/60hz. But that really only tells you if it's gonna blow when you plug it in. Then there's open circuit voltage and then voltage under load. There'shttps://www.midwestcurrent.com/how-do-i-calculate-my-va-ratingBut asking a transformer to be like "hey...yeah....i'm going to need you to come in and work saturday" Somewhere in my mess I have a 10v transformer and a 12v transformer. The open circuit voltage on those are gonna be pretty close. Once I uncover my good LCR meter, I'll make some drawings.

author: MathWizard
author_rank: Super Contributor
timestamp: August 30, 2023, 10:47:44 am
content: You could use your little transformer, and feed that 10-12V into the unknown one, and measure the "open circuit" voltage with an oscilloscope, or use some fairly big resistor and measure the rms voltage with a DMM. The voltage ratio Vin/Vout will pretty much match the turns ratios Nin/Nout, and the sqrt(Lin/Lout). For some transformers from certain things, you can guess from the DC resistance, what winding's would be what.Lately I used a signal generator to measure the mutual inductance of some AM radio coils I have, and the ferrite ones measured about k=1, so like perfect coupling.I've load tested some of my power transformers, just with different sized resistors. Most were under 10W resistors, but I have 200W variable 10 Ohm resistor, that's good enough for a quick measurement. I keep track of currents and voltages, with different loads, and can work out the load line.I'm just getting deeper into all this stuff, I never tried measuring when some transformer saturates.
Transformer identification.. - Page 1
Forum section: electronics / beginners

author: KBJ62
author_rank: Newbie
timestamp: March 20, 2021, 06:11:07 am
content: Hey,Trying to figure out what sort of transformer this is..

author: drvtech
author_rank: Regular Contributor
timestamp: March 20, 2021, 10:21:46 am
content: It's a Coilcraft part. Looks like one of their coupled inductors/transformers but I can't see one on their website with that number on it. Have a trawl at coilcraft.com

author: Jwillis
author_rank: Super Contributor
timestamp: March 20, 2021, 09:45:10 pm
content: Coupled Inductorhttps://www.coilcraft.com/en-us/edu/series/a-guide-to-coupled-inductors/https://www.coilcraft.com/getmedia/c6cab3a9-7293-495e-8614-c9a8ce247721/LPD8035V.pdf

author: drvtech
author_rank: Regular Contributor
timestamp: March 21, 2021, 09:54:05 am
content: Can't be that one - it only has two windings. The one in the pic has six pads so must have three windings.

author: drussell
author_rank: Super Contributor
timestamp: March 21, 2021, 11:17:46 am
content: Quote from: drvtech on March 21, 2021, 09:54:05 amWhy not? Things like the LPH8045 series are 1:1:1...You can use them as three separate windings or wire them up to make them into 2:1 or whatever, depending on what you're trying to accomplish.

author: Zero999
author_rank: Super Contributor
timestamp: March 21, 2021, 01:19:20 pm
content: Quote from: drvtech on March 21, 2021, 09:54:05 amHave you checked that all six pads are connected to the windings? Quite often not all of the pins are connected and are just for mechanical support.

author: KBJ62
author_rank: Newbie
timestamp: March 22, 2021, 05:22:50 am
content: Wow thanks for the help. The device is used in LVDC generation ( 100V - 400V). It is used for voltage setup but I had a problem identifying this exact part. It could be their LPR series (low profile 1:N trnsformer).

author: drussell
author_rank: Super Contributor
timestamp: March 22, 2021, 08:05:33 am
content: Quote from: KBJ62 on March 22, 2021, 05:22:50 amYeah, I figured that is what they were used for but I couldn't find an actual datasheet for that HV53001 driver "with boost" or the HV53011 there to try to guess the circuit values or see if there was a recommended inductor formula or suggested part in an example or something.I didn't see one that matched in my quick look through a couple different series, and various searches for anything likely with a -352 suffix only yielded a regular ferrite rod through-hole inductor, so you'll have to do a bit more digging.Remember, it is also possible it is some sort of custom part, it may not be in a standard series datasheet.

author: crossroad
author_rank: Contributor
timestamp: March 22, 2021, 08:19:22 am
content: Quote from: Zero999 on March 21, 2021, 01:19:20 pmMy 2 cents from brief observation: looks like there's tracks going to three pads, one pad is to a power pour, and one is to ground, with one more to some sort of via stitching. I'd imagine that they're for more than just mechanical support in this instance
Transformer Identification - Page 1
Forum section: electronics / beginners

author: froswrangler
author_rank: Newbie
timestamp: December 29, 2022, 03:16:48 pm
content: I am trying to find a replacement for this transformer, can anyone point me in the right direction? I can not locate anything using what is written on it. [ Specified attachment is not available ]

author: wasedadoc
author_rank: Super Contributor
timestamp: December 29, 2022, 03:31:37 pm
content: That IC202 beside the transformer is an optocoupler which means it is almost certain the transformer is part of a switch mode power supply. Transformers for those are usually custom made for the specific equipment design. You will not find a replacement or details in a catalogue.Transformers are perhaps the most reliable element of a SMPS. Unless you already have good reason to suspect it I would look elsewhere for whatever trouble there is.
Transformer Identification - Page 1
Forum section: electronics / beginners

author: wn1fju
author_rank: Frequent Contributor
timestamp: November 28, 2023, 03:15:44 pm
content: Photo shows schematic of an amplifier which is supposed to provide a 1 MHz signal to the output jack on the rear panel of an old French Adret signal generator. The transformer, T1, gives me open readings on both primary and secondary coils. Probably someone in the past applied some excessive voltage to the output jack and fried the transformer.On the schematic, T1 is marked "38/6" and "38 uH." I'm guessing the 38 and 6 are the primary and secondary turns? Is the 38 uH the impedance of the primary?

author: CaptDon
author_rank: Super Contributor
timestamp: November 28, 2023, 03:27:16 pm
content: Why is it marked F2 38/6 ?

author: wn1fju
author_rank: Frequent Contributor
timestamp: November 28, 2023, 04:38:55 pm
content: Why is it marked F2 38/6 ?I'm pretty sure the 38/6 refers to the turns. The "F2" is a mystery. Several of the other transformers on the schematics also have markings like F2, F40, F10B, etc., independent of the numbers and uH values shown. Perhaps the F-designations have something to do with the form factor.
Transistor Identification Help - Page 1
Forum section: electronics / beginners

author: Robbie010
author_rank: Contributor
timestamp: February 02, 2019, 11:33:15 pm
content: Hi all,I'm currently trying to identify the components on an old amplifier circuit so that I can try and draw up a schematic, but I'm struggling to indentify some transistors.The markings on them read as follows:MHPS L01MHPS L51BF2 45A M131F420 PH5NThey all look pretty much the same as per the attached picture but can anyone tell me the correct values for these transistors??Thanks in advance.

author: helius
author_rank: Super Contributor
timestamp: February 02, 2019, 11:40:48 pm
content: MPSL01MPSL51BF245ABF420

author: Mortymore
author_rank: Frequent Contributor
timestamp: February 02, 2019, 11:41:33 pm
content: See if this make sense on your circuit:MPSL01NPNMPSL51PNPBF245AJFET-NBF420NPN high-voltage

author: Robbie010
author_rank: Contributor
timestamp: February 03, 2019, 12:02:15 am
content: Thats excellent, thank you very much!!I am yet to fully test the components but, assuming the transistors are all functioning properly would there be any benefit to swap these out for a modern replacement whilst I've got the amp stripped down?I note that some of the transistors are now obsolete so would there be a benefit to swapping the out for modern replacements?Thanks again.

author: Mortymore
author_rank: Frequent Contributor
timestamp: February 03, 2019, 01:13:04 pm
content: You actually may be forced to move to compatible replacements if you can't find the original references.My advise is, since it's an audio amplifier, the transistor replaced in the right/left channel should be replaced on the other channel also. It would be even better, even if it's just one transistor needed to be replaced, that you buy not only one for each channel, but a few more and try to match a pair of them with the same gain (hfe), so you wont end up with unbalanced right/left channels.Try to put the amplifier working, first of all. Next you can play (an educated play) with different components to achieve better results.Good luck.

author: Robbie010
author_rank: Contributor
timestamp: February 05, 2019, 06:30:44 pm
content: Thanks everyone, those detais were very useful!I am still struggling with this component, I am going to pull it tomorrow and test it but I had a poke around with a multifunction tester today (in-circuit) and got a better look at the markings.It has a feignt red band at one end (like a diode) and is marked HSG 39F.When testing it as a zener diode it came back with a Zener voltage of between 16 - 21v, however, when testing it as a normal diode its forward voltage was 3.9v with a capacitance of and 68pFAny thoughts?

author: Benta
author_rank: Super Contributor
timestamp: February 05, 2019, 06:43:40 pm
content: Quote from: Robbie010 on February 05, 2019, 06:30:44 pmThis has already been answered in a different thread. 39 pF polystyrene.
Transformer Impedance Matching - effect of absolute number of turns vs ratio - Page 1
Forum section: electronics / beginners

author: cadr
author_rank: Contributor
timestamp: April 02, 2021, 05:06:18 pm
content: I am playing with an RF amplifier design, and I need to transform my 50 ohm load to something higher to make the transistors not need to work so hard. I was going to make a transformer with a bifilar wired toroid. I can set the turn ratio to do what I need, but I am confused on how the absolute number of turns matter. As long as I have the desired ratio of turns, how does the primary having 10 turns vs 20 turns affect things?Thanks!

author: TimFox
author_rank: Super Contributor
timestamp: April 02, 2021, 05:46:14 pm
content: In general with transformers, the absolute number of turns affects the magnetizing inductance, one of the two important parasitic inductances in the model. At low frequencies, the magnetizing inductance shunts the ideal transformer inside the model, and steals AC current from the load. Of course, it also affects the leakage inductance, the other important parasitic inductance, which is important at high frequencies. The ideal transformer, governed only by the turns ratio, is inside the parasitic components.

author: cadr
author_rank: Contributor
timestamp: April 02, 2021, 05:57:33 pm
content: Thanks!Any suggestion about how I determine what impedance/# of primary turns I should aim for if I am using this at 7MHz?

author: TimFox
author_rank: Super Contributor
timestamp: April 02, 2021, 06:04:37 pm
content: You want the magnetizing inductance's reactance (essentially the inductance of the primary winding) to be much higher than the load impedance that the primary winding presents to the active devices at 7 MHz. However, the leakage inductance's absolute value will also increase with more turns, but the high coupling of the bifilar winding is good for low leakage. This is why such transformers have a relatively high bandwidth. For a simple 1:1 ratio model, the low-frequency cutoff (at -3 dB) is where the magnetizing inductance reactance equals the load impedance, and the high-frequency cutoff is where the leakage inductance reactance equals the load impedance (ignoring parasitic capacitance).One of many articles in the literature:http://mwl.diet.uniroma1.it/people/pisa/SISTEMI_RF/MATERIALE%20INTEGRATIVO/Kikkert_RF_Electronics_Course/05-RF_Electronics_Kikkert_Ch3_RFTransformers.pdf
Transformer induced voltage - Page 1
Forum section: electronics / beginners

author: zzlong94
author_rank: Contributor
timestamp: June 30, 2018, 05:11:26 am
content: Hi guys! I using oscilloscope to probe the induced voltage in the transformer.why the induced voltage is not in sine wave? is there any theory behind?Thanks!

author: zzlong94
author_rank: Contributor
timestamp: June 30, 2018, 06:17:46 am
content: Thanks for ur useful info! Appreciate it!
Transformer Nomenclature - Page 1
Forum section: electronics / beginners

author: Ron Reeland
author_rank: Newbie
timestamp: May 29, 2017, 10:16:01 pm
content: Hi:I picked up a relatively high voltage transformer at a Hamfest recently. It is a sealed unit, gray painted steel housing, leading me to think it is military spec.There are some abbreviations shown on the transformer schematic that are not clear to me. Please see the attachment of the schematic.What does "PWV" designate?Normally, I would guess "peak working voltage", but that does not make sense to me at this time, especially when you look at the primary where the higher "PWV" of 535 does not seem to relate to the maximum 125 RMS input voltage.But the secondaries have "PWV's" lower than the RMS values. Apparently, the transformer was meant to be used in full-wave, center-tapped rectifying circuits as DC currents are given for each secondary.Any insight would be appreciated.Thanks,Ron Reeland

author: tautech
author_rank: Super Contributor
timestamp: May 29, 2017, 10:31:28 pm
content: I'm gunna stick my neck out and say it's related to insulation tests.BTW there's applications where windings might be subjected to elevated voltages and as each one is initially not referenced to circuit ground, it's a manufacturers spec to indicate the maximums that apply.

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: May 30, 2017, 04:33:13 am
content: Had a quick google and there are a few results with different PWV "values" - might just be a part number?eghttp://bibbteck.com/chicago-standard-transformer-corp-pwv-715-power-transformer

author: Shock
author_rank: Super Contributor
timestamp: May 30, 2017, 09:02:01 am
content: This?Quotehttp://www.miinet.com/Portals/0/DataSheets/Power_Transducer_Users_Guide_Moore_Industries.pdfQuotehttp://www.miinet.com/Portals/0/DataSheets/PVT_PWT_PWV_Datasheet_Moore_Industries.pdf

author: TimFox
author_rank: Super Contributor
timestamp: May 30, 2017, 01:40:36 pm
content: PWV usually indicates the maximum voltage between conductors and each other and to the case. In rectifier usage, there may be a large DC voltage as well as the winding's AC voltage on a given wire.
Transformer Options for 60kHz signal - Page 1
Forum section: electronics / beginners

author: iwcraig
author_rank: Newbie
timestamp: June 16, 2020, 03:29:13 am
content: Hello! I’m a composer who has taken to tinkering with old audio equipment like reel to reels and cassette machines to try and coax new and interesting sounds from them. I’ve recently become enamoured with trying to tamper with the bias oscillator to introduce distortion during the recording process as an experiment. The oscillators are all very sensitive to any alterations however, so I was toying with the idea of replacing the oscillator altogether with something of my own design over which I’d have a greater degree of control. The challenge is how to provide the heads with a proper signal.Usually bias signals are a high frequency sine (~60kHz) anywhere between 60Vpp and 300Vpp. Decks usually don’t run hotter than +/-15V max, so the way the deck generates such a large voltage without a massive power supply is including a transformer within the oscillator. It doesn’t need to pass much current at all, so this works out just fine to boost it up. This is my understanding anyways! I have breadboarded an oscillator that puts out the appropriate waveform, but since it’s running on +/-15V, it can’t get up to the voltage necessary to erase and record.I had the idea I could use a transformer as well, but one whose sole purpose was to step things up instead of helping to form the oscillation directly. So my question is whether or not a standalone transformer exists that I could pass this smaller 10Vpp 60 kHz signal through to boost it up to what the tape needs (which is about 60Vpp for a smaller deck and 300Vpp for the bigger ones). I can’t measure the impedance of the heads since I don’t have the proper equipment, so I don’t know exactly, but I know from my other experiments that I need to get the resistance of any signal to the eraser head down to about 25 ohms or it won’t go through.Any help would be greatly appreciated! Thanks for taking the time, hope you’re all taking care out there.
transformer or switchmode PS for linear regulator? - Page 1
Forum section: electronics / beginners

author: jeroen79
author_rank: Frequent Contributor
timestamp: December 03, 2016, 12:15:55 am
content: So I am thinking of making a low voltage powersupply with a linear regulator for the output.What would be the best way to bring the mains voltage down to a low voltage?Traditionally you'd get a transformer, rectifier and capacitor but these get heavier and bulkier as the output current or voltage increases.Would an off the shelf switchmode powermodule be a good alternative?It would certainly be lighter and more compact but would it have any drawbacks?They may have more high frequency noise on the output (instead of 50Hz ripple) but the linear regulator would reduce that.It may also radiate HF interference but with a shielded version that would also be reduced.Am I right?

author: Simon
author_rank: Unknown
timestamp: December 03, 2016, 06:19:09 am
content: This commonly done, I have a £1000 power supply at work that has a linear output with a switchmode pre-regulator. The advantage is that there is minimal power woss because you can get the SMPS to track the output voltage so that it is just a few volts higher all of the time so that you don't get large voltages that need droppig across the linear reg causing much heating and power loss.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 03, 2016, 08:28:00 am
content: There still is some disadvantage in having more RF noise. The tricky part is so called common mode voltage due to capacitive coupling in the transformer of a switched mode supply. So unless you have the output grounded this is very difficult to filter. With a SMPS you will essentially always see some RF ripple if you measure the voltage to ground - e.g. scope probe to the supply, ground not connected (so PE via scope).So for lowest noise the classical transformer still has advantages. For higher power a SMPS has advantages, like possible power factor correction, preregulation and thus less heat and cheaper filter caps.
Transformer output impedance - Page 1
Forum section: electronics / beginners

author: fonograph
author_rank: Frequent Contributor
timestamp: August 26, 2018, 06:22:58 pm
content: Does 2:1 step up transformer double or quadruple the impedance? I am not sure but I think I read in book that it quadruples for every doubling of voltage,but when I think about it some time later,it seems wrong becose if we send same amount of power through double voltage,we only need to halve the current so just doubling the output impedance should be enough to avoid breaking the law of conservation of energy.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: August 26, 2018, 06:55:18 pm
content: Keep Ohms law in mind:sqrt(P/R)=Iandsqrt(P*R)=Uresistance/impedance and power are in exponential relationso a turn ratio of 1:2 leads to an impedance ratio of 1:4

author: David Hess
author_rank: Super Contributor
timestamp: August 26, 2018, 06:56:14 pm
content: The impedance is the voltage divided by the current. A 2:1 step up transformer doubles the voltage and halves the current so:2 / 0.5 = 4So the impedance is raised by 4 times.

author: fonograph
author_rank: Frequent Contributor
timestamp: August 26, 2018, 07:00:14 pm
content: Ahhh yesI am embarrassed that I made such basic mistake,now it seems so obvious.
Transformer output - Page 1
Forum section: electronics / beginners

author: Deathwish
author_rank: Unknown
timestamp: August 12, 2015, 11:46:48 am
content: Will a 2x18v output at 18VA give me 1amp output or .5 amp.I am looking at this..https://uk.rs-online.com/web/p/pcb-transformers/2017280/

author: McBryce
author_rank: Super Contributor
timestamp: August 12, 2015, 12:02:19 pm
content: If you look at the print on the actual transformer it gives it away: It's 9VA per secondary winding. So each of the 18V can give you 500mA.McBryce.

author: Deathwish
author_rank: Unknown
timestamp: August 12, 2015, 12:16:35 pm
content: but , and there is always one of those, if I centre tap the two lines is that then 1 amp or .500 , line to line voltage confuses me.

author: McBryce
author_rank: Super Contributor
timestamp: August 12, 2015, 12:20:08 pm
content: If you join the two 0 - 18V secondary windings together you'll have 36V at 500mA. Or if you tap the centre to make a split rail to supply +18V / 0V / -18V, you'll get +18V at 500mA and -18V at 500mA.McBryce.

author: Deathwish
author_rank: Unknown
timestamp: August 12, 2015, 12:36:13 pm
content: Thank you McB that was what I was after. I need to split rail it so i will get 500mA which is enough. Your a star.
Transformer pinout? - Page 1
Forum section: electronics / beginners

author: dog80
author_rank: Regular Contributor
timestamp: September 19, 2013, 02:08:55 pm
content: I have a small board mounted transformer that I desoldered from a PSU. It has a EEL-16-2005 marking and is probably the same as the one in the middle in this picture:http://www.it.com.cn/f/diy/058/25/20050825_csdy_bmeng_10.jpgI want to determine the pinout. I tried to find a datasheet but had no luck.It has three pins on the one side with a single strand of wire each (guess this is the high voltage side) and there are five pins with multi strand wires on the other side.I tried supplying 16 volts AC on the high side but it was drawing too much current.What am I doing wrong?

author: mariush
author_rank: Super Contributor
timestamp: September 19, 2013, 02:59:39 pm
content: Those transformers are designed to run at high frequency (40kHz-100 kHz), they won't run properly at mains frequency (50-100Hz). It's almost useless to you, it's not the same thing as a regular, classic transformer.

author: Skippy
author_rank: Contributor
timestamp: September 19, 2013, 07:24:37 pm
content: Specifically it's aFlyback transformer

author: Phaedrus
author_rank: Frequent Contributor
timestamp: September 19, 2013, 08:39:10 pm
content: The two smaller transformers will be of more use. One of them should be a 1:1 isolation transformer, and another should be suitable for a single transistor forward +5V DC power supply from mains.
Transformer power countrol - Page 1
Forum section: electronics / beginners

author: anishkgt
author_rank: Frequent Contributor
timestamp: March 17, 2017, 02:37:42 pm
content: An arduino can control be used as an Ac light dimmer. Would it be ok to control the power of a microwave oven transformer modified for spot welding.Thank you all.Sent from my iPhone using Tapatalk
Transformer primary pinout - Page 1
Forum section: electronics / beginners

author: AngraMelo
author_rank: Regular Contributor
timestamp: October 15, 2018, 02:41:44 am
content: Hello guys,I cant for the life of me figure out the wirering of the primary side of the main transformer (attached) for when using 110v or 220v. The DPDT switch is making things hard for me. I want to use the transformer for a different project.Could anyone help me out?

author: ArthurDent
author_rank: Super Contributor
timestamp: October 15, 2018, 04:32:09 am
content: The transformer has two primary windings for 120VAC each. If the switch is in the upper position, the two halves of the primary are wired in parallel to run on 120VAC.If the switch is in the lower position, the lower winding has a 100VAC tap so with the switch in the lower position the 120VAC upper winding is in series with the 100VAC tap on the lower winding to allow it to operate on 220VAC.Note that there is a thermal fuse within the transformer so if you use the transformer for another purpose and overload the transformer it will overheat and the thermal fuse will open and the transformer will no longer operate.See the attached modified drawing to trace out the connections which I put in colors to show how it works.

author: AngraMelo
author_rank: Regular Contributor
timestamp: October 15, 2018, 06:58:50 am
content: Thank you so much for this!!!!
Transformer protection - Page 1
Forum section: electronics / beginners

author: sureshot
author_rank: Regular Contributor
timestamp: August 22, 2018, 12:17:06 pm
content: I'm looking at a second hand transformer, specs below. My question is these are listed at automation use, the thermal fuse wires and thermistor wires, would they connect to the powered equipment. In it original use that is ? If repurposed where would the thermistor and thermal fuse wires connect to ? Any help appreciated thanks for reading.Connection detailsBlue - 0v AC PrimaryBrown - 230v AC primaryBlack - ThermistorBlack - ThermistorWhite - Thermal cut offWhite- Thermal cut offOrange - 0v secondary O/PYellow- 27.5v secondary O/PPrimary Input voltage0 - 230 Volts ± 10% 50 Hz

author: 09d08
author_rank: Contributor
timestamp: August 22, 2018, 01:10:32 pm
content: The thermistor would probably be connected to the appliance powered by the transformer for monitoring purposes. As for the thermal fuse I assume that it would be connected in series with the mains connection and the primary so that it can interrupt the flow of current through the transformer when it overheats.

author: sureshot
author_rank: Regular Contributor
timestamp: August 22, 2018, 01:18:50 pm
content: Thank you for the help, i was thinking similar for the thermistor, but wasn't sure on the thermal fuse. Mainly because there normally buried in the windings and the user doesn't usually have control over its connection. Just didn't want to kill the transformer on power up test.

author: 09d08
author_rank: Contributor
timestamp: August 22, 2018, 02:59:28 pm
content: No problem, the thermal fuse being accessible sounded weird to me too but the added option to omit or do something else with is certainly is a good thing.

author: sureshot
author_rank: Regular Contributor
timestamp: August 22, 2018, 06:52:26 pm
content: Hopefully straight forward to power up, thanks again for your help.
transformer question. - Page 1
Forum section: electronics / beginners

author: zerorisers
author_rank: Regular Contributor
timestamp: March 28, 2015, 12:36:56 am
content: For something like a microwave transformer, would It pull to much current a set off the circuit breaker to initially create the magnetic field inside of the iron core? would I have to put a resistor on the primary end? if so how would i judge the size resistor needed?

author: radix
author_rank: Contributor
timestamp: March 28, 2015, 12:56:23 am
content: No, you wouldn't normally need inrush current limiting. After all the transformer in the microwave is switched on by connecting it directly to the mains.

author: zerorisers
author_rank: Regular Contributor
timestamp: March 28, 2015, 12:58:54 am
content: Quote from: radix on March 28, 2015, 12:56:23 amThank you for the input and I will keep this in mind!

author: Zero999
author_rank: Super Contributor
timestamp: March 28, 2015, 02:40:58 pm
content: Obviously be very careful with micro wave oven transformers: not only is the output high voltage but it's also high current and is deadly.
Transformer replacement wiring question - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: April 17, 2022, 11:52:32 am
content: Hello all, I’m installing a new transformer and when looking at the Hammond Data sheet compared to the original schematic how would I cross reference the wiring color from old to new? They show a black dot on the original transformer schematic on the center tap but on he Hammond data sheet the black dots aren’t on the center tap?

author: bob91343
author_rank: Super Contributor
timestamp: April 17, 2022, 04:50:39 pm
content: Just overlay the Hammond unit on the original. The connections are shown in the correct positions.

author: Crambone
author_rank: Frequent Contributor
timestamp: April 17, 2022, 05:25:32 pm
content: Thanks Bob that’s what I assumed as a center tap is a center tap per the drawings.Andrew

author: Ian.M
author_rank: Super Contributor
timestamp: April 17, 2022, 05:57:34 pm
content: I agree with Bob.Quote from: Crambone on April 17, 2022, 05:25:32 pmErr. *NO* its not acentertap on either the original or replacement diagram, because it isn't at the center of the winding with equal turns count either side of it. Its a 'boost' tap that increases the secondary voltage when the switch is in SSB mode by removing a small part of each primary winding from the circuit, increasing the turns ratio.
Transformer replacement wiring question - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: November 16, 2021, 06:38:09 pm
content: Hello, I have a Heathkit SB-220 linear that the transformer went bad in and the replacement has different color wires. I have included a schematic for the SB-220 showing the SB-220 transformer wiring and colors. I have also included a data sheet for the replacement transformer. If someone can cross reference the colors from old to new for me I would greatly appreciate it.Thank you,Andrew

author: SeanB
author_rank: Super Contributor
timestamp: November 16, 2021, 06:50:54 pm
content: Secondary side old red becomes new black. Old red/yellow becomes red.Primary side old black becomes brown. Old blk/yell becomes brown/white. Old yellow becomes white.Other primary old black/green becomes green/white. Old black/red becomes red/white. Old blue becomes green.Simple enough, and should work no problem.

author: Crambone
author_rank: Frequent Contributor
timestamp: November 17, 2021, 02:14:34 am
content: Thanks I had it correct but self doubt made me check.
Transformer replacement  - Page 1
Forum section: electronics / beginners

author: Peter E
author_rank: Newbie
timestamp: September 03, 2019, 08:40:19 pm
content: Hello all,I am repairing a full size Yamaha digital piano with aim to donate it to a day centre.I have some basic experience if fixing electric and electronic equipments. The piano works normally but no sounds comes out! So far with help from a few clever friends, we narrow it down to problem with Transformer. It overheats and been told it needs to be replaced. The problem is that I just find it any supplier in UK or out who supplies such specification.The input is: 220v and outputs: 20VAC x2 & 8VACx2. (Please see the photo)I would be grateful for any advise.Many thanksPeter

author: james_s
author_rank: Super Contributor
timestamp: September 03, 2019, 09:17:11 pm
content: It seems very unlikely that the problem is the transformer, in my entire life I think I have seen one power transformer that failed not due to something on the secondary side shorting out and overloading it to the point that it burned up.What tests have you done to confirm that the transformer is the problem? Does it overheat with the secondary disconnected completely from the load?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 04, 2019, 07:32:18 pm
content: Transformers indeed tend to be pretty reliable (but they can fail).Wen overheating, it's usually beause the circuit behind it is faulty and draws too much current.Does the transformer still get hot if you disconnect the secondary circuit?How much current is drawn from each of the sectundary windings? (is it within spec?)If it really is the transformer that is faulty, you can replace it with a few other transformers.
Transformer saturation tests - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: November 29, 2013, 09:06:00 pm
content: I have a big high voltage single phase mains transformer. Two bobbin type, bobbins in parallel. I want a tad more volts from the secondary. I am running on the 0 and 240V primary taps. Mains here is variable, as I am out in the sticks. I know when it's cold, or dinner time, the mains can drop to 220V. The transformer has -10, 0, 180, 220, and 240 volt taps. If I mess with the taps 10 volts at a time, how can I tell if it's close to saturation? I considered a couple of loose turns of insulated wire around the outside of one of the bobbins, connected to my scope. is this a viable way to see if the waveform is beginning to flat top? It's duty cycle will be low, but it was actually built for CCS, so I feel I have some leeway. Thanks.

author: megajocke
author_rank: Regular Contributor
timestamp: November 29, 2013, 11:41:03 pm
content: Saturation will start to happen just before the zero crossings of the voltage so not much will happen to the tops. I'd suggest looking at the primary current. It tends to increase sharply as saturation is reached.

author: moepower
author_rank: Contributor
timestamp: November 30, 2013, 03:25:42 am
content: Yeah it is not clear exactly what the specifications of that transformer is. However, the previous post is right. Evidence of saturation is when your current waveform, under no-load, exhibits sharp "peaky" type wave-shape. Under no-load, the current should be around 5% of it's rating, which is the magnetizing current. If your current is peaking much above 5% of its rating (e.g., 5% of sqrt(2) * rated current(rms)), then you're getting into saturation.

author: SeanB
author_rank: Super Contributor
timestamp: November 30, 2013, 08:22:48 am
content: Why not just wind a few extra turns on the secondary side using the same size wire as the existing wire? Simple to do and will not result in saturation of the core at all. Most transformers are run pretty close to saturation unless they were designed and built 20 years ago when copper prices were lower so manufacturers would not skimp on copper or iron losses much. If there is not enough room then I would suggest pulling off the secondary covering to get some room.
Transformer secondaries in series backwards - Page 1
Forum section: electronics / beginners

author: soligen
author_rank: Contributor
timestamp: April 06, 2016, 10:03:27 pm
content: What happens if I wire Transformer secondaries in series backwards?What I am trying to do is wire 2 secondaries in series so that their voltages add together, but as both ends on each secondary have the same color wire, I have no way to tell the polarity (Phase?) to get the right 2 secondary wires connected to each other.Does it matter? I assume it does since the transformer data sheets I look at have polarity markings.I figure a 50/50 chance of wiring it right. If I put the secondaries in series properly, the voltage will be the 2 added together, but if I get it wrong, what happens? I am assuming I'll see a lower voltage, but is it safe? Will it damage the transformer?One winding is 16V, the other 3V. 16V is just shy of what I need, so 19 will do, with some extra voltage to spare. I am rectifying this into a DC regulator.Thanks

author: Andy Watson
author_rank: Super Contributor
timestamp: April 06, 2016, 10:08:50 pm
content: Quote from: soligen on April 06, 2016, 10:03:27 pmIt will be ok to connect the windings in series. If you get it wrong you will measure 13V instead of 19V - but no harm done, just reverse one of the windings.

author: AF6LJ
author_rank: Unknown
timestamp: April 06, 2016, 10:09:25 pm
content: you won't hurt anything.You will ether get the expected voltage or much less.

author: soligen
author_rank: Contributor
timestamp: April 06, 2016, 11:03:55 pm
content: Thanks. guessed right on the first try. Now I can do more testing.

author: Kappes Buur
author_rank: Regular Contributor
timestamp: April 07, 2016, 12:18:59 am
content: Hopefully both windings have the same current range.If not, then only supply current at the lower limit.
Transformer secondary switching and EMF - Page 1
Forum section: electronics / beginners

author: e100
author_rank: Frequent Contributor
timestamp: September 28, 2012, 11:16:50 pm
content: When using a typical mains 240 to 12v transformer to power a resistive load, does it generate a voltage spike when you interrupt the secondary, or does the stored magnetic energy go back to the primary side?On the web there's lots of info about inductive loads, but not much about inductive sources.The application I'm thinking about is a low voltage trailing edge dimmer circuit for rectified 12v. Effectively PWM synchronised to the mains frequency. Do I need to plan for higher than expected voltages other than the 1.4 x RMS?Mike
Transformer Secondary Windings : Can I parallel them? - Page 1
Forum section: electronics / beginners

author: NivagSwerdna
author_rank: Super Contributor
timestamp: January 15, 2023, 11:30:32 am
content: So I have my hands on a TIM 100 Block Isolating Transformer and would like to use it to power an old arcade CRT during repair...It'shttps://www.farnell.com/datasheets/3160338.pdfI only need 1 output at 110V....Can I parallel the two secondaries? Are there any cases where this might ruin my day? I notice a dot on the schematic... should I connect the dotted wires?Sorry for the ignorance

author: Benta
author_rank: Super Contributor
timestamp: January 15, 2023, 11:44:11 am
content: Yes, you can parallel them, but as you say yourself: watch out for polarity.

author: Vincent
author_rank: Regular Contributor
timestamp: January 15, 2023, 12:18:15 pm
content: Yeah it's tricky, but it can be done.And for the dots, that's precisely the thing to do if you want this to work. Otherwise the two secondaries are going to cancel each other out.

author: inse
author_rank: Super Contributor
timestamp: January 15, 2023, 12:34:52 pm
content: Cancelling out like matter and antimatter 😎

author: Ian.M
author_rank: Super Contributor
timestamp: January 15, 2023, 12:54:21 pm
content: Quote from: inse on January 15, 2023, 12:34:52 pmNot *quite* that bad,but unless you limit the supply current, that's an easy way to 'elect a pope!'*.I would strongly advise bringing the transformer up fed by a dim bulb tester, any time you are paralleling windings (or wiring primaries in series). Seehttps://www.eevblog.com/forum/beginners/ask-determining-transformers-windings-phase/*AKA: 'let the magic smoke out'

author: wasedadoc
author_rank: Super Contributor
timestamp: January 15, 2023, 04:09:18 pm
content: Connect together one end of each winding. Put a voltmeter between the other two ends. Power up the transformer. If you get zero volts or very close to it then you have the correct ends paired up. If you get about 220 volts then you haven't.
Transformer - Single Primary w/Aux, Single Secondary - Confused as hell - Page 1
Forum section: electronics / beginners

author: bkochis
author_rank: Contributor
timestamp: April 16, 2012, 08:12:54 pm
content: More than a little confused about how to find a primary, aux and secondary transformer. I ran a design tool from TI for a UCC28610 flyback controller. (See attached pdf)My problem is: I have been to Mouser, Digikey and Farnell. I cannot figure out how to search for one! Would something like this be a custom part?Thanks in advance.

author: ejeffrey
author_rank: Super Contributor
timestamp: April 16, 2012, 08:50:17 pm
content: You can look at the coilcraft website. In general, transformers are tricky. There are just too many variations to always find what you want. You may have to wind your own (for small quantities) or order a custom part.

author: Neilm
author_rank: Super Contributor
timestamp: April 17, 2012, 06:14:20 pm
content: That looks like you will have to get that custom made. Assuming that the input is mains the TX will be main safety barrier so it would be worth getting it done by people who are used to doing this and can do the necessary safety tests prior to powering up.Unless of course you are happy to trust your life to something you have made you self.Neil

author: bkochis
author_rank: Contributor
timestamp: April 27, 2012, 02:09:20 am
content: Actually, I found a number of these transformers at Coilcraft.http://www.coilcraft-cps.com/products/transsel_ac.cfmI wound up getting a sample B0570-BL, which costs $3.57 USD for a single copy. This item provides 12v, 1.2a from a 110v input at the secondary. I will have to figure out what the AUX will output.BOOYAH!

author: bkochis
author_rank: Contributor
timestamp: April 28, 2012, 12:23:18 pm
content: Thanks for the info. I will give it try someday soon for the educational experience.Actually I need 1,000 copies a month for a commercial project, so building them myself is not an option.
Transformer Tap Query - Page 1
Forum section: electronics / beginners

author: Sam__
author_rank: Regular Contributor
timestamp: January 07, 2014, 10:49:43 pm
content: This feels like a very basic question that I should know the answer to but I just can't figure it out.I've pulled a transformer from an old scope. It has a bunch of tap offs, as expected, but one of them is a thick black wire which seems to be connected to no other taps. I've checked multiple times with multiple multimeters and they always read open circuit. I was wondering what it's purpose is?Thanks in advance.

author: JackOfVA
author_rank: Unknown
timestamp: January 07, 2014, 10:54:26 pm
content: Some high quality transformers have an electrostatic shield between the primary and secondary windings and the shield is brought out to a wire or terminal so that it may be connected to the chassis ground.

author: Sam__
author_rank: Regular Contributor
timestamp: January 07, 2014, 10:59:27 pm
content: Thanks for the reply.I just connected it to earth through a resistor and no current flowed, so it looks like it is a shield.
Transformer VA rating - Page 1
Forum section: electronics / beginners

author: IvoS
author_rank: Frequent Contributor
timestamp: September 22, 2013, 05:36:12 pm
content: I have an old EI 120/2x24V transformer and I need to find out its approximate power. Could it be determined by core size in in2 or cm2 ?

author: Zero999
author_rank: Super Contributor
timestamp: September 22, 2013, 05:54:46 pm
content: That's one way of doing it but it's easier just to weigh it and compare it to the rating of transformers of a similar mass.

author: Paul Price
author_rank: Super Contributor
timestamp: September 23, 2013, 09:50:14 am
content: Apply a 1 amp then 2 amp than 3 amp then 4 amp resistive load to the secondary and notice the voltage drop. When the output voltage falls below 24V RMS on a DVM under load and the temperature of the transformer rises no more than 50 Deg C above room ambient over a half-hour interval, you've then determined the useful output capacity of the transformer.In this current situation, Size Matters.
Transformer values for SMPS design - Page 1
Forum section: electronics / beginners

author: Shubham
author_rank: Contributor
timestamp: August 31, 2023, 11:32:04 am
content: Hello everyone, I need few values required for designing the smps. I am trying to design 5V/2A SMPS. I have used Viper22A IC and intend to use tdk E 16/8/5 (EF 16) N87 core, vertical version bobbin for the transformer. In order to make the transformer calculation I need the following values: Maximum Duty Cycle, Core Geometry(Kg), Core weight(Wtfe), Iron area(Ac), Window Area( Wa), Area Product(Ap), Surface area(At), Core Permeability, Fringing Flux. I am unable to locate this values in tdk datasheethttps://www.tdk-electronics.tdk.com/inf/80/db/fer/e_16_8_5.pdf. Could anyone please help me to find this values? Thanks in Advance.

author: SuzyC
author_rank: Frequent Contributor
timestamp: August 31, 2023, 12:21:22 pm
content: You are barking up the wrong tree here. Contact a sales or tech sup rep at TDK re your inquires. Good luck with that.https://product.tdk.com/en/contact/index.html
Transformer voltage question  - Page 1
Forum section: electronics / beginners

author: Biff383
author_rank: Regular Contributor
timestamp: February 08, 2015, 07:33:14 pm
content: What are the pitfalls of running a transformer under its rated voltage? I have noticed that if you put 120V thru a 480V to 120V transformer you get an output around 26 or so volts. What parameters do we have to adjust when we do this?

author: IanB
author_rank: Super Contributor
timestamp: February 08, 2015, 07:42:37 pm
content: The input/output voltage ratio is constant, it depends on the turns ratio. The transformer will have a specified primary voltage, operating frequency and power (or VA) rating.If you deviate from the design spec (in permitted ways) you will have to re-rate the transformer. A search will provide rules of thumb for this.Decreasing the input voltage is harmless. I think the only consequence is that you may no longer achieve the specified power handling.

author: Biff383
author_rank: Regular Contributor
timestamp: February 08, 2015, 07:47:15 pm
content: That was what I thought. I didn't know anywhere to find how much I should derate . I'll look around a bit.Thanks.

author: Zero999
author_rank: Super Contributor
timestamp: February 08, 2015, 09:08:08 pm
content: The secondary current rating of the secondary winding will be the same.
transformer windings  in between transformer windings - Page 1
Forum section: electronics / beginners

author: J4e8a16n
author_rank: Regular Contributor
timestamp: April 20, 2017, 05:18:10 pm
content: Hi,What would happen if I wind 28 turns of .75 mm wire in the middle (200-28-200) of 400 turns of .5 mm windings? Would I have a better K factor?Thanks for your attention.JPD

author: Zero999
author_rank: Super Contributor
timestamp: April 20, 2017, 05:21:37 pm
content: I don't see how it would make any difference to the transformer's ability to withstand harmonic content.

author: J4e8a16n
author_rank: Regular Contributor
timestamp: April 20, 2017, 07:43:15 pm
content: Hi, Well I did it and it heats up a lot at 60 Hz....... This gapped core was a high-frequency one. Maybe that's why although I doubt it.I tried it at 50KHz with a 555 timer. It doesn't heat.Approximately:I have .5 ohm and .23mH on the primary (28 turns) and2.8 ohms and 28 mH on the secondary (330 turns).The primary pumps 20 Watts at 4 volts. But I don't read a significant voltage on the secondary.This seems consistent with Np/Ns= sqrt(Lp/Ls))