transformer schematic - Page 1
Forum section: electronics / beginners

author: v0ltair3
author_rank: Contributor
timestamp: May 19, 2024, 04:41:33 pm
content: Hello,I found an old Siemens transformer that I wanted to reuse as an isolation transformer, but I'm not sure how to interpret it, firstly because I'm very familiar with industrial-like transformers, and it's written in German.From some images I read, the diagram defines where we should apply a "jumper" (again it's in German, so not able to interpret). i.e., shall I connect 37 and 38 to supply 220V our of the secondary ? I saw some images in the internet where I see a jumperwire between 37 and 38, but I not 100% sure. But more important, how should interpret the primary to have a 220 input. link 23 and 26?I'd rather ask for help than do something stupid. Thank you in advance for your support.Thanks

author: v0ltair3
author_rank: Contributor
timestamp: May 19, 2024, 04:48:01 pm
content: Here some examples I saw, one of them not even corresponds to the schematic, so I am even more puzzled....

author: jmelson
author_rank: Super Contributor
timestamp: May 19, 2024, 04:55:22 pm
content: Connect input (eingang) to terminals 20 and 28. connect a jumper from various terminals as listed on the right side of the chart for various mains voltages. Output if from terminals 36 to 39. You have two isolated secondary windings there, so you can put them in parallel for lower voltage and more current, or in series for twice the voltage, or connect 37 and 38 as a center tap. You can also set the jumpers for a higher mains voltage to reduce the output voltage as needed. I think for 200 and 220 V, you use two SEPARATE jumpers as listed.Jon

author: v0ltair3
author_rank: Contributor
timestamp: May 19, 2024, 04:58:48 pm
content: My purpose is to do 220V In and 220V Out (hopefully it will give me 230 output if I input 230)... doe sit mean I need to have 2 jumpers in the input ?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 19, 2024, 05:07:29 pm
content: I would wait for a native German speaker to be absolutely sure, but I read this the following way.The input voltage is connected to terminals 20 and 28 (From the lower left corner (Eingang > Input)The output voltage is taken (usually) from terminals 36 and 39 (From the lower left corner (Ausgang > Output)The rest is a jumper table to select input and output voltages (Verbdg. > Verbindung > connection, binding or jumper)Your picture shows a transformer that has been connected for 400 V input and 220 V output.If you want to test this you could wire your transformer to match the picture you have. (note that inputs and outputs have connections as described above and have been cut off in the picture). Assuming you don't have or don't want to play with 400 V on the input, just apply what you have (220?) and then see if the output is your voltage divided by 400 times 220.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 19, 2024, 05:08:28 pm
content: Quote from: v0ltair3 on May 19, 2024, 04:58:48 pmYes

author: madires
author_rank: Super Contributor
timestamp: May 19, 2024, 05:34:24 pm
content: Jmelson and CatalinaWOW got it right:- primary: input 20 and 28, jumper between 20 and 26, and another jumper between 23 and 28- secondary: output 26 and 39, jumper between 37 and 38

author: v0ltair3
author_rank: Contributor
timestamp: May 19, 2024, 05:41:01 pm
content: So it should be something like this correct ?

author: m k
author_rank: Super Contributor
timestamp: May 19, 2024, 05:55:22 pm
content: Yes.Top side is in series and bottom side is parallel.Total ratio is 220:550.So 1/1.25 of both bottom sides, that way most of the total power is available.

author: v0ltair3
author_rank: Contributor
timestamp: May 19, 2024, 06:23:18 pm
content: Thanks m k,Can I ask you to kindly educate me on the 220:550 ratio ?This is how I wire it, but it blew the 1A fuse that I had in the input upon connecting it to mains.If I interpret correctly, P=400/1160VA means that I have 400/220 = 1.8A in the input (please correct me if I am wrong)... will the transformer draw this current even if it is completely idle ?

author: soldar
author_rank: Super Contributor
timestamp: May 19, 2024, 07:09:34 pm
content: You do the old trick of the lightbulb in series and measure voltages and currents and resistances etc

author: v0ltair3
author_rank: Contributor
timestamp: May 19, 2024, 07:42:23 pm
content: I don't have an incandescent light, I might still find the small 25-watt ones from the fridges...I run some test..resistance on the output is 3,18 ohmsI add only the first link (20-26), I get a resistance of 3.8 ohms in the input, works fine but I get a more elevated outputI add only the second link (23-28), I get a resistance of 3.18 ohms (just as the output), but the fuse gets burnedI add both links as per the depicted figure, I get a resistance of 1.81 ohms (isn't smaller than it should ? ) but with the second link, the fuse goes away...

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 20, 2024, 01:24:17 am
content: Your picture is right by my understanding. The transformer may have a defect. One thing to check is the resistance between terminals 23 and 26 (with jumpers removed). Also compare resistance from 20 to 24 with resistance from 25 to 28.

author: MrAl
author_rank: Super Contributor
timestamp: May 20, 2024, 03:49:19 am
content: Quote from: v0ltair3 on May 19, 2024, 04:41:33 pmHi,This is a fairly complicated transformer and may possibly be made for a special purpose. That makes it very unknown more so than most other transformers. That means you have to test it, there's no other way. Before you can parallel any windings you have to test for voltage AND phase. If the phase of one winding is opposite to what you think it is, the transformer windings can blow or you blow the fuse or circuit breaker.The idea would be to discover the voltage and the phase of each winding so you can create the schematic with all voltages shown clearly. That would mean you can get a lot of different output voltages, and easily figure out what goes where.It does look like the top two windings are 110vac each. If you connect the two centermost terminals of those, you get 220vac on the two outermost terminals, with the right windings on the lower set connected correctly. That gives us a convenient place to start.By applying 110v to one of those windings or 220vac across the outer two, you can easily measure the voltage of the lower windings, every single one. You can then label each winding with the voltage you measure. If you use a light bulb in series, then you have to measure the actual voltage across the 110vac winding also and do the math to get the actual winding voltage on the lower windings (as if 110vac was really applied without the light bulb). This would quickly wrap this up, but you do have to measure the phase too.To measure the phases, you connect the center most two terminals of the lower windings together and then check the voltage across those windings like you did before, except now you look for either a voltage increase or a voltage decrease. If the voltage increases, then the windings are of the same phase (left most terminal on one winding is the same phase as the left most terminal on the second winding).Once you get all this information it should be easy to figure out what windings you have to connect and any jumpers, and also figure out ANY combination of winding connections that are possible and the output voltages from that.The remaining possibility is that there are actually two transformers in one case. The leftmost transformer and the rightmost transformer. This would mean other connections might be possible. If you take more pictures especially of the sides of the transformer, this might help figure this question out.To parallel two windings you have to first find the phase of each winding, and assuming that the leftmost terminal of each winding is the same phase, you connect the two leftmost terminals together and the two rightmost terminals together. You only have to do that though if you need the full power output.The power outputs bring up another question. How much power can you draw from each winding.To find that out the best way is to look at the diameter of each wire lead where it connects to the respective screw. You can infer the current rating from that and with the measured voltages you can calculate the power ratings.If you need a diagram I can draw one up for you. Wordy descriptions in electrical work do not always come out clear enough that's why we draw schematics

author: mariush
author_rank: Super Contributor
timestamp: May 20, 2024, 04:44:25 am
content: The way I read it is the two primary windings should have the same voltage , 275v AC in total ... but each of the two primary windings has taps at various points on the winding ... so you get something like this :20 --155v?-- 21 --40v-- 22 --20v-- 23 --60v-- 24 25 --50v-- 26 --20v-- 27 --205v?-- 28So if you want 220-230v AC on input, I think you would aim to get each of the two primary windings equal to close to 220-230v and then parallel themso 20 to 23 should be 275v - 60v = 215v and 27 to 28v should give you 205v or 26-28 is 225v AC ... and now you can parallel them to get 215v AC primary winding with double current. It should tolerate 220-230v AC on each of the two windings.The ratio is 550 : 220 = 1.83 , so with 215v on input you'd get 215/1.83 = 117v AC ? I'm not sure, the lower number of windings could result in less voltage on output, you'd have to test.Quote from: v0ltair3 on May 19, 2024, 05:41:01 pm

author: m k
author_rank: Super Contributor
timestamp: May 20, 2024, 08:28:40 am
content: Quote from: v0ltair3 on May 19, 2024, 07:42:23 pmContinue from here.Remove all jumpers and connect input between 25 and 28.Both output parts should have a same voltage, some above 110/225 * input voltage.Unused input has also a voltage.Voltage between 20 and 24 should be a bit less than the input of the other side.It's possible that one wire insulation has failed, means possibly that you get the voltage but can't load it.You can connect a small enough mains device to unused input side and see what happens.You can still have your isolation transformer, even if one input side is faulty, if less than a half of the total power is enough.There you just leave bottom side jumpers off and put input between 26 and 28.E,idle voltages are higher and lowers when loaded.And lowers much when overloaded.Maybe a newish battery charger can be a test device.Pick one that accepts wide range of input voltages.

author: v0ltair3
author_rank: Contributor
timestamp: May 20, 2024, 02:21:29 pm
content: Thank you so much for your kind help, this is becoming quite learning experience for me... trying to reverse engineering it as per your guidance (by reversing the input), I've made a schema of how this looks regarding voltage and resistance and also included the excel file@MrAl, by linking the innermost of the bottom windings to look at phase, I don't detect any specific deviation on the voltages, I've rounded them up but we're looking at decimals of AV volt deviation (added a few extra pictures from the transformer)As for available power, I would like to have something like 220-230v in and 220-230v out at least with 1AmpNow for personal education:1- Could in theory operate the transformer in reverse?2- By linking 20-26 and 23-28 the idea was to create a parallel in the input? If that is so, then by reversing it should I also be able to make it parallel (although most likely the fuse will blow once again)?3- Is there a way to understand why the fuse gets burned when I add the jumpers? Could it be that it peaks at the start and therefore thus burns the fuse? (I used a 1Amp and a 2Amp)Thank you in advance

author: mariush
author_rank: Super Contributor
timestamp: May 20, 2024, 03:35:24 pm
content: So i think i was pretty much right in the voltages i estimated.20-23 would give you 158+60 = 218v , 26-28 would give you 198+20 = 218v .... so you could parallel these two windings for more current.Yeah at cold start, this transfer would pull several amps of current... so at the very least you'd want to use a time delay / slow blow fuse ... rated for a few amps, 1A is just too little.

author: madires
author_rank: Super Contributor
timestamp: May 20, 2024, 03:35:59 pm
content: Quote from: v0ltair3 on May 19, 2024, 06:23:18 pmTransformers have a high inrush current which can be multiple times the normal current draw. For smaller transformers use a slow-blow/time-lag fuse rated a bit higher then the normal current draw. For larger transformers, which could trip the mains circuit breaker, the best solution is to add a soft start circuit. And as already mentioned, the transformer could have a fault when blowing a reasonably rated fuse.Quote from: v0ltair3 on May 20, 2024, 02:21:29 pmThe transformer has two primary windings and the jumpers connect them in parallel, i.e. higher current draw and higher inrush current. Based on the transformer's max VA rating I'd would try 6.3 A.

author: MrAl
author_rank: Super Contributor
timestamp: May 21, 2024, 04:37:15 am
content: Quote from: v0ltair3 on May 20, 2024, 02:21:29 pmHi,Yes you can sometimes run a transformer in reverse, but the excitation current may be different, or inrush current could be higher, so you'd have to check for that.Ok if those voltage measurements are correct, then it looks like the two windings in question are the same voltage and the same phase, although the resistances look slightly different but that could be just measurement error. If the resistances are not the same then one winding will put out more power than the other, but the difference isn't that big.If you only need 1 amp you should be able to get that with just one of those two windings.As to the fuse blowing, was it a fast blow fuse or slow blow fuse? A fast blow fuse would probably blow with this larger transformer, with a slow blow it may not blow but only 1 amp probably isn't high enough.1 amp only requires around maybe #22 AWG wire, maybe #20 AWG so you could check that as those lead wires are quite visible.Another question would come up too though. If you intend to use this as an isolation transformer, you should probably read up on isolation transformers and their specifications. You would need to check for leakage from input to output, and if there is a problem with the old insulation that could be a problem which brings the issue of safety into question.I had an old oscilloscope a long time ago, but it was even old back then, and one of the high voltage transformers had high leakage. I went to measure a point on a calculator PC board while the calculator was powered up and a spark jumped from the probe tip to the calculator. The calculator was nonfunctional after that, so the spark blew it out. That was a nice calculator too loved the display it was vacuum fluorescent. Never found another one like it.I had to replace the transformer with three other lower voltage transformers as I did not have one with a high enough voltage to run the scope. To bad it was too late for that beautiful calculator.When it comes to human safety though that's an even bigger issue of course.How expensive these days is a brand-new transformer of the type you need if you were to buy a new one? 1 amp current is not very much current.

author: v0ltair3
author_rank: Contributor
timestamp: May 21, 2024, 08:41:31 am
content: Thank you all for the amazing support, this is becoming a master class for me personally...Quote from: madires on May 20, 2024, 03:35:59 pmUsing a slow 5A fuse it holdsQuote from: MrAl on May 21, 2024, 04:37:15 amIs there a way to verify that? The only thing I notice is that I connect in the normal operation I get 0.4A, and in reverse about 0,6A, I don't really know how to interpret this fact... The only drawback I see is that if I use it normally is that I get almost 248 (18v above the normal) out of the above secondary, and in reverse, I get 220v out of the bottom part, so I would rather stay as close as possible to the 230v. Btw, is it better to be above or below the reference voltage?Quote from: MrAl on May 21, 2024, 04:37:15 amMeasuring it by connecting 20-23 and 26-28 I get basically the same thing our of the secondary, so I don't believe it will make such of a difference.Quote from: MrAl on May 21, 2024, 04:37:15 amIt's actually 1mm^2 without isolation, so It would be able to hold way above 1 amp.How shall I read the P=400/1160? 1160/230=5Amp??Quote from: MrAl on May 21, 2024, 04:37:15 amWhat I looked was at continuity between all the primary and secondary windings as well as the transformer metallic support, and it's an open circuit between all of them. Is there any other measure I could do to ensure I don't run into safety issues?Again, thank you so much of all your support!

author: m k
author_rank: Super Contributor
timestamp: May 21, 2024, 10:52:07 am
content: 1. yes, not in theory.Believe your head, there's no magic.2. yes, note that partial taps are not symmetrical.Since transformer is not ideal it's leaving something behind.So 1:1 ratio is actually a bit more for output.In your case a full width of bottom half can be just that.3. yes, nominal current is1160VA/400V, so 2.9Aand inrush current is easily 10x.But in your case the input side is in parallel, so maybe 20x, though not for long.Timed fuse can do the trick, or motor start fuse, or NTC resistor for soft start.Magic there can be, but not in this case.Your transformer is a regular, and pretty standard, power transformer.Even in reverse it's still completely in its normal operation range.You can also put it fully in reverse and still be in safety margin.But it's old, so don't do it.Current, you can't add it up like you did, it's the other way around.You keep the original current and drop the overall power, if not then it finally overheats.Keep in mind that upper part is still just one.E,you can expect that upper part can stand 2.5 times (550:220) the current of lower part.So you can double the current of both sides if you put them in parallel, but you can't use more voltage than overall power indicates.It's also likely that sides are not equal, so one is stressed more than the other.It's also possible that 1160VA is not for 550V.E2,Closer to the magic section.Winding wire has a thickness, that defines how much current can go through.It also has an insulation material layer around it, with two major properties, max. voltage and max. temperature.Too hot and insulation melts and too high voltage and insulation can't insulate anymore.The voltage is why you normally do not reverse a transformer, but there original input remains and step down becomes a step up using possibly way too high voltages.

author: MrAl
author_rank: Super Contributor
timestamp: May 22, 2024, 01:46:00 pm
content: Quote from: v0ltair3 on May 21, 2024, 08:41:31 amHi,The leakage inductance primary to secondary can measure differently than from secondary to primary. That could be why you measure different currents depending on how you power it up. The excitation currents would be different because the inductance seen by the input voltage source is different. The simpler expression is v=w*L*i, with 'i' being the AC current, L the inductance, w the angular frequency (w=2*pi*f), v the AC voltage.If by reference voltage you mean the output voltage, very often the voltage is slightly higher with no load. 248v sounds a little high though.About the P=400/1160, I do not know why they specify two power ratings. I think it would be better to measure the wire diameter in each lead to the windings and go from there.About continuity between primary and secondary, when you check for leakage you have to use a rather high voltage. They sometimes call it "hipot".Did you by any chance check into how much a new transformer would cost that does what you need?

author: m k
author_rank: Super Contributor
timestamp: May 22, 2024, 02:16:51 pm
content: Quote from: MrAl on May 22, 2024, 01:46:00 pmI read it first so that 400 is a voltage and the thing is to take single phase out from 400V main voltage 3-phase system.E,now my guess for power is 400 continuous and 1160 peak VA.Alternative primary is also possible.

author: MrAl
author_rank: Super Contributor
timestamp: May 24, 2024, 05:02:37 am
content: Hello again,One of the other wiring possibilities is to wire this up as an autotransformer. That would provide many other voltage outputs but would no longer be able to provide galvanic isolation. This can still be very useful, but only when isolation is not required.Of course none of the wiring possibilities will be optimum except the way the transformer was actually designed to be used, which I do not think we have the full story on yet. For short term product testing this usually does not matter, only for long term usage at normal power levels.

author: v0ltair3
author_rank: Contributor
timestamp: May 24, 2024, 09:16:55 am
content: Thank you all once againWhat do you mean wiring it up as an autotransfomer ? I was planing to add a variac in "front" of it, but I didn't got any good deal on one so far...

author: m k
author_rank: Super Contributor
timestamp: May 24, 2024, 01:30:47 pm
content: Transformer is finally just nested loops.If you put all wires in series you can still put voltage in and take it out freely, or sort of freely, insulation is still what it is and wire thickness also.It happens so that you connect one end of primary and secondary together, winding direction is meaningful here, one end increase and other end decrease the overall voltage.In early days galvanic connection was not an issue, so cheap transformers had only one winding.There middle taps were used for different voltages, the picture has a regular way.But it doesn't need to be from 0 to something.

author: MrAl
author_rank: Super Contributor
timestamp: May 24, 2024, 04:26:53 pm
content: Quote from: v0ltair3 on May 24, 2024, 09:16:55 amHello again,An autotransformer has just one winding with taps for different voltages. Because it's just one winding you can not get isolation.For example, say your primary is 200vac and you have a secondary winding of 20vac. You can connect one lead of the 20vac winding to one lead of the 200vac so that they are in series (series aiding) and then you get 220vac out of the combined windings. This provides a lot of other possibilities too. If you take that same connection and apply 220vac to the open ends, then where the 200vac lead was you get 200vac out. There are many other possibilities with so many windings to work with.There are some rules though. All of the windings used have to be able to handle the current you intend to draw off of it, and NO winding can be used for a higher voltage (across itself that is) than what it was originally capable of. For example, if a winding was for 200vac then you cannot apply 300vac maybe not even 220vac as that would overdrive the core and cause a high excitation current. If you do have a 220vac winding though of course that's ok to apply 220vac to.The other rule is the windings have to be in phase if you want the voltages to add (series aiding) or if you want the voltages to subtract then reverse one phase (series opposing). For example, with that same 200vac winding if you connect a 20vac winding in series opposing the total voltage would now be 180vac. Series opposing just means the second winding has its phase reversed with respect to the other winding.When you consider all this and all the taps on that transformer, you might be up all night trying to figure out all the combinations (ha ha) because you can use three or more windings to get even more output voltage combinations.The main thing is though that you lose the isolation as mentioned. The other thing is that you have to consider the loading factor. As you add windings, the loading factor becomes more significant. It may not be too bad though but you do have to be aware of that and test it for whatever you intend to use it for. Losing isolation though may mean the circuit you use with it becomes more dangerous to a user. That's something to be very aware of.The kind of transformer I think you are looking at is a variac which is also usually an autotransformer but you can get isolated versions too at higher cost. Check out Circuit Specialists (online store) if you haven't already they have (or had) good prices on variacs. Variacs are very handy for testing things like this transformer.