@Talon FWIW take a sniff at the linked page and see if that gets closer to meeting your needs.
https://electronics.stackexchange.com/questions/171748/how-to-measure-ratings-of-a-transformer
https://electronics.stackexchange.com/questions/171748/how-to-measure-ratings-of-a-transformer
Transformers - they have a strong tendency vary according to what they cost. This is the sort of info that should be available where they are sold if bought from an electronics parts type place
Those are toroidal but the same applies to all. As you can see the temp rise fully loaded will be ~50C on a 50va part. It is possible to buy stuff that will get hotter than that and assume ambient is lower than 40C. The regulation will suffer as a result.
This range has split primaries and secondaries, They can be used in series or parallel. These are
Dual primary winding for connection in series or parallel only Input Voltage : 115 or 230V ±10% 50/60Hz.DC Resistance : 2x 2.13Ω to 79.1Ω ±15% @ 20°C Magnetising Current : 2.5mA to 47mA approx.@ 230V 50Hz (5mA to 94mA approx. @ 115V 50Hz)
The dual 115v primaries are pretty common as they can be used in the USA and Europe.
A point on the secondary is that a 2 diode rectifier on the secondaries used in series tends to give a higher DC voltage than a full bridge, The centre tap is then Ov. The coil's starts and finishes are colour coded.
Those are toroidal but the same applies to all. As you can see the temp rise fully loaded will be ~50C on a 50va part. It is possible to buy stuff that will get hotter than that and assume ambient is lower than 40C. The regulation will suffer as a result.
This range has split primaries and secondaries, They can be used in series or parallel. These are
Dual primary winding for connection in series or parallel only Input Voltage : 115 or 230V ±10% 50/60Hz.DC Resistance : 2x 2.13Ω to 79.1Ω ±15% @ 20°C Magnetising Current : 2.5mA to 47mA approx.@ 230V 50Hz (5mA to 94mA approx. @ 115V 50Hz)
The dual 115v primaries are pretty common as they can be used in the USA and Europe.
A point on the secondary is that a 2 diode rectifier on the secondaries used in series tends to give a higher DC voltage than a full bridge, The centre tap is then Ov. The coil's starts and finishes are colour coded.
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i have been in this forum for 20 years, and this is the first time afaik that a question like this has been raised....
from the basic transformer formula, there are many many variations, but for me, the quality of the iron used is first, since that determines the maximum flux density that can be applied, without the core saturating and burning out, or the losses being high and temperature getting so high that insulations can burn out...
of course you are free to design based on your allowable temperature rise, and voltage regulations, these two traces back to flux density...
what is the best way to measure transformer output? by output i take it to mean secondary volt amperes, and if power factor is unity, then secondary watts equals secondary volt amperes...
now secondary volt amperes is determined by the mass of the transformer cores that is used, i.e. a 10kg core will have higher va capacity than a 1kg core..
then you have the copper windings, how much copper can you stick into the winding window, how much current you can safely draw without the copper insulation burning down..
how to measure transformer output? by load testing, say your traffo is rated at 200va with 100vac (unloaded) so that these two represented a load R of (200x100)^2 or 141 ohms, so by connecting this load resistor, you can know the regulation as the 100 volt unloaded will surely drop some....
you can also monitor the core temperature rise, from an ambient of say 25 deg. C how high will the core temperature be after 15 minutes, after 30 minutes? after 2 hours....
so that asking such questions, all depends on your priority, if you ask me, temperature rise is number one...
from the basic transformer formula, there are many many variations, but for me, the quality of the iron used is first, since that determines the maximum flux density that can be applied, without the core saturating and burning out, or the losses being high and temperature getting so high that insulations can burn out...
of course you are free to design based on your allowable temperature rise, and voltage regulations, these two traces back to flux density...
what is the best way to measure transformer output? by output i take it to mean secondary volt amperes, and if power factor is unity, then secondary watts equals secondary volt amperes...
now secondary volt amperes is determined by the mass of the transformer cores that is used, i.e. a 10kg core will have higher va capacity than a 1kg core..
then you have the copper windings, how much copper can you stick into the winding window, how much current you can safely draw without the copper insulation burning down..
how to measure transformer output? by load testing, say your traffo is rated at 200va with 100vac (unloaded) so that these two represented a load R of (200x100)^2 or 141 ohms, so by connecting this load resistor, you can know the regulation as the 100 volt unloaded will surely drop some....
you can also monitor the core temperature rise, from an ambient of say 25 deg. C how high will the core temperature be after 15 minutes, after 30 minutes? after 2 hours....
so that asking such questions, all depends on your priority, if you ask me, temperature rise is number one...
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You can get a pretty good idea of safe output from current density in the wire. The temperature rise will usually be reasonable at 3A per sq. mm, as long as core losses don’t get stupid from running at a high flux density. Of course, that’s RMS current which can be a lot higher than the DC load.
It seems an idle question, the OP is unwilling to describe the transformer or the intended use , or the item it was removed from.
Even a picture is not being provided.
I am 'un-watching' this thread.
Even a picture is not being provided.
I am 'un-watching' this thread.
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A transformer with the secondary disconnected is the same as an inductance which is usually high to keep the magnetising current low. Transformer action is having two currents producing opposing magnetising currents in accordance to Lenz's Law. Provided the magnetising current is small compared with the currents a transformer is designed to work with, it obeys the rule:
Vp/Vs = Np/Ns
Where V is voltage, p stands for primary and s stands for secondary. The voltages in the winding are in proportion to the turns of the respective coils. This hints at that the voltage per turn is constant for all turns and all coils.
The equation above assumes the magnetising current is negligible. However, any accurate analysis worthy of consideration requires taking into account all currents.
Vp/Vs = Np/Ns
Where V is voltage, p stands for primary and s stands for secondary. The voltages in the winding are in proportion to the turns of the respective coils. This hints at that the voltage per turn is constant for all turns and all coils.
The equation above assumes the magnetising current is negligible. However, any accurate analysis worthy of consideration requires taking into account all currents.
This goes through what goes on within mains transformers in some detail
https://www.electronics-tutorials.ws/transformer/transformer-construction.html
I just ordered one for a project. This one in 25-0-25
https://docs.rs-online.com/db71/0900766b8157a9ee.pdf
I know it will give 25v fully loaded and the open circuit voltage. Past projects using say ebay bargains have contained some surprises especially on regulation which relates to heat. It might be possible to rate this one for a 100va but with a higher temperature rise or some maker may have decided on 80va and a different max temperature rise. 🙂 Annoying aspect is that this supplier doesn't provide the mounting kit. 🙁 The one that does didn't have stock.
https://www.electronics-tutorials.ws/transformer/transformer-construction.html
I just ordered one for a project. This one in 25-0-25
https://docs.rs-online.com/db71/0900766b8157a9ee.pdf
I know it will give 25v fully loaded and the open circuit voltage. Past projects using say ebay bargains have contained some surprises especially on regulation which relates to heat. It might be possible to rate this one for a 100va but with a higher temperature rise or some maker may have decided on 80va and a different max temperature rise. 🙂 Annoying aspect is that this supplier doesn't provide the mounting kit. 🙁 The one that does didn't have stock.
Normal mains drop down transformers are fairly basic.
Input voltage and output voltage(s).
The VA of the transformer is just sum of output voltages times max current they can draw.
The fun starts with valve output transformers where relative impedances are relative to number of turns squared.
But we wont go there yet.
Input voltage and output voltage(s).
The VA of the transformer is just sum of output voltages times max current they can draw.
The fun starts with valve output transformers where relative impedances are relative to number of turns squared.
But we wont go there yet.
FWIW, i use the 0,6 factor to reckon primary volt amperes, like if your total secondary load is as 200 watts, then 200/0.6 = 334 volt amperes....so i design my transformers this way, from the volt amperes i can calculate the core area needed...
others may use a factor of 0.8....
others may use a factor of 0.8....
A trasformer has to satisfy these requirements:
a) run sufficiently cool at the operating powers
b) provide good DC voltage regulation after rectification
c) provide mains isolation
DC voltage regulation requires the secondaries to have low DC resistance. A resistance of 1 Ohm is normally too high, unless the expected current is well below 1A.
My advice, if you already have an identical transformer, is to test the transformer where you want it or in a simulated load condition. After a few minutes measure the transformer temperature and also measure the output voltage. Put a capacitor in series with an AC voltmeter and get a rough measure for the ripple. If the AC voltmeter is a peak measurer, multiply the reading by the square root of two times two (2.8 approximately) to get the peak to peak ripple voltage.
Finally, you have to decide the amount of ripple ripple/DC_voltag that you tolerate. You will never get a perfect DC with only a rectifier and smoothing capacitors. In some circumstances, a ripple ratio of 0.1 (10%) is tolerated, but in others it may not.
You also have the option to use a power transistor to block the ripple using the so called capacitance multiplier. This gives more freedom in the choice of transformer at the expense of some wasted power.
a) run sufficiently cool at the operating powers
b) provide good DC voltage regulation after rectification
c) provide mains isolation
DC voltage regulation requires the secondaries to have low DC resistance. A resistance of 1 Ohm is normally too high, unless the expected current is well below 1A.
My advice, if you already have an identical transformer, is to test the transformer where you want it or in a simulated load condition. After a few minutes measure the transformer temperature and also measure the output voltage. Put a capacitor in series with an AC voltmeter and get a rough measure for the ripple. If the AC voltmeter is a peak measurer, multiply the reading by the square root of two times two (2.8 approximately) to get the peak to peak ripple voltage.
Finally, you have to decide the amount of ripple ripple/DC_voltag that you tolerate. You will never get a perfect DC with only a rectifier and smoothing capacitors. In some circumstances, a ripple ratio of 0.1 (10%) is tolerated, but in others it may not.
You also have the option to use a power transistor to block the ripple using the so called capacitance multiplier. This gives more freedom in the choice of transformer at the expense of some wasted power.
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I tried to get you to understand I'm not working on any particular project, but you kept asking me for pictures and a description of this non-existent project, over and over, and nothing I said could get you to see otherwise. I finally got to the point where I wished I could just delete the thread, so I took some time off from it. I'm glad you're done here because I just don't have the patience to deal with that.
To the rest of the guys who have participated, I really appreciate the time you've spent trying to explain transformer theory.
I honestly thought that since every transformer catalog I've reviewed listed a couple of electrical characteristics plus the physical dimensions, thats what mattered. I had no idea that transformer specification was so involved. I had no idea that temperature rise and resistance and coil area etc were the big concerns. Now I know better.
I also know that this stuff is way over my head. I'm going to leave this to the experts and go back to doing refurbs.
Let's start at the beginning from what I understand.
1) You have or don't have the original transformer?
2) You know the dimensions of the original transformer
3) You know how it was connected in the original circuit
4) You know whether it operated from 110VAC or 230VAC
5) You have an RMS voltmeter and a resistance meter (Ohmmeter)
6) Is it a step-down or step-up transformer
7) you can measure the resistance or continuity of both secondary and primary (secondary will be the lower resistance if it is step down, higher if stepped up)
8) You can measure the secondary voltage when primary is connected to mains
9) you can weigh the transformer and apply the rule of thumb 1 kg equal to 100VA (approximately)
Knowing the above, you can start selecting an equivalent transformer from Hammond starting with the approximate VA rating
If you could measure the secondary voltage, then you can select the exact or close to equivalent Hammond transformer.
If your transformer could not be identified at all, or you don't have one, then you need to offer your application schematic and one of us here may be able to shed light on what you may require.
If this is not helpful, then we have to follow another approach.
1) You have or don't have the original transformer?
2) You know the dimensions of the original transformer
3) You know how it was connected in the original circuit
4) You know whether it operated from 110VAC or 230VAC
5) You have an RMS voltmeter and a resistance meter (Ohmmeter)
6) Is it a step-down or step-up transformer
7) you can measure the resistance or continuity of both secondary and primary (secondary will be the lower resistance if it is step down, higher if stepped up)
8) You can measure the secondary voltage when primary is connected to mains
9) you can weigh the transformer and apply the rule of thumb 1 kg equal to 100VA (approximately)
Knowing the above, you can start selecting an equivalent transformer from Hammond starting with the approximate VA rating
If you could measure the secondary voltage, then you can select the exact or close to equivalent Hammond transformer.
If your transformer could not be identified at all, or you don't have one, then you need to offer your application schematic and one of us here may be able to shed light on what you may require.
If this is not helpful, then we have to follow another approach.
Okay, I have designed bespoke transformers for industrial/commercial applications. Where would you like to start. Designing a transformer from scratch for a typical application is a little beyond a DIYAudio thread, it can become a very complex feat and some have spent many years doing so. There are many programs here on the internet that will do the basics for you, and you could have quite a successful outcome.