I can be as snide as anyone. Do you prefer Thelma or Louise? Also, may I suggest a course in reading comprehension?
I saved this file from the original OpenOffice spreadsheet which was developed by Tom Gotee several years ago for consumption on DIYAudio, it is quite informative and works well for audio application.
I will do my best here to reframe the original purpose of this thread. Here we have member Talon. Talon likes fixing up old equipment. Although I find transformer failure fairly rare, he has an imaginary piece of equipment in which he has identified the mains transformer to be faulty. There are no markings on said transformer so he cannot simply research to find the parameters of said transformer. Let us assume that Talon is able to identify the primary and secondary windings and find a fault. Now to fix this Talon needs to replace said transformer, but he has no idea of the capacity(VA) of said transformer. His question simply is "Is there some method by which I can determine the (VA) or capacity of this imaginary transformer?" Hell, I came to this thread because I would like to know that myself but instead got caught up in a ******* contest. The most direct answer I have identified so far is to weigh the damned thing. Okay. I cannot see that transformer technology has changed all that much since Tesla, but just for a moment let's imagine a similar case with an unidentified electrolytic capacitor. Judging by the size you go to Mouser and order a replacement. Let's see- 1 inch diameter, 3 inches long with a weight of 3 ounces. That should work! Okay folks. Talon doesn't know Lenz's law from running a red light. To be honest he doesn't give a flying ---- about Lenz's law-he just needs to replace a transformer and wants to find a suitable replacement. Again, "Is there some way I can determine the capacity of this transformer?" Jesus Christ on a raft. He and I are not the only ones on this forum that require kindergarten level discourse.
Then still weigh the thing it is related to VA, find what the capacitor ratings are on the power side of the board, if 35V or 16V or whatever be sure that your transformer peak open cct voltage would not exceed this value, be at least 10% less. That is it simple, straight forward.
If the designer was a DIYer then you have problems, but if it is commercial equipment the manufacturer did not scratch in his scrap component box for parts he had on hand, commercially your design products as cost-effective as possible. You would not use an 80V capacitor if a 16V would be suitable.
After you see the power capacitor voltage rating, knock off 10 - 15% say the resulting operating voltage is 10V divide that by 1.4 add 1.4 for the anticipated volt drop across the rectifier take that number and find a Hammond transformer with roughly this voltage and VA.
I think that is about as good an answer as you will get.
I think that is about as good an answer as you will get.
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I know there are smart Alex's on this forum that will try and outdo each other in any contest, it takes a while to sometimes figure out the level of science to bring to a question because you follow what others say. I hope this simple explanation would fix the equipment, it may not be optimal, but you can have it working without having a laboratory of test equipment. Another way would be to use a variable power supply hooked up to the equipment and adjust the voltage up until the equipment is operating as expected, then use this voltage to size your transformer.
I give up. Not only was a post removed that also removed the context for my subsequent posts, I totally forgot that South Africans speak the Queen's English.
I am very sorry for the inconvenience, I may have removed a less accurate post, I trust that you can follow my train of thought I am not intending any offence. A simple practical procedure to try solving your dilemma.
Mike you have precisely framed my frustration with this thread, and with a lot of the thread responses I've had over the past 10 years. If I look into details on a topic I've been told "you're overthinking this!", but if I try to simplify things I hear "you simply don't understand how complicated this is!".
Nico actually gave a pretty interesting approach in posts 45 and 47. And - thankfully - he didn't keep asking me for pictures of a non-existent power supply.
Nico actually gave a pretty interesting approach in posts 45 and 47. And - thankfully - he didn't keep asking me for pictures of a non-existent power supply.
Hello,
I would like to ask for advice on determining the output voltage on the secondaries of the attached transformer, to see if it is suitable for use in a future build. I gutted it from one of the many commercial amps I tore apart looking for some parts. So here is a pic and some info I have obtained already.
The transformer has written on the top:
LAHB-85-00
Denki Onyko Co Ltd
CN223149
PT-1183
My measurements with DMM and no mains power:
There is continuity between:
1. 2 thick separate black wires, measured 3.3 ohms.
2. The thin black wire and both the orange wires, measured 0.7 ohms on each blacl/orange combination.
3. The 2 orange wires, measured 1.0 ohms.
4. The 2 blue wires, measured 0.3 ohms.
There is no continuity between :
1. The thin black wire and the blue wires.
2. The orange wires and the blue wires.
Also, I got brave and hooked up the mains to the 2 black thick wires as I thought these were the primaries. I then proceeded to test the thin black wire ( I assumed as ground) in combinations of the blue and orange wires. Below are the results.
Voltage at the mains: 122V, measured at 2 black thick wires
Voltage with the thin black wire / 1st blue wire was 7.8V
Voltage with the thin black wire / 2nd blue wire was 3.4 V
Voltage with the thin black wire / 1st orange wire was 29.3V
Voltage with the thin black wire / 2nd orange wire was 29.3V
I am just flying by the seat of my pants trying to learn something here, and any testing advice would be welcome. Have built a bunch of projects, but transformers were always a given.
Thanks,
Myles
I would like to ask for advice on determining the output voltage on the secondaries of the attached transformer, to see if it is suitable for use in a future build. I gutted it from one of the many commercial amps I tore apart looking for some parts. So here is a pic and some info I have obtained already.
The transformer has written on the top:
LAHB-85-00
Denki Onyko Co Ltd
CN223149
PT-1183
My measurements with DMM and no mains power:
There is continuity between:
1. 2 thick separate black wires, measured 3.3 ohms.
2. The thin black wire and both the orange wires, measured 0.7 ohms on each blacl/orange combination.
3. The 2 orange wires, measured 1.0 ohms.
4. The 2 blue wires, measured 0.3 ohms.
There is no continuity between :
1. The thin black wire and the blue wires.
2. The orange wires and the blue wires.
Also, I got brave and hooked up the mains to the 2 black thick wires as I thought these were the primaries. I then proceeded to test the thin black wire ( I assumed as ground) in combinations of the blue and orange wires. Below are the results.
Voltage at the mains: 122V, measured at 2 black thick wires
Voltage with the thin black wire / 1st blue wire was 7.8V
Voltage with the thin black wire / 2nd blue wire was 3.4 V
Voltage with the thin black wire / 1st orange wire was 29.3V
Voltage with the thin black wire / 2nd orange wire was 29.3V
I am just flying by the seat of my pants trying to learn something here, and any testing advice would be welcome. Have built a bunch of projects, but transformers were always a given.
Thanks,
Myles
I too have repeatedly the problem of determining the power rating of transformers. Regarding the regulation behaviour, this is simple to measure, but how to determine the temperature rise in a transformer?
At https://forum.allaboutcircuits.com/threads/assessing-an-unknown-transformer.38273/
I found this graph, which is a first hint about the power rating of a transformer:
Regarding the regulation, I made measurements on a small transformer (23x51x62 mm core size, 430g):
For estimating the power rating, I used the physics of temperature-dependent resistance of copper. The temperature coefficient for copper is 0.00393 / °C. So I measured first the resistance of the transformer secondary winding at room temperature without load with a Kelvin probe (four-terminal leads going into a 34465A DMM), then the transformer was loaded with various ohmic loads for at least 1.5 hours. Then the resistance of the secondary winding was measured immediately (to avoid cooling). The results look like this:
Not a perfect relationship, but it is possible to estimate the maximum power for a given/wanted/accepted rise in internal temperature.
Inserting the mass of the transformer into the first graph would give a power rating of about 25VA, which, IMHO, would give a too high temperature of about 90°C. But considering the logarithmic scaling of the first figure, the measurements seem to agree roughly.
RDH4, Chapter 5, page 237 gives an approximation of volt amperes based on core area, i use that all the time, and work from there, copper density, i start at 500 circular mils per ampere, then adjust accordingly as winding windows allow, 700 to 300 cm/A is a practice in traffo making...http://www.tubebooks.org/books/rdh4.pdf
The E core I measured above has a core of 21x21 mm, which is equal to 0.827 inch sqared. Using equation 1 on page 235 of the RDH4 chapter 5 (thanks to @TonyTecson for the reference!) a power rating of about 21 VA is calculated. Not too far away from my initial guess of 25 VA.
A very important hint on page 237 top about a temperature correction: The temperatures measured with the (average) resistance of the total winding have to be increased by about 10Kelvin to allow for hot spots in the winding.
Extrapolating the regression of the T-VA figure to 21VA gives a core temperature of 82°C, which seems reasonable.
A very important hint on page 237 top about a temperature correction: The temperatures measured with the (average) resistance of the total winding have to be increased by about 10Kelvin to allow for hot spots in the winding.
Extrapolating the regression of the T-VA figure to 21VA gives a core temperature of 82°C, which seems reasonable.
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Hi, Myles,
for estimating the power rating of your transformer, just measure the area inside of the coil, which is easy to do for one dimension (just the thickness of the metal pile), but a bit tricky for the length inside the coil. If not possible to measure/estimate, assume the same dimension as the thickness, because mostly a 1:1 ratio of both dimensions is used in the tranny design. Then calculate the area (in inches squared), multiply it with 5.58 and you get the sqare root of the VA value. Squaring the latter is then the VA ouput (see equation 1 on page 235 top of the RDH4 chapter 5).
For getting an idea about voltage regulation (from this RDH4 chapter I learned that Americans use a different way of calculating it than the British), you should add ohmic loads at the output and measure both voltage and current (AC). Within the power rating you should get a linear relationship between power and voltage as shown above in my first post.
A safety note is due here: I use an isolating transformer for doing such measurements. It may not only prolong my life substantially, it avoids killing test equipment by inadvertenly connecting a life wire to the ground terminal of the multimeters. So check your secondary windings with a Ohm meter for a possible connection to the primary winding (auto transformers have this!).
Thanks a lot guys for the tutorial on determining the approximate VA of a transformer, great info. I was really just looking for a confirmation on determining which of the wires were the primary and which were the secondary, and whether my testing procedure was correct in determining the voltages.
Should I have tested orange / orange and blue/blue also?
Should I have tested orange / orange and blue/blue also?