I have acquired a box of chokes transformers. I would like some help identifying some of them. Many are Thordarson, Stancor, Triad. Those I can find literature for.
One of particular interest id a Sangamo Push-Pull Output Transformer, Type H-171. I have not found any references for Sangamo so far. Can anyone ID?
Also, I have a few transformers that are unlabeled. I can determine the ratio but how do you determine any other specs? In addition to those, I have a friend with a box full of trannies that were pulled off of old amps and organs. Similar situation,
Once ID'd, what is the view on using "vintage iron"? Many of these are NOS, still in boxes. What should be done to qualify them to be safe to use?
One of particular interest id a Sangamo Push-Pull Output Transformer, Type H-171. I have not found any references for Sangamo so far. Can anyone ID?
Also, I have a few transformers that are unlabeled. I can determine the ratio but how do you determine any other specs? In addition to those, I have a friend with a box full of trannies that were pulled off of old amps and organs. Similar situation,
Once ID'd, what is the view on using "vintage iron"? Many of these are NOS, still in boxes. What should be done to qualify them to be safe to use?
Warning, Potentially lethal High Voltages may be produced with some transformers, and line voltage is lethal.
How familiar are you with electrical/electronic theory? Power safety?
The inductors will be the easy part. Measure them on an inductance bridge.
The transformers will be a bit more difficult. If you can identify the windings by color code, you can make an educated guess, given you know enough about electrical theory and searching for old transformer manuals.
Those can be tested by applying a variac with in line fuse to the primary and measuring the outputs. That said there are probably thousands of winding ratios that you must make educated guesses at.
Once you have identified them as power transformers you probably should test them for insulation integrity with a HyPot test set. 2500V with no more than 2mA leakage current would be a good starting point. Once you are sure they are safe, I'l hook line voltage up to the primary and let them run with no load for a couple of hours to make sure they don't get hot. They will get slightly warm. Be sure to tape off the secondary leads at this point to avoid electrical hazards.
Output transformers can sometimes be identified by the wiring color codes as well.
You can measure the turns ratio with a signal generator and oscilloscope.
What is left will require testing with a signal generator and oscilloscope.
There are several threads about transformers that I suggest doing a lot of digging with the search engine.
I got a bunch of transformers from a TV shop that shut down. About half were shorted internally and dangerous.
How familiar are you with electrical/electronic theory? Power safety?
The inductors will be the easy part. Measure them on an inductance bridge.
The transformers will be a bit more difficult. If you can identify the windings by color code, you can make an educated guess, given you know enough about electrical theory and searching for old transformer manuals.
Those can be tested by applying a variac with in line fuse to the primary and measuring the outputs. That said there are probably thousands of winding ratios that you must make educated guesses at.
Once you have identified them as power transformers you probably should test them for insulation integrity with a HyPot test set. 2500V with no more than 2mA leakage current would be a good starting point. Once you are sure they are safe, I'l hook line voltage up to the primary and let them run with no load for a couple of hours to make sure they don't get hot. They will get slightly warm. Be sure to tape off the secondary leads at this point to avoid electrical hazards.
Output transformers can sometimes be identified by the wiring color codes as well.
You can measure the turns ratio with a signal generator and oscilloscope.
What is left will require testing with a signal generator and oscilloscope.
There are several threads about transformers that I suggest doing a lot of digging with the search engine.
I got a bunch of transformers from a TV shop that shut down. About half were shorted internally and dangerous.
Is there a help page for the specific search tool for this forum? I can find many threads on transformers but I have not been very successful with specific multi term searches.
I think a HiPot test is probably a bit out of reach, at the moment. I do have a couple of GR megohm bridges that I use for insulation testing on AC motors. They only have a max voltage of 550V, however.
I think a HiPot test is probably a bit out of reach, at the moment. I do have a couple of GR megohm bridges that I use for insulation testing on AC motors. They only have a max voltage of 550V, however.
The top toolbar has a search function. Also if you try to start a thread about a subject like "Transfomrer Identification" it will prompt you with a screen of similar threads you can look at.
Transformer codes
Transformer wiring
etc.
Someone pointed to a link to two jpg files called XFMR1.jpg and XFMR2.jpg that dealt with testing transformers, but I can't find the thread.
550V is a bit low for safety testing the isolation between primary and secondary, etc. These transformers can develop peak output voltages in the 700-1000V range and a leakage path to primary or core can be dangerous.
Transformer codes
Transformer wiring
etc.
Someone pointed to a link to two jpg files called XFMR1.jpg and XFMR2.jpg that dealt with testing transformers, but I can't find the thread.
550V is a bit low for safety testing the isolation between primary and secondary, etc. These transformers can develop peak output voltages in the 700-1000V range and a leakage path to primary or core can be dangerous.
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Only applies to US transformers, and only sometimes.
TRANSFORMER COLOR CODE (RMA STANDARD)
RETMA transformer lead color codes
TRANSFORMER COLOR CODE (RMA STANDARD)
RETMA transformer lead color codes
The safest way to test for turns ratio and absolute turns is to use a ten turn search coil. Look to see if there is enough space between core and coil, if you can see daylight for perhaps half the width of the coil, you are in. Take some thin insulated wire, preferably coil winding magnet wire and loop ten turns around the coil. Tape them on one side, hook an accurate ac volt meter up , apply a variac to the highest DCR winding and run the voltage up in the search coil to 0.100 volts. Measure all other windings and assume a couple of additional turns for the highest DCR winding and you have your absolute turns and turns ratio.
You can also do this with just one full turn of wire, if that is all the space you have, but it is not as accurate.
Bud
You can also do this with just one full turn of wire, if that is all the space you have, but it is not as accurate.
Bud
I use a variac and a volt-meter to determine OPT ratios and power transformers. 10 V is convient for OPTs, 12V for power trafos.
dave
I appreciate the safety comments. I work around industrial type electrical gear, on a regular basis. I spent five years in a research lab working with high voltage RF power supplies, 5-30kW. (They were pretty cool. Big water cooled power tubes, glass capacitors). That has been a while though. Tube electronics is a new distraction for me, however, at least from a DIY perspective. I have been a lurker here for a while. I have been slowly getting in to this hobby. I have read through the (sticky) safety thread a couple times.
I have a pair Edcor SE transformers coming, should be here tomorrow. That will be my first real project. A small little amp for the shop or office. I just seem to accumulate lots of cast off old equipment and components. Looking to see what use I can make of them.
I can handle the ratio determination (but I do appreciate the comments posted). My interest/question is how do you get a handle on power handling capacity both for the power transformers and output transformers.
I have a pair Edcor SE transformers coming, should be here tomorrow. That will be my first real project. A small little amp for the shop or office. I just seem to accumulate lots of cast off old equipment and components. Looking to see what use I can make of them.
I can handle the ratio determination (but I do appreciate the comments posted). My interest/question is how do you get a handle on power handling capacity both for the power transformers and output transformers.
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The limits to power handling are two. One is the inherent dielectric strength of the transformer in question. If it can pass a 2500 volt stress for 1 minute it should be safe as houses.... which should provide at least a moment of disquiet, but essentially safe. The other is heat. Should you run a transformer beyond it's insulation system maximum temperature, every ten degrees beyond that limit will shorten the life of the insulation by 50%. A short term balisitic foray past that point will not be of appreciable duress unless it exceeds that point by 40C, for more than a few minutes.
To forsee a particular transformers power rating you need the winding DCR at 20 C and the watts per pound, lost in the core of the particular type, found in your transformer times the pounds of core. You also need a thermal model that will provide you with s reasonably accurate model of total temperature, from the above information. I have these documents, but it will take quite a while to put them into an electronic format
This is a lot of information needed to accurately predict the power limits. An alternative, if you have a thermocouple style attachment for your multimeter, is to measure temperature,as you incrementally load the transformer secondary. This is very inaccurate.
The third form is to measure the temperature rise by the change in DC resistance in the wire of the coil. Loading a transformer for two hours will provide you with 80% of the total temperature that the device will achieve after 8 hours, which is considered the heat soak point. If you also have a thermocouple stuck on the coil, at the junction of core and coil, just inside the window, you can watch for what looks like a thermal run away condition before it stresses the insulation and thereby monitor your approach to a two hour test point by change in DCR. Transformers have thermal ballistics so you have some time to do these measurements.
This type of test is an absolute determinant of thermal rise and is used by all safety agencies, so you can count on it's accuracy. You should be able to find documentation on how to perform the tests on line, but if not I can probably provide enough documentation so you can use this format. I just can't imagine it isn't already available. The difficulty with this type of test is how much time you will use up in incremental load heat runs.
As before, there really is nothing easy about transformers. I can and will provide a document that provides a general VA loading for a particular core size, this will provide the least possible accuracy but will get you into the ballpark.
Bud
To forsee a particular transformers power rating you need the winding DCR at 20 C and the watts per pound, lost in the core of the particular type, found in your transformer times the pounds of core. You also need a thermal model that will provide you with s reasonably accurate model of total temperature, from the above information. I have these documents, but it will take quite a while to put them into an electronic format
This is a lot of information needed to accurately predict the power limits. An alternative, if you have a thermocouple style attachment for your multimeter, is to measure temperature,as you incrementally load the transformer secondary. This is very inaccurate.
The third form is to measure the temperature rise by the change in DC resistance in the wire of the coil. Loading a transformer for two hours will provide you with 80% of the total temperature that the device will achieve after 8 hours, which is considered the heat soak point. If you also have a thermocouple stuck on the coil, at the junction of core and coil, just inside the window, you can watch for what looks like a thermal run away condition before it stresses the insulation and thereby monitor your approach to a two hour test point by change in DCR. Transformers have thermal ballistics so you have some time to do these measurements.
This type of test is an absolute determinant of thermal rise and is used by all safety agencies, so you can count on it's accuracy. You should be able to find documentation on how to perform the tests on line, but if not I can probably provide enough documentation so you can use this format. I just can't imagine it isn't already available. The difficulty with this type of test is how much time you will use up in incremental load heat runs.
As before, there really is nothing easy about transformers. I can and will provide a document that provides a general VA loading for a particular core size, this will provide the least possible accuracy but will get you into the ballpark.
Bud
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