quote:
Originally posted by jneutron
1. What is the cross section of the core?
Nixie: ""What does it matter, if both transformers have identical cores?""
Using the cross section of the core, the length of the core, and the number of turns in the primary, it is possible to calculate such things as inductance and zero load current. And, it is possible to see if the primary turns is overstressing the core magnetically, or close to the edge.
quote:
2. How many turns is the primary?
Nixie: ""How should I know? As I said, I never touched the primaries; they are the original ones. And again, they are identical on both transformers.""
You should know by the voltage developed on the secondaries, by the ratio..if you have half the voltage on a 10 turn secondary, for example, then the primary has 20 turns.
When one winds a transformer, one needs to know the primary turn count to calculate how many turns are required on the secondary. How did you do this without that information?
quote:
3. What is the no load current of each tranny?
Nixie: ""I already answered this at least twice. Why reply if you didn't bother to read the thread?""
Instead of being snippy, why don't you answer the question? I have reviewed this thread three times now, and I have yet to see any current expressed in amperes or milliamperes, to state the amount of current that is being drawn by the primary when it is connected directly to the line with no secondary load. If I have missed it three times, please tell me which post number you provided the numerical information at.
You did mention another forum, perhaps you put the numbers up there? a 5% difference between cores is meaningless without a magnitude to go with it.
The no load current will have two components. First is the inductive comp, it will be 90 degrees out of phase with the line, this is the pure inductance part, and will not be responsible for any significant dissipation losses at no load.. Then, a second component will be the "real" part, this is the dissipated loss within the core laminations. It is this part of the current draw that is responsible for the 3 degree difference in core temperatures. It is also most likely that the eddy reaction of the cores is the reason your inductances differ so much, it would appear they have different BH curves.
Are both tranny laminations the same thickness?
I have attempted to assist you, but it is difficult if you do not provide information I ask for.
Cheers, John
Originally posted by jneutron
1. What is the cross section of the core?
Nixie: ""What does it matter, if both transformers have identical cores?""
Using the cross section of the core, the length of the core, and the number of turns in the primary, it is possible to calculate such things as inductance and zero load current. And, it is possible to see if the primary turns is overstressing the core magnetically, or close to the edge.
quote:
2. How many turns is the primary?
Nixie: ""How should I know? As I said, I never touched the primaries; they are the original ones. And again, they are identical on both transformers.""
You should know by the voltage developed on the secondaries, by the ratio..if you have half the voltage on a 10 turn secondary, for example, then the primary has 20 turns.
When one winds a transformer, one needs to know the primary turn count to calculate how many turns are required on the secondary. How did you do this without that information?
quote:
3. What is the no load current of each tranny?
Nixie: ""I already answered this at least twice. Why reply if you didn't bother to read the thread?""
Instead of being snippy, why don't you answer the question? I have reviewed this thread three times now, and I have yet to see any current expressed in amperes or milliamperes, to state the amount of current that is being drawn by the primary when it is connected directly to the line with no secondary load. If I have missed it three times, please tell me which post number you provided the numerical information at.
You did mention another forum, perhaps you put the numbers up there? a 5% difference between cores is meaningless without a magnitude to go with it.
The no load current will have two components. First is the inductive comp, it will be 90 degrees out of phase with the line, this is the pure inductance part, and will not be responsible for any significant dissipation losses at no load.. Then, a second component will be the "real" part, this is the dissipated loss within the core laminations. It is this part of the current draw that is responsible for the 3 degree difference in core temperatures. It is also most likely that the eddy reaction of the cores is the reason your inductances differ so much, it would appear they have different BH curves.
Are both tranny laminations the same thickness?
I have attempted to assist you, but it is difficult if you do not provide information I ask for.
Cheers, John
I don't know how I can determine the phase of the current waveform. What I said is both draw the same RMS current from the mains with open secondaries.
Since I wound these a long time ago (several months at least), I no longer remember the turns per volt.
I also have a second question. I've just finished winding two sets of 600 turns on the bobbin of a 300 VA transformer that was two turns per volt. Of course I can't test by connecting the primary to mains before I assemble the core. However, inductance of one measures 2% more even though I wound them exatly the same way, split bobbin style, 12 layers of 50 turns each. Also, when feeding a high frequency test signal to the primary, I get 5% higher voltage on one of these. I don't get this...the only difference is that one has a bit longer leads sticking out of it.
The only difference is that the one with the slighly higher inductance has the nail polish less dry...
Since I wound these a long time ago (several months at least), I no longer remember the turns per volt.
I also have a second question. I've just finished winding two sets of 600 turns on the bobbin of a 300 VA transformer that was two turns per volt. Of course I can't test by connecting the primary to mains before I assemble the core. However, inductance of one measures 2% more even though I wound them exatly the same way, split bobbin style, 12 layers of 50 turns each. Also, when feeding a high frequency test signal to the primary, I get 5% higher voltage on one of these. I don't get this...the only difference is that one has a bit longer leads sticking out of it.
The only difference is that the one with the slighly higher inductance has the nail polish less dry...
Nixie said:
Do you have a numerical value for the current?
The real and imaginary components can be determined by vector analysis and the use of a scope.
Or, using an isolation transformer and a pair of 1 ohm series resistors, power both primaries. Put the resistors in the low side of the primary feed, so they share a common terminal.., use a meter to measure the difference between the two resistors on the xfmr side. The voltages across each resistor will have the two current parts, but the difference voltage will represent the difference in the xfmr draws that you are concerned with.
Honestly, I'd punt..load each secondary with the max load they will see, and do a heat run again. If the core temps stabilize at a reasonable temperature, just go with it. Watch for stability, as marginal could run away during full load test.
Nixie said:
Memory is the second thing to go...I forgot what the first thing was..
Nixie said:
A 2% higher inductance represents about .99% more turns, or 6 turns. That is, with all else equal.
Is this two different bobbins, or 1 bobbin. Are the secondaries side by side, or one pack wound over the other. Random wind or uniform lay.
Inductive variations can be due to all of these.
If you're gonna do all this winding, maybe you should consider investing in a variac. That way, you could quickly put the E's together loosly, close the core with the I's, and do a quick sanity check with 80 to 90% of the core in place, doing a spot check of the primary without jumping into the deep end of the pool right away..yah, it'll hum a bit, but it'll give you a better indication that all is well.
Cheers, John
1 A on the more buzzing one, and 1.07 A on the other one (with an RMS DMM). And of course, I blew my last fuse for the low-amp connection of the meter...jneutron said:
I don't have an isolation transformer, but I do have a scope. What do I do?
48*C and 45*C with the least-turn primary tap. Is that reasonable?
I don't understand.
One bobbin. Secondaries are wound over the primaries, but these 300 V secondaries are side by side, split bobbin style (under the 300 V secondaries there are heavy gauge 6.5 V ones; the leads for these come off onto one side, so more under one of the high voltage ones). I always use uniform lay, one layer going left the next one right etc.
Inductive variations can be due to all of these.
Thing is, I know the number of turns is exact, since I'm using a winding tool that has a turn counter.
Ah, thanks. Wasn't the buzzing one the hotter?? Definitely confusing.. did buzz go away when compressed?Nixie said:
Nothing with the scope, I don't recommend probing line-hot circuits with scope probes, specially if ground is to be connected to hot.Nixie said:
Nixie said:
For no load, seems good.
Your main concern isn't inductance, or primary no load current, or buzzing. Your main concern is that it doesn't runaway thermally when you use it. By powering it full bore, the temperature should eventually stabilize at some reasonable temperature. If it is not stable, it will continue to climb until it blows up. This because eventually the core dissipation losses will increase as temperature rises.Nixie said:
Nixie said:
Ah. So one wind has a slightly larger inner wind diameter. That explains the difference. That will only give a slightly different parasitic inductance, which should not be a problem for your application.
Cool...I sometimes have problems when the turns go over 20 per layer, as I run out of shoes to take off..Nixie said:
Cheers, John
I fixed the noise; it was apparently due to loose windings.
I mixed two or three types of wood varnish, urethane and some other I had laying around, and diluted them with methanol and acetone. I then poured them in a large coffee can and set the transformers inside. On the lid of the can I had epoxied a nib (piece of a plastic pen's body) to which I connected with a rubber hose my water aspirator for vacuum. The lid lasted about 1 minute under vacuum before imploding, but that appears to have been enough, as after two days of drying on top of my oil-filled radiator, the transformers are both virtually silent.
I mixed two or three types of wood varnish, urethane and some other I had laying around, and diluted them with methanol and acetone. I then poured them in a large coffee can and set the transformers inside. On the lid of the can I had epoxied a nib (piece of a plastic pen's body) to which I connected with a rubber hose my water aspirator for vacuum. The lid lasted about 1 minute under vacuum before imploding, but that appears to have been enough, as after two days of drying on top of my oil-filled radiator, the transformers are both virtually silent.
I can't believe this thread is still going...wow
Is it possible the core material is different in the two transformers??? When you rewound one of the windings, did you re-install new core material??? If so, lets say you used M6, but theold stell was M19 or lower..that would explain the L being different since the permeablities are different..
I would not test any transformer with secondary shorted, this can cause serious damage of winding....The only time you do this is when you control , not limit, the current for leakage inductance testing..
Remember that inductance will vary greatly with this EI stack...
The applied AC voltage will directly vary flux density assuming fixed frequency .... When you alternate stack EI lamination... the reluctance is greatest between the E and I lams....So, the magnetic path will only be in the E laminations initially.... The flux will jump sideways between the E laminations since this is the smallest gap... Then when you get to roughly .53 of Saturation of that material you will reach PEAK inductance, then at that point the flux path will jump from E to I laminations....
Get a variac hooked up to the primary winding..... And a notebook.... make sure all secondaries are open and unloaded..
Put a AC ammeter in SERIES with the primary winding and then put another meter to measure AC voltage across the primary winding, after the ammeter of course....
In increments of 10 Volts write down the coresponding AC current, known as the excitation current....
You can go a bit beyond the operating voltage but not to far ...just enough to see the hump in the inductance curve...since it is power and not audio transformer you will most likely be operating after the peak L....
Now for each pair of numbers you can easily find the inductance...
Divide E/I and to get the inductive reactance, and no the winding capacatance will not be an issue at mains frequency and the DC winding resistance will be negligibly small in this case...
Now divide the inductive reactance by (2*pi*fr) to get L, freq being your mains freq, 50 or 60 HZ.....
You can plot L vs. AC applied voltage to see your inductance curve....
If you knew the turns then you could plot the flux density vs. the L which is most appropriate....
A quick and dirty method to figure turns is to put a known number of turns onto the bobbin... SO you get some tiny enamel coated transformer wire, you can use a small gauge wire since you will not be drawing any current from the wire...instead you will be measureing voltage... You need to slip the wire between the outer wrap of the bobbin and the core...if you can get atleast 10 turns your OK.... BUT do not excite this winding...instead excite the primary winding and use this winding to measure the voltage ratio....and the rest is straight forward...
Chris
Is it possible the core material is different in the two transformers??? When you rewound one of the windings, did you re-install new core material??? If so, lets say you used M6, but theold stell was M19 or lower..that would explain the L being different since the permeablities are different..
I would not test any transformer with secondary shorted, this can cause serious damage of winding....The only time you do this is when you control , not limit, the current for leakage inductance testing..
Remember that inductance will vary greatly with this EI stack...
The applied AC voltage will directly vary flux density assuming fixed frequency .... When you alternate stack EI lamination... the reluctance is greatest between the E and I lams....So, the magnetic path will only be in the E laminations initially.... The flux will jump sideways between the E laminations since this is the smallest gap... Then when you get to roughly .53 of Saturation of that material you will reach PEAK inductance, then at that point the flux path will jump from E to I laminations....
Get a variac hooked up to the primary winding..... And a notebook.... make sure all secondaries are open and unloaded..
Put a AC ammeter in SERIES with the primary winding and then put another meter to measure AC voltage across the primary winding, after the ammeter of course....
In increments of 10 Volts write down the coresponding AC current, known as the excitation current....
You can go a bit beyond the operating voltage but not to far ...just enough to see the hump in the inductance curve...since it is power and not audio transformer you will most likely be operating after the peak L....
Now for each pair of numbers you can easily find the inductance...
Divide E/I and to get the inductive reactance, and no the winding capacatance will not be an issue at mains frequency and the DC winding resistance will be negligibly small in this case...
Now divide the inductive reactance by (2*pi*fr) to get L, freq being your mains freq, 50 or 60 HZ.....
You can plot L vs. AC applied voltage to see your inductance curve....
If you knew the turns then you could plot the flux density vs. the L which is most appropriate....
A quick and dirty method to figure turns is to put a known number of turns onto the bobbin... SO you get some tiny enamel coated transformer wire, you can use a small gauge wire since you will not be drawing any current from the wire...instead you will be measureing voltage... You need to slip the wire between the outer wrap of the bobbin and the core...if you can get atleast 10 turns your OK.... BUT do not excite this winding...instead excite the primary winding and use this winding to measure the voltage ratio....and the rest is straight forward...
Chris
One word of caution...
The mixture you whipped up to varnish the transformer is lethal to the health of the windings...especially the acetone... Even though it is dry now.....The time it spent in that wet mix is not good..
That kind of mix can eat away at the enamel coating of the wire..even if you don't have a short right now... The enamel coating of the wires can be weakened and more prone to breakdown...
Chris
The mixture you whipped up to varnish the transformer is lethal to the health of the windings...especially the acetone... Even though it is dry now.....The time it spent in that wet mix is not good..
That kind of mix can eat away at the enamel coating of the wire..even if you don't have a short right now... The enamel coating of the wires can be weakened and more prone to breakdown...
Chris
That may be a worry, save for two things. First, I have a layer of insulating plastic over each wound layer, so that only enamel between adjacent wires with the mere half volt between them is of concern. Second, in addition to the original enamel, windings were put together using nylon-containing nail polish (also diluted with acetone) over every layer some months ago, which is quite hard and takes a long time to dissolve in acetone. I also dried out the transformers with heating for the first couple of hours, so everything was quite thick very quickly. The acetone is only a fraction of the content and with its low boiling point makes it evaporate first, with alcohol being the main dilutant left behind, and that's safe for the enamel. I could have used shellac which dissolves in alcohol only, but I didn't find a cheap local source.
I also put a 15 kV high frequency transformer using a similar technique, but wax paper instead of plastic for the inter-layer insulator. If it didn't short there, it won't at the low voltages here.
I also put a 15 kV high frequency transformer using a similar technique, but wax paper instead of plastic for the inter-layer insulator. If it didn't short there, it won't at the low voltages here.
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