Hello,
I did put two chokes in series with the same dcr but the first one 500mH and the second one 1000mH and i use them for choke input, put a large capacitor with a big power resistor to draw about 1A.
Use a simple meter to check the AC across each choke. The 500mH gives a 5 volt reading and the 1000mH gives a 7 volt reading. I wonder why?
Should the last one not give 2*5 volts because mH is double? The 1000mH has a lower current rating could it be that it is saturating?
Greetings, eduard
I did put two chokes in series with the same dcr but the first one 500mH and the second one 1000mH and i use them for choke input, put a large capacitor with a big power resistor to draw about 1A.
Use a simple meter to check the AC across each choke. The 500mH gives a 5 volt reading and the 1000mH gives a 7 volt reading. I wonder why?
Should the last one not give 2*5 volts because mH is double? The 1000mH has a lower current rating could it be that it is saturating?
Greetings, eduard
I would expect the 1000mH to read 10 volts if the 500Mh choke reads 5 volts.
The 7 volt reading may mean the two chokes start to have lower inductance with increasing DC current.
Chokes may be rated for AC or possible some inductance with a given DC current.
Also some manufacturers may make a swinging choke for choke input where it may have a large inductance at low current decreasing to come other lower value at full current.
A swinging choke helps lower your minimum supply current.
The 7 volt reading may mean the two chokes start to have lower inductance with increasing DC current.
Chokes may be rated for AC or possible some inductance with a given DC current.
Also some manufacturers may make a swinging choke for choke input where it may have a large inductance at low current decreasing to come other lower value at full current.
A swinging choke helps lower your minimum supply current.
Hello,
Both chokes are the same except the airgap and the 1000mH has a lower current rating. Making the load higher gave a bigger voltage drop at the 544 mH and with the 1000mH the voltage drop got lower so that is a sign it is saturating and acting as a wire with 3,4 ohm dcr.
Will two 500 mH chokes in series give the same drop as one 1000mH if the total dcr is the same?
Greetings, Eduard
Both chokes are the same except the airgap and the 1000mH has a lower current rating. Making the load higher gave a bigger voltage drop at the 544 mH and with the 1000mH the voltage drop got lower so that is a sign it is saturating and acting as a wire with 3,4 ohm dcr.
Will two 500 mH chokes in series give the same drop as one 1000mH if the total dcr is the same?
Greetings, Eduard
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Many thanks for the schematic. Solid inductors: 1H and 0.5H! Your "m" is for milli, not micro?
The voltage should be shared according to the impedance values, thus 5Vac and 10Vac as you expected. At 100Hz, the 0.5H choke has an inductance of 314Ohm, the 1H 628Ohm. Here saturation and core losses can influence the result such that saturation or increased core losses will leave an effectively lower impedance.
In my younger days I designed chokes for test-gear with similar values that could handle slightly less DC current as you use. They were big and heavy. Not something you would find around. Could it be that your "m" is micro (u) and not milli (m)? If it would be the case, your inductance values at 100Hz would be 0.314Ohm and 0.628Ohm. Then, your resistance values would be dominating and, as the inductance goes with the square of number of turns while the resistance with the length of the wire, you would have resistance values in the relation 5 to 7 with the same wire diameter. That could explain the 5V and 7V readings.
The voltage should be shared according to the impedance values, thus 5Vac and 10Vac as you expected. At 100Hz, the 0.5H choke has an inductance of 314Ohm, the 1H 628Ohm. Here saturation and core losses can influence the result such that saturation or increased core losses will leave an effectively lower impedance.
In my younger days I designed chokes for test-gear with similar values that could handle slightly less DC current as you use. They were big and heavy. Not something you would find around. Could it be that your "m" is micro (u) and not milli (m)? If it would be the case, your inductance values at 100Hz would be 0.314Ohm and 0.628Ohm. Then, your resistance values would be dominating and, as the inductance goes with the square of number of turns while the resistance with the length of the wire, you would have resistance values in the relation 5 to 7 with the same wire diameter. That could explain the 5V and 7V readings.
Hello,
No these are BIG chokes so millihenries.
The 500 mH has a 1,25A rating the 1000mH has a 0,7A rating but the German seller told me at lower AC voltages it could take more current but probably not 0,3A more. The choke has a nominal current at a maximum ac voltage of 120 volts 100 hertz. This German seller publishes some figures stating a relative big higher current. I think especially with choke input it can be just a little more.
Greetings, Ed
P.s i will have to getr a current closer to the 0,7 A and see what happens then.
No these are BIG chokes so millihenries.
The 500 mH has a 1,25A rating the 1000mH has a 0,7A rating but the German seller told me at lower AC voltages it could take more current but probably not 0,3A more. The choke has a nominal current at a maximum ac voltage of 120 volts 100 hertz. This German seller publishes some figures stating a relative big higher current. I think especially with choke input it can be just a little more.
Greetings, Ed
P.s i will have to getr a current closer to the 0,7 A and see what happens then.
I have just been looking at some EI-type chokes, looking like transformers, with 1H values and some hundreds of milliamperes rating. That must be what you have.
You have an 1A DC current with an AC current super-posed on top of that 1A DC current. The amplitude of that AC current is decided by the peak voltage at the output of the bridge rectifier and the DC value at the capacitor but divided by the ac impedance of the chokes (314Ohm+628Ohm=942Ohm). The AC current element amplitude should be well below the DC element.
Would you know the DC resistance of your two chokes in series?
You have an 1A DC current with an AC current super-posed on top of that 1A DC current. The amplitude of that AC current is decided by the peak voltage at the output of the bridge rectifier and the DC value at the capacitor but divided by the ac impedance of the chokes (314Ohm+628Ohm=942Ohm). The AC current element amplitude should be well below the DC element.
Would you know the DC resistance of your two chokes in series?
Hi Ed,
I am duly impressed. Swedish 1.35Kg Lundahl HQ filament transformers - the quality is undeniable. The LL2733 is standard 0.4H with the coils in series for which they recommend a DC current up to 1.7A and a with a saturation current of 2.7A.
I understand you bought the chokes from Germans who had customized versions made (by adaption of the airgap) with 0.5H and 1.0H.
My impression is that the flux is proportional to the current and number of windings while the inductance raises with the square of the number of windings. Thus, when you increase the inductance the flux stress on the core is increased less than proportional. In other words, when you double the inductance the saturation current is more than half of what it was before. My guess is your max. recommended operating current values are at least 1A for both, more for the 0.5H version.
I guess your concern is the real value of the customized versions you have bought and the max. current you can apply. There is a chance that Lundahl has marked the transformers with the customized inductance value. If not, you can estimate the value yourself by using a transformer with some 24Vac output and load the secondary with one of the chokes in series with a 4.7Ohm resistor. If you measure the voltage across the 4.7Ohm resistor you can estimate the current. Knowing the current and the AC input voltage you can estimate the impedance at 50Hz. From that you can calculate the inductance.
Perhaps their real inductance values are not 1:2 but more equal as your first measurements indicate. Will that be a problem?
I am duly impressed. Swedish 1.35Kg Lundahl HQ filament transformers - the quality is undeniable. The LL2733 is standard 0.4H with the coils in series for which they recommend a DC current up to 1.7A and a with a saturation current of 2.7A.
I understand you bought the chokes from Germans who had customized versions made (by adaption of the airgap) with 0.5H and 1.0H.
My impression is that the flux is proportional to the current and number of windings while the inductance raises with the square of the number of windings. Thus, when you increase the inductance the flux stress on the core is increased less than proportional. In other words, when you double the inductance the saturation current is more than half of what it was before. My guess is your max. recommended operating current values are at least 1A for both, more for the 0.5H version.
I guess your concern is the real value of the customized versions you have bought and the max. current you can apply. There is a chance that Lundahl has marked the transformers with the customized inductance value. If not, you can estimate the value yourself by using a transformer with some 24Vac output and load the secondary with one of the chokes in series with a 4.7Ohm resistor. If you measure the voltage across the 4.7Ohm resistor you can estimate the current. Knowing the current and the AC input voltage you can estimate the impedance at 50Hz. From that you can calculate the inductance.
Perhaps their real inductance values are not 1:2 but more equal as your first measurements indicate. Will that be a problem?
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Hello,
I did make a kind of test circuit to find out how my future choke will behave with a 1A load presented by my DDDAC.
The mH and current rating i mentionned were indicated on the chokes by the manufacturer so i am pretty sure they are ok.
Friday i will receive a BIG 3Henry 1A choke with a total dcr of 11,2 ohm. The DDDAC uses 7810 regulators in front of Tent shunt supplies. So far i used a LCLC with an output voltage around 13 volts. The second choke is a 544 mH 1,25a and i will leave it where it is. So i need around 16,5 volts at the first cap after the 3 Henry choke.
I always use a small bleeder just in case something goes wrong in the dddac circuit and there will be no load. 3000mH will not need a lot of bleeder current!.
But because of 11,2 ohm i might need quiet a lot of ac voltage.
The 7810 has a maximum input voltage of 35 volts. There is a trick using a big zener to stop going the voltage above let us say 30 volts. But how?
I expect an improvem,ent from raising the mH rating of the input choke.
Greetings, eduard
P.s will post photos of the new test set up once everything is connected. The choke is huge!
I did make a kind of test circuit to find out how my future choke will behave with a 1A load presented by my DDDAC.
The mH and current rating i mentionned were indicated on the chokes by the manufacturer so i am pretty sure they are ok.
Friday i will receive a BIG 3Henry 1A choke with a total dcr of 11,2 ohm. The DDDAC uses 7810 regulators in front of Tent shunt supplies. So far i used a LCLC with an output voltage around 13 volts. The second choke is a 544 mH 1,25a and i will leave it where it is. So i need around 16,5 volts at the first cap after the 3 Henry choke.
I always use a small bleeder just in case something goes wrong in the dddac circuit and there will be no load. 3000mH will not need a lot of bleeder current!.
But because of 11,2 ohm i might need quiet a lot of ac voltage.
The 7810 has a maximum input voltage of 35 volts. There is a trick using a big zener to stop going the voltage above let us say 30 volts. But how?
I expect an improvem,ent from raising the mH rating of the input choke.
Greetings, eduard
P.s will post photos of the new test set up once everything is connected. The choke is huge!
Ed, the inductance will vary with the AC voltage across the choke, as well as with the DC current through the choke, so any comparison or test circuit really needs to apply the same VAC and IDC conditions otherwise there is some doubt.
If the seller doesn't provide both test conditions for the inductance then there is some doubt.
Even if you set up your test circuit and use just one choke and vary the DC load to get a benchmark IDC, you also have to vary the transformer voltage to get the same benchmark VAC across the choke.
But that is the same general test circuit that has been used for chokes: https://dalmura.com.au/static/Choke%20measurement.pdf
If the seller doesn't provide both test conditions for the inductance then there is some doubt.
Even if you set up your test circuit and use just one choke and vary the DC load to get a benchmark IDC, you also have to vary the transformer voltage to get the same benchmark VAC across the choke.
But that is the same general test circuit that has been used for chokes: https://dalmura.com.au/static/Choke%20measurement.pdf
Hello,
I only know it is using a 7810 which serves as a kind of pre regulation and stopping the voltage from being to high for the Tent shunt supply that comes after the 7810.
I bought as as a compl;eted circuit board but i guess it will be something like this.
Because the choke is 3000mH and 11,2 ohm and the current is around 1A and i need about 16,5 volts at the first cap i am a bit afraid that during start up the load will be to small and the voltage will rise above the 35 volt input limit of the 7810 Maybe not because the 11,2 and a10000microfarad cap after the choke will slow down the charging? If not i will put a big 5 watt 30 volt zener acros the first cap.
Greetings, Eduard
> the choke is 3000mH and 11,2 ohm and the current is around 1A and i need about 16,5 volts at the first cap
Simplify.
You want 1A DC at 16V.
1A in the 11 Ohm choke drops 11 Volts.
Your choke-loss is nearly as big as your useful power. That seems a bad plan.
Also 11 Watts of heat in a reasonable size choke is a lot. (Maybe OK in two chokes.)
How did you come up with several Henries (and a dozen Ohms)? A quick sim suggests <0.1H and 1 Ohm is a better fit.
BTW: you don't say what "Tent" but the one I found says 100mA (0.1A) load current and 140mA feed current. Are you running seven of these?
They want the input ripple <1V. 0.1H and 10,000uFd at 1 Amp will make 0.12V ripple. Your '7810 will reduce this hundreds of times, 0.001V. Then the Tent reduces it more. I would think a simple rectifier-capacitor, then '7810, would be as clean as anybody could want.
Simplify.
You want 1A DC at 16V.
1A in the 11 Ohm choke drops 11 Volts.
Your choke-loss is nearly as big as your useful power. That seems a bad plan.
Also 11 Watts of heat in a reasonable size choke is a lot. (Maybe OK in two chokes.)
How did you come up with several Henries (and a dozen Ohms)? A quick sim suggests <0.1H and 1 Ohm is a better fit.
BTW: you don't say what "Tent" but the one I found says 100mA (0.1A) load current and 140mA feed current. Are you running seven of these?
They want the input ripple <1V. 0.1H and 10,000uFd at 1 Amp will make 0.12V ripple. Your '7810 will reduce this hundreds of times, 0.001V. Then the Tent reduces it more. I would think a simple rectifier-capacitor, then '7810, would be as clean as anybody could want.
Hello ,
So far i have been using a 1000mH choke but i wanna try a bigger one.
Because it is used in choke input it is not just 11 volt votage drop but much more. I will know tomorrow because i just received the choke.
Greetings, Ed
P.s there have been people who did skip the 7810 and just used a choke input and they say it sounds better. But i first wanna try a bigger choke.
So far i have been using a 1000mH choke but i wanna try a bigger one.
Because it is used in choke input it is not just 11 volt votage drop but much more. I will know tomorrow because i just received the choke.
Greetings, Ed
P.s there have been people who did skip the 7810 and just used a choke input and they say it sounds better. But i first wanna try a bigger choke.
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