hi all! 😀
maybe a lot of people uses the Promitheus circuit to limit the inrush current in the transformer when they power up their ampli, and i'd like to do it too, but i got some problems using the values he gives: the resistors blow up!
so let's try to do some calculations...
i have an 800VA transformer, 2x25V outputs, 2x 20.000uF, 220V line, so max current is 3,5A and to limit it now i'll use 80 ohm resistor, but how many watts?!
and not less important...the RC doubles, so maybe I have to change the delay, but which are the components that determine the delay??ok, the 2 capacitors of 470uF but which resistor?
please, if someone can give me some more specific formulas to fit this circuit i'll be very happy because i'm stopped with my diy amp!!!
maybe a lot of people uses the Promitheus circuit to limit the inrush current in the transformer when they power up their ampli, and i'd like to do it too, but i got some problems using the values he gives: the resistors blow up!
so let's try to do some calculations...
i have an 800VA transformer, 2x25V outputs, 2x 20.000uF, 220V line, so max current is 3,5A and to limit it now i'll use 80 ohm resistor, but how many watts?!
and not less important...the RC doubles, so maybe I have to change the delay, but which are the components that determine the delay??ok, the 2 capacitors of 470uF but which resistor?
please, if someone can give me some more specific formulas to fit this circuit i'll be very happy because i'm stopped with my diy amp!!!
What are you using now?
The resistor will initially dissipate 3.5 A x 240 V = 840W. Obviously you aren't going to put a kilowatt resistor in there.
How much power handling you need depends on the delay before they are removed from the circuit and the resistors' thermal characteristics. You should probably be in the area of 50 W - so three 200R/15+W in parallel should be OK - a little higher inrush but not terrible. Higher power ratings wouldn't hurt.
The resistor will initially dissipate 3.5 A x 240 V = 840W. Obviously you aren't going to put a kilowatt resistor in there.
How much power handling you need depends on the delay before they are removed from the circuit and the resistors' thermal characteristics. You should probably be in the area of 50 W - so three 200R/15+W in parallel should be OK - a little higher inrush but not terrible. Higher power ratings wouldn't hurt.
sure!my calculation was the same, because he uses 4 series resistors 10ohms,5w, so 40 ohm 20 watts for 1200watts initial power...my intention was to use 4 series resistors 22ohm,5 watts in series, not parallel to have the same power dissipation.
the transformer ratio is 9 so the resistor would be a (80/n^2)=1ohm at the secondary of the transformer, giving an rc of 20ms; the delay is about 0,5 sec(measured listening to the relay...)now, so the transient will be much more than fully completed!!!but i can't understand what's wrong with the first circuit, why the resistors blow up...😕
the transformer ratio is 9 so the resistor would be a (80/n^2)=1ohm at the secondary of the transformer, giving an rc of 20ms; the delay is about 0,5 sec(measured listening to the relay...)now, so the transient will be much more than fully completed!!!but i can't understand what's wrong with the first circuit, why the resistors blow up...😕
I don't know the exact circuit you are using, but perhaps a wiring error. If the resistors are across the mains they will blow up.
Verify that the resistors are in series with the mains line and that the relay closes across them when the delay trips.
Verify that the resistors are in series with the mains line and that the relay closes across them when the delay trips.
this is the circuit:
http://mitglied.lycos.de/Promitheus...for_toroids.htm
do you know the formula to calculate the delay?and my rc calculation is right or i'm doing someting wrong?😕
http://mitglied.lycos.de/Promitheus...for_toroids.htm
do you know the formula to calculate the delay?and my rc calculation is right or i'm doing someting wrong?😕
The delay needed is about 300-500ms or so, only for the toroid to get magnetized. I use 100 ohms /4-5 watts at 300 or 600 ms and this works fine, has done so for 20 years.morpheus82 said:
We have talked pretty much about this subject.
http://www.diyaudio.com/forums/sear...d=531635&sortby=lastpost&sortorder=descending
thanx a lot!but what did you change to obtain the delay you need?the 470uf capacitors?or a resistor?
nice, and probably works well...but i've done already my boards and don't want to change now...they must work!!😀
The Elektor solution is rather complex if you want to change it because you have capacitive voltage division. One of the odd things are higher voltage if the smoothing is made less!
One way to find out is to simulate it. Use my schematics and change it for your needs. The relay will activate at 15-16 V DC so measure the coil voltage and observe when the coil voltage is over 15 VDC.
Use the freeware LTSpice from Linear Tech.
http://www.linear.com/designtools/softwareRegistration.jsp
One way to find out is to simulate it. Use my schematics and change it for your needs. The relay will activate at 15-16 V DC so measure the coil voltage and observe when the coil voltage is over 15 VDC.
Use the freeware LTSpice from Linear Tech.
http://www.linear.com/designtools/softwareRegistration.jsp
i was thinking about the capacitor's voltage divider problem...many thanx, i'll simulate asap!(i've got the pspice...😀 )
sometimes pspice is useful...
i found you can change the capacitors without any poblem!! 😀
but the final voltage strongly depends on the relay coil resistance...isn't it strange??😕
i found you can change the capacitors without any poblem!! 😀
but the final voltage strongly depends on the relay coil resistance...isn't it strange??😕
You should use the actual values of the relay coil but it isn't necessary to have the inductance. When I tested it LTSpice went on it's knees and the result was pretty good using only a resistance.
This kind of circuit isn't easy to understand at the first sight so simulation is very giving when you do the finetuning.
Mike, I'm very flattered
Can you do it better 
My design idea was to use very simple parts and to get a very fast reset time.
This kind of circuit isn't easy to understand at the first sight so simulation is very giving when you do the finetuning.
Mike, I'm very flattered
Can you do it better My design idea was to use very simple parts and to get a very fast reset time.
The first link you gave is not a circuit for a toroid transformer and the second one is the one we are discussing more or less.
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