Power Supply Soft Start Board (V3)

[AndrewT]

Can you measure the voltage across the Zener?
But be VERY CAREFUL.
This is direct to Mains circuit, which is normally banned from this Forum.

 

[AndrewT]

post46, C9
Where is C9? I can see C1, 2, & 3

 

[Liliya]

Yes, the voltage across the zener is 4.72V DC(another zener have been tried)

E.Stillingen

 

[AndrewT]

If this was not direct to mains, I would give advice on taking more measurements.

But, I fear for your LIFE.

I duck out and let the Forum answer to the consequences.

 

[Liliya]

I always measure main voltage with "one hand in my pocket", actually both.
C2 (I called it C9) =220nF not 1uF as in the schematic. I cant see that this is the troublemaker. The value only influence on how quick the relay act. But it is from the "end" of resistor 220 ohm and on the other side of 1 Mohm/ble /220nF that the voltage drop so much that the diodebridge are not able to feed the zener with a proper voltage.

E. Stillingen

 

[JojoD818]

What is the value of your C2? And what is your mains voltage?

 

[Liliya]

C2=220 nF. Main voltage(measured 240 V.

E. Stillingen

 

[JojoD818]

I would suggest you increase C2 to around 1uf to ensure that your relay contacts will close.

 

[AndrewT]

That's quite high.
1uF has a reactance @ 50Hz of ~3180ohms.

The capacitance should be the mains reactance. Resistances here would heat and probably overheat if the capacitance is too high.

With 240Vac that allows ~ 75mAac.

 

[Liliya]

Problem solved. I put a 220 nF in parallell with C2(220nF). Total C2 is now 440 nF.

Eivind Stillingen

 

[BigE]

I have adjusted the formula in the V2 thread to calculate the inrush current limit as:

I = Vp^2 / ( Vs * R/4 ) where R is the value of one of the current limiting resistors.

This allows you to choose R to set I. Given the relay is 10A max, how does one choose R?

Thanks!

 

[AndrewT]

Is the relay the bypass across the current limiting resistors?

If so, I have explained more than twice that this bypassing relay does not need a high breaking capacity.
It never has to break any current.

 

[AndrewT]

I = Vp^2 / ( Vs * R/4 )

what is Vs?
Vp is the peak primary voltage. (Vpk)
I is the peak starting current. (Ipk)
Where is the primary and mains wiring resistance? It too limits the peak starting current.

 

[BigE]

Vs = V secondary

The primary and mains wiring was not present in the calculation of the V2 thread. This will overestimate Ipk.

 

[BigE]

Thanks for reiterating that the relay will not arc and fuse closed.

If that is the case, then I do not understand the need to change the value of the current limiting resistor bank from it's original 45 ohms.

 

[PKI]

Ok, it is out of stock again :-( Any estimates on availability, please?

 

[AndrewT]

Vs = V secondary

The primary and mains wiring was not present in the calculation of the V2 thread. This will overestimate Ipk.

Vs = Vsecondary does not make sense.

The current is predicted using a voltage and a resistance.
I=V/R

 

[BigE]

From the V2 thread:

The formula is based on the equation of turns ratio Vs / Vp = Ns / Np = Ip / Is. The primary current is derived from the desired current on the secondary transformed by the turns ratio then ohms law R = V / I. This assumes that the transformer is 100% efficient. In real life, the loss is very small and can be ignored.

 

[BobEllis]

BigE, that's the formula for determining the steady state current draw, not the peak inrush current. For peak inrush, use AndrewT's equation.

 

[vintess]

CL-60 Needed with V3 Soft Start Board?

Thank you to all who have contributed to the Soft-start board project and to those that have posted their finished products/questions. This forum is a tremendous help to me, as I have never quite grasped electronics! The pic's were/are very helpful to me. As already mentioned, the C-3 polarity was in question (at least to me) and was subsequently solved by Toecutter's post/pic. Thanks Toecutter!

I would assume that there is no need for a CL-60 as shown in the original Nelson Pass PSU schematic? Or, is it still needed? I do understand, as previously posted/answered, that there is still a need for the .033uf, x1 rated cap.

Now it is on to the next sub-project, the speaker protection board...

Again, many thanks to the diyAudio team/Toecutter for developing such awesome boards for the DIY audio community...