OK! I still think there must be more distance to small signal voltages ...
IEC60950 calculator: WWW.CREEPAGE.COM Welcome!
The resulting values are minimum values interpolated.
IMHO: DIY PCB's should/could deliver higher safety as industrial minimum as most of us do not have the testing equipment to check the safety...
BR, Toni
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I'm not really sure if this is the right place for this question, but I've finally got to a point where I can boot the system, but I'm not sure I've got the inrush resistor right. I had tried a 230ohm 20w resistor for it, but it keeps blowing a 4A slow blow fuse as soon as the inrush cycle completes.
I'm not sure how to calculate the inrush resistor size to be honest. I thought I wanted to limit the current as much as possible, but now I realise that isn't right either. Please could someone help me to understand if I want a smaller value and higher wattage resistor or longer inrush cycle.
I'm using the compact supply with 20000uF per rail. I'm also out of fuses now, so will have to order some more!
I'm not sure how to calculate the inrush resistor size to be honest. I thought I wanted to limit the current as much as possible, but now I realise that isn't right either. Please could someone help me to understand if I want a smaller value and higher wattage resistor or longer inrush cycle.
I'm using the compact supply with 20000uF per rail. I'm also out of fuses now, so will have to order some more!
Hi Andrew, thanks for the reply. I'm using the standard two relay design PCB that is published in the thread. I'm using a version that has been built by other people so can be pretty sure that the PCB is correct.
When the system is powered up it puts the inrush resistor in series with the transformer, and when the inrush cycle is complete it switches in another relay that short circuits the inrush resistor and then turns off the inrush resistor altogether.
I have a 700VA transformer that feeds the supply boards.
I am using the standard compact supply board that is basically just a bridge with 20000uf of capacitance per rail. Bleed resistors are >5Kohm per rail.
When the system is powered up it puts the inrush resistor in series with the transformer, and when the inrush cycle is complete it switches in another relay that short circuits the inrush resistor and then turns off the inrush resistor altogether.
I have a 700VA transformer that feeds the supply boards.
I am using the standard compact supply board that is basically just a bridge with 20000uf of capacitance per rail. Bleed resistors are >5Kohm per rail.
It should be said, I have checked the function of the inrush with no supply board connected, and everything works as expected: inrush resistor is in circuit for a few seconds, then turns off and the mains is directly connected.
With the supply board connected, the fuse blows pretty much as the inrush switches out.
With the supply board connected, the fuse blows pretty much as the inrush switches out.
Yes, the 15-30 ohm resistance sounds right. But the proper wattage rating has to do with how well the resistor handles transient energy or pulse load for its type. I don't have a direct answer as I usually use NTC thermistor instead of fixed resistors, often several of them in series for larger VA transfos and larger cap banks.
Hi Daavelovesvinyl,
If the relays, transformer and inrush resistor are connected correctly altogether, it looks like you've got some problem with your transformer.
What I would suggest - create a test setup. Remove all the relays circuitry for the time being. Connect your transformer, inrush resistor (I'm using 47R/50W), power switch and the fuse in series. Connect the other switch in parallel with the resistor. That's it.
Now - switch the power on with the resistor switch being off. Inrush mode is on. if everything is fine - close the other switch (short the inrush resistor). Now PSU is running in normal mode - full power. If it blows your fuse - something is wrong.
Disconnect the PSU board at all - try the transformer standalone. And so on.
If the relays, transformer and inrush resistor are connected correctly altogether, it looks like you've got some problem with your transformer.
What I would suggest - create a test setup. Remove all the relays circuitry for the time being. Connect your transformer, inrush resistor (I'm using 47R/50W), power switch and the fuse in series. Connect the other switch in parallel with the resistor. That's it.
Now - switch the power on with the resistor switch being off. Inrush mode is on. if everything is fine - close the other switch (short the inrush resistor). Now PSU is running in normal mode - full power. If it blows your fuse - something is wrong.
Disconnect the PSU board at all - try the transformer standalone. And so on.
15 - 30 ohm resistor is also fine. I believe, the problem is not in your resistor.
I simulated it, may be a bit overly simplified, but it should give a valid idea. Assuming the bleeding resistors are the only load, the DC rail voltage should be able to reach 42V at 1.2S mark.
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Perhaps not so quickly. I mean, the simulation shows even with a 230-ohm inrush limiting resistor, the DC rail should be far greater than 10V as you measured after a few seconds. Something is not quite right.
Is your transformer connected to the supply correctly?
Yes I believe so, as long as the GOSS screen should be earthed, that is the only thing I am not sure about. It measures 76V across the 36-0-36 secondaries when checked.
Did I send you the supply or is it your own?
Yes, it is from the kit. It is a compact supply board.
It actually runs fine with just the relays and transformer in play. It's only when adding the supply that the issue occurs.
I'll take out the supply board and have a good look over it at the weekend. ensure everything is installed correctly / check voltages at various points on the board and then reply again.
Yes I believe so, as long as the GOSS screen should be earthed, that is the only thing I am not sure about. It measures 76V across the 36-0-36 secondaries when checked.
Did I send you the supply or is it your own?
Yes, it is from the kit. It is a compact supply board.
It actually runs fine with just the relays and transformer in play. It's only when adding the supply that the issue occurs.
I'll take out the supply board and have a good look over it at the weekend. ensure everything is installed correctly / check voltages at various points on the board and then reply again.