SST01 problems

[peranders]

Stefan, could describe how much is working? Do you get OK function when you apply 24 v DC?

[turner]

Hi,

ok, here are my self-inflicted problems with the softstart circuit:

- I used 470R resistors instead of 470K for R3-5 and R11
- when I first attached the pcb to 230V, the resistors catched almost fire
- I replaced the resistors with the right ones and also replaced the DZ1 and all transistors because they could have been damaged

When I apply 230V on X1 and activate the switch on X3, K1 switches but K2 does not.

When I apply 24V DC across DZ1 or across Neutral in and R9 then both K1 and K2 switches.

I have 0,6V across base and emitter of all three transistors.

So where is the problem? What else could be damaged because I used the wrong resistors at the beginning?

so long
Stefan

[peranders]

Do you get a proper delay when you use DC?

What type of relays do you use? Coil resistance?

What voltage do you have when both relays are activated and you use 230 VAC? Is it more than 20 volts?

It may be the case that the relay coils are a bit thirsty and C3 have to be adjusted. Higher value means in fact lower voltage!

[turner]

Hi,

when I apply 24V DC, the second relay switches with a delay of a few ms, i did not measure the time.

I use finder 40.52 relays for 24V from www.reichelt.de

I have 0,2V across DZ1 when the switch is off and 24,7V when the switch is on and K1 is aktivated.

Across D4 are 0V in both cases, switch on or off.

so long
Stefan

[peranders]

You should have a delay even if you use 24 VDC. Have you checked the D3 and R11? Not 470 ohms?

If D4/K2 has zero voltss you must check the transistors feeding that relay. Can you measure the voltages around T1 and T2? Base emitter voltages = 0.6-0.75 volts?

[turner]

R11 is 470K - definitly.

What is about D3? What can I check here? Is it possible that D3 is damaged?

0,53V across base emitter of T2 and 0,59 on T1 and 0,52 on T3.

How long should the delay be?

[peranders]

How much voltage do you have across C4, C5?

The delay should be 300 or 600 ms with 1 uF or 2 uF (C4, C5).

What type of transistors do you use? Are you aware of different pinning for different types?

[turner]

Hi Per,

I have 12V across C4/C5

Yes, I am aware of different transistor types. I use the BC550C type like you recommend in the layout.

Some delay between K1 and K2 is still there, when I apply 24V across DZ1 but it is hard to tell whether it is 300 or 600ms.

Stefan

[peranders]

If you can hear two distinct "clicks" from the relays, then the delay is sufficient.

It's a bit little though with only 12 volts across C4, C5. How much do you have over C3? R10 is 10k?

R12, R13 correct values, 22k and 2k2?

[turner]

Hi Per,

almost a year passed by since my last post, that must be a record!

Sorry, but I had a few other project with higher priority in the meantime, for example my second daughter ... 

Unfortunately, my softstart circuit still does not work. I measured again and I think I can imagine where the problem is. I have round about 30V AC between R9 and Neutral, but only 15,6V DC across DZ1. I wonder, why K1 is even switching? The specs of this kind of relays require between 17,5 and 36 Volts to work. Across D4 there are only 12V, so it is clear that K2 is not switching.

The question is: why do I have only 15,6V after B1 rectifying the voltage? How can I increase the AV Voltage before B1? I think I should have at least 40V AC to get 20V DC after B1. I desoldered C1 (220nF) to see what happens, but the voltage stayed the same.

Do you have an idea?

so long
Turner

[turner]

Hi Per,

I added another capacitor with 470nF parallel to C1 and C2, now it works. K1 and after a short delay K2 are switching. Voltage across DZ1 is now 18,5V and within the specification of the relays.

But: all the resistors from R3 to R9 get really hot. I wonder how long they will last when the unit is always on. Is this a normal condition?   

so long
Turner

[peranders]

Through R6-R9 you should have the current of two relays plus some more. They should not be hot but under 60 deg C (140F)is not "hot". If you test the circuit with 30 VDC, then you can see if everything is working alright. Notice also that it's hard to measure only with a DVM because you don't have pure DC nore pure sinus AC.

How much resistance does your relay coils have?

[turner]

Hi Per,

Ri of the relay coils is 900 ohm. I'm thinking of replacing R6-R9 with a single 480 ohm 5W resistor. This one should not have any problems with getting to hot. The circuit works properly, when I close the switch, first K1 and after a few ms K2 closes. I think this is what the circuit is supposed to do. I just worried about the heat on the resistors ...

so long
Turner

[peranders]

The reason I have four resistors in series is because of better transient capability but if you take a wirewound resistor it will be equally good. The delay should be 300 or 600 ms. You should notice a clear delay.

[turner]

Hi Per.

I changed R6-R9 with a 470 ohm 5Watt wire-wound resistor. It works well, but even this 5W resistor gets so hot, you can hardly touch it after a few minutes. Is this normal? I wonder what will happen after a couple of hours??? I tested the circuit without load on the mains output, could this be the reason? If the DC Voltage would be higher than 18V, could this probably reduce the heat on R6-R9 and how can I increase the DC voltage?

The resistor is quite big and with the extra capacitor parallel to C1, C2 the pcb looks quite funny now ...

so long
Turner