Power-On Time Delay Circuit

[LinuksGuru]

Hi!

Anyone has damn-simple power-on time delay circuit, for 600-800V and 35 - 60 sec wait time?

I could use RC + zenner + photo-triac + thyristor, but unfortunately, it will not work with "normal" components. With U(C) = U(dc in)*(1-EXP(-t/RC)), U(dc in) = 600V, t=35 sec, R = 150k, 200V zenner diode, C needs to be as much 600uF (600uF/300V cap is simply put too big for so simple purpose). R could not be increased much more otherwise photo-triac will not fire up, or current will be too small for zenner diode.

Schematic should be public domain material.

Thanks in advance for any suggestions.

 

[boywonder]

I have 2 schematics that I've found while doing a search here, this is the first one. I've built this and it works fine. Uses an amperite time delay relay and an additional single pole relay. You could also use a SS time delay relay instead of the amperite. One nice thing about this design is that is takes the amperite out of the circuit after the delay, allowing it to cool off for proper delay on the next power cycle.

These are both delaying the mains voltage to the power transformer (not 600-800V)

 

[boywonder]

Here is the other schem, which I have not tried:

 

[Zero Cool]

I found a circuit in glass audio that uses a 555 timer, very very simple and low parts count and it works great!...wish i could find that article again now...

 

[Fenris]

I usually use an op-amp as a comparator. It uses a fixed voltage and a R-C and trips a transistor/relay when the R-C reaches that fixed voltage. It's powered from the heater supply, is pretty voltage flexible, and uses only a small number of standard parts.

 

[zigzagflux]

An option:

http://www.diyaudio.com/forums/showthread.php?postid=1560015#post1560015

 

[Wavebourn]

In my version power is delayed until tubes start consuming the current, but I don't think it is useful except when you want to avoid turn-on currents causing thumps in speakers.

A positive feedback by current senses an output current, and starts charging time-delay capacitor faster as soon as senses that the load started to draw current. After an output voltage is set to the regulating value the positive feedback stops working leaving the place on stage to the negative feedback by voltage that keeps output voltage stable.

 

[LinuksGuru]

Thanks a lot, folks! Actually I have power-on time delay circuit in PS I am going to build, but it also uses relay and Schmitt-trigger based on 6N1P (schematic is back from the 60th).

Replacing relay with photo-triac + thyristor would be just great.

This is simple as 2 * 2 = 4, but my background is software, computers, and printing industry, unfortunately, I do not design schematic for myself.

 

[Wavebourn]

This is simple as 2 * 2 = 4, but my background is software, computers, and printing industry, unfortunately, I do not design schematic for myself.

Hi Andrei,

let me know what you need and I will help you to design. Ask Kubeek, Hearinspace, and others who I helped to, it is an interesting journey!

 

[atarashi]

Hi,

well, I use the following, it's cheap and works like a charm...

L1 is a relay, the rest should be self explanatory?

 

[ray_moth]

Anyone has damn-simple power-on time delay circuit, for 600-800V and 35 - 60 sec wait time?

The solution that atarashi posted is a great solution, but I think your problem is likely to be with the voltage you're trying to switch. Most relays are voltage-challenged, although current usually is not a problem. If you could use the relay to switch the primary of the power tranny, it would be much easier.

An alternative approach could be to use a TV damper diode to give you a delay of about 30 sec. It would cause a voltage drop of about 8 - 15 volts and there would be a nice gentle ramp-up once it starts conducting, as opposed to the sudden step in voltage that you'd get from a relay.

 

[LinuksGuru]

Draft

Thanks to all who replied. Yes, you all guessed right, it is 30 - 60 sec delay for B+ supply.

Please look at my draft schematic attached (it is far from being finished). I opted to use 2 separate coils (at the expense of extra diode bridge) to get 550-600VDC, because electrolytes with over 500V rating are rather obscure and expensive. Caps connected in series with bleeder resistors is not the best solution in this case.

Now look. Rectified 6.3V heater voltage feeds time relay on Darlington MPSA14 and RC delay circuit. Base-emitter on voltage for MPSA14 is 2V. With U(c)=U(dc in)*(1-EXP(-t/tRC)) voltage reaches 2V in about 45 sec. MPSA14 will fire up photo-coupler and open high-voltage thyristor. Current through photo-coupler LED will be about 5mA.

2 thyristors perfectly fit for this purpose, all 800V and 10-16A ratings - 2N6405 and MCR16M.

I think this damn simple schematic should work. The question is - what should be correct values for R3/R4/R5 to safely open the gate of TH1?

I see no reasons whatsoever to use relays, programmable timers, etc. for so primitive task. The only problem I'm not an electrical but rather software engineer. If anyone could finish calcs (and tell me how to add short-protection circuit) it would be simply great. I will post final design as public domain.

 

[Wavebourn]

I would hesitate to use that because you will definitely have some capacitors after the thyristor, right?

I have a very bad experience of one capacitor blown up not exactly such a way, but similarly. Also, what happens to grids if you apply B+ to the amp that has discharged coupling capacitors, but already ready to conduct hot toobs?

 

[gingertube]

Don't overlook off the shelf industrial control time relays. By the time you buy all the parts you would require you are in the ball park of what these things cost. If using a separate HV power tranny then switch the primary, else switch the secondary HV wires before the rectifier.

One of many commercially available options (as an example):
http://pewa.panasonic.com/acsd/timers/pm5s/

This particular one I just pulled out of a Farnell Catalog. Its cost in OZ is A$89 (about US$60) from Farnell which means you could probably get it for 20 to 30 bucks less from a Panasonic distributor.

I've used units made by Siemens in the past for the DIY hobby work and have used other manufacturers items (OMRON, FINDER, ABB etc.) in the day job (Electronic Design Eng.).

Cheers,
Ian

 

[Michael Koster]

$29.94 for an octal base timer from Allied

http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=8197107&MPN=SS-6262-08

 

[atarashi]

Hi LinuksGuru,

well, you still have two Caps in series...

and, as Waveburn told you it might not be the best idea to suddenly apply the full B+ to the tube.
My recommendation: use two relays and switch the AC side (your two 195V windings). AC switching is much better for the relays and the somewhat slower startup (your caps are not charged yet) helps a lot!

btw. a circuit like mine could be built for about €3,- or so, far from what a time relay costs...

Michael

 

[LinuksGuru]

$29.94 for an octal base timer from Allied
http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=8197107&MPN=SS-6262-08

Yes, thanks, but these relays (and other suggested) CANNOT handle 600V, they are rated 120V only. The plate voltage to 6080/6N13S/6N5S must be applied AFTER 30 sec of heater voltage. So switching on primary winding 120/220V of the power transformer after 30 sec of whatever does not make any sense.

 

[LinuksGuru]

Hi LinuksGuru,
well, you still have two Caps in series...

Yes, but they run at full capacity, and no possibility of over-voltage failure if one of the caps suddenly develop short.

and, as Waveburn told you it might not be the best idea to suddenly apply the full B+ to the tube.
My recommendation: use two relays and switch the AC side (your two 195V windings). AC switching is much better for the relays and the somewhat slower startup (your caps are not charged yet) helps a lot!
[/B]

I will use inrush current limiter for B+. I have not drawn it on the schematic yet.

 

[atarashi]

Hi,

still, switching the two 195V windings might be the easiest thing to do?
and, as you switch ac, the relays will last much longer!

Michael

 

[LinuksGuru]

Hi,
still, switching the two 195V windings might be the easiest thing to do?
and, as you switch ac, the relays will last much longer!
Michael

Original schematic used relay, and 4H choke to limit inrush current and prevent burning contacts, but I would like to get rid of all that. Thyristor is more reliable then mechanical device.