Relay Delay

[mrd]

Hi thanks guys.

There's no individual switches for power, so will be just when mains gets disconnected. The power supply is like a 'rack system' powering many modules.

One thing that I haven't mentioned is that I can't draw to much power for this as there's not alot going spare. Would like to keep it around 8mA across the whole 32V if possible.
(Apologies for not saying this earlier)

So the mosfet solution I think with the 1k would be more 30ishmA?


Sorry to keep banging on about this circuit.. but I'm not sure why this wouldn't work...
https://i44.tinypic.com/ji25w4.jpg (+V being +16V and -V being -16V)
Any clues to enlightenment much appreciated!

Thanks for your patience.

 

[KMoffett]

The R1 and R2 can be increased and C1 decreased be a factor of X10. May not be a problem. I don't have a simulator or the time to bench test your original circuit. Maybe others can.

Ken

 

[mrd]

The R1 and R2 can be increased and C1 decreased be a factor of X10. May not be a problem. I don't have a simulator or the time to bench test your original circuit. Maybe others can.

Ken

Thanks.
Ah ok. Is that at the expense of 'reset' time?

I've uploaded the LTspice file of my original circuit if that's any help.




I'd try the thing in real for myself, but gotta order those relays from mouser (Im in UK) so have to order over £50 for free shipping. So I wanna make sure I'm on the right lines before commiting to an order.

 

[mrd]

Here's the spice file attatched

There's the 24V relay circuit and also +-16V circuit too

 

[KMoffett]

I think the reset time should be the same.

gotta order those relays from mouser (Im in UK) so have to order over £50 for free shipping.

Why not shop local. Farnell? RS?

PANASONIC EW|AGQ200A24.|PCB Relay | Farnell United Kingdom L 2.65+ L15.95 Shipping from US
or PANASONIC EW|AGQ200A24|RELAY, DPDT, 24VDC | Farnell United Kingdom L3.03 if you don't mind messing with surface mount tabs.

There are probably others. Farnell has a parametric search.

Ken

 

[mrd]

I think the reset time should be the same.



Why not shop local. Farnell? RS?

PANASONIC EW|AGQ200A24.|PCB Relay | Farnell United Kingdom L 2.65+ L15.95 Shipping from US
or PANASONIC EW|AGQ200A24|RELAY, DPDT, 24VDC | Farnell United Kingdom L3.03 if you don't mind messing with surface mount tabs.

There are probably others. Farnell has a parametric search.

Ken

Hi, thanks.

Bit scared of surface mount! I don't mind doing an order from mouser if you think there's a good chance that the circuit will work. Tweaking of resistors, caps etc no problem. Or is it a flat 'that'll blow up' kind of thing?!

 

[KMoffett]

OK, I bench tested my circuit on a +/-15V supply with a 24V relay. The problem seems to be the time constant of R1 and C1 and your current limitation on R1. So, without an active element to discharge C1, it won't work with you limitations. If your circuit simulates OK, it may be the answer you started with.

Ken

 

[mrd]

OK, I bench tested my circuit on a +/-15V supply with a 24V relay. The problem seems to be the time constant of R1 and C1 and your current limitation on R1. So, without an active element to discharge C1, it won't work with you limitations. If your circuit simulates OK, it may be the answer you started with.

Ken

Thanks Ken. Thanks so much for doing that! Appreciate it!
Ok, I'll go with the circuit I have and hope for the best! Simulates fine. It's just I wasn't 100% sure that the anode of TL431 likes being on -16VDC (maybe it doesn't care) and as such whether the ref pin is 2.5V from the anode.

I guess the simulation would have shown up any problems if this was the case?

 

[KMoffett]

As long as there is no connections to common, it just sees a 32V supply. Keep us posted on you progress.

Ken

 

[mrd]

As long as there is no connections to common, it just sees a 32V supply. Keep us posted on you progress.

Ken

Yep, no connections to 0V. I'll let you know how I get on.

Thanks so much again.

 

[ljcox]

Len,
It's +/-16V not 24V. Look at Post #15
Ken

Thanks Ken, I'd glossed over that one.

So if he wants the relay to operate when the voltage rises to +/- 16 Volt, then a voltage threshold detector would be better than a delay.

One way to do this would be to insert a 27 Volt Zener diode in series with the coil of a 5 Volt relay (with a normal diode across the coil - just to be sure to be sure).

Thus the relay will operate when the PS differential voltage rises to about 30 Volt, ie. 27 V + the relay operate voltage.

The relay will release when the PS is turned off and the diff voltage drops to about 28 Volt.

 

[ljcox]

Please note that the above suggestion will need careful consideration of the various tolerances.

1. The PS won't be exactly +/- 16 V. It may be say +15.7 & -15.5 V hence a V diff of 31.2 Volt.

2. The Zener won't be exactly 27 V. You may need to buy 5 and choose the one with the lowest voltage.

3. How well regulated is the PS? ie. how much do the output voltages drop at maximum load?

4. The relay also has operate, hold & release current tolerances.

 

[mrd]

Please note that the above suggestion will need careful consideration of the various tolerances.

1. The PS won't be exactly +/- 16 V. It may be say +15.7 & -15.5 V hence a V diff of 31.2 Volt.

2. The Zener won't be exactly 27 V. You may need to buy 5 and choose the one with the lowest voltage.

3. How well regulated is the PS? ie. how much do the output voltages drop at maximum load?

4. The relay also has operate, hold & release current tolerances.

Hi,

thanks, thats a nice simple option.. the only thing is, ideally I'd like a couple sec delay after the powersupply rails are up.

Added a pic of the simulation graphs im getting at the minute. Seems to be ideal

 

[ljcox]

I think it could be simplified.

I assume that U1 is a SCR. I don't have a data sheet for it.

I feel that Q3 and some of the resistors could be removed.

My idea is that you can discharge C7 by connecting a capacitor from the switched side of the -16 V line to C7. Thus when the relay operates, C7 is discharged.

Then when the power is turned off, U1 goes open and the circuit goes back to its initial state.

You would need a diode across C7 to prevent it charging too far in the negative direction. It may even have to be a germanium or Schotty diode in order to minimise the reverse voltage.

Otherwise, U1 may be switched off by the negative potential. I would have to look at its data sheet to be sure.

 

[mrd]

Hi, thanks.

U1 is https://www.electro-tech-online.com/custompdfs/2010/04/TL2FTL431-1.pdf

I see what you mean about using another cap.. clever..wouldn't have thought of that.

I'll have a play with spice

Cheers

 

[ljcox]

Sorry,
I meant resistor, not a capacitor.

I'll study your circuit in more detail, draw what I mean and post it later.

Also, I see that U1 is a regulator, not an SCR.

 

[ljcox]

I studied your circuit and now realise that U1 is a shunt regulator, not an SCR.

That is a novel idea.

Attached is my suggestion using an SCR.

C1 delays the operate of the relay by about 2 sec.

The 9V1 Zener prevents the trigger of the SCR until C1 has charged to about 10 Volt.

C1 starts discharging immediately the relay operates and needs about 13 sec to fully discharge. If that is too long, it could be reduced significantly by connecting a diode across R1.

This would reduce it to about 2 sec. It could be further reduced by reducing R2 to 10k.

The circuit can operate from either 16 Volt as shown or 32 Volt.

For 32 Volt I suggest that you would use a 22 V Zener and R1 could be reduced in value.

I don't know if this circuit has any real advantages over yours. But I've posted it anyway.

 

[ljcox]

Here is a better option.

The discharge of C1 starts when the SCR conducts.

If D2 & R3 are included, the discharge time of C1 will be about 100 ms.

If they are not included, it will be about 13 sec.