New here - relay logic question (time delay)

"delaying a 12v pulse"

Hey guys,

Just registered here as I'm just starting out doing a couple of little projects and could do with some advise on this one.

**broken link removed**

The problem I have is that, when pressing a button (or touching wires, whatever ), the relays are rapidly switching back/forth. Obviously the 12V pulse from the switch is much longer than the relays' switching times so it's going through e.g RL4, Setting RL1, which is routing 12V to the coil of RL4, energising it and routing the 12v from the switch to the Reset winding of RL1, and so on and so on.

I had anticipated this but sadly only after having ordered the components!!

Now what I was considering was a time delay on the feed to the coils of the SPCO relays (RL4 and RL5):

**broken link removed**

The second series resistor is to slow the discharge of the capacitor so the situation above doesn't occur on a reset pulse.

The quesitons are essentially:
a) will the above work? and
b) what component values would you suggest to get a useful time delay (would estimate at least 0.25s) and not stop RL4/RL5 from working?

(I'm conscious that a high series resistance would drop the voltage too much. The coil resistance is 700ohm and 'must operate' voltage is 9V. Nominal current is 17mA).

Hope this makes sense and would be immensly grateful of any help as I need to sort this asap

Best regards,
Chris Wood

(N.B. project is not for profit but being made under my company name for insurance reasons)

cd4013+relay

You may want to describe the intended circuit operation more clearly. To my opinion it's hard to understand either from the circuits or your description.

Generally, introducing a delay in the said range involves capacitors of about 1000 uF. It can be implemented more easily with active parts, either timer circuits with 555 or transistors in combination with RC circuits.

tagalog logic question

Hi there,

Thanks for the response

The circuit uses a single push-button to operate a magnetically latching relay. The relay is a double-winding type, so an SPCO relay is used to swap the winding being energised by the push button. There are two of these arrangements in the device, the second of which drives a 40A rated relay switch power to an ECU type device.

Can you suggest an example of an active circuit? Can't accomodate a pair of 555s due to space on board require for those and a 5v regulator, so transistors would seem to be the way forward?

Cheers,
Chris

After your more detailed explanation, I understood the basic circuit intention. Clearly, the first version can't work. It's neces,sary to delay the DT relays action, as doen in the second circuit. Unfortunately, if button is pressed too long, it stil swiches back.

I would prefer either an electronical toggle circuit, that gives a clear output, no depending on a specific timing of input signals or a electromechanical toggle relays (impulse switch). See this thread for reference

**broken link removed** - I've seen a few potential ideas on here.

The solution entitled 'Bistable flip flop' appears to be a cheap and easy way to get around the problem and negates having to use the latching relays.

Added after 1 minutes:

Hey sorry didn't see your second response before I posted that - will have a look through the thread

CHeers!
Chris

Yes, the shown circuits are basically what I meant with an electronical toggle circuit. Your bistable relay as well as the impulse switch I suggested have the advantage of keeping the state in case of power loss, no idea, if it's required at all. For an electronical solution operated from a 12V supply, I would prefer CD4xxx logic. One half of CD4013 with a debounce circuit is already a complete toggle design.

Thanks for that - in your experience, would you recommend switches/debounce circuits that pull down or up for use with the cd4013?

Cheers,
Chris