12v time delay relay

[awdowns]

I have been looking for a good 12v time delay relay with a 2-3min delay. Does anyone know where to find a good one?

 

[ericgibbs]

I have been looking for a good 12v time delay relay with a 2-3min delay. Does anyone know where to find a good one?

hi,
Look at this link, they are not cheap.

Time Delay | Farnell United Kingdom

 

[MikeMl]

Are you wanting to buy a readymade one, or do you want to homebrew one?

 

[awdowns]

Homebrew would be pretty neat. That would be the route for me to go if there isnt a premade one to be found for under 40 dollars. Do you have any links for either one?

hi,
Look at this link, they are not cheap.

Time Delay | Farnell United Kingdom

 

[MikeMl]

What is your Load? Does one end of the Load have to be grounded?

 

[awdowns]

Im not sure of the load, the wiring diagram is at home. Ill check after work. I wouldn't think it would be a high load, I am using it to keep power to another relay for the peroid of time. The 2nd relay would be doing the work, and the job of the timed one would just be to power it. All the grounds are in place, but the timed relay shoud have a ground, shouldnt it? I think I explained it, but let me know if I confused you.

 

[ljcox]

Here is one I designed some time ago.

You should make the capacitor 18 or 22 uF for 2 ~ 3 minutes.

You need an NPN transistor or a MOSFET connected to X to drive the relay.

The NPN will need a base resistor. Do you know how to calculate the resistor value? If not, tell us the relay coil resistance and I'll do it for you.

Don't forget to connect a diode across the coil to prevent damage to the transistor due to the back EMF.

 

[ljcox]

I just remembered that there is a 4.5 minute timer in the garage door opener that I designed & built some years ago.

The timer holds the light on for about 4.5 minutes each time the door is opened or closed.

Here is an extract from the GDO circuit. I've modified it so the timer is started by a switch.

For a delay of 2 ~ 3 minutes, use a 10 or 15 uF in lieu of the 22 uF.

Note that RC timers are not highly accurate but it is quite adequate for the GDO.

 

[ljcox]

JayCar sell a simple timer kit that may be of interest to you.

See Jaycar Electronics - Better. More Technical. and search for catalogue number KJ-8202 and the instructions KJ-8203.

However, the relay operates after the delay.

 

[Hero999]

What do you mean by time delay?

Everyone as assumed you need delayed off which is harder because the delay starts when the power is disconnected so the coil needs to be remain powered with a capacitor. I have a feeling that a ready made relay won't use a capacitor but some sort of mechanical or therma timing device but I could be wrong.

If it's delayed on, then it's much more simple, a 555 timer can be used.

 

[awdowns]

ljcox thank you very much for posting the diagrams and link. When you say the relay operates after the delay, does that mean it will just be drawing a 12v current from the battery, or continue to power the components?


I an pretty new at electonics, so would someone have a good link to help me understand how to read a circut diagram. I understand half way, but I need to know how to read it correctly before attempting to make one.

What do you mean by time delay?

Everyone as assumed you need delayed off which is harder because the delay starts when the power is disconnected so the coil needs to be remain powered with a capacitor. I have a feeling that a ready made relay won't use a capacitor but some sort of mechanical or therma timing device but I could be wrong.

If it's delayed on, then it's much more simple, a 555 timer can be used.

I need a delay off. Just like the diagram ljcox posted for the light on his garage door opener.

 

[ljcox]

ljcox thank you very much for posting the diagrams and link. When you say the relay operates after the delay, does that mean it will just be drawing a 12v current from the battery, or continue to power the components?
You're welcome. I don't recall saying that the relay operates after the delay.
The relay operates when you press the button and releases after the delay.
The circuit will only draw current while the relay is operated since the CMOS Schmitt trigger IC draws very little while it is in the quescent state.

I an pretty new at electonics, so would someone have a good link to help me understand how to read a circut diagram. I understand half way, but I need to know how to read it correctly before attempting to make one.

I tried to find a suitable link but couldn't. I have seen them in the past, but I don't recall where. What you need is a link that has both a circuit diagram and a wiring diagram so you can compare them. There are tutorial sites, perhaps you could search for "electronics tutorials"

I need a delay off. Just like the diagram ljcox posted for the light on his garage door opener.

I realised that the GDO circuit can be further simplified for your purpose. It also needs a bypass capacitor on the supply line. The GDO certainly has one, so I must have neglected to add it to the circuit.

So I'll modify the diagram and post it later (after breakfast)

 

[ljcox]

Here it is.

Hero999 suggested using a 555 timer. This has the advantage that it can drive the relay directly, but has the disadvantage that it draws significant quescent current. Even the CMOS version (7555) draws about 180 uA (typical).

Whereas, the 40106 draws 4 uA max at 15 Volt

The MC14584 Schmitt Trigger IC draws typically 1.5 nA & 1 uA max at 15 Volt.

So he would need an on/off switch for a 555 or 7555, but it won't be necessary for a 40106 or MC14584.

 

[ljcox]

Here is a rough wiring diagram for the Delay 5.gif circuit.

I just realised where I said the relay operates after the delay. I was referring to the JayCar kit.

 

[Hero999]

Sorry but none of the circuits will do what the original poster wants.

He wants a delayed off relay: connect it to 12V, it turns on immediately, disconnect it from 12V and it waits for 2 to 3 minutes before turning off.

You need a huge capacitor and a relay with as high coil resistance and low release voltage.

Here's the only relay I could find suitable.

**broken link removed**
Connect a 68,000µF capacitor in parallel for a 3 minute delay and a 47,000µF capacitor for a 2 minute delay. This is assuming your supply is exactly 12V.

How much current does it need to switch and at what votlage?

The relay linked above and only handle low currents and is not suitable for switching mains.

The simple method using a capacitor will be expensive and you need a high current source to charge the capacitor in the first place.

For the mains, it's probably better to go with an opto-TRIAC switching a larger TRIAC.

If it doesn't need isolation it might be better to use a MOSFET circuit, although there needs to be a ways to avoid the saturation region.

Another possibility is MOSFET output solid state relay, you can make your own (I have a circuit) or buy it ready made.

In fact a sold state relay is better in any case. Depending on your answers you the previous questions, I'll have a go at modifying an existing design I know of.

 

[kinarfi]

https://www.alliedelec.com/search/productdetail.aspx?SKU=8922003
Where are you? Europe, USA, ETC.
**broken link removed**

do you want delay on make
or do you delay on break

 

[ljcox]

Sorry but none of the circuits will do what the original poster wants. He told me in a PM that it is exactly what he wants, ie. press a button to operate the relay.

He wants a delayed off relay: connect it to 12V, it turns on immediately, disconnect it from 12V and it waits for 2 to 3 minutes before turning off.

If it doesn't need isolation it might be better to use a MOSFET circuit, although there needs to be a ways to avoid the saturation region.
Do you mean the active region? I don't see why you would need a way to avoid the saturation region.
You need to avoid the active region in order to minimise the power dissipation while passing through the active region.
Schmitt Trigger circuits avoid the active region by applying positive feedback.

Another possibility is MOSFET output solid state relay, you can make your own (I have a circuit) or buy it ready made.

In fact a sold state relay is better in any case. Depending on your answers you the previous questions, I'll have a go at modifying an existing design I know of.

He said he wants the relay to drive another high current relay. This makes me wonder whether he could drive the other relay directly from the timer.

 

[Hero999]

I agree it's more sensible to have it permanently powered rather than using a huge capacitor.

By the way confusingly, the saturation region is the active region in a MOSFET, I think you got confused with the BJT.

MOSFET - Wikipedia, the free encyclopedia

 

[ljcox]

By the way confusingly, the saturation region is the active region in a MOSFET, I think you got confused with the BJT.

Thanks. Yes I probably knew that some years ago but had forgotten.

Nevertheless, my comment is still valid once the terminology is correted.

 

[awdowns]

https://www.alliedelec.com/search/productdetail.aspx?SKU=8922003
Where are you? Europe, USA, ETC.
**broken link removed**

do you want delay on make
or do you delay on break

Delay on break (letting off switch) just like the first link appears to be.


Im going to give the timer ljcox has supplied a shot. If for some reason I fail, I will use that as my back up plan.

I really appreciate everyones help! I'll post up my results when I get everything together.


-Steve