Relay Delay

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mrd

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Hi,

I'm wondering if you could double check this circuit.

I would like a delay before relay turns on, and a fast 'reset' time. Less parts the better, due to space restrictions.

I'm using this for reference, **broken link removed**

Will I need an extra 1k resistor between the 47uF and Vref pin? On simulation I'm only getting 3uA max. (not sure how 'real-life' this is)

Any 'tips or pointers' much appreciated.

Thanks
 

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hi,
Your ref link says the 1K is required, if the cap is charged and the main power rail disconnected its possible that the cap could discharge thru ref pin.!
 
ericgibbs said:
hi,
Your ref link says the 1K is required, if the cap is charged and the main power rail disconnected its possible that the cap could discharge thru ref pin.!
Click to expand...


Ah ok, I'll try and squeeze him in there.

Also, on a related note, I also want to use this circuit over +-16V. I assume the reference pin is 2.5V in reference to anode?

So would this circuit work ok? Again, simulation seems ok.
 

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This has worked for me.
**broken link removed**
Should work on a 16VDC supply with a different relay. Play with R2 and C1 for the specific time delay you need. A non-logic level MOSFET might give you a longer delay.

Ken
 
wouldn't changes in the capacitance due to temperature/surroundings affect the delay? Just wondering..
 
Yes! But there was no indication that a precision delay was needed. Variations due to temperature will likely be present in all RC timing circuits.

Ken
 
mrd said:
Ah ok, I'll try and squeeze him in there.

Also, on a related note, I also want to use this circuit over +-16V. I assume the reference pin is 2.5V in reference to anode?

So would this circuit work ok? Again, simulation seems ok.
Click to expand...

hi,
In your LTS sim circuit you are showing a 2880m relay coil inductance!, thats 2.88Henry.???
 
haha.. yeah coz I wondered since BJTs are extremely sensitive to changes to the base current.. so I thought that MOSFETs might be so too in the case for it's gate voltage... so when the capacitance changes and so on.. well you know..
 
mrd,

By "+-16V" do you mean +16V>Common>-16V...so there is 32V between +16V and -16? Or do you just mean that the supply is 16VDC?

Ken
 
Hi. Sorry for vagueness. Its 32V between them.
Power supply is dual 16V. +16V and -16V with ground in between.

Thanks
 
So, can the delay circuit be powered off of one side of the supply...+16v to ground? And, does the delay to the relay occur when the +/-16V supply is turned on? Or, is the +/-16v supply always on and there is a switch between it and the delay circuit?

Ken
 
Hi. Thanks. No switch. Its more that I'd like a delay to let the powersupply up before putting my load on. Ideally I'd like it across +16 and -16 rather than one side and 0V but if this can't be done then sure. Is it possible to use it over +-16V do u think?
Thanks again
 
Not bench tested, but I think this should work.

Ken
 

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The simplest way to delay the operate of a relay is to connect a capacitor across the coil and a resistor in series.

So in your case, you could use a 12 Volt relay in series with a resistor equal to that of the coil resistance with a capacitor across the coil of such a value as to provide the delay you need.
 

Simple! I like it. But, will it meet mrd's second spec?:

delay before relay turns on, and a fast 'reset' time
Click to expand...

ken
 
KMoffett said:
Simple! I like it. But, will it meet mrd's second spec?:

ken
Click to expand...

Ken,
No it won't as the capacitor will keep the relay operated while it is discharging.

So it needs something extra to release it quickly.

I assume that he wants it to release when the 24 Volt supply is disconnected.

mrd, how is the 24V disconnected? Is it with a switch? We need more info.
 
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