Not wishing to highjack the previous post. –
I have been looking for a 4 sec time on break relay, those that state a delay seem to cost mega bucks. The ones linked to are cheap, but nowhere does it state that they are time delayed; apart from a T in the part number and maybe an adjuster on the top. Any comments appreciated.

 

So your looking for a relay that delays ~4 seconds before turning on? Or maybe a curcuit that could use a regular relay and accomplish what the single expensive part can do?
Please tell us what sort of application you will be using this in?


iONic

 

Ionic – I was going to post a schematic in a couple of days; I will do that and look forward to any help you can give, I only asked now because the subject came up.

 

You don't have to use this circuit but it would be cheap as dirt. Use a 555 timer to implement it and you'd be done for under $5 not counting a high amp relay for whatever is being delayed.

The 1 Meg pot will give a 1 to 4 second time on delay with these component values. Check out some 555 web sites for more circuit ideas. I've been told that using two ICs for this is a waste, so whatever you come up with. It will surely be much less expensive than anything sold as a dedicated time delay relay.

 

@Kermit2,
I might have suggested such a circuit, but am still do not understand the application or where and when the delay is required. It's possible that the requirements are, "no user intervention".

 

These were my first two projects before finding this forum, I didn’t know much then and I still don’t. Now I feel I am being a little frivolous with the site by posting this, but the first question at least does bug me. Scavenging in skips (with permission) the two projects cost around $15. The schematic for my second project the charger was from an old Elektor magazine from 1998. I want to make another one, for a couple of reasons, one is the existing one isn’t very neat as you can see. The resistors for the LED’s are 10k Ω, (I used 820) this can’t be a typo because the text states to reduce it to 3k9 for a 6V version if the lights are too dim! Were things different in 1998? The ground from the 7805 continues past the rail; that had me worried, but eventually decided it was for parity with the 100n cap. The battery polarity check light is on all the time, when only needed at battery connection, if at all, a momentary switch should cure that. The initial setting of the ref voltage for the comparator is carried out with power on and battery disconnected. The relay should close for 1 second and be open for 4 to allow time for ref adjustment, it doesn’t, it opens and closes about once a second making adjustment impossible. Being ignorant of delayed relays I used a 12V BTK 1012 H (15 cents at an autojumble). The relay number on the schematic refers to a Siemans delay relay but I can find out nothing about either relay. I overcame this problem by having the charger close by, when at work, and, should I happen to see it, checking the battery voltage at the beginning and end of the charging cycle (drawn out and tedious, seems to work though). Should the power be interrupted during a charging cycle the 3 LED’s remain lit (negating their purpose), or 1 if off charge. This discharges the battery; since it is in my shed I don’t see it that often, this has happened three times thanks to helpful family members switching the power off. After much head scratching I have just realised a secondary mains powered relay circuit that opens with a power failure and breaks the link between the battery and the existing relay might solve that. I used a 900mA wall wart for power. If anyone thinks the post worthy of a comment I would be pleased to hear it. Thanks for that Kermit.
As an aside, whilst making this project it occurred to me that the same circuit principle may solve a problem the company I worked for didn’t know they had. It did and was more successful than I imagined it would be; for the company anyway. I gained nothing financially in fact the reverse was true. However none of it would have been possible without this forum. The guys on here know they are not only helping the poster but also other people. A certain ex-military man (not forgetting others) when addressing a poster: “The op-amp will only do what it is supposed to do......” wouldn’t know that my whole project hinged on those few words, and had inadvertently found a cure for headache.

 

Can’t think now why I ruled out a diode, or more so why the circuit designer didn’t include one; and with a modified temperature sensor the project may be fit for purpose, and with a reason to play with some 555’s should make an interesting project – for me at least.