[Diy_efi] Time delay relay?

[Mike]

Here I go commenting on my own posts,

<cough> Whats the duty cycle of your relat and whats it meant
to drive ?

rgds

mike



At 11:54 AM 24/12/2002, you wrote:
>What the heck, I just realised you only want a few milliseconds,
>then thats not a problem unless your coil has very low resitance,
>but if its for driving something in an auot then its prob at least
>a few hundred ohms,
>
>Here's my go at ascii art <sigh>
>
>     ----------------------------
>     |                          |
>+ve--+---->|------+----->|------+---- coil +ve
>                  |
>                  |+
>                 --- electrolyic
>                 --- cap
>                  |-
>                  |
>                  +------------------ coil -ve
>                  |
>                  |
>                  |
>             To device which normally pulls relay on
>
>
>Where -->|-- is a diode say a 1N4004 (1Amp) or if you
>need something a bit meatier go for a 1N5404 (3A)
>
>and your electrolytic cap should be 2200uF 25V if your
>coil resistance is about 270 Ohms, the 2200 is a preferred
>value, you can go up a bit at a time, 3300, 4700 etc or have
>a couple if parallel to trim the delay to what you want,
>I'm guessing on your coil resistance though, higher coil
>resistance wont need such a large capacitor.
>
>Overall shouldnt cost more than $AUD 3. (since you already
>have the coil)
>
>rgds
>
>mike
>
>
>
>
>
>
>
>
>At 11:41 AM 24/12/2002, you wrote:
>>One very basic method is a big fat capacitor across coil with
>>a pair of diodes to isolate the cap from the coil when off...
>>
>>Discharge time is approx t=1.1xRxC
>>
>>where R= reistance of coil, and C is the cap value in Farads,
>>this way you can get a few seconds with practical caps and
>>a K or so or coil resistance,
>>
>>But to get 100s best to put a schmitt trigger and caps on the
>>drive to the coil transistor, others prob already have a circuit,
>>its fairly straightforward,
>>
>>rgds
>>
>>mike
>>
>>
>>
>>At 02:48 PM 23/12/2002 -0800, you wrote:
>>>Where can I find some relays with time delay? I have seen plenty of
>>adjustable
>>>.1-100s relays, up in the $50-$70 range. I need something simpler. A
instant
>>>ON/fixed delay OFF relay with a delay of about 250-500ms.
>>>
>>>
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>
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