[Diy_efi] Time delay relay?

[Mike]

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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