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Relay delay circuits

:: EPE Chat Zone ≠:: ≠Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 27 June, 2012 » Relay delay circuits « Previous Next »

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echase
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Username: echase

Post Number: 646
Registered: 07-2007

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Posted on Thursday, 07 June, 2012 - 11:31 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I was left a self designed circuit to maintain by someone else and itís a bit of a nightmare. Itís for a water saving urinal flusher and has a design law in that a slight glitch on the mains will cause a relay to momentarily drop out thus instigating a flush when one is not needed. Itís a miniature plug in relay with one N/C contact used and a 20kohm 230VAC coil. Would like to add a capacitor across it and bridge rectifier so when a mains glitch occurs the capacitor holds up the coil for a few ms. 22uF gives time constant of 0.4s which should be enough.

Will converting it from AC to DC stop it working e.g. due to magnetising of the core? I see that a few relays of this size are available in 220DC versions which implies that running an AC one off DC is not recommended. The capacitor will also result in 300VDC being present which is a bit high.

Anyone else think of a simple solution that does not require a low voltage DC feed as none available? Nothing too big as size in box is limited. Maybe a triac to feed relay coil but how to get the gate to hold it on as would have to be DC fed if simply capacitor fed? Also 20k might give too low a current to hold the triac on.
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externet
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Username: externet

Post Number: 165
Registered: 05-2005


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Posted on Thursday, 07 June, 2012 - 01:38 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Try half way rectifier -single diode 1N4007- and capacitor instead of a full wave, to keep DC voltage fed to the AC rated coil lower.
Abolish the deciBel !
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cjaysharp
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Username: cjaysharp

Post Number: 292
Registered: 06-2010

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Posted on Thursday, 07 June, 2012 - 11:09 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Capacitor/transformerless PSU and a low voltage DC relay?
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echase
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Username: echase

Post Number: 649
Registered: 07-2007

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Posted on Friday, 08 June, 2012 - 01:06 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Good ideas thanks.

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