Relay shut down circuit needed please................... 1

[zomaxx]

I am asking for help to design a circuit that will remove/interrupt ground on coil of standard bosh type relay (terminal #86) when monitored circuit voltage exceeds 15.5 volts.

Thank you for your help.

 

[MacGyverS2000]

You're going to need to give us more detail than that... we could give you a quick and dirty example tat involves a Zener diode, but I doubt it would last more than a handful of cycles in a typical automotive application.

What is going to be switched (do we have to worry about transients), what's doing the switching (does it have enough power), how many are going to be produced (whats the cost factor), etc.


Dan - Owner

http://www.Hi-TecDesigns.com

 

[zomaxx]

Thanks for the reply.........

Not concerned with transits/spikes.

The relay coil I want to interrupt pulls less than an amp (around 400 mA).

Would like the "CIRCUIT" to remove/interrupt ground on coil if vehicle voltage exceeds 15.5 amps.

This relay is the standard Bosch type relay.

Hope this helps.

Thanks.

 

[MacGyverS2000]

You claim not to be worried about transients, but the circuit designer does... again, what is this controlling, what is controlling it, and how many are to be made?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[zomaxx]

You claim not to be worried about transients, but the circuit designer does... again, what is this controlling, what is controlling it, and how many are to be made?

The requested "CIRCUIT" is controlling the Bosch relay.

The requested "CIRCUIT" will be powered by vehicle system voltage (14 - 15 volts).

Only want to build 2 or 3 of these.

Thank for your help.

 

[melone]

Use a N.C. relay connected to the supply with series Zenzer to achieve your desired voltage. It's not very accurate, but should work.

 

[zomaxx]

Thanks melone for answering my question.

I'll give it a shot!!!!!

 

[LionelHutz]

I don't see how a series zener will work.

You need a circuit that switches on a certain voltage. Look to using a battery monitor IC driving a transistor. Battery monitor IC's are the type of thing put into a device to ensure the battery does not get overly discharged. Just invert the logic.

 

[Skogsgurra]

It will work, in a way. The key is "NC". So, melone is probably thinking about an auxiliary relay with a zener diode in series with the coil. When zener voltage + coil pull in voltage are selected to be 15.5 V at nominal coil current consumption, the relay will pull in and interrupt the ground of the Bosch relay.

The auxiliary relay coil will protect the zener from transients.

What worries me is that the OP probably wants to keep a load dump from hitting some equipment. A relay that makes another relay drop out will probably not be fast enough. But since the OP is not willing to reveal more "secrets", we will have to do with this not so well specified or designed "circuit".

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[OperaHouse]

A LM431 amplified zener would be perfect for the job, but from memory this can only handle about 200mA. A smaller relay could operate a larger relay. Do you want it to cut out and not reset? What you haven't thought about is relay chatter. a simple circuit will cut out at 15.5V, but turn back on at 15.4999 volts. Typically you want to turn back on .5 to 1 volt lower and also implement a 5 second time delay with either action.

 

[GonzaloEE]

My 2 cents:

You may have a comparator w/some hysteresis to drive the 2d N/C relay, already suggested for breaking the coil's GND path. Also a TL431 as ref. input for the opamp.