Circuit to identify the voltage on the dc bus

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aless2056

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Hey guys,

I have equipment that has a DC bus of around 800Vdc. How can I make a circuit to read the voltage value and when there is no voltage on the bus, activate a relay.

I thought about measuring the voltage on the dc bus with an op amp and then using a voltage comparator to activate the relay.

What would be your suggestions? Any examples?
 

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Potential divider to bring the voltage to a manageable level and a comparator is all you need. A few resistors in series to handle the high voltage then one to ground to make the divider and a comparator will do the job, no need for an op-amp. Depending on the relay you might need a current booster (a transistor) to drive its coil.

Brian.
 

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I failed to mention the purpose, which is for security. The relay contact would prevent the door from opening if there was still power on the dc bus.
 

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Do you need isolation., and/or wireless approach preferred ?


Regards, Dana.
 

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Hi,

basically
* resistive voltage divider ( --> COMP)
* reference voltage (--> COMP)
* comparator (--> BJT)
* bjt (--> relay)
* relay

***
in detail you additionally need to
* define lowest level to activate the output
* define highest level to deactivate the output (bot combined give the hysteresis)
* timing
* expected noise level (to design a suitable filter)

Klaus
 
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