Current flow sensor switch

Discussion in 'General Electronics Chat' started by pafitis, Sep 2, 2015.

1. pafitis Thread Starter New Member

May 8, 2015
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I'am new here to this wonderfull site and im glad that i find it. Now i believe each and every one should be creative and and must be happy to spread their knowledge freely every were.
What im asking its simple circuit consisting of a small current transformer that will detect an ac current (from 220V water pump),where the live wire is passing thru its hole.
As we all know that will produce an ac voltage of around (200-300mV) at its leads.
As long as there such voltage, can anyone design a circuit that will drive a relay of 12v and then by using
its contacts to connect an 220V hour meter for example.

2. Alec_t AAC Fanatic!

Sep 17, 2013
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Welcome to AAC!
Actually, we don't all know that . The voltage generated will depend on a) the turns ratio of the current transformer, b) the value of the burden resistor across the transformer output and c) the current through the input. Can you post the spec/datasheet of the transformer? Do you know the current draw of the pump?

3. pafitis Thread Starter New Member

May 8, 2015
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Thank you for your reply........i know that because i had my experiment....i took that small current transformer i run the live wire thru its hole,then i switch on the pump (6 amps load) and it gaves me
220mV !!!
Now, do you have a circuit for driving a 12V relay???

4. dl324 Distinguished Member

Mar 30, 2015
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Welcome to AAC!
For this example, you could simply connect the hour meter across the power leads to the well pump.

5. pafitis Thread Starter New Member

May 8, 2015
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Thank you for your reply...If it is so simple as what you said, i won't to ask for help .
Cannot have access.

6. dl324 Distinguished Member

Mar 30, 2015
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In that case, you could take the signal from the current transformer, amplify, rectify, filter, and use the presence of voltage on the filter cap to control the relay driver.

7. Alec_t AAC Fanatic!

Sep 17, 2013
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What value burden resistor? What is the transformer rating?
If you can increase the resistor value without exceeding that rating then you should get a high enough output voltage from the transformer to switch a transistor without the amplification step that dl324 mentioned.

8. AnalogKid Distinguished Member

Aug 1, 2013
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220 mV isn't much to work with. And, I wonder where that number comes from. If it is an AC DVM reading of an open circuit CT secondary, that's not very much. Still some information missing.

OP - please post a sketch of the AC power source, pump wiring, and current transformer. Also, what did you use to measure thee CT secondary?

ak

Oct 2, 2009
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10. pafitis Thread Starter New Member

May 8, 2015
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Thank you for your reply.......all i can see its sensors,sensors,sensors, sensors,sensors, sensors.....a complete and customade design/circuit for the purpose i need, cannot see nowhere. ??????

11. pafitis Thread Starter New Member

May 8, 2015
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I believe your miles away from analog circuits.........you don't need a special meter to measure it, this reading came out from the secondary of this current transformer. Its similar to power transfomers you apply for example 220V onto primary and you get 12V onto secondary. In that case you run the wire thru its core and you get voltage which depends on how much amps, and how many turns are winding the core.

12. blocco a spirale AAC Fanatic!

Jun 18, 2008
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Will someone please provide him with a complete custom made design before he demands a full refund and takes his business elsewhere?

sirch2 likes this.
13. AnalogKid Distinguished Member

Aug 1, 2013
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I believe you are miles away from understanding what a current transformer is. It is *not* "similar to power transformers." You do not "get voltage which depends on how much amps". You get *current* based on how much amps. Its output resembles a current source more than a voltage source. Because of this, the input impedance of the measurement instrument (scope, meter, etc.) has a direct effect on the reading and its accuracy. What did you use to measure the output of the current transformer? Is there a terminating or burden resistor on the output? If you don't understand the difference between a voltage source and a current source, none of the answers you get here will make any sense.

ak

14. BillB3857 Senior Member

Feb 28, 2009
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I scavenged the coil from an old GFCI, tied an LED and properly positioned diode to protect the LED to it and made my own Opto Isolator using a photo transistor. The GFCI coil is monitoring my sump pump and the photo transistor is triggering a counter to tell me how many times the pump cycles. A similar setup could be used to trigger a relay.

15. pafitis Thread Starter New Member

May 8, 2015
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If you don't have something usefull to say or suggest, will you please remain silinced ??

16. pafitis Thread Starter New Member

May 8, 2015
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Many thanks for your usefull reply .....this is first positive posted answer from this member. Iam now close to what im try to achieve,if i get more like this i believe at the end of this week i will be able to made this circuit happen, thanks again.!!!!

17. AnalogKid Distinguished Member

Aug 1, 2013
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With the coil driving an opto, isn't that two isolation barriers in series? Excellent safety, but you needed the system to work with lower input current you could have the coil drive a 2N4401 directly. or something like that.

ak

18. ScottWang Moderator

Aug 23, 2012
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Will you draw a circuit or block diagram and labeling the V/I and parameters, it will make members have the same target to discuss with you and you can get the answer more fast as you wish?

19. sirch2 Well-Known Member

Jan 21, 2013
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blocco a spirale likes this.
20. blocco a spirale AAC Fanatic!

Jun 18, 2008
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ScottWang likes this.