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'[PICLIST] [EE] current sensing circuit'
2001\08\01@154848 by Frank Tarsitano

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I'm looking for a circuit that will detect current
flow. I want to know when a particular appliance is
turned ON.

If any one can help it would be greatly appreciated.



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2001\08\01@155910 by Douglas Butler

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What is wrong with this?  For small appliances running off of 120/220VAC
it works great.

Sherpa Doug

> {Original Message removed}

2001\08\01@162822 by hard Prosser

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Possibly a bit more info would assist in suggesting an easy method.
AC or DC ?
110V/220V or 6/9/12V etc?
Low (<1A) or High >10A current?
Internal Equipment access available or need to sense from wiring?
Can cut into power cable or have to leave as-is?

Sorry if this sounds a bit negative but there are a lot of ways of doing
it.

Richard P




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I'm looking for a circuit that will detect current
flow. I want to know when a particular appliance is
turned ON.

If any one can help it would be greatly appreciated.



_______________________________________________________
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Get your free @yahoo.ca address at http://mail.yahoo.ca

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(like ads or off topics) for you. See http://www.piclist.com/#topics

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2001\08\01@194953 by Thomas McGahee

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What is the normal operating current of the appliance?

A simple AC current transformer might be appropriate. You
can fabricate your own from a toroid core. You wrap
multiple turns of insulated wire around the core,
going through the middle and then around the outside.
This is the secondary. The primary usually consists of
omly one or two turns of wire. If using a "single"
turn, you just have the wire going through the center
of the core. The secondary MUST be connected to a load
resistor. You monitor the voltage across the resistor,
as it is proportional to the primary current.

[NOTE: the AC power line has a hot and a neutral.
you may use EITHER one as the primary wire, but
ONLY one of the wires goes through the center.]

[NOTE: the current transformer provides 100% isolation
between the primary and the secondary, which makes
the current transformer also a SAFE way to measure current]

Let's make up an example so you can see how it all
goes together.

Max current to be measured: 10 Amps AC.
Desired secondary current when primary has 10 Amps: 100 milliamps.

Current ratio is 100:1

Use a "single" turn primary and 100 turn secondary.

Primary must be capable of handling 10 Amps.
Secondary must be capable of handling 100 milliamps.

A 1 ohm resistor will develop .010 V  per Amp and .1 V at 10 Amps.
A 10 ohm resistor will develop .100 V per Amp and 1 V at 10 Amps.
A 100 ohm resistor will develop 1.00 V per Amp and 10 V at 10 Amps.

Secondary resistor power dissipation at 10 Amps through primary
will be P=I^2*R, where I^2 = .01, so
.01*1 = .01 Watts for 1 ohm
.01*10 = .1 Watt for 10 ohms
.01*100= 1 Watt for 100 ohms

Personally, I would go for a 10 ohm 1/2 watt resistor and expect
an output of 1 volt at 10 Amps primary current.

Expect some error with a homemade current transformer.

Fr. Tom McGahee


{Original Message removed}

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