Current Sensor / Monitor / Logger

[Paul_B]

Is anyone or has anyone discovered a way to measure current drawn when a device is running?

I am after a small device / pcb board to measure current and output an analogue signal so that I can log current /power consumption for key appliances; washing machine, dishwasher, television, etc

[toscal]

Try these sites
http://www.energymonitor.com/features.html
http://www.conrad.com then look under electronics & metering - measurement systems then Environmental Analysis Devices
They have a few power meters to choose from

[toscal]

Finally found the sites I was originally looking for.
If you are handy with a soldering iron then this might be worth a look;
inductive current detection
and also
CR Magnetics
CR Magnetics do all sorts of detectors and transducers for power, current and voltage.

[JohnEM]

Is anyone or has anyone discovered a way to measure current drawn when a device is running?

I am after a small device / pcb board to measure current and output an analogue signal so that I can log current /power consumption for key appliances; washing machine, dishwasher, television, etc

Try www.electrisave.co.uk

(just got one and it works a treat)

John.

[Paul_B]

Thanks Toscal and John,

I am going to have a play with some of the Conrad Inductive Resistors. I'll report back on my success.

Paul

[Karam]

Generally speaking you need to get a voltage signal measurement as well as the current (i.e. need instantaneous values for both), since for non resistive loads, e.g. motors, the voltage and current will not be in phase and so the power is not just current x line voltage.

In typical electronic energy meters the current is either sensed by a current transformer (coil) wrapped around the current bearing conductor, or by placing a precision low value resistance in series with the load and measuring the small voltage drop across this. A microprocessor is then used to sample rpresentative values of current and line voltage which can then be multiplied or processed in other ways to give various measures of power.

There may well be easier/different ways to achieve the same result, after all until recently most electricity meters used electromechanical methods.

Another consideration is safe isolation if the measurement is to be logged by a human touchable device e.g. a PC. 8O

Karam

[NicBetts]

I like the simplicity of the Electrisave product but want, as always, to tie it in with my HomeAutomation system.

Does anyone know of, or can think of an easy way to integrate this or similar with a computer. Thinking of some sort of stream hitting the serial or USB port that I can then read off.

Thoughts ???

[Otto-Mate]

Ian Goodhew posted a message on our mailing list about this early in the week...

http://www.ukha-archive.com/ml/ukhad.../msg00653.html

M.

[b_weijenberg]

The RFXPower is able to do what you want. http://www.rfxcom.com/sensors.htm
It measures the real power by multiplying the measured voltage and the measured current. So even when the voltage drops the measured power is accurate. A clamp-on current transformer is used and this can be clamped around the phase wire from the main breaker to the fuse bus. Or it can be clamped around 1 wire from the wall outlet to the device.

It is supported by the ACRF and xAP plug-in in Homeseer.
See a nice implementation at http://board.homeseer.com/showthread.php?t=118165

The RFXCOM USB 433.92MHz X10/Oregon receiver can receive the full 48 bits RF packets from the RFXPower. This RFXCOM receiver is able to receive:
- Oregon Scientific 1.0, 2.1 and the latest 3.0 protocols (433.92MHz is used worldwide)
- "NON-US" X10 sensors and remotes
- Digimax
- RFXSensor
- RFXPower.
A second receiver can be inserted in the USB interface. This can be a 310MHz X10 receiver (for US X10 sensors) or a Visonic/VP1000 receiver or a KlikOn-KlikOff/Nexa receiver.

Bert

[Karam]

Had a quick look at Electrisave product and as far as I can tell there is only a current transformer. This means that it could be relying on the (simplistic) calculation of power based on multiplying measured current by assumed RMS voltage. As I mentioned earlier this is only a good approximation for resistive loads such as incadescent lights or electric heaters.

Perhaps for the 'average' home power is mostly consumed by resistive loads in which case it may provide a reasonable rough guide.

Karam