Cheap analog device to measure power or current

antsrealm

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Dec 2010
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Hi,

I'm looking to find a solution for a home power monitoring project to allow me to measure either the power or just the current of as much as 20 circuits. Obviously buying 20 current transmitter will blow the budget to I'm looking for a cheap yet still effective way to get a 4-20ma or 0-10v signal to read on my analog input cards.

Does anyone know a cost effective way to achieve this? Is there an IC I could purchase or some cheap china product that will work well enough for the home environment?

Thanks,
Tony.
 
Thanks but I might need a bit more help. I'm finding it challenging to find a product that will do what I need.

I probably need someone to suggest something to me as I look at all the cheap current sensors and they don't seem quite right on the output voltages etc. Hence why I have posted here, to get some guidance :)
 
arduino is way cheaper as any plc, however please be cautios as the voltage is pretty high.
arduino has many solutions for above.
you will need many coils, however one input is enough as you can switch them with relais.
search for power measurement and arduino.
also possible with a PLC,
connect the coil to a bridge rectifier , a capacitor and a resistor the voltage can be 5 volts, or with a shunt you can maybe even make 20 mA
 
shooter said:
arduino is way cheaper as any plc, however please be cautios as the voltage is pretty high.
arduino has many solutions for above.
you will need many coils, however one input is enough as you can switch them with relais.
search for power measurement and arduino.
also possible with a PLC,
connect the coil to a bridge rectifier , a capacitor and a resistor the voltage can be 5 volts, or with a shunt you can maybe even make 20 mA
Click to expand...

Yeah I already have the PLC and analog cards in my house so that is why I haven't gone arduino. Looks like I'll follow the cap / resistor method. The one I was looking at didn't use a bridge rectifier but instead used a voltage divider. I heard something about not measuring small current draws as the diodes in the rectifier needed to overcome there forward bias and that didn't occur at low readings.
 
antsrealm said:
Hi,

I'm looking to find a solution for a home power monitoring project to allow me to measure either the power or just the current of as much as 20 circuits. Obviously buying 20 current transmitter will blow the budget to I'm looking for a cheap yet still effective way to get a 4-20ma or 0-10v signal to read on my analog input cards.

Does anyone know a cost effective way to achieve this? Is there an IC I could purchase or some cheap china product that will work well enough for the home environment?

Thanks,
Tony.
Click to expand...
Define "cheap".

What you want is a "current transducer". There are several types, the cheapest will be ones that you must remove a wire connection and insert the wire through it (donut CT) and it will give you a DCV output, which you can maybe convert to a mA signal if you have to. If you buy one that is already 4-20mA, it will be more expensive because it will likely include some filtering and isolation, which will cost money.

These people seem to have some "cheap" options but their information is somewhat sketchy and it isn't likely you will get anyone that can help you with what you will want to do.

http://www.aliexpress.com/store/group/Split-core-current-transformer/113159_211708851.html
 
jraef said:
Define "cheap".

What you want is a "current transducer". There are several types, the cheapest will be ones that you must remove a wire connection and insert the wire through it (donut CT) and it will give you a DCV output, which you can maybe convert to a mA signal if you have to. If you buy one that is already 4-20mA, it will be more expensive because it will likely include some filtering and isolation, which will cost money.

These people seem to have some "cheap" options but their information is somewhat sketchy and it isn't likely you will get anyone that can help you with what you will want to do.

http://www.aliexpress.com/store/group/Split-core-current-transformer/113159_211708851.html
Click to expand...

Cheap would be preferably under $50 AUD per sensor/ transducer. I realise I can get a current transducer with 4-20ma output for eg but I cant find anything under $100 and the next thing is the accuracy. To monitor lots of circuits the cost quickly adds up and my first objective is to make sure there is not a cost effective way of doing this before I am forced to consider more expensive sesnors.
 
antsrealm said:
Cheap would be preferably under $50 AUD per sensor/ transducer. I realise I can get a current transducer with 4-20ma output for eg but I cant find anything under $100 and the next thing is the accuracy. To monitor lots of circuits the cost quickly adds up and my first objective is to make sure there is not a cost effective way of doing this before I am forced to consider more expensive sesnors.
Click to expand...


This one from Veris lists for $83.18 US. It has 0-5 VDC output. They might give you a volume discount? ;)
 
Last edited:
Yeah both those recommendation fall within an acceptable price range. The Ebay ones especially. The next thing I need to work out would be accuracy, for eg the veris state +-2% of full scale. So if it's measuring 20A full scale does that mean the smallest reading could be out by 400mA ? I want to monitor power consumption in my house and if a power circuit is only running devices in standby I want to accurately monitor that power consumption. Is that possible with these types of current sensors ? Obviously I'll need a voltage sensor at some point to get the supply voltage to do the calcs to get power.
 
I believe you are correct on the 400mA accuracy thought.

You sure this is worth the trouble?


Divide your total bottom line electricity bill by the number of kilowatts you used. that will give you your total cost per kilowatt, including all the weird charges and fees.

Some of the charges won't go away no matter how little you use.

If this is a hobby thing, by all means carry on... I once had my oil boiler hooked up with all kinds of sensors, and wrote programs in visual basic with charts and graphs etc.... It was a lot of fun
 
what type of home automation system needs 20 cts
and monitors all 20
what are you reading this too (what type of PLC)
most standard houses have 2~3 power ccts and 2~3 light ccts
 
antsrealm said:
Yeah both those recommendation fall within an acceptable price range. The Ebay ones especially. The next thing I need to work out would be accuracy, for eg the veris state +-2% of full scale. So if it's measuring 20A full scale does that mean the smallest reading could be out by 400mA ? I want to monitor power consumption in my house and if a power circuit is only running devices in standby I want to accurately monitor that power consumption. Is that possible with these types of current sensors ? Obviously I'll need a voltage sensor at some point to get the supply voltage to do the calcs to get power.
Click to expand...

All that these sensors tell you is how much current is flowing. Even with a voltage reading you can not expect to calculate power consumption. Aside from the simple power factors involved for things like fridge and aircon motors you will find that a lot of domestic load, especially electronic equipment, is very non linear and a basic VI calculation will not give you any kind of realistic estimate of power consumption. You really need a proper energy meter for your application.
 
you will need high resolution as most of this stand by is very small like mA.
the accuracy is 2% dont mind that one as you can easily calibrate it.
 

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