I am trying to find a cheap solution to measure amps at half-hour signals from a 230V, 50hz supply.

I want to do this for energy monitoring on different buildings and want non-electricians to do the visits so a CT clamp solution is required.

I want to use off-the-shelf components because I want the system to be durable and simple to use.

No requirment to measure the voltage as accuracy s not important ( +-10% is fine)

The all-in-one offerings are very expensive such as the HOBO monitor with their own CTs, or the Tinytag offering. these are expensive because they need CTs with built-in ACD chip to convert the analogue CT output to a digital voltage signal to be read by the logger. they also have lots of functionality I dont require.

Im wondering if the below solution might work - essentially cheep split core CTs connected to standard pulse power meters and a pulse logger

3 * 5V output CTs (approx £30 each) https://uk.rs-online.com/web/p/current-transformers/5330637
3 * single phase energy meter with a voltage pulse output (approx £80) https://uk.rs-online.com/web/p/energy-meters/1242437
1* pulse reading data logger (approx £100) - https://docs.rs-online.com/ffbf/A700000008456228.pdf

This solution comes out as £300 whereas most other solutions are £600 plus.

However, power meters have an input for line voltage which is not satisfied - my main questions are

1. Can you set a power meter to assume a voltage of say 230V and not need to measure it?
2. Could I connect a constant DC or AC voltage source (low voltage) to the voltage inputs and then manipulate the results afterwards to give actual power assuming 230V
3. Is there any other way to get around this issue?
4. are there any other ways to achieve what im trying to achieve without paying for the all-in-one solutions? bearing in mind size and accuracy are not of importance

thanks for reading!

 

https://www.toolstation.com/project-ev-ct-clamp/p34753 is priced at £14 if you are in the UK. The "Toostation technical specification" is worse than useless and it may be designed for higher currents than you are hoping to measure, but I do like the price! I believe the grid voltage in Ghana is fairly stable these days so if +/- 10% is okay, you could use a fairly inexpenisve multimeter - of the order of £10 - to measure the CT current output and multiply by the scaling factor whatever that is. The CT clamp is reading the current so when you mention voltage you are really interested in power consumption?

 

Hi there, so measuring instantaneous current isn't too much of a problem as you say,

but I realise my description above misses the key fact that I want to log the results in half-hourly periods over a month or so. that is the challenging thing when using cheep ac- ac CTs

 

You may find this pdf helpful: https://www.nict.go.jp/en/asean_ivo/lde9n2000000amww-att/a1480310360346.pdf

 

I want to log the results in half-hourly periods over a month or so. that is the challenging thing when using cheep ac- ac CTs

This sounds more like continuous monitoring where the instrument would be left on site and the power usage would be monitored and a record of total power usage during each successive half hour would be logged?

This could be relatively inexpensively achieved by a processor like the Arduino UNO https://www.ebay.co.uk/itm/322898299808 and a memory shield https://www.ebay.co.uk/itm/191866322774. Plugged into the mains with a conventional linear power supply (transformer, full wave rectifier, smoothing capacitor) in a project box, with a bit of analogue electronics, you could continuously sniff the mains voltage and CT clamp current, get a real power usage maybe once a second (or even continuously) and sum usage over each half hour. Measuring 3 phases would just need 3 CT clamps. Internal rechargeable battery to ride out power outages and even record them would be a relatively simple enhancement. Genuinely not difficult to do, possibly a worthwhile student project?

Had to add this link to a current transformer made with washers and the circuit for converting from current to low voltage to voltage from o to 5V.

Actually, whilst you'd need the amplify and precision rectify the processor A/D can do the rest.

 

https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/introduction