Energy Monitoring Project

Hi everybody!

I has been following the site for several months and finally I decided to open an account.

I'm developing a energy monitoring system based on the tutorials of this page, basically I want to measure the energy spending of a house, store the data in some files or database, and graph the data in a localhost, webpage or mobile device.

I'm using an Arduino Uno and a Ethernet shield for the task, also, I'm developing an automation system to open or close the energy switches and sockets with 2 relays, and also a lighting dimmer (a simple LED matrix).

Well, that's the history, my problem is:

I'm from Mexico, I bought the CT sensor on line, but, here in Mexico I can't find an AC-to-AC converter, I thought buying it online, but I didn't for the difference in the electrical specifications. So, I decided to buy an 120VAC to 9VAC, 300mA transformer. Here is the product page (is from a local store here in Monterrey)

Is there any problem for the change? Bad compatibility, error measures, electrical problems or warnings?

I hope you can help me. Greetings from Monterrey Mexico!

Mr. Sharkey's picture

Re: Energy Monitoring Project

That transformer should work fine, but $69 ???!!!! Is there some currency exchange rate that we should be aware of? I'd expect such a device to be a tenth of that in US$.

Here are two suitable transformers from Mouser Electronics that turned up in a quick search, the first is at end-of-life and will be discontinued: US$4.24

Her's a rather high-end unit at US$21.94, but that's still 1/3 the price of the one you specified:

Also, it doesn't have to be a 9 volt transformer for the voltage sample. By changing the value of the scaling resistors, nearly any voltage transformer can be used, from 3 up to 48 if you design carefully and make sure that the higher voltage is properly insulated, etc. All you really need is a sample of the AC waveform, which disn'e involve and real current draw. The scaling resistors take it down to a volt or so for input to the Arduino analog input. About the only way to go wrong is if the transformer causes waveform distortion, which would mess up the power calculations.

If it was me, I'd find some old scrap-box transformer or a old hunk of discarded electronics to tear apart for the power supply transformer before I'd spend a week's grocery money on a new one.

juank_kenny's picture

Re: Energy Monitoring Project

Oh! Sorry about the confusion, the price is in MXN, with the current exchange rate, the price of the transformer is about US$5.00

And thanks for the observation, also I have an old AC-DC converter which has an output of 12VCD, I thought remove the rectifier and those things, and use only the transformer which provides an output of 8.5VAC(aprox), but, for security reasons I'll buy the transformer.

Thanks for the answer, very helpful

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