# Voltage sensing with the voltage adapter

I took some advice and went through some article in the learn section on electricity monitoring. Albeit, I have figured out how a ac to ac voltage adapter works I still cant rap my head around on how to install it. Maybe its just my potato brain.

Do you really mean that, or do you mean how to utilise it?

Yes that. How to utilise it?

It’s time to study the ‘Learn’ section again. I suggest you start at the very beginning with Learn→Electricity Monitoring→AC Power Theory→Introduction→An Introduction to AC Power and the next two pages “Arduino Maths” and “Advanced Maths”.

When you’ve read and understood those pages, you will know why you need to sample and use the voltage. (And don’t believe your voltage is a steady 220 V - it isn’t. You’ll find it varies second by second almost, and by time of day, as the load on the system changes.)

To see how to utilise the voltage, you need to move on to the first page of the “Current & Voltage” section. You might find it useful to look at the code inside emonLib - especially at how calcVI( ) reads the two inputs and processes the numbers.

Will surely go thru it. But my question is a bit different. I was asking like how we clamp the ct on live wire how and where do we plug the voltage adapter.

Have you tried looking at the ‘Guide’ - particularly this page Install emonTx & emonBase - Guide | OpenEnergyMonitor

I know you have not got the emonPi or the emonTx, but the principle is the same.

Thanks for the link. But I am still confused on how the power adapter knows what amount of voltage is going through the mains without physically connecting to it. Maybe it is elementary electronics that I am missing but as far as I have read it seems that its just a simple AC-AC adapter that gives an output signal that furthermore we tone it down with the help of voltage dividers and step down resistors for the ADC REF input. TLDR: how does the power adapter know what amount of volts are flowing through the mains wires if its not clamped/connected over(like the CT)?

But it IS connected to it. The a.c. adapter taps off a sample of the voltage and your emonTx, emonPi or in your case whatever you are building reads that voltage.

## NO THEY DON’T

Now finally I see your problem - you were right after all, it’s inside your brain.
Voltage is what drives the current through your load - your kettle (say). If the voltage is high, it drives more current, that makes the heating element (a resistor) dissipate more power, it gets hotter and the water boils faster. If the voltage is low, less current is driven through the resistor, it dissipates less power, doesn’t get so hot and the water doesn’t boil as quickly.
The a.c. adapter measures the voltage, the current transformer measures the current. The device you’re building, or our emonTx, multiplies the current and voltage together and gives you a measure of the power.

Thanks for explaining it to me like I am a 5 year old. The part I didn’t understand earlier was about the ac adapter taps off the sample voltage. Now I get it. Also, as I have read in the guide for emonTx you can use an extension board and then plug the ac adapter in. Thats fine right(confirming)?

Yes.