Detecting AC current

[rhino]

Did a quick search and didn't see anything that really stood out. What I would like to do is sense when my sump pump turns on and off. One way I was thinking of doing this is by sensing when the current draw on the AC line went up and down.... something like an AC clamp meter (out of the AC circuit and non-distructive). Is there a device out there that I can do this with and be able to interface to a pic? Don't need a high resolution output, just something to indicate there is current draw past the idle threshold... assuming there is a small amount of current draw in the idle state. Any enlightenment would be appreciated. Voltage = 120V 60 Hz .Thanks

[mister_e]

Current transformer in serie with the load is the way to go. You can easily built your own with few feets of wire.

[Acetronics2]

The simple Way : use three power Si diodes in series with the line to create a voltage loss. Three other diodes anti-paralled will allow full wave transmission.
Or two diodes and a small value resistor, if there's an offset.

Then use this loss to power on the led of an opto-coupler ...an have the looked-for info from the opto's transistor.

plus a free zero voltage detector for synchro-switching !!!

so simple ...

Have a look to slave supplies sold for powering computer accessoiries ...

Alain

[rhino]

Thanks for your enlightenment. I went the route of a current transformer, just to keep out of the high voltage circuit. Did a google seach to read up some more on it. Snagged one of those iron donughts you see on computer cables for the core. When I get to the point of filtering the signal, I may also incorporate the opto as Acetronics suggested. Seems to work pretty good. I have to play around some more with the # of turns on the secondary to get the right voltage. Built it last night while watching TV... my kids thought it was pretty cool when I explained the operation. Thanks again!

[mister_e]

Yet another problem solved. I did many things with current transformer as now without any opto isolator wich are working really great. But i guess it's still a good practice... safer but not cheaper

Many more turn on te secondary will cure the problem but you can also use an opamp to raise the voltage and filter the signal in the same package too. Voltage comparator could be another way and will act as a buffer.

As always... endless possibility are in your hands ]

[Dwayne]

Hello Rhino,

I notice you are working on a sump pump project...

I know this is "off the wall", but it may be worth checking into..

they have a "Water Sump Pump"... NO electricity at all...It relys on your water provided by the city/town. The only way this would not work, is if you have well water, and use a electrical pump to pump water from your well...

DWayne