I am looking to implement the emonTX around the house to allow monitoring of rooms where I spen time to see the consumption of key appliances such as in the living room, office and various bits in the kitchen.
The problem I have is getting the CT sensors and calibrating them and using a couple of plug sockets to power just the measurement thing.
I have been looking at using a single transformer to give the AC to the plug and then isolating this and then running through a bridge rectifier and voltage reg to bring down to 5V (without reading datasheet for the onboard reg).
Theoretically, this would be fine from what I know, but what I would like to do if possible is use a shunt or similar and have the unit inside the plug socket, or in a empty blank to the side. All the plug sockets I want to measure have an extension lead in them and a remote control on the socket so I can turn off the whole bank at a time.
Is this feasible? safe? Or would I need to look into using separate emonTX type things?
Many thanks
Jimmy
Re: Safe or Not
I think you need to read about GIVmon to understand some of the safety issues.
Basically, if you built it into a sealed plug-in box with absolutely no metallic connection to the outside world (that means you can't connect a computer to monitor directly) and take care of fusing and fire risks, then you can probably do as you suggest. But you will need to do the maths on shunts, voltage drop and power dissipation - you could be in for a nasty shock.
Re: Safe or Not
Very good link, That has suitably put me off for now.
There is a lot of safety things in there, I will have a good read up on this later on when I come up with the idea again, for now I think the extension leads will be the best option for the job.
Cheers again.
Jimmy
Re: Safe or Not
And of course you can't use the same transformer winding for both power and voltage measurement if you have a bridge rectifier unless you isolate it with a differential op.amp, or can use a half-wave rectifier.
The problem with your idea, as you've gathered, is there's no guarantee the neutral won't be at line voltage, therefore you have to treat both line and neutral conductors as potentially live.
I've posted this before and I'll do so again: a neighbour had an electric shower fitted by an idiot and incompetent bathroom fitter, who cut the tails between his meter and consumer unit and added Henley blocks. In doing so, he swapped line and neutral to the consumer unit. Just think through the consequences of that, like what value fuse was protecting anything in the case of an earth fault?
Re: Safe or Not
Again very valid point as to how something so simple can be deadly.
Another point to hammer home the importance of getting all the facts before starting out.
I will stick to "relatively safe" Low voltage for now until I get all my facts in place and have read a lot more.
Jimmy