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Forum Index : Microcontroller and PC projects : Maximite Power Logger
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Nick Guru  Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Has anyone build/written a main power logger using the Maximite? I have a need to monitor a suspect power line. I assume it needs some circuit to plug into the AC power and have the Maximite read the result. I'd like to have it running a graph to look for power spikes. Could a transformer based power adaptor be used with suitable protection circuitry, fed into an analogue input of the Maximite? The Maximite can log the data to a file for creating a graph. Nick |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 3663 |
I guess the transformer might filter out the very spike you'd like to see. Why not just a resistor-divider network to reduce the volts to a sane range. You'd need a bias voltage, too, so that (say) 240V AC which is sort of +120 to -120 (it's not, see below) divided to +1.2 to -1.2 would get 1.2 added and thus a +2.4 to 0 range. OK, so why isn't 240 the same as +120 to -120? because 240 is the RMS voltage as I recall. The peak would be +120 times root 2 I think. Someone help as I'm out of my comfort zone! John |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5913 |
I would start with a transformer and rectifier. I would use a low value filter capacitor so that the sudden changes in voltage are not smoothed out too much. This is the safe way to do it but it might not catch small spikes in the AC. We used to use a transformer and feed the output into a tape recorder for analysis. You could feed the output (with suitable attenuation) into the audio in of a PC. Jim VK7JH MMedit MMBasic Help |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
http://www.stahlke.org/dan/powermeter/ Microblocks. Build with logic. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2290 |
if you desire to remain in the land of the living, you should probably proceed with some caution. monitoring the mains voltage directly and feeding it into a recording device is not a task to jump into lightly. if you are chiefly interested in just seeing that a spike is present (without too much concern for the exact level), a safe approach is to connect a MOV in series with a low-value resistor and a fuse across the mains. use a 285v MOV that will only start to conduct on a spike (i guess you could use a 250v one if you insist) and a resistor that will allow a fair current to flow, start out with a few 10s of ohms. remember that a MOV can absorb an enormous amount of power for a fraction of a second. now, place a current transformer around the lead running to the MOV and measure the current with your maximite/etc with complete safety. remember the burden resistor across the CT. you can also place a second CT around the live conductor of the mains (outside of the above circuit) and monitor the current on the actual feed. you can then use the MOV current to 'gate' the data from the second CT to record just current spikes due to overvoltage hitting your appliances. |
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| Ray B Senior Member  Joined: 16/02/2007 Location: AustraliaPosts: 219 |
If your only looking at a single phase & just want to monitor current go for a clamp on current tranducer for a multimeter and use that to produce a signal source. A year or so back I purchased one from Altronics, was a Hong Da model UR-41 and it was surplus stock so cost only maybe $20. It works in a range of 3 Amperes (output .03V ac) to 300A (output 3V ac). With any type of CT device if you want to magnify (multiply) the output signal take more turns through the CT e.g. 2 turns will double the magnetic field etc, good for low currents. I used it to monitor the current consumption of a beer fridge on the back verandah through some hot summer periods. At the time I used the Maximite as the logger which was based upon some sample code. I'm wanting to do eventually something more comprehensive using split CTs (current transformers) to monitor the current produced at home from my solar array & current imported and exported to the street then produce logging data. Still on my "one day" list. Last time I looked Clipsal were about to release in Australia split CTs which make it simpler (safer)to monitor the current feed. Strictly speaking if your going to cut back the outer insulation to expose the inner insulated cores of an electrical cable this should done by a licensed electrical tradesman. From my experience in the past with CT's in commercial buildings you should not run them open circuit you require a burden resister to load down the signals produced. Not too sure how this works with the modern CTs around these days. Cheers RayB from Perth WA |
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James_From_Canb Senior Member Joined: 19/06/2011 Location: AustraliaPosts: 265 |
Nick, Have you asked your power provider if you can borrow some of their monitoring gear? I did that a few decades back when I lived in Sydney. I think they lent it to me for a fortnight. James My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention. Hedley Lamarr, Blazing Saddles (1974) |
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| Ray B Senior Member Joined: 16/02/2007 Location: AustraliaPosts: 219 |
To add to my previous post. If you just want to monitor a single phase appliance with a 3 pin plug on it there is another option with these Wireless Energy monitors like the PowerTech Plus which are available for about $50 with 3 remote wireless devices. Just need to crack the wireless code.... 
Cheers RayB from Perth WA |
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