Thanks, yes I agree completely about the sampling strategy, but I'd sort out details once I knew the capability of the device. My point was that I think I am looking for slowish variations rather than microsecond transients. (I am trying to find what is killing electric kettle elements).
As you say, small mains transformer, a few resistors and of course a 5 volt Zener on the ADC input.
Yes, I'm not necessarily worried about exact time. Unless I suppose I want to escalate the results to the distribution company.
Fun is good :-)
You need a simple mains transformer to a few volts and feed it into the A-D converter on an arduino and do some maths on the samples. Only a couple of resistors required to set the voltage range to be within the ADC input range.
A nodeMCU will almost certainly do everything you want including logging to a remote database.
How often will it sample and what sort levels of spikes and transcients. And don't forget the ADC can only really 'see' DC voltages.
doesn't help much though, in fact depending on these spikes you might not 'see' much after reducing it through a transformer and rectifier.
Problem is dealing with mains AC voltages and having to reduce them first.
My point is, do the low pass filtering in software, though.
A bridge rectifier and smoothing cap is a peak voltage reading abortion for this: you want to do an RMS average especially for kettle elements.
My solution is less components, but more code.
Code is cheap!
Only issue is doing a square root in binary integers...arduinos don't have native floating point shit!
Well i'd just clamp that to the 5V rails.
You will run at a high impedance so no damage dumping the odd mA into the supply
Depending on how long it takes you. The idea device would just be a pen holder that respondened to changes in the voltage a bit like an old chart recorder and I'm still not sure how you'll detect what's blowing a kettle elimante I wouldn't have thought they'd be suseptable to transients.
I'm still note sure how you'll know what caused teh transcient even after detecting it.
How long will this kettle element be ON for ?
OK, it's not an element in a kettle. It's in a wallpaper stripper, used as a steam generator. They are typically failing after half a dozen (separate) 20 minute sessions. They are not being boiled dry, they are on a timer to prevent that. Oh, and nothing else seems to be blowing. I
*originally* thought it must be a problem with the chemistry of the local water supply but two separate chemists with long experience are convinced that this is unlikely.I just thought that for less than £100 worth of re-useable bits it would be nice to investigate the electrics.
Let's park that for the moment
Clamp what? I'm confused.
The input.
resistor and reverse biased diode to +5V. If it goes above 5V the diode clamps it to the suplly rail plus half a volt or so. Standsard technique.
is a perfect example
from a similar app.
Arduino, hands-down. Otherwise you're paying about 3 times the price for a lot of fancy graphics rendering power you will not be needing. Personally I also much prefer C to Bash.
Not really. Loads of suitable sub-min mains transformers in every local recycling site; help yourself for free. Or just a couple of quid new from China through Ebay.
So let me get this right your trying to find out why a steam wallpaper stripper is failing?.
I'd ask what make is it ?. Where is it made?
What's the actual specified mains voltage of the element in use for it?
What the local mains voltage as measured over few days sampling and are you in a rural overhead line fed area or urban underground?
And has the same thing happened to any like for like replacements?...
Finally does it take any RCD trip out when it fails?.
AC is just DC with an offset.
So we have something else you don't know much about.
Isolating transformers isolate the mains and reduce them to safe levels.
OK perhaps I am getting my Zeners and Shottkys mixed up, it is a long time since I actually built anything like that. But that's the principle I was trying to convey.
It's ridiculous to imagine that mains quality has anything to do with your wallpaper strippers failing.
Failing in what way? Permanently? Open circuit? Short circuit? Resettably? What make & model?
If it is failing open or short circuit, that suggests that the element is "burning out" - that its temperature is rising to a point that it melts and either breaks or else makes contact with earth. Over-voltage would seem to be a plausible cause of this. But with a large amount of water around it (the water that the wallpaper stripper is boiling) and presumably good conduction from the element wire to the surface and from there to the water, I'd be surprised if over-voltage would cause *that* much of a temperature rise.
Sounds an intriguing problem. I'll be interested to hear whether the mains voltage *is* varying that much, if you manage to get a data logger working.
No: using a zener is a completely different technique. There you aim to divert extra overvoltage current to ground. The clamp diverts it to the power supply first.
Shottkys are only necessary to clamp fast transients, also: Ordinary diodes work OK. Just put a small cap after the resistor.
Like this
Thanks very much, that makes sense now!
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