Logging mains voltage: Arduino or Raspberry Pi?

[The Natural Philosopher]

THis is like renewable energy.

Solving nonexistent problems in the most expensive and complicated way possible

It's a CRAP approach

[dennis]

You can say what you like now, but this is a DIY group and some people won't know what an isolating transformer does or why to use one. Only a fool expects everyone in a public audience to understand what they say. Don't give out advice on dangerous stuff unless you make it clear.

Its the same with the advice for 12V supplies people give out, there are

12V supplies that are isolated from the mains but there are some that aren't and you really don't want the ones that aren't for "projects". Its hard to tell on ebay/amazon what is and isn't live so I tend not to buy them when cpc is just as cheap.

[Roger Hayter]

Absolutely. The only reason for using a transformer capable of supplying significant power is to obtain one with proper mains voltage insulation. Otherwise any small signal 50:1 transformer with a suitable low frequency bandwidth would do the job.

[newshound]

This is one of the mysteries, there are a couple of incandescent bulbs and AFAIK they are not prone to failure. These are 2.3 kW heaters. As an alternative to logging data, I suppose I could knock up a diac/triac "dimmer" to drop the power by (say) 10%.

[Fredxx]

I'm with Dave here. As long as the unit doesn't become dry I wouldn't expect it to be sensitive on voltage. Methinks a failing batch.

The fact incandescent bulbs can cope with the higher voltage just confirms these thoughts.

It is possible your DVM reads high. Some are very poor at measuring rms voltage.

[newshound]

You are both making reasonable points. Roger, I don't *think* we are suffering from low water level or tilting, but this is something that I can't be absolutely certain about. John, I don't *think* it is fast transients causing insulation failure because then I would be expecting it to "blow" other stuff like fluorescent lights, phone chargers, the electronics of the washing machine, etc. But I could be wrong. I originally thought it must be something in the local water chemistry. Seeing 250 volts on my single measurement makes me more inclined to think it is worth doing some logging.

[newshound]

This one read 240V at home. But I will try again with the Robin PSC/loop tester which is probably more accurate.

[Johnny B Good]

Which statement is total and utter bollocks. :-)

Essentially true in this case but totally beside the point.

Wow! Here's me thinking that it's only TNP that doesn't properly understand basic electrical theory. :-)

Saturation issues have nothing to do with drawing power via a transformer's secondary. The problem arises out of the magnetization current increasing (due to either insufficient turns or else, equivalently, excess voltage) to the point that the magnetic flux in the core reaches a level that saturates the magnetic core material used.

There is an art to manufacturing an old fashioned wallwart transformer as cheaply as possible such as those often hot running chinese wallwarts where they've calculated not only the thinnest of wire to be used but also the minimum number of turns required for the nominal voltage rating without inducing excessive saturation effects. As a consequence, such transformer designs leave no margin whatsoever for over-volting events in the mains supply.

The heating effect in such transformers under no-load conditions is typically a watt or two both from I squared losses due to the saturation peaks causing transient reductions in the primary inductance which results in corresponding current spikes and the increased hysteresis losses in the core material itself.

In my search to find some figures on the magnitude of 'magnetisation current' compared to the full load current, I noticed some interesting animated graphs of core saturation effects in this wikipedia article

.

Unfortunately, I wasn't able to find figures for transformer magnetisation current which ISTR as being typically an order of magnitude or so less than that due to their maximum load current ratings.

Using a pair of transformers wired as I suggested is an effective way to eliminate any question regarding transformer saturation effects for the sort of over-volting events being monitored. It's an arrangement that allows for a 100% over-volting event to be measured without saturation effects spoiling the integrity of the measurement of an event that would instantly fry incandescent lamps and heater elements alike.

It doesn't matter that the transformers are only operating at half their designed voltage rating. The arbitrarily low secondary voltage is simply a faithful, low voltage, galvanically isolated replica of the mains voltage being monitored anyway, the level of which will be calibrated so that 240v corresponds to -10 or -20 dB of FSD in the audio recording itself. Using an audio recording application to log the mains waveform is just a quick 'n' dirty way to see whether or not there is anything of interest to be logged in the first place.

[The Natural Philosopher]

I give up. What is the use of a degree in it and a year spent designing transformers?

[tony sayer]

Isolating transformers are generally known to isolate a direct mains connection.....

[tony sayer]

In article , charles scribeth thus

Indeed they were, still got one 240 in and 240 out at around 5 kW..

[charles]

Mine's not a big as that, but still quite heavy.

[whisky-dave]

All you do then is reducing the overvolage to a level you might not detect with an ardunio.

[The Natural Philosopher]

????

Hsa the government been putting somnething in the water supply?

[whisky-dave]

Yeah sure it is. Idiot.

In direct current (DC), the electric charge (current) only flows in one dir ection. Electric charge in alternating current (AC), on the other hand, cha nges direction periodically. The voltage in AC circuits also periodically r everses because the current changes direction.

Offset has nothing to do with it.

but still a lot more than you do. DC is NOT AC with an offset.

Isoltaing transformers isolate that is why they are called Isolating transformers. It is NOT always about reducing to a safe level, because ther e are pulse isolating transformer nothing to do woith isolating for safety reasons.

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No who knows nothing. isolating transformers aren't just about safer voltages.

[whisky-dave]

A data logger won;t fix the problem, niether will buying an ardunio whether it's fakeardunio from ebay or the latest verion with wifi/bluetooth it'll be a waste of money, if you know you have 250V when you should really only have 230V then that is what needs sorting, an ardunio can't sort this prob lem out.

Perhaps you need a flying ardunio then ;-)

time to stop measuring the problem and start sorting it.

[whisky-dave]

Not sure who puts stuff in the water.

[Johnny B Good]

Heavy! I should say so! Based on my collection of 360VA transformers which each weigh 16 Lbs or so. I'd estimate a 'Ballpark' figure for that

5KVA transformer to be somewhere around a couple of CWT! :-)

[NY]

It doesn't *solve* the problem, but it supplies evidence of the fact that there is a problem and the times when it occurs, which will (hopefully) persuade the electricity supply company to investigate and rectify.

What intrigues me is that a fairly small over-voltage of 10V (*) is shorting the life of the wallpaper stripper element so much. You'd expect other heating elements (kettle, immersion heater, electric fire, cooker) would suffer the same fate.

(*)

says

230V + 6% -10% (so 216V to 253V) with a nominal voltage of 240V

[whisky-dave]

Seems a lot of effort if you already know that the mains gets to 250V can't you just photography the display on the DMM, if that isn't enough proof for the elec company, will a homemade measuring system be enough ?.

I would think the same, my wallpaper stripper has been in the loft for the past 8 years, so while I used mine for a few days that was it.

I assume the unit doesn't boil dry easily or moving it about has been eliminated as the cause, maybe there's a dodgy connection somewhere.

It does seem starnge that a voltage of just 250V would have this effect even if it was for 10 mins or so I'd expect a cutout to go.

I'd expect the electric company would be able to provide a mains monitor for their own satisfaction rathe rthan believe some home made device.