Simple DIY power transient monitor?

Try this. Get a digital multimeter with an RS-232 output. Write a BASIC program to monitor the multimeter output. Have it record all deviations from a norm you either establish or from a running average computed by your software. The response of your multimeter will determine the bandwidth you can monitor.

Al

I remember seeing a VERY simple circuit in something like Radio Electronics way back in the early 1970's. Once or twice I went back and searched to try to find that again, without success. It seems like it was only a few components but would latch to record spikes or power failures. I can't remember which, too many years, too many dead brain cells.

However, having talked with a few of the guys who spent a bunch of their time on the subject, they said that the more accurate you want to be about this the harder it gets, and it ramps up quickly. They were looking at lots of the cheap "surge protectors" and were not impressed. I kept mumbling I should find get a big heavy Sola transformer. Any single cycle, or less, spikes or dropouts should meet some stiff opposition with one of those, even if they are hot and weigh fifty kilos.

Sound card, resistors, job done.

What you are referring to as a "brick" is more correctly called a "wall-wart." AIUI, "bricks" are line-powered, switching DC power supplies. They are not transformer-based, and the outputs are usually fully regulated. Wall warts usually output uh, got to be careful here, uh let me just say that what they put out is not fully-regulated DC. ;-)

I could be wrong.

--Mac

YOU FORGOT THE ISOLATION TRANSFORMER!!! Other than that, it could work pretty well (if you lived). GG

Transients may be of short durationg. Typical cheap RS232 compatible multimeters have a 1 or 2 second integration time. Might miss it.

A cheap data acquisition board would be better.

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w_tom wrote: >>I've Googled but don't see any circuits for a simple mains power >>transient monitor. >>

Damn, Dave. You sure know how to rain on a parade. ;-)

John

Oops! I meant to address w_tom. Sorry.

John

True. Personally, I'm happy with only the resistors. Three in series in each of the legs, two different makes, each one of a rating able to take 2* the input voltage, and rated for the input voltage, and three in parallel for the shunt resistors). As well as output isolation resistors after the shunt. So a dangerous fault would be at least 4 failures away.

Your utility does this all the time.Why reinvent the wheel?

-- Tzortzakakis Dimitrios major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr Ï "Al" Ýãñáøå óôï ìÞíõìá news: snipped-for-privacy@news.verizon.net...

You used to be able to get a free data acquisition kit at Dataq. It was crippled, of course. But you might be able to write your own program for it. It was a promo to get you to buy better modules and/or software. Try this web site:

Al

: I remember seeing a VERY simple circuit in something like Radio : Electronics way back in the early 1970's. Once or twice I went : back and searched to try to find that again, without success. It : seems like it was only a few components but would latch to record : spikes or power failures. I can't remember which, too many years, : too many dead brain cells.

In the same boat here with memory, so take this with a grain of salt...

I think the project was in Popular Electronics, being Elementary Electronics was more "kids" and Radio Electronics was more "adult".

From what I remember, I'm pretty sure I built one, but it wasn't very good. It was a simple over or under voltage monitor (one led for each and a reset button).

I think it used a "surplus junk transformer" out of your junk drawer that had either a 6.3v or 12.6v secondary. Whatever chip it used (could of been like a LM317) had a simple circuit around it to monitor the secondary voltage of the transformer (probably after passing through a 1N4004, no filters). I think the point of the article was if you used a 12.6v transformer, you were dealing with 10:1 ratios or something.

Anyway, whatever adjustment was inside set the high or over voltage led to come on and stay on. Think that was set to (in theory) to 130v.

It didn't really detect low voltage if I remember correctly, was it did was if voltage was lost completely, when restored the other led would light. Same bit when you first plugged it in, the low led automatically lit, you pressed reset to clear.

So I guess if you came home and the low led was on, you knew you lost power.

I remember this thing because it was around the same time Radio Shack started selling that chip, which for the life of me I can't remember now, it was like designed for building an audio sound VU meter. There was a follow up at some point on building "an improved version" of the monitoring gizmo using it. So instead of a simple two led thing, you could read the voltage directly using 10 or so led's.

Remember this was all prior to cheap LCD meters being around (probably pixie tubes were the closest digital meters) so it was sort of neat having a visual multi-led ac meter, even if it only worked from 108-130 or whatever the range was.

Point is, even the fancy version didn't detect spikes.

Pretty sure Sam G. had articles in all those mags at that time, if there is an index to be had, he should know.

-bruce snipped-for-privacy@ripco.com

Offer now is "Chart Recorder Starter Kit for $24.95"

N

Thus spake Ian Stirling:

I'm sure there's a *bit* more to it than that. Care to elaborate?

In alt.engineering.electrical Ian Stirling wrote: | In sci.electronics.design snipped-for-privacy@yahoo.com wrote: |> Ian Stirling wrote: |>> In sci.electronics.design DaveC wrote: |>> > I've Googled but don't see any circuits for a simple mains power transient |>> > monitor. |>> >

|>> > Nothing fancy. I'd be happy to have an array of LEDs, calibrated to certain |>> > levels of dropout, spike, etc. |>> >

|>> > Does such a DIY circuit exist? |>>

|>> Sound card, resistors, job done. |> |> YOU FORGOT THE ISOLATION TRANSFORMER!!! Other than that, it could work |> pretty well (if you lived). | | True. | Personally, I'm happy with only the resistors. | Three in series in each of the legs, two different makes, each one | of a rating able to take 2* the input voltage, and rated for the input | voltage, and three in parallel for the shunt resistors). As well as output | isolation resistors after the shunt. | So a dangerous fault would be at least 4 failures away.

Add a fuse. Put it on a branch circuit.

| Thus spake Ian Stirling: | |> Sound card, resistors, job done. | | I'm sure there's a *bit* more to it than that. Care to elaborate?

I've been putting some thought into a power monitor. But I want to not only monitor voltage, but also current. And I do want some reasonable resolution out of it but I am not sure how much I'll really need. What I have in mind right now is to run the power from the main breaker to an enclosure having 2 sets of terminal blocks. The first set would just be a connection point. The 2nd set would distribute power to the branch panels. In between there would be three current transformers. Tapped into the terminal block will be fused voltage sensors. All this will drive a circuit board (to be designed) that will convert levels to 16-bit digital at some data rate like 96 kHz, serialize all channels, and drive an LED viewed through a small covered window. A pickup with then feed all that data to a computer to de-serialize and process as desired. This should be sure to keep high voltages away from the computer (especially the CT voltages). The only metal in and out of that box would be the power conductors themselves, and ground (also metered).

Current transformers are of course good. However, I needed something quickly to monitor power usage. I ended up with a simple box, with a .1R resistor in the live, and three similar resistor networks from live/neutral/sense (3 of

3 500V rated resistors in series, to 3 resistors in parallel to form the shunt, and another 3 resistors on the output to isolate the output. (using neutral as 'ground', and bringing that out through another 3 resistors in parallel.)

I actually used a scope - however, there is in principle no reason why this couldn't be done with a sound card. The basic idea is to keep impedances high, and all currents low, so that even in the event of multiple failures, nothing bad happens. This does of course greatly reduce the speed, but in many cases that's not a problem - I would have been quite happy with a bandwidth of 1Khz, which was comfortably exceeded.

This is not an approach to take lightly, you need to understand the reasons why this sort of circuit is not allowed in production, and carefully engineer in the safety, rather than taking the 'easy' approach with current/voltage transformers, when it can be more or less obvious from construction that nothing very bad can happen. Otherwise, you can win a Darwin award.

Thus spake Ian Stirling:

Posthumously (by definition).