Sense Power Line Cord, Turn-on Fan

I can't find the specification for adjustability. Is the LCG3 what you have, or a different model? Thanks!

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Ah, I see.

Maybe you should approach the problem the other way. You could use a PID controller to turn on or off the TV, and thus precisely regulate the temperature of the cabinet ;-)

Now *there's* the trick! Sno-o-o-o-o-ort ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Have you been getting enough power to run an LED? (or a solid state relay)?

It is easy enough to get signal to drive a high impedance, but when one tries to drive lower impedances, the energy isn't there.

I didn't spend much time with ferrites since I was interesting in directly driving LED's or SSR's with the output. With my iron cored transformers I plotted out the power for given loadings.

I rigged a selector switch with 47 ohm resistors (easier than a pot) and measured the secondary voltage and current with 5 turns to 25 turns on the primary.

With 5 turns (and my 40 watt soldering iron on the input) I got 1.3 milliamps, .6 volts into 470 ohms. Secondary was the 120 volt winding.

With 25 turns (and 40 watts in) 1128 ohms loading 5.26 volts @ 4.56 milliamps. Enough to run some LEDs and do useful work directly, no amplifiers, no other power source. Elegant.

The peak power points for 5 and 25 turns was 470 and 1128 ohms respectively (with the 40 watt load)

Peak current was 3 milliamps 5T into zero ohms and 11 milliamps with

25 turns. Peak voltage was 1.04 volts 5T open circuit, and 11.15 for 25 turns.

I plotted this out for 5-10-15-20-25 turns with the 40 watt load and that gave me a quick reference to use for current sensing relays (at least with that particular transformer)

With the ferrites I tried the power wasn't there to drive an led (at least in a reasonably small size current transformer). The output waveform wasn't sinusoidal either (probably due to saturation).

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OK, here's a trick from one of us 'low tech' guys. Use a filament transformer in reverse. 0.5 ohm resistor in parallel with secondary, in series with TV. 'Primary' runs into a bridge rectifier and RC to drive a solid state relay. Whole thing fits into a standard electrical box. I used mine for 10 years to turn on the audio amp with the TV. GG

Sure Bob

Schmidt trigger would require a separate power supply. I was using a $5 part for my current transformer but factor in the cost of a supply for the signal amplification of a ferrite and there's no advantage to using it. Can't get much simpler than a small transformer driving a SSR via a diode and cap.

Safety . . . I didn't fool around with any open circuit transients on the high turns ratio iron lamination transformer. Presumably a high voltage spike could be generated if it were unloaded and power applied. One MOV would fix that. I did use a pair of zeners to clamp my "X-ray warning beacon back up horn" since I couldn't control what wattage lamp someone might install in it.

I didn't take any safety precautions on the output side of my transformer test rig and didn't get zapped, but that might be luck. The load switches only had one open circuit position, and I only took five readings OC (or into the 10 Mohm meter).

Well. if I had the circuitry and supply voltages there for some other purpose a ferrite is smaller and might be a better choice.

Is it possible to get an accurate RMS voltage from a ferrite current trans at 60 HZ? What load impedance?

Regards Bob

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Hello Watson,

You just have to calculate it so that the core is staying clear of saturation at the maximum current. I usually maintain a 30% distance from that point. So the core has to be big enough that one turn at whatever current Jim's stuff is drawing at the peaks of the 60Hz cycle is in the kosher range. Plus some margin.

For this app you don't need a large core. But you can, depending on what's in the garage boxes.

Regards, Joerg

Compare the power consumption of a modern LCD and CRT monitor of the same sizes.

They are often very comparable, due to the small fluorescant tubes having lousy efficiency even before the 50% loss in the polariser, and 66% loss in the colour filters.

IMHO, you'd be better off putting some foil-lined polystyrene 'tiles' on the under side of the affected cabinets to try to isolate them from the TV heat. I think putting a fan in there will only increase the chance of blowing warm air into the cracks around the door.

Swap around the cabinet contents to place stuff which could benefit from a warmer/dryer environment in the warmer places.

-- Graham W

PGM-FI page updated, Graphics Tutorial WIMBORNE Wessex Dorset UK Astro Society's Web pages, Info, Meeting Dates, Sites & Maps Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

Hello Jim,

In case all you need to do is turn on the fan when it gets toasty you might be able to do that with an attic fan thermostat. Every large hardware store has these. At HD usually way in the back behind the lumber, where the roofing accessories are. Last time I looked they were around $10 and are adjustable. I was thinking about using one to turn on the pool pump when frost sets in but they can't be adjusted this low.

Regards, Joerg

I had no problems with ferrites here. They can even be used to check whether or not a DC current is there by running them into saturation. The DC trip level can be set by the number of turns.

Regards, Joerg

Yes, I have the LCG3 models. According to the "documentation" that came with the strips, at max sensitivity, they will switch on with a 40W incandescent lamp load. They state that the strips will work reliably with home entertainment eqpt, TVs, computers, medium & large shop eqpt, fans, heaters, pumps, and "some kitchen appliances", etc. No specs for the current sensitivity are given, but I can say that they live up to the claims. I use one on my computer system to turn on the monitor and sound system connected to the computer. The other one is connected to the home entertainment system. When I turn on the TV, the sound system turns on in unison. No need to collect all the remotes to switch everything on. You might find a better deal on Ebay... maybe not.

I remember the unit that Radio Shack sold a number of years ago.. very similar in operation, but none of the sockets were always hot. Sensitivity was not adjustable either. Heathkit sold one too... it was the model GD-1295. You can get a copy of the schematic at

I was thinking about building a copy of that unit, but just never seemed to get the time. From what I can remember from the schematic, the current sensing device is R1, and is likely to be something like a Thermometrics current limiting thermistor. I seem to remember doing the calculations and came up with a Thermometrics model CL-80 for the sensor. I think I was using something like 0.5A as the threshold for the device to switch on. The relay is a 115 VDC coil, and the 417-834 transistor is equivalent to an MPSU10 (that kinda dates this design). The 56-44 is a 1N4653 4.7V zener. D1 and D2 are 1N4004 units. The varistor R4 is an everyday MOV for a 117V line. That's about as much as I can remember about it. I have all the parts but not the time to build it. Maybe that will be still on my agenda when I retire .

Oh, BTW, if you're interested in building one of these strips using a current transformer, I have several units that I had left over from a project. Be glad to send you a couple if you want them. They're 200 turns, rated at about 10A AC. About 1.25" dia, and 0.625" high with a 3/16" hole, just about big enough for a single turn of 14 ga wire. Would work out great for one of these strips.

Cheers!!!

--
Dave M
MasonDG44 at comcast dot net  (Just subsitute the appropriate characters in 
the address)

Never take a laxative and a sleeping pill at the same time!!

Hello,

Could you give us a first name? It's just nicer to communicate then.

That wasn't the task at hand here. Jim wanted an easy (and I suppose safe) method to measure the current in an AC circuit. You do not need any power to do that and ferrites can perform nicely. Plus they are very cheap. All you need in this case is a voltage across a load resistor on the secondary that is proportional to the current flowing though that one turn of primary. I guess in Jim's case this voltage would be rectified and fed into a Schmitt trigger that controls a fan.

If you want to transfer power at 60Hz the classic lamination core of the usual power transformer is the ticket. Ferrites excel when you are above several kHz. But for current sensing it doesn't really matter.

Regards, Joerg

snip

Are you sure about this? MOV's do fail, and sometimes quite spectacularly, but if the energy they are asked to dissipate is within their ratings (and repetitive hits, heat build up or a steady state over voltage condition isn't encountered) they survive to do it again.

MOV's can be degraded by repetitive strikes, no argument there. But the joule rating, isn't the number of strikes. e.g. 150 joule rating doesn't mean it fails if asked to take 300 hits of one joule each time (assuming heat build up isn't a factor).

The typical failure mode, as I understand it, is when the device reaches a thermal runaway condition and shorts, shunting the power supply. Well within its energy rating and thermal limits, it is expected to last for a very long time.

Some parts will always fail the first time . . . infant mortality.

I always trust the empirical data . . . "Never argue with empirical data."

Particularly interesting because we are supposed to get electronic meters in the next year or so. The mechanical ones suck - particularly with things like proportioning heaters - the meter seems to spin up in less than a 1/8 revolution and coasts back in a 1/4 to

1/2 revolution, and their accuracy is limited in the best of conditions. At least with an electronic one they can use a look up table to correct for environmental conditions and loading.

I do wonder about the loss of privacy - the ones we are getting can report when power is consumed, how much, and the power factor of the load - I think you could tell a lot by that (like when someone's home and what they might be doing).

I guess I'd take issue with the statement: "in a current transformer you don't have to" (have low impedance - or high permeability) That all depends on what you plan to do - what load impedance you want to drive.

Regards bob

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Hey Jim, Time to rearrange the cabinets! Put your plates and coffee cups in this one. Always nice to have a pre-warmed plate and cup... 8-)

Charlie

But it's the closest to the RO water, necessary to take the pills ;-)

(I've ordered the LCG3 Smart Power Strip that "DaveM" recommended. That will resolve the issue.)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I think I found that thread.

Look at who the author of the solution is. 8-)

I had a Radio Shack strip, and I did adjust it.

Hello Bob,

Thank you for giving us your first name.

A Schmitt needs power but very little in the case of HC or CD4000 logic. If you want to directly drive the power device or a relay the classic transformer is certainly better here.

Just keep in mind that MOVs are like bank accounts. Every zap takes away some of the assets (Joules). Then one day .... kablouie.

Magnetics, Inc. offers SW to calculate all that but I have not used it yet. I am old-fashioned in this respect, using the graphs and the old HP11C calculator. When I feel nostalgic I crack out the slide rule calculator. Anyway, here is the link:

Getting an accurate RMS voltage is possible. However, while ferrites are cheap and easily available (or even already present in the junk box) they aren't ideal. Strip-wound cores (tape cores) are better but more expensive. Here is a link with more detail:

Impedance with ferrite cores at low frequencies is low, you can't get too many turns on them. But in a current transformer you don't have to.

Regards, Joerg