Hi, I'm looking for something with AC male on one end, and AC female on the other, that can plug an AC device (sump pump) into, that will emit an audible tone when the device is running and consuming current. Kind of like an audible pilot light, or an electric meter that sings.. I want this so I can be aware upstairs when the sump pump runs in the cellar, since occasionally it sticks on. This would also alert us to a plumbing problem. It's a dirt cellar.
It seems like would be a simple device, but I don't know what it would be called.
What you are describing is called a "current transformer". It uses a toroid coil with only one of the ac mains wire going thru it to detect current flow. The toroid has maybe 30-40 turns of wire wrapped around it which acts like a "one-turn transformer". That is fed to an op-amp, then a rectifier and filter, then could feed a sonalert.
But I agree with the person that replied before me. If you don't actually require that you sense that CURRENT is flowing, (in other words, the pump is turning), you could just wire a parallel connection so that when the pump has power, so does a radio or a buzzer (with a transformer), etc.
I would use a big, heavy full-wave bridge rectifier, something rated for more amps than the sump pump will draw. I've seen 25A bridge rectifiers available for several dollar each. Or I might try a bridge rectifier out of an old scrapped AT power supply if it's rated at 6A or more. Depends on the pump.
Then I'd get a pigtail with a plug on it and a socket and insert the bridge's two "~" AC leads in series with the hot AC wire between the plug and socket.
Then I'd put a 1 ohm, ten watt resistor across the bridge's + and - leads. With the pump plugged into it, I'd measure the voltage drop across the resistor. Be Careful around AC, it can be deadly! The idea here is to get the voltage drop across the resistor to be enough to make a buzzer sound. It might take only a 1 ohm resistor if the pump draws a few amps, giving a few volts drop across the resistor. Or if the pump is lower current, then it might take 2 or 5 ohms. But the resistor has to be a power resistor to handle the current. With a 1 ohm resistor, 3 volts drop times 3 amps gives 9 watts of dissipation, so the resistor will get hot. Of course, a piezo buzzer goes across the resistor, in the proper polarity.
Make sure everything is well insulated, since the components have the AC line voltage on them. I would put all of it inside a metal electrical outlet box, wide enough for both an outlet and a switch. Instead of the switch, leave the hole for the switch handle empty and mount the buzzer so that it's below and the sound can come out the hole.
Remember all this has to reliable enough to never prevent the pump from working. It could be messy if it doesn't do its job.
Problem is that the AC line going to the motor is usually hot all the time. The soundmaker would have to be wired _after_ the float switch, which in the sump pumps I've seen, isn't easily accessible because it has to be insulated from the water.
I saw a gadget advertised in a PC mag recently... It looked like a 4 way extension block with one special socket into which you plug your PC. It detected when you switched off your PC (by measuring the current drop) and then 10 seconds later it automatically switched off power to the other devices. Perhaps this would do the job.
Well, you could use a piezo buzzer and a few other parts. One resistor, one diode and one capacitor. The piezo buzzer should be the type that operates on a low DC voltage and doesn't require a driver.
Just wire the circuit in parallel with the AC connections to the pump. You can adjust the 16K resistor for more or less volume, but don't take it too low or the thing might fry. The diode needs to be a 200 volt variety or greater for 120 AC use. A 1N4003 or 1N4004 should work.
He said that wasn't possible because the float switch and motor connections are sealed inside the pump. He only has access to power going in so he has to measure the current somehow.
Select the lowest voltage buzzer (beeper, Sonalert, etc.) you can find, and choose R so that the current drawn by the pump motor will drop the voltage needed by the buzzer plus 1.4V for the diodes in the bridge. That is:
R = (Vbuzzer + 1.4V) / I motor
The capacitor, C, will be:
C = IdT/dV
where C = the capacitance in Farads I = the steady-state current ion the buzzer dt = the period of the rectified waveform dv = the permissible ripple voltage across the buzzer
For example, lets say you have a pump which draws 1A and you've chosen a 6 volt Sonalert which needs 100mA.
For R,
R = (Vb + 1.4V) / 1A = 7.4/1 = 7.4 ohms.
7.5 ohms is a standard value, and then, since the resistor will drop
7.5V at 1A, it will dissipate 7.5 watts, so you'll need to get something like a 15 or 20 watt resistor. A 20 watter won't get as hot as a 10 watter, so that would be the way to go, IMO. A good idea would be to use a wirewound metal-cased 25 watt resistor which you could bolt onto the inside of a small metal minibox which you could use to house the rest of the components. Restricting all of the electrical connections to the inside of the enclosure and making sure there were no electrical connections made to the [metal] housing itself would go a long way to reducing the danger of shock, since you're using the unisolated mains to run the buzzer.
For C, assuming you can tolerate 1/2 a volt of ripple:
C = Idt / dV = 0.1A*0.0083s/0.5V = .00166µF ~ 1700µF
Since the tolerance on the capacitance of cheap electrolytics is often rated at -20 to +80%, you'd need about 2200µF to make sure you got 1700µF, and the cap would need to be rated for at least 6V. 12V wouldn't hurt.
Pretty much any old bridge would work, or you could make up something out of 1N4000s, so your circuit would wind up looking like this:
"AC Line Current Detector". You can build it with common components. Should do your task nicely.
--
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!!
You omitted one very important specification. The 16k resistor must be able to handle the power, and IMNSHO, it should be able to handle the amount of power the whole AC line would put on it. In this case that's
120VAC * 120VAC / 16000, which is 0.9 watts. So call it an even watt. And it should be flameproof.
This solution is simple and cheap. The only drawback is heat. The heat production can be lowered by using schottky- or germanium diodes in the rectifier bridge and finding a buzzer that requires a low voltage. The lower the better.
A low voltage AC buzzer should be even better as you don't need a rectifier and a capacitor to drive it.
Another possibility is replacing the DC buzzer by a solid state relay (SSR). The common ones can be driven by a voltage as low as 3V. The switch can drive a mains powered buzzer. A simple electrical doorbel for instance (through its transformer of course.) A drawback may be the cost. A simple SSR will do about $10,--.
As for producing the less heat possible, a current transformer is the best solution I can imagine. But even if you can find one it will be expensive. You can make one yourself by disassembling a mains to low voltage transformer. An old wallwart will contain one. (Not the newer ones. They are SMPSs.) Remove the mains coil and replace it by some turns of thick wire, thick enough to handle the current to your pump. The series resistor has to be replaced by that coil. To find out the number of turns required you will have to do some experimenting. Start with let's say ten turns and increase this number until the secundary voltage is high enough to drive the buzzer. (The voltage/turn will be more or less constant. So if ten turns produce 2V you will require twentyfive turns to produce 5V.)
The most important and may be most expensive part is the enclosure. To stay on the safe side you need a solid one. Make sure that any metal part that can be touched from the outside has been firmly tied to the protective ground. Otherwise you may have build a killing gadget.
petrus bitbyter
--
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.754 / Virus Database: 504 - Release Date: 6-9-2004
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.