Looking for a way to activate a small lamp to show when a remote mounted water pump is running. I know I have seen the method before but my dusty brain cannot seem to find it. The pump is a 120volt unit mounted in a remote pump house out of visual range or I would wire a light across the pressure switch. I was thinking of something like an inductive coil around the hot lead feeding a circuit that would power the light. No problem working on the panel end. Ideas?
Perhaps a current meter is called for. And I am sure there are current sensing relays that would light a bulb. Also a pair of wires from the remote pump house would be a way. I am sure there are other solutions.
I have seen it done using a small current transformer made by feeding the cable through a ferrite ring, and winding a few extra turns of thin wire on there, which is then fed to a little opamp circuit, the output of which, you can do what you like with - feed a relay, switch a bulb, switch a little license-exempt transmitter, and so on. I'm pretty sure that Elektor magazine did a circuit like this as a project not so long back. You could try searching the archive on their website at
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Also, I think that you can get ready made units for control of computer peripherals. You just plug your computer in through it, and when it detects that the primary load - your computer - is drawing current, it switches power to auxilliary devices like your printer. Subbing the pump for the computer, and using one of its switched aux outputs to drive a relay or whatever, should work. Also, simplest way perhaps, connect a wall wart power supply across the pump feed. Then when the pump comes on, you will have a low voltage of any value you choose, available to do what you like with. If you can't get wires easily to where you need to know that the pump is running, then a wireless link is probably going to be best. You can get all sorts of ready built modules for transmit and receive now. The ranges, and directivity, can be extended considerably, by adding home brew external antennas.
Maybe I am stupid, but couldn't you just wire a 120 lamp cord and bulb in parallel with the pump? You would do this at the switch. When the pressure switch closed, then the pump and the bulb would come on.
Or you could wire in after the controller box, if you have one.
But make sure that this really is a 120 pump. Most are 240 and then you would wire one hot to one side of the bulb and neutral to the other side of the bulb.
Not stupid and I could do that BUT The pump itself is almost 200 feet away down over a bank in a pump house. I am hoping to be able to connect something inside the house on the feed to the pump to tell me when it is operating, rather than burying a lot more wire.
If I had a transformer here that could handle the 15 amps I would hook one side of it into the hot side of the feed and use it to power a light since current/voltage would only be flowing when the pump was on but that would be a good sized transformer. I think my current course of action will be to wrap a section of the hot side through a toroidal core with a larger section of magnet wire and see what I get voltage wise. Kind of a crossbreed current transformer.
Could you put an ammeter inline with the circuit? It would take a sizeable shunt. There is a place in my city that sells used and surplus electronics. They have AC ammeters for $15(?).
You're fairly unlikely to get enough to be able to do much with on it's own, but if you slung it across the inputs of an opamp, and smoothed the result at the output, you'd have enough to drive a small relay to switch a low power transmitter - like a WalMart baby alarm, as someone suggested elsewhere in the thread.
Don't know what your budget for this contraption is, but I think what you're looking for is a current-operated switch, such as these:
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Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)
"In theory, there isn't any difference between theory and practice. In
practice, there is." - Yogi Berra
Don't know what your budget for this contraption is, but I think what you're looking for is a current-operated switch, such as these:
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Find more manufacturers, distributors and prices by Googling for "current operated switch".
An alternative would be a Smart Strip power strip
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This is a power strip that has a number of outlets, just like the cheap "surge suppressor" strips, the difference being that there is one outlet that is used to control all the other outlets. When the device that is plugged into the control outlet is on (drawing current), the other outlets are switched on. These are usually used to control computer systems, home theater systems, etc, where a number of devices need to be turned on at the same time. I have one of these strips in my home and two more in my shop. Great devices. You could run the pump through the smart switch, and then plug a small lamp or other device into one of the controlled outlets for a visual or audible indication that the pump is drawing current.
Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)
"In theory, there isn't any difference between theory and practice. In
practice, there is." - Yogi Berra
Get a Panelmount ammeter with Current Transformer (CT). Hook the CT up to the ammeter, and pass one of the phase wires going to the pump assy through the CT.
You can get current relays from HVAC surplus type places, they're just a relay wound with a heavy wire designed to carry the load current, the relay closes when current flows through the coil. I think I paid $2 for the one I bought, you could probably rewind the stator of an AC relay with some #12 enameled wire in a pinch too.
If I am not mistaken, the sensor in a smart strip is nothing but a pair of rectifier diodes connected in anti-parallel. You put the pair in series with the line. When the load (the pump in this case) draws current, the voltage across the diodes is a near square wave with an amplitude of 1.4 volts peak-to-peak. You can use this voltage to pull in a small relay, which in turn lights your indicator light - or whatever.
Obviously, the diodes have to be hefty enough to withstand the pump's starting current. And the relay's coil, which is connected to the line at all times, must be well isolated from the relay frame, from ground, from its own contacts, etc. But none of this is hard.
You are mistaken. The Smart Strip that I mentioned uses a current transformer to sense current. The CT feeds a transistor that switches a relay when current in the control receptacle is sensed. However, CTs aren't hard to find, and are pretty cheap. The circuitry behind the CT is fairly trivial as well... just connect a burden resistor across the CT secondary, rectify and filter, then feed the resulting voltage to the base of a transistor. The transistor drives the relay coil, which switches power to the load(s). The transistor circuitry can easily be replaced with an opamp if you're more comfortable with those. The Smart Strip is rated at 15A.
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)
"In theory, there isn't any difference between theory and practice. In
practice, there is." - Yogi Berra
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