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Does it exist? 120v inductive indicator light system. Answered

 I run a car wash and I need a way to quickly tell if equipment located in hard to get to places is on and working or not. What would be great would be a remote bank of lights that came on when a device was drawing current. What would be perfect is if I didn't have to wire it into everything - for instance inductive sensors (like the cheap ones you can buy at HD that beep and flash when current or voltage is present) that can be placed on the outside of a wire run and report back to the bank of lights whether or not there is current flowing.

Anybody ever seen anything like this?



The hallsensors will work great and tell you it the unit is getting power or not, but it won't tell you whether or not the unit is working.  It will only tell you whether or not you have power to the unit.  It the unit is jammed or off the track you won't get any indication of that.

A remote camera would give you all of the information that you are looking for.

I would just like to point out that I have not suggested a reed switch for this application. So there.

I would, however, like to second/third/whatever what Pedro and Steve have said regarding Hall effect sensors.

If I was building one, I'd follow Pedro's idea and go for hall effect sensors. If you want to know how much current, just put cheap ebay 3.5 digit meters on the outputs of the sensors.

The sensors have the great benefit of needing no connection to the circuit.

Here is a very quick google-found data sheet on a "split core" hall sensor - split means that you can just clip it round the wire.
There'll be local sources of something similar whereever you are in the world.


Hall effect current sensor

expensive, or you can build your own.

The ring in the image is the Hall effect current sensor. It measures the current in the wire running through it.


There is a commercial product (or several) that follow the principles of the above, using a Current Clamp to clip on and sense the current going to the motor.

There are ones built into multimeters, and I've seen ones that just output a signal for another computer to sense - thats what you would want for a prebuilt solution, otherwise, do as others say, wrap a power wire from the motor around a nail a few times, then wrap many turns of magnet wire around the nail and hook up sensors/lights to those secondaries.

like these...


One method to determine whether amperage is flowing or not... is to place a very LOW resistance in SERIES with each item you want to monitor.  Then place an LED diode in PARALLEL with the very low resistance.  It would take some designing because you don't want to add very much resistance in series with motors, or they wont run properly.  So the resistance must be as close to zero as possible... for example maybe 0.10 Ohms (that's POINT ONE ohms, not TEN ohms).  The wattage of the resistor must be large enough to handle the amperage used by the motor. 

ANOTHER method, would be to use SENSING transformers.. They work on AC powered devices.  It is a SMALL transformer with a very THICK primary wire and a secondary winding of a few hundred turns of wire.  You could probably BULD such a thing using THICK wire wound around a thick nail, and THIN wire wound around it as a SECONDARY winding. Be sure to wrap electrical tape around the coil BEFORE you wrap the secondary winding. 
Then you just connect ONE wire of your motor in series with the thick wire.  The motor will draw current and generate a magnetic field in the nail (or thick bolt) that generates a voltage in the THIN wire of your secondary winding.  Put a diode in series with this and a resistor and you could light an LED bulb... or you could run a milliampmeter, which would indicate a kind of ROUGH estimate of how much amperage the motor is using.  If the motor was attached to an AIR FILTER for example.... the amperage would start to INCREASE when the air filter started to get clogged! 

If you are detecting DC motors... i would go with the LOW RESISTANCE shunts described first.... if they are AC operated i would go with the SENSE transformers either commercial or handbuilt.  I have included a picture of a typical sense transformer as one example.  Notice the THICKwire wraps at the bottom right and the THINwire wraps around the remaining torroid transformer.  You dont have to have a TORROID... just a thick nail or bolt will work also if you like to homebrew it. 


These use a coil of wire to sence current in a wire, then amplify the induced current enough to cause a buzzer to buzz.

you could do the same thing with a little "fiddling".

if they beep or flash they can be modified to drive a relay, which in turn can turn on your bank of lights...