Current sensing switch...or something like that....

[G._Hoffman]

I've got a project in mind for around the shop - kind of based on Doug's ring of LED's on his CNC machine - to help light up the work piece on our over arm router, and I need help with part of it.  What I want is for the LED's to turn on when the router is turned on, without using an external switch.  It seems to me what is needed is some kind of current sensing switch - something which detects the current being drawn by router, and uses that to trip a relay or some such for the LEDs. 

The ideas my mind is coming up with seem a bit on the less than wise side (things like making use of the voltage drop across a resistor in line with the router, which just doesn't seem right for some reason!)


Any hints, or preferably links to existing circuits that won't fry my router or burn down my shop?


Gabriel

[G._Hoffman]

OK, better idea - a small(ish) transformer with the primary in series with the router, and run the LED's off the secondary.  The only problem I see, though, is that it will need to be rated for the current draw from the router, right?  Which makes the small transformer not very small.

Anybody?


Gabriel

[PRR]

Lights (supply) in parallel with motor.

Why wait until the motor starts? First thing you see may be the cutter spinning-up with your thumb or tie caught in it. Put the light on before you start the motor? LEAVE the light on 9-5? Specially _if_ LEDs are ample, the running cost of the light is less than the cost to buy bad news from the hand-surgeon. (Just met a guy going -back- for MRI. He nearly severed his hand, they put it on with a screw, years later the tendons are growing around the screw and could lead to total loss of motion.)

[G._Hoffman]

Lights (supply) in parallel with motor.

Why wait until the motor starts? First thing you see may be the cutter spinning-up with your thumb or tie caught in it. Put the light on before you start the motor? LEAVE the light on 9-5? Specially _if_ LEDs are ample, the running cost of the light is less than the cost to buy bad news from the hand-surgeon. (Just met a guy going -back- for MRI. He nearly severed his hand, they put it on with a screw, years later the tendons are growing around the screw and could lead to total loss of motion.)

40 years of business (well, it will be 40 years tomorrow!) without a single major injury (I've lost a few fingerprints in struggle with the belt sander, as have we all, but that's about it) - I wouldn't say I'm not worried about that issue, but our guys are all smart and careful, every time.  And the overarm router only gets used a few times a week, so leaving the light on would be silly.  Besides, you can see pretty well just from the area lights - I'm just trying to make it better.

Is there really anyone in the world stupid enough to wear a TIE while using a router?  I think the last time anyone around here wore a tie - other than at a funeral or maybe a wedding - was when my dad was a lawyer and was in front of the Minnesota PUC - over a decade ago!


Gabriel

[sluckey]

I've thought about your project for a couple days now. I have some modular relays with current sense loops in an obstruction lighting system at my (FAA's) radar tower. The sense loops are little doughnut shaped pickup coils. The power lead for the tower lights is routed through the doughnut. The doughnut senses current thru the wire that feeds the tower lights and is connected to a modular relay. As long as there is current to the tower lights, the modular relay is energized and happy. Relay contacts will signal an alarm if the tower lights burn out. You can adjust the sensitivity of the modular relay to cover a wide range of current, up to about 10 amps, which would cover most routers.

This circuit could be easily adapted to turn on your LEDs by sensing current to the router. However, this relay and current sense loop will cost much more than your router! That's why I haven't jumped in sooner.

Why are you against using an external switch? That's the simplest solution. I have a router permanently mounted to a router table. I leave the router's power switch turned on all the time. The router's AC cord is plugged into a receptacle/switch box that is conveniently mounted at the front of the table. I could very easily change my switch box to a double box and use a double receptacle and standard switch. Then I could also plug in a gooseneck lamp that turns on when my router turns on. Probably cost $10 if I had to buy everything except the lamp.

Couldn't you adapt something similar for your router? You could still use LEDs if desired.

[G._Hoffman]

Why are you against using an external switch? That's the simplest solution.

Because I have a hard enough time getting people around here to turn off the lights on the drill presses we use every day.    Trying to get them to turn off the lights on the router is just...

Oh, I see, you mean an external switch for both the router and the lights.  That might work.


Gabriel

[PRR]

Tool and Vacuum Switch, $37

[G._Hoffman]

Tool and Vacuum Switch, $37

Yeah, I know about those.  That's actually what I wanted to copy.  I was hoping not to spend any, or at least much, money. 


Gabriel

[jjasilli]

Here's another idea: an off delay relay set to trigger to OFF after a pre-determined time interval up to say 10 hours.  Still with the low current draw of LED's, it might be cheaper to occaisionally forget and leave them ON.

[G._Hoffman]

Here's another idea: an off delay relay set to trigger to OFF after a pre-determined time interval up to say 10 hours.  Still with the low current draw of LED's, it might be cheaper to occaisionally forget and leave them ON.

Not a bad idea.  It would be a bit of a challenge to program the μC, but one that would teach me some useful new programing knowledge.  You'd have to do it with an ultra low power consumption set-up to make it worth while, but I've never done that before, and it could be interesting.


Gabriel

[jjasilli]

Mouse sells Magnecraft time delay relays with octal bases that you set with a screw driver.  (Right now I'm using their on-delay relays as automatic standby SW's on the power amps for home theater sytem. )

Sometimes we forget to turn off the sytem or fall asleep, leaving on 3 power amps burning 175W's apiece.  I'm about to install an off-delay relay so the power amps will shut-off after a pre-set interval of say 4 or 6 hours.