Best Way - Indicator LED - AC Pump

[DustinB]

I have a couple 110VAC pumps coming in soon to dose supplements to my fish tank. The pumps will be controlled by a power strip with relays built in. My controller will turn the relays on/off for each plug in the strip. There will be 2 pumps in my enclosure with 2 standard cords coming out of the box.

I would like to have indicator LED's in the enclosure to show when the pumps are on, possibly flashing if possible.

What would be the best way to do this? Figured I would ask, I'm going to open up a standard power strip and see how they wire the indicator lights in those.

Thanks

 

[cr0sh]

The pumps will be controlled by a power strip with relays built in...Figured I would ask, I'm going to open up a standard power strip and see how they wire the indicator lights in those.

Generally as cheaply as possible; most power-strips simple have a neon lamp attached to tell when it is on, wired nearly directly with the power from the wall. But you say your strip isn't like that, and has relays to turn sockets on/off (sounds kinda cool - got a link?).

If so, and you seem to not mind opening it up, what I would do is look for the LED, and likely it will be connected between a ground and a resistor; note the size of this resistor (it may be all SMD - if so, hopefully its not so tiny as to not have numbers on it - ie, "103" would indicate 1K ohm). With that in mind, get another LED and a length of two conductor wire (phone cable will work), and hook one wire to the -other- side of the resistor, then to another resistor of the same size, then the LED, and to the other conductor, and the other conductors end would go to ground.

Basically, you are making an LED extension cable in parallel with the existing LED/resistor combo; you don't want to just wire up the LED to the resistor in parallel, because that might over-tax the resistor (which is likely a very low wattage device), causing it to burn out. Generally, whatever is powering the LED (without a schematics, hard to say) - is likely a transistor or mosfet, or some other kind of buffer output (or a microcontroller with pins that can source/sink enough current - if it is wired directly to a microcontroller, you might want to look up the spec on the controller to find out how much current its pins -can- source/sink) that can handle the extra very small load (you might want to run the numbers thru an LED/resistor calc online to make sure you are using the minimum, so as not to overtax anything).

The extension cable shouldn't be very long; you could probably get away with a few feet - but if you are concerned, you could drop the resistance of the LED and figure out the wire resistance to add it back in to make up the difference (there are online refs for this as well).

Finally, make sure your connections inside the power strip are -very- secure; you may want to blob some hot glue or silicone on top of them - so that they don't come loose and short with the house current output from the relays. Use grommets with strain-reliefing, or add jacks to plug in the extensions if you want (and can - if there is room).

Hope this helps and is understandable...good luck!

 

[Mike_2545]

You could use a neon bulb as the indicator and this **broken link removed**
to flash it.

 

[Sceadwian]

Use any small signal diode with a reverse breakdown voltage of a minimum of 200 volts in series with a small LED and a resistor to limit current.
1ma will light up a red indicator diode pretty brightly, the small signal diode with the reverse breakdown of 200+ volts is to prevent the LED from conducting in reverse (they conduct in reverse at... MUCH lower voltages than 'real' diodes do)
A 200k quarter watt resistor should work fine for a resistance in both cases.

Mike what is that circuit? The upper resistor is 1meg, the lower cap is 10 farads?!

 

[Mike_2545]

Mike what is that circuit? The upper resistor is 1meg, the lower cap is 10 farads?!

Its know as a relaxation oscillator. The cap is 10uf of sufficient voltage for 120AC

 

[Sceadwian]

The schematic should say 10u then. I would question an electrolytic caps ripple current handling capacitor for that application over the long term.

 

[georgetwo]

you gat two options, 1. Tap dc from the relay to make ur indicator, or 2. Tap ac from the two wires which supplies ur pumping machine. Simple

 

[Reloadron]

If the pumps are 120 VAC and you want to monitor at the pump maybe use something like this. The Red LED units have a turn on of 750 mA AC. However you can loop through twice and half that depending on what your pumps draw. I use them to monitor large heaters so I know when a heater has burned open. They run about $12 each (single units) I believe so your call on that note. Anyway, it's yet another option depending on how you want to go about things. The merit to a device like this is that it will tell you if the pump is drawing current and not that there is just 120 VAC across the pump leads. If you measure just across the pump voltage you won't know if a pump has failed open at a glance.

The relaxation oscillator I believe is used for a DC circuit, you can read about them here. Also more information can be found here. Years ago I built a few from old fluorescent tube starters. Pretty cool little device at the time.

Ron

 

[DustinB]

Thanks for the ideas everyone. I took the easy way out and found some at radio shack. 120v, neon lamps.

120-Volt Neon Green Lamp (2-Pack) - RadioShack.com