float switch to led output


Thread Starter

Raychon Betts

I'm building a small tank water indication system using float switches in the tank and using led connect to them for the output. Can anyone help me figure out how to make the connection to the leds powered by a 24 vdc source happen.
The LED's are OK direct - using the right size resistor of course for the LED voltage. Neon can be used as well. Make sure the switch is rated over 24V - ours are 240 V at 0.5A resistive for example. A standard light will burn out the switch on startup. The reeds act just like a wall switch - so wire them in as such. If you go to our web page at:
"http://www.almegcontrols.com":http://www.almegcontrols.com and go to "FAQ" - then look at "what a reed switch can do" you will find all the information you need.

Bob Hogg
Hello Raychon!

You need to connect a resistor in series with the LED. I don't know if there is an LED in the market today that has a 24 VDC supply. If there are LEDS in the market with a 24 VDC supply, you don't need a resistor. At least 250 ohm resistor should be in series with a 12 VDC supply LED (of course, you also need to connect the 24 VDC supply in series with the loop). that is all you need.

About a quarter watt, 2.2K ohm resistor in series with each LED should be about right. I use LEDs across 240 volts, with half watt resistors of a hundred k or so - in that case I trade off a bit of LED brightness (& current) to keep less than a half watt dissipated in the resistor.
The float switch contacts can be connected in series with the 24Volt supply and a 20k resistor, depending on the LED current drain. Consult your dealer how much is the current drain. If the drain is say 1ma then, size the resistor as
R=(24-2)/1ma = 22k, where 2 is the usual LED voltage drop. Note of the LED terminals. Make sure they are not reversed, otherwise, they still wouldn't light up.

Mazin Halawani

first of all let me know if i understand your question correctly. you would like to install level switches in your water tank such that u get a light indication when the water is at a specific level. am i correct?

if this is the case, then you would connect the 24 VDC power supply to the level switch. then connect the other terminal of the level switch to the light indicator. the level switch contact shall be normally open, that is open contact when the water level is low. so when the water level is high, contact is closed, and power is supplied to the light indication.

i hope this would help.
If it is a small single point switch - most manufacturers build them so that reversing the float reverses the state. N/O to N/C and back. If you put an OHM meter (not a light) on the level sensor and move the float back and forth and
the contacts stay closed - then - the reed switch has been burnt. You will need to buy another one - we can fix it for you at about 3/4 the cost of a new one - but by the time you pay shipping!!! You can get another one from the
origional supplier or call us via our web site below. Also - go to FAQ and you will get information on what the switch can take.
Thanks Bob Hogg
How about . . .

\ R1
| FL1 R2 LED1
+-----\ ------/\/\/------->|---+
| |\ |
| O |
\ |
/ |
\ R3 |
/ |
\ |
| |
| |
| |
| |
| |
| |
--- ---
- -

R1 = voltage divider resistor
R2 = current limiting resistor
R3 = voltage divider resistor
FL1 = float switch
LED1 = light emitting diode

Graphics by myASCIIcad

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