2 Switch Relay Activator - Pilot LED for each branch

[flynmoose]

Hello,

I am installing two water float switches - one in each wet well of a basement septic system.

The purpose of these switches is two-fold. First, to activate a horn and give a visual indication of which well has a high water state.

The second is to drive an input coil on a commercial off the shelf relay box that will cut the power to the well pump. This box takes 24VAC (or DC) input and drives a DPST contactor capable of breaking both legs of the 240VAC well pump supply. The circuit simulator didn't have the correct drawing for this relay - so ignore the relay functionality. It is a DPST Normally Closed contactor. When I measure the resistance across the input wires, it reads "open" - so there must be some electronics inside the box that ultimately drive the coil on the contactor.

I can create a simple 120VAC circuit which would drive a 120VAC horn and drive a 5:1 transformer to output the 24VAC "signal" for the RIB24.

What I can't figure out is how to put a LED pilot light circuit on each float switch to indicate WHICH float is high. Since they are driving a common source it is giving me fits. I breadboarded a circuit that used diodes to half-wave rectify each branch and put a "polarized" pilot light on each branch, but the transformer didn't like that (got very hot very fast.)

I've got a handful of LEDs, 1N4004 Diodes, .22µF caps (250V), the transformer and some 3K resistors. I could buy a few more components, but am trying to keep the circuit cheap.

I borrowed the pilot light circuit that is illustrated here for the 120VAC side from a web resource (hence the components on hand.)

The floats are SPST "on when up" type switches. They are rated for 120VAC submersed and have 15A contacts (made for direct activation of a sump pump).

Would also prefer to have the entire circuit dead (other than possibly the shown pilot light for the power side) when the switches are down. ie - didn't really want to drive the transformer 24x7.

Any ideas?

**broken link removed**

 

[crutschow]

Yes, transformers can not tolerate 1/2 wave rectified voltage as that generates a large DC current which saturates the core and rapidly overheats it as you noted.

If the relay current is 125mA @ 24VAC from the transformer, then the transformer input current is only about 25mA (neglecting magnetizing current). I would suggest putting a LED in series with each float switch. You would put a small resistor in series with the LED to limit the current (with the inverse diode across the LED as you show), and with another small resistor in parallel across the LED and series resistor, to bypass any current above the desired LED current. You would need to measure the primary transformer current with the relay connected to determine the proper series and parallel resistor values for the LEDs. I would calculate the resistor values to give perhaps a 4-5V drop across the LED resistor combo.

 

[Reloadron]

Not to deter from where you are going with this, but if there is any way possible to get the 120 VAC out of the sumps I would consider it. Generally for safety reasons whenever possible I try to kep the float switch voltages in sumps around 12 or 24 VDC maximun. Not to say don't use 120 VAC sump pumps with built in switches but whenever possible I like all my sump control to be low voltage DC. However, your call on that note.

Ron

 

[MikeMl]

Do it with a DC relay as shown: (Seems very complicated just to get the indication, though). I'd just use two AC relays with multiple contacts, and do all of the logic on the output side of the relays)